Method and Apparatus for Performance Prediction of Multi-Layered Oil Reservoirs

Abstract

The present invention discloses a method and an apparatus for predicting performance profiles of multi-layered oil reservoirs, wherein the method comprises: dividing the multi-layered oil reservoirs into a plurality of blocks, and determining a reservoir type, formation factor Kh and an evaluated reserves of each layer in each block; selecting a block representing geologic features of the multi-layered oil reservoirs from the plurality of blocks as a representative block, to build a fine geological model of the representative block; building corresponding fine numerical simulation model according to the fine geological model of the representative block, and determining type curves of different reservoir types under different development strategies; determining a relation curve between Kh and well injection rate for injectors and a relation curve between Kh and well production rate for producers in the multi-layered oil reservoirs under different restrictive conditions; predicting performance of the multi-layered oil reservoirs according to the type curve, the relation curve between Kh and well injection rate, the relation curve between Kh and well production rate, and the reservoir type, formation factor Kh and evaluated reserves of each layer in each block.

Description

RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 or 365 to China, Application No. 201510349577.8, filed Jun. 23, 2105.

The entire teachings of the above application(s) are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the field of performance prediction techniques for oil and gas reservoir development, and particularly, to a method and an apparatus for performance profile prediction of the multi-layered oil reservoirs.

BACKGROUND OF THE INVENTION

Lots of human and material resources will be spent in building a fine geological model for the large oil and gas field, while it is still difficult to ensure that the sand body distribution, reservoir connectivity across the whole oil field for the fine geological model are consistent with the expectations. Meanwhile, the fine geological model of the whole oil reservoirs is also usually up-scaled due to the reasons such as a large number of grids, much slow calculation and time consuming of numerical simulation, etc., and then the numerical simulation is performed based on the up-scaled model. However, the up-scaled model cannot accurately represent some strong heterogeneity inside the reservoirs.

Currently, the unconventional oil and gas reservoirs at home and abroad have problems on the large whole field reservoir numerical simulation, thus the numerical simulation research on the whole oil and gas reservoirs cannot be carried out. Usually, typical production curves of different types (high, middle, low, etc.) of production wells are determined based on the trial-development or development curves of the actual production wells, so as to predict the whole development performance of the reservoirs. The method is feasible for the unconventional oil and gas reservoirs at some extent because usually only primary depletion is used for unconventional reservoirs. But the development of the conventional multi-layered oil reservoirs is complex, and the total performance of the oil reservoirs cannot be simply predicted based on performance curves of the existed production wells. The development of the multi-layered oil and gas reservoirs concerns different development modes such as different well patterns and spacing, water injection of secondary recovery and gas injection of tertiary recovery, and stimulations such as layer water shut-off because of high water cut. Thus the influences of different development modes and stimulations on the development performance cannot be characterized by typical performance curves through classifying the producers into several typical types, which is restrictive and one-sided at certain extent, and the accuracy of the prediction of the performance of multi-layered reservoirs is low.

SUMMARY OF THE INVENTION

The embodiments of the present invention provide a method for predicting the whole performance profiles of the multi-layered reservoirs, which not only ensures the prediction accuracy of the multi-layered oil reservoirs, but also reduces the man-power and improves the working efficiency. The method comprises:

dividing the multi-layered oil reservoirs into different blocks according to the stacked style of reservoir types, and determining the specific reservoir type, Kh (permeability multiplied by thickness) and original oil in place (OOIP) of each layer for each block;

selecting a block representing the typical geologic features of the multi-layered oil reservoirs from all the blocks as a representative block, building a fine geological model of the selected block;

determining the relationship between water cut and oil recovery efficiency (type curves) of every reservoir type under different development modes or strategies, based on the simulation result of the fine geological model of the representative block;

determining a relation between Kh and injection rate of single injector, and a relation between Kh and production rate of single producer in the multi-layered oil reservoirs under different operational conditions;

predicting a performance profile of the multi-layered oil reservoirs according to the relation between water cut and oil recovery efficiency, the relation between Kh and well injection rate, the relation between Kh and well production rate, and the reservoir type, Kh and OOIP of each layer in each block.

The embodiments of the present invention provide an apparatus for predicting performance profile of multi-layered oil reservoirs, which not only ensures the accuracy of the prediction of the total output of the multi-layered oil reservoirs, but also reduces the man-power and improves the working efficiency. The apparatus comprises a processor configured to:

dividing the multi-layered oil reservoirs into different blocks according to the stacked style of reservoir types, and determining the specific reservoir type, Kh (permeability multiplied by thickness) and original oil in place (OOIP) of each layer for each block;

selecting a block representing the typical geologic features of the multi-layered oil reservoirs from all the blocks as a representative block, building a fine geological model of the selected block;

determining the relationship between water cut and oil recovery efficiency of every reservoir type under different development modes or strategies, based on the simulation result of the fine geological model of the representative block;

determining a relation between Kh and injection rate of single injector, and a relation between Kh and production rate of single producer in the multi-layered oil reservoirs under different operational conditions;

predicting a performance profile of the multi-layered oil reservoirs according to the relation between water cut and oil recovery efficiency, the relation between Kh and well injection rate, the relation between Kh and well production rate, and the reservoir type, Kh and OOIP of each layer in each block.

As compared with the current universal method which predicts the performance profile of the whole oil reservoirs just according to the typical production curves of different types (high, middle, low, etc.) of production wells, the technical solution provided by the embodiment of the present invention divides the whole oil reservoirs into a lot of blocks according to the stacked style of reservoir types for the whole oil reservoirs, selects a representative block representing geologic features of the whole reservoirs from the plurality of blocks to build a fine geological model, carries out numerical simulation based on the fine geological model of the block to study the optimum development strategies for the multi-layered oil reservoirs, and generates relations between water cut and oil recovery efficiency of different reservoir types under different development strategies which is used to predict the performance profile of the whole oil field combined with the classification result of the reservoir types of the whole oil reservoirs, and results of the relationship between well production rate and Kh, and the relation between well injection rate and Kh. The prediction result based on the proposed method is more accurate and reliable, and performance profiles of development plans for the whole oil reservoirs can be quickly generated, thus the man-power are greatly saved and the working efficiency is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings described herein provide further understandings of the present invention, and constitute a part of the present application, rather than limiting the present invention. In which,

FIG. 1 is a workflow diagram of the method for predicting performance profiles of multi-layered oil reservoirs in an embodiment of the present invention;

FIG. 2 is a workflow diagram of a method for block production rate and block injection rate prediction of the multi-layered oil reservoirs in another embodiment of the present invention;

FIG. 3 is a schematic diagram of dividing the whole oil reservoirs into a plurality of blocks in an embodiment of the present invention;

FIG. 4 is a schematic diagram of a classification result of reservoir type of a layer in the oil reservoirs in an embodiment of the present invention;

FIG. 5 illustrates a 700 m five-spot well pattern set up based on a representative block (3_2) in an embodiment of the present invention;

FIG. 6 illustrates the type curves of different reservoir types under a development mode (700 m inverted nine-spot well pattern) in an embodiment of the present invention;

FIG. 7 illustrates the type curves under a development mode (500 m five-spot well pattern) of different reservoir types in an embodiment of the present invention;

FIG. 8 illustrates a relation curve between Kh and well production rate of an individual producer in an embodiment of the present invention;

FIG. 9 illustrates a relation curve between Kh and well injection rate of an individual injector in an embodiment of the present invention;

FIG. 10 is a well position chart of 1000 m inverted nine-spot well pattern of block (5_3) in an embodiment of the present invention;

FIG. 11 is a layer production curve diagram of layer USM4.2 in block (5_3) under a development mode of 700 m inverted nine-spot well pattern obtained in the method for predicting whole performance profile of multi-layered oil reservoirs provided by the embodiment of the present invention;

FIG. 12 is a block production profile diagram of block (5_3) under a development mode of 700 m inverted nine-spot well pattern obtained in the method for predicting whole performance profile of multi-layered oil reservoirs provided by the embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order that the objects, technical solutions and advantages of the present invention are clearer, the present invention is further described in details as follows in conjunction with the embodiments and the accompanying drawings. Here the exemplary embodiments of the present invention and the descriptions thereof are used to construe the present invention, rather than limitations thereto.

FIG. 1 is a workflow diagram of the method for predicting performance profiles of multi-layered oil reservoirs in an embodiment of the present invention. As illustrated in FIG. 1, the method comprises:

Step 101: determining reservoir type distribution of each layer for the multi-layered oil reservoirs;

Step 102: dividing the multi-layered oil reservoirs into a plurality of blocks according to the stacked styles of reservoir types of the multi-layered oil reservoirs, and determining the specific reservoir type, formation factor Kh and OOIP of each layer in each block;

Step 103: selecting a block representing geologic features of the multi-layered oil reservoirs from the plurality of blocks as a representative block, and building a fine geological model of the representative block;

Step 104: building corresponding fine numerical simulation model according to the fine geological model of the representative block, and determining type curves of every reservoir type under different development modes or strategies according to the fine numerical simulation model;

Step 105: determining a relation curve between Kh and injection rate of single injector in the multi-layered oil reservoirs under different operational conditions, and determining a relation curve between Kh and production rate of single producer in the multi-layered oil reservoirs under different operational conditions;

Step 106: predicting a performance profile of the multi-layered oil reservoirs according to the type curves, the relation curve between Kh and well injection rate, the relation curve between Kh and well production rate, and the reservoir type, Kh and OOIP of each layer in each block.

As compared with the current universal method which predicts the performance profile of the whole oil reservoirs just according to the typical production curves of different types (high, middle, low, etc.) of production wells, the technical solution provided by the embodiment of the present invention divides the whole oil reservoirs into a lot of blocks according to the stacked style of reservoir types for the whole oil reservoirs, selects a representative block representing geologic features of the whole reservoirs from the plurality of blocks to build a fine geological model, carries out numerical simulation based on the fine geological model of the block to study the optimum development strategies for the multi-layered oil reservoirs, and generates the type curves of different reservoir types under different development strategies which are used to predict the performance profile of the whole oil field combined with the classification result of the reservoir types of the whole oil reservoirs, and results of the relationship between well production rate and Kh, and the relation between well injection rate and Kh. The prediction result based on the proposed method is more accurate and reliable, and performance profiles of development plans for the whole oil reservoirs can be quickly generated, thus the man-power are greatly saved and the working efficiency is improved.

During implementation, in step 101, determining reservoir type distribution of the whole multi-layered oil reservoirs specifically may include: performing a stratigraphic correlation for the whole oil reservoirs, and classifying and evaluating the reservoir type distribution of each layer. There are multiple specific methods for determining the reservoir types, and they are not described herein. The purpose of the step is to prepare for the subsequent block division for the whole oil reservoirs, and then lay a foundation for a more accurate output prediction result at the last. The distribution of formation factor Kh of each layer is obtained with a certain interpolation algorithm based on individual well logging interpretation. The distribution of formation factor Kh is for the purpose of calculating the total injection rate or production rate of an individual well and the injection rate or production rate of each layer for an individual well subsequently with Kh of the individual well and Kh of each layer of the individual well.

During implementation, in step 102, dividing the whole multi-layered oil reservoirs into a plurality of blocks according to the stacked style of reservoir types of the whole multi-layered oil reservoirs (as illustrated in FIG. 3); the purpose of block division for the whole oil reservoirs is to ensure the rationality and accuracy of the result of prediction of the performance profile of the whole oil reservoirs based on type curves of different reservoir types under different development strategies. The whole oil reservoirs are divided into blocks as many as possible on a plane. In the process of block division, it shall be ensured so far as possible that the interior of each sublayer in each block is dominated by one reservoir type, thus the exploitation effect is predicted by applying the type curves of different reservoir types under different development strategies. In this step, it is necessary to determine the (dominant) reservoir type of each layer (as illustrated in FIG. 4), the reserve of each layer in each block, and the formation factor Kh of each layer in each block at the same time, so as to lay a foundation for the subsequent actual performance prediction.

In addition, during implementation, the boundary line of each block is matched with the deployed well pattern, i.e., the boundary line of the block is coincident with, adjacent to, or parallel with a certain well spacing connection line or well array spacing connection line of the well pattern as much as possible, so as to ensure continuity and consistency of well pattern deployment between different blocks.

During implementation, the number of the representative blocks selected in step 103 may be dependent on the actual working conditions. In this embodiment, one representative block is selected for a certain multi-layered oil reservoirs to build a fine geological model.

In step 104, the horizontal axis of each type curve (as illustrated in FIGS. 6 and 7) of different reservoir types under different development strategies (as illustrated in FIG. 5) is the oil recovery efficiency, and the vertical axis of each type curve of different reservoir types under different development strategies is the water cut.

In one embodiment, the above development strategies includes one of pressure maintenance level, well pattern and spacing, well type, pressure-maintenance mode such as water injection and gas injection, perforating strategy, oil offtake rate, injection-production ratio or arbitrary combinations thereof.

In step 105, determining a relation curve between Kh and well injection rate of an individual injector in the multi-layered oil reservoirs under different restrictive conditions (as illustrated in FIG. 9) includes:

determining a relation curve between Kh and injection rate of an individual water injection well in the multi-layered oil reservoirs under different restrictive conditions with an inflow and outflow performance evaluation method;

determining a relation curve between Kh and production rate of an individual producer in the multi-layered oil reservoirs under different restrictive conditions (as illustrated in FIG. 8) includes:

determining a relation curve between Kh and production rate of an individual producer in the multi-layered oil reservoirs under different restrictive conditions with an inflow and outflow performance evaluation method.

During implementation, the production capacity and injection capacity of an individual well can be determined in the inflow and outflow performance evaluation method. The inflow and outflow performance evaluation method determines a reasonable rate of the individual well by considering restrictions of the subsurface oil reservoir condition, the wellbore condition and the surface wellhead condition comprehensively. The relation curve between the well injection rate and the formation factor Kh and the relation curve between the well production rate and Kh determined in the inflow and outflow performance evaluation method are more accurate.

In one embodiment, different restrictive conditions include any of different oil tubing sizes, different lifting modes, different wellhead restrictive conditions or arbitrary combinations thereof under the given oil reservoir pressure.

In one embodiment, step 106 of predicting performance profile of the whole multi-layered oil reservoirs according to the type curve, the relation curve between Kh and well injection rate, the relation curve between Kh and well recovery rate, and the reservoir type, formation factor Kh and evaluated reserves of each layer in each block may include:

determining an offtake of each sublayer in each block according to the type curve, the relation curve between Kh and well injection rate, the relation curve between Kh and well production rate, and the reservoir type, formation factor Kh and evaluated reserves of each layer in each block;

accumulating the offtake of each layer in each block to obtain an offtake of each block;

accumulating the offtake of each block to obtain a total offtake of the whole oil reservoirs.

In one embodiment, determining an offtake of each layer in each block according to the type curve, the relation curve between Kh and well injection rate, the relation curve between Kh and well production rate, and the reservoir type, formation factor Kh and evaluated reserves of each layer in each block may include:

determining individual well injection rates of all water injectors in each block according to the relation curve between Kh and well injection rate and Kh of the individual well; determining individual well production rates of all producers in each block according to the relation curve between Kh and well production rate and Kh value of the individual well;

obtaining injection rate of each layer of an individual water injector by multiplying the individual well injection rate by a ratio of Kh of each layer of the well to Kh of the well; obtaining production rate of each layer of an individual producer by multiplying the well production rate by a ratio of Kh of each layer of the well to Kh of the well;

obtaining injection rate of each layer in each block by accumulating injection rates of all water injectors at the same layer in each block; obtaining production rate of each layer in each block by accumulating production rates of all oil producers at the same layer in each block;

determining the corresponding type curve of each layer according to the reservoir type and the development mode of each layer;

predicting the performance of each layer in each block according to the type curve, injection rate, production rate and evaluated reserves of each layer.

During implementation, because the embodiment of the present invention considers the production rate and the injection rate of each layer in each block, the influence of water plugging stimulation on the production can be considered. When a certain block has high water cut, one or more layers having high water cut in the block may be plugged separately, i.e., the production and injection rates of those layers are deducted from the performance profiles.

During implementation, after production rate and injection rate of each well are obtained, production rate and injection rate of each layer of each well are calculated according to a ratio of Kh of each layer of each well to a total Kh of the corresponding well. Next, production rate and an injection rate of each layer of each well in the block are determined in the above method.

Next, how to determine the production rate and the injection rate of each layer in each block will be introduced: for example, regarding a layer, the production rate of the layer is obtained by accumulating production rates of all wells of the same layer in the block, and the injection rate of the layer is obtained by accumulating injection rates of all wells of the same layer in the block.

Next, the prediction of the performance profile of each layer in each block will be introduced (i.e., the oil production rate, the water injection rate, etc. as illustrated in FIGS. 11 and 12; the rate mentioned in the embodiments of the present invention is the actual oil production rate, water production rate, injection rate, etc. which are finally predicted): the production rate and the injection rate of each layer in each block can be obtained in the above method, while the actual oil production rate and water production rate are calculated in conjunction with the type curves of different reservoir types under different development strategies as illustrated in FIGS. 6 and 7. Once the reservoir type of each layer in each block is determined, the type curve under the development strategy that corresponds to the reservoir type of each layer in the block can be determined according to the reservoir type of each layer in the block and based on the type curves of different reservoir types under different development strategies, i.e., the performance of the layer can be predicted in conjunction with the type curve corresponding to the layer, the production rate and the injection rate of the layer, and the reserves of the layer.

Through those descriptions, the performance of one layer in a block is obtained. Similarly, the performance of other layers in the block are predicted in the above method. Then, the performance of all the layers in the block are accumulated to obtain the total performance of the block. Next, with the same method, the performance of other blocks in the oil reservoirs are predicted to obtain the performance curves of all the blocks. Finally, the performance curves of all the blocks are accumulated to finally obtain the predicted performance of the whole oil reservoirs.

Next, descriptions will be made through examples to facilitate the implementation of the present invention.

FIG. 2 is a workflow diagram of a method for predicting a total performance profile of multi-layered oil reservoirs based on a type curve in another embodiment of the present invention. As illustrated in FIG. 2, the technical solution provided by the present invention may include the steps of:

1. performing a stratigraphic correlation for the whole oil reservoirs, and performing reservoir types classification and evaluation, to determine the reservoir type of each layer and the distribution of formation factor Kh;

2. selecting a representative block of the whole oil reservoirs to build a fine geological model;

3. carrying out development strategy optimization of pressure maintenance level, well pattern and spacing, well type, pressure maintenance modes such as water injection and gas injection, perforating strategies, oil offtake rate and injection-production ratio, and determining type curves (as illustrated in FIGS. 6 and 7) of different reservoir types (such as reservoir types B and reservoir type C as illustrated in FIG. 4) under different development strategies (e.g., the 700 m five-spot well pattern as illustrated in FIG. 5 and the 1000 m inverted nine-spot well pattern as illustrated in FIG. 10);

4. using an inflow and outflow performance evaluation method to set up a relational expression (i.e., the relational expression in FIG. 8) between the individual well production rate (i.e., the liquid rate indicated by the vertical coordinate in FIG. 8) and the formation factor Kh, and a relational expression (i.e., the relational expression in FIG. 9) between the injection rate and the formation factor Kh for different oil tubing sizes, different lifting modes and different wellhead restrictive conditions under the given oil reservoir pressure;

5. dividing the whole oil reservoirs into blocks as many as possible (as illustrated in FIG. 3); ensuring so far as possible that the interior of each layer in each block is dominated by one reservoir type, i.e., all or most of the layers in the block have the same reservoir type; and determining the dominant reservoir type of each layer in each block (as illustrated in FIG. 4);

6. evaluating the reserves of each layer of the whole oil reservoirs, and determining the reserves of each block of each layer;

7. determining the well pattern and well site deployment for the development plan of the whole oil reservoirs; evaluating the production rate of all the producers and the injection rate of all the injection wells based on the well position, the distribution of formation factor Kh of the whole oil reservoirs, as well as the relational expression (e.g., the relational expression in FIG. 8) between the production rate (the production rate mentioned in the present invention is the vertical coordinate “liquid rate” in FIG. 8) and Kh and the relational expression (e.g., the relational expression in FIG. 9) between the injection rate and Kh for the individual well; and determining the offtake rate (i.e., the production rate) and the injection rate of the layer of the individual well based on the distribution of formation factor Kh of the layer;

8. determining an accumulated production rate and an accumulated injection rate of all wells in each layer of each block, and considering an injection-production ratio of 1 and the oil-water formation volume factor, selecting the values of the subsurface accumulated production rate and the subsurface accumulated injection rate of each layer in each block as the finally verified subsurface injection rate and production rate of the layer in the block;

9. determining production rate and injection rate curves of each layer of each block based on the reservoir types classification result, the reserves evaluation result, the type curves of different reservoir types under different development strategies, and evaluation results of the injection rate and production rate relationship with Kh;

10. obtaining the total production rate and injection rate curves of the block by superposing the production rate and injection rate curves of all layers in the block;

11. obtaining a total production rate and injection rate curves of the whole oil reservoirs by superposing the production rate and injection rate curves of all blocks in the whole oil reservoirs;

12. generating various curves and graphics (as illustrated in FIG. 11, including the water cut curve of the block) such as the oil recovery efficiency variation curve, water cut variation curve and residual recoverable oil reserves of each block and each layer for each block, based on the reserves evaluation result and the production rate and injection rate curve of each layer and each block.

The general oil reservoir researches include those on stratigraphic correlation, reservoir type classification and evaluation, distribution of formation factor Kh, fine geological sector modeling, numerical simulation, etc., which are omitted herein. Next, several key points concerned in the present invention are mainly introduced as follows.

(1) Setup of Type Curves of Different Reservoir Types Under Different Development Strategies

According to the geological understanding of the whole oil reservoirs, as illustrated in FIGS. 3-4, it is deemed that block 3_2 represents the geological characteristics of the whole oil reservoirs, and block 3_2 may be selected as a representative typical block; and the block fine geological model of the representative block 3_2 can be built based on all static data (structure, well logging, sedimentary facies, etc.), geological and dynamic understandings of all wells included in block 3_2.

Based on the block fine geological model, researches on the development strategies (different well patterns and spacing, well types, etc.) and the technical development strategies can be carried out, so as to determine the optimum development strategy for the oil reservoirs. FIG. 5 illustrates 700 m five-spot well patterns deployment based on block 3_2, including two complete 700 m five-spot well patterns in total. Similarly, numerical simulation models under conditions of different well patterns, well spacing, perforating modes, etc. may be established based on the built geologic model, so as to form the type curves of different reservoir types under different development strategies. The present invention proposes to predict the performance profiles of the whole oil reservoirs by taking a relation curve using water cut and oil recovery efficiency as the vertical ordinate and the horizontal ordinate, respectively, as the type curve. Generally, different reservoir types under different development strategies have different type curves. For example, different reservoir types under different well patterns and spacing (one type of development strategies) have different type curves, and also different reservoir types under different well type development have different type curves. Thus the type curves of different reservoir types under different development strategies shall be determined. In the block model, the representative layer for each reservoir type is selected, and the performance curve of the layer is taken as the type curve of the reservoir type. FIGS. 6 and 7 respectively illustrate the type curves of different reservoir types of a certain oil reservoirs under the conditions of 700 m inverted nine-spot well pattern and 500 m five-spot well pattern. When the performance of other block is predicted with the type curve, for example if the reservoir type of a certain layer in that block is reservoir type B, the curve of reservoir type B in FIG. 6 may be selected for the block under the development mode of 700 m inverted nine-spot well pattern; then the performance of the layer in the block (the performance in the present invention may be the oil production rate, water production rate and water injection rate as illustrated in FIGS. 11 and 12) is predicted in conjunction with evaluation results such as the reserves of the block, and the injection rate and production rate of the individual well, thereby predicting the performance of the block and the performance of the whole oil reservoirs. In a case where different development strategies are used for different oil reservoirs, the method for determining the type curves is the similar, and herein is omitted.

(2) Block Division for the Whole Oil Reservoirs

The block division for the whole oil reservoirs is for the purpose of ensuring the rationality and accuracy of the result of prediction of the development performance of the whole oil reservoirs based on type curves of different reservoir types of the block under different development strategies. The whole oil reservoirs are divided into blocks as many as possible on a plane, thereby ensuring so far as possible that the interior of each layer in each block is dominated by one reservoir type, thus the performance is predicted by applying the type curves of different reservoir types under different development strategies.

In addition, the boundary line of the block is matched with the deployed well pattern, i.e., the boundary line of the block is coincident with, adjacent to, or parallel with a certain well spacing connection line or well array spacing connection line of the well pattern as much as possible, so as to ensure continuity and consistency of well pattern deployment between different blocks. FIG. 3 illustrates a block distribution diagram of division of the whole oil reservoirs of an oil field, wherein the whole oil reservoirs are divided into 65 blocks in total. FIG. 4 illustrates a classification result of the reservoir type of a layer in the oil reservoirs (the areal distribution diagram of the reservoir type of the layer). As can be seen from FIG. 4, there is only one reservoir type at the interiors of most blocks, such as block 5_2 and block 5_3. The interiors of other blocks are also dominated by one reservoir layer type so far as possible (e.g., block 4_3 and block 4_4). As to those blocks having more than one reservoir type, the dominant reservoir type shall be determined. For example, block 4_3 has three reservoir types, type B, type C and type D, and most of the reservoirs are type D, thus the dominant reservoir type of block 4_3 of the layer is type D, and then the type curve of type D is used to predict the development performance of the layer for the block.

Meanwhile, after the block division for the whole oil reservoirs is made, the reserves of blocks in each layer of the whole oil reservoirs shall be evaluated (i.e., step 6).

(3) Evaluations of Production Capacity and Injection Capacity

FIG. 8 illustrates a relation curve between Kh and production rate of individual well in an embodiment of the present invention, i.e., a relation curve between Kh and reasonable production rate of individual well determined with an inflow and outflow performance evaluation method (reservoir pressure: 4200 psi; tubing size: 2⅞; wellhead pressure: 300 psi); FIG. 9 illustrates a relation curve between Kh and injection rate of individual well in an embodiment of the present invention, i.e., a relation curve between Kh and reasonable injection rate of individual well determined with an inflow and outflow performance evaluation method (reservoir pressure: 4200 psi; tubing size: 3½; wellhead pressure: 2900 psi). The evaluations of production capacity and injection capacity in the embodiment of the present invention will be described as follows with reference to FIGS. 8 and 9.

The production capacity and injection capacity of an individual well can be determined with an inflow and outflow performance evaluation method. The inflow and outflow performance evaluation method determines a reasonable system rate of the individual well by considering restrictions of the subsurface reservoir condition, the wellbore condition and the surface wellhead condition comprehensively. The relation curve between the injection rate and the formation factor Kh and the relation curve between the production rate and Kh determined in the inflow and outflow performance evaluation method are more accurate. The present invention proposes to use the inflow and outflow performance evaluation method to determine the individual well reasonable system production capacity and the individual well injection capacity under different conditions, and establish a relation between the formation factor (Kh) and the production capacity and injection capacity of the individual well, i.e., to determine the system production rate and the injection rate of the individual well in case of different reservoirs (i.e., different Kh) under a given reservoir pressure, a given wellbore and given surface restrictive conditions. Next, it can return to the determination of the relational expression of the individual well production rate, the injection rate and Kh, for evaluating production capacity and injection capacity of the new well.

FIG. 8 illustrates a relation between Kh and an individual well system production rate determined based on characteristic parameters of an oil reservoirs. The production rate of any new well at any given position under the same production conditions can be obtained from the relational expression in FIG. 8 and the oil reservoir Kh distribution map. Similarly, as illustrated in FIG. 9, the relation between Kh and an individual well injection rate can also be determined (the relational expression in FIG. 9), which may be used to obtain an injection rate of a well at any given position. Next, the injection rate and the production rate of each layer of each well can be calculated by multiplying the total injection rate or production rate of each well by a ratio of Kh of each layer of each well to a total Kh of each well. The injection rate of each layer in a block is a sum of injection rate of all the injection wells at the layer in the block, and the production rate of each layer in a block is a sum of production rate of all the producers at the layer in the block.

In addition, graphics such as circles and squares in FIGS. 8 and 9 represent production rates and injection rates calculated with the inflow and outflow performance evaluation method under different Kh. The curves in the figures are those regressing based on the calculated points, and are used for calculations of production rates and injection rates of wells having different Kh based on the regression formula. In the embodiment of the present invention, each layer mentioned in the well is corresponding to each layer in each block.

The technical solution provided by the embodiment of the present invention has been applied in the development plan of large-scale marine sandstone oil reservoirs at home and abroad. The prediction result by using the present invention is compared with the fine numerical simulation result of the whole oil reservoirs, which are very consistent with each other. Thus the reliability of the present invention is verified. The actual application in multiple oil fields is successful, the prediction result is reliable, the man-power are greatly reduced and the working efficiency is improved.

Next, the development of block 5_3 of FIG. 4 in the inverted nine-spot well pattern of 700 m well spacing is taken as an example to explain how to calculate the block production from the type curve, and finally obtain the production of the whole oil reservoirs by accumulating the outputs of all the blocks.

Block 5_3 includes a complete inverted nine-spot well pattern of 700 m well spacing, as illustrated in FIG. 10, wherein N14_31 is a water injection well, the rest eight wells are producers, and all the water injection wells and production wells perforate all the layers in the reservoirs.

In block 5_3, the water injection well is N14_31, and all the layer of the reservoirs for this well are perforated. The total formation factor Kh of this well is 1426.46 mD-m. The total injection rate of the well is obtained as 16741 b/d from the relation between Kh and well injection rate as illustrated in FIG. 9. The injection rate of each layer for the well is calculated according to a ratio of Kh of the layer to the total Kh of the well, as shown in Table 1. If there are multiple water injection wells in the block, the total injection rate of all the water injection wells and the layer injection rates shall be calculated, respectively. And then the layer injection rates of all the water injection wells in each layer are accumulated to obtain a total injection rate of the layer.

TABLE 1
Layer injection rate of injection well N14_31
		Calculated Layer Water
	Formation Factor KH	Injection rate
Layer Name	(mD · m)	(b/d)
USM2.1	699.95	8214.62
USM2.2	21.49	252.21
USM3.1	0	0.00
USM3.2	47.21	554.06
USM3.3	29.59	347.27
USM4.1	90.55	1062.70
USM4.2	82.52	968.46
USM5.1	219.72	2578.64
USM5.2	0.9	10.56
USM5.3	2.86	33.56
USM6	231.67	2718.88
Total	1426.46	16740.95

There are totally eight production wells in block 5_3, and the production well N13_31 is taken as an example to describe the calculation of the block liquid production. All layer of the reservoirs for this well are perforated, total formation factor Kh of the well is 1403.8 mD-m, and the total liquid production rate of the well is calculated as 2436.17 b/d according to the relation between Kh and well production rate in FIG. 8. The liquid rate (production rate) of each layer of the well is calculated from a ratio of Kh of the layer to a total Kh of the well, as shown in Table 2. The total liquid production rate and the layer liquid production rate of each eight producers in block 5_3 are calculated, respectively, and then the layer liquid production rate of all the producers of each layer are accumulated to obtain the total liquid production rate of each layer.

TABLE 2
Layer production rate of production well N13_31
			Calculated Layer Oil
		Formation Factor KH	Production Rate
	Layer Name	(mD · m)	(b/d)
	USM2.1	229.1	397.66
	USM2.2	214.2	371.79
	USM3.1	6.8	11.78
	USM3.2	0.0	0.00
	USM3.3	12.7	21.99
	USM4.1	46.6	80.85
	USM4.2	494.2	857.59
	USM5.1	165.2	286.63
	USM5.2	0.8	1.32
	USM5.3	234.1	406.27
	USM6	0.2	0.28
	Total	1403.8	2436.17

Considering the injection-production balancing development (i.e. the injection-production ratio is 1), subsurface volumes of the injection rate and the production rate are the same. The total injection rate and the total production rate of each sublayer of block 5_3 are converted into subsurface volumes (multiplying the surface production rate or surface injection rate by a volume factor), the subsurface volumes of the total injection rates and total production rates of all the layers of block 5_3 are compared, and the smaller value between subsurface total injection rate and subsurface total production rate are taken as the finally verified to be the same to subsurface total injection rate and subsurface total offtake rate of the layer (in the embodiment of the present invention, the offtake rate and the production rate have the same meaning), so as to determine the finally verified total injection rate and total production rate of each layer, and predict the performance curve of the layer in conjunction with the type curve and the reserves evaluation result.

For example, layer USM4.2 of block 5_3 is a reservoir layer of type A with reserves of 6.015×106 bbl, and the finally verified injection rate of the layer is 1247.13 b/d, thus based on the type curve of 700 m inverted nine-spot well pattern of reservoir layer of type A in FIG. 6, related data (oil production rate, water production rate, water cut, injection rate, etc.) of layer USM4.2 of block 5_3 is calculated based on day time step, as illustrated in FIG. 11. Similarly, related data (oil production rate, water production rate, water cut, etc.) of each layer of block 5_3 can be calculated. The total output of block 5_3 can be obtained by accumulating the output of each layer from top to bottom, as illustrated in FIG. 12.

When situations such as infilling well pattern or well pattern type conversion occur in the production process of the block, the output calculation is continued by selecting the corresponding type curves of the new well pattern at corresponding time point, i.e., the timing at which the well pattern type is changed. Similarly, the performance curves of other blocks can be calculated, and the performance curve of the whole oil reservoirs can be obtained by accumulating the performance curves of all the blocks.

With the technical solution provided by the embodiment of the present invention, the following beneficial technical effect can be achieved: the embodiment of the present invention carries out oil reservoir technical development strategy researches based on the fine geological model of the block, and forms type curves of different reservoir types under different development strategies; at the same time, it predicts the performance of the whole oil field based on the classification result of the reservoir types of the whole oil reservoirs, the reserves evaluation result, and the evaluation results of the well production rate and injection rate. The prediction result of the present invention is more accurate and reliable; meanwhile, development performance of the complex oil reservoirs under different development strategies and different measures and conditions can be predicted, thus development performance of different schemes for the whole oil reservoirs can be quickly generated, so the man-power are greatly saved and the working efficiency is improved.

The above descriptions are just preferred embodiments of the present invention, rather than limitations thereto. As known to a person skilled in the art, various changes and modifications may be made to the embodiments of the present invention. Any amendment, equivalent change or improvement made within the spirit and principle of the present invention shall be covered by the protection scope of the present invention.

Claims

1. A method for predicting performance profile of a multi-layered oil reservoirs, comprising:

dividing the multi-layered oil reservoirs into a plurality of blocks according to reservoir types of the multi-layered oil reservoirs, and determining the reservoir type, formation factor Kh and reserves of each layer in each block;

selecting a block representing geologic features of the multi-layered oil reservoirs from the plurality of blocks as a representative block, and building a fine geological model of the representative block;

determining a relation between water cut and oil recovery efficiency of different reservoir types under different development strategies, according to the fine geological model of the representative block;

determining a relation between Kh and injection rate of single injector, and a relation between Kh and production rate of single producer in the multi-layered oil reservoirs under different operational conditions;

predicting a performance profile of the multi-layered oil reservoirs according to the relation between water cut and oil recovery efficiency, the relation between Kh and well injection rate, the relation between Kh and well production rate, and the reservoir type, Kh and OOIP of each layer in each block.

2. The method for predicting performance profile of a multi-layered oil reservoirs according to claim 1, wherein predicting performance profile of the multi-layered oil reservoirs according to the relation between water cut and oil recovery efficiency, the relation between Kh and well injection rate, the relation between Kh and well production rate, and the reservoir type, Kh and the reserves of each layer in each block comprises:

determining an offtake of each sublayer in each block according to the type curve, the relation curve between Kh and well injection rate, the relation curve between Kh and well production rate, and the reservoir type, formation factor Kh and evaluated reserves of each layer in each block;

accumulating the offtake of each layer in each block to obtain an offtake of each block;

accumulating the offtake of each block to obtain a total offtake of the whole multi-layered oil reservoirs.

3. The method for predicting performance profile of multi-layered oil reservoirs according to claim 2, wherein determining an offtake of each layer in each block according to the type curve, the relation curve between Kh and well injection rate, the relation curve between Kh and well production rate, and the reservoir type, formation factor Kh and evaluated reserves of each layer in each block comprises:

determining individual well injection rates of all water injectors in each block according to the relation curve between Kh and well injection rate and Kh of the individual well; determining individual well production rates of all producers in each block according to the relation curve between Kh and well production rate and Kh value of the individual well;

obtaining injection rate of each layer of an individual water injector by multiplying the individual well injection rate by a ratio of Kh of each layer of the well to Kh of the well; obtaining production rate of each layer of an individual producer by multiplying the well production rate by a ratio of Kh of each layer of the well to Kh of the well;

obtaining injection rate of each layer in each block by accumulating injection rates of all water injectors at the same layer in each block; obtaining production rate of each layer in each block by accumulating production rates of all oil producers at the same layer in each block;

determining the corresponding type curve of each layer according to the reservoir type and the development mode of each layer;

predicting the performance of each layer in each block according to the type curve relation between water cut and oil recovery efficiency, injection rate, production rate and evaluated reserves of each layer.

4. The method for predicting performance profile of multi-layered oil reservoirs according to claim 1, wherein the relation between water cut and oil recovery efficiency of different reservoir types under different development strategies is represented in the form of type curves, of which the horizontal axis indicates the oil recovery efficiency and the vertical axis indicates the water cut.

5. The method for predicting performance profile of multi-layered oil reservoirs according to claim 1, wherein in each block, each layer has one reservoir type, or layers more than a preset number have one reservoir type;

and/or, the boundary line of each block is matched with the deployed well pattern.

6. The method for predicting performance profile of multi-layered oil reservoirs according to claim 1, wherein the development strategies includes one of pressure maintenance level, well pattern and spacing, well type, pressure maintenance mode of water injection and gas injection, perforating strategy, oil offtake rate, injection-production ratio or arbitrary combinations thereof.

7. The method for predicting performance profile of multi-layered oil reservoirs according to claim 1, wherein the different restrictive conditions include one of different oil tubing sizes, different lifting modes, different wellhead restrictive conditions or arbitrary combinations thereof under a given oil reservoir pressure.

8. The method for predicting performance profile of multi-layered oil reservoirs according to claim 1, wherein determining a relation between Kh and well injection rate, and a relation between Kh and well production rate, of an individual water injection well in the multi-layered oil reservoirs under different restrictive conditions comprises:

determining the relation between Kh and well injection rate, and the relation between Kh and well production rate, of the individual water injection well in the multi-layered oil reservoirs under different restrictive conditions in an inflow and outflow performance evaluation method.

9. An apparatus for predicting performance profile of multi-layered oil reservoirs, comprising a processor configured to:

divide the multi-layered oil reservoirs into a plurality of blocks according to reservoir types of the multi-layered oil reservoirs, and determine a reservoir type, formation factor Kh and reserves of each layer in each block;

select a block representing geologic features of the multi-layered oil reservoirs from the plurality of blocks as a representative block, and building a fine geological model of the representative block;

determine a relation between water cut and oil recovery efficiency of different reservoir types under different development strategies, according to the fine geological model of the representative block;

determine a relation between Kh and well injection rate, and a relation between Kh and well production rate, of an individual water injection well in the multi-layered oil reservoirs under different restrictive conditions;

predict performance of the multi-layered oil reservoirs according to the relation between water cut and oil recovery efficiency, the relation between Kh and well injection rate, the relation between Kh and well production rate, and the reservoir type, Kh and the reserves of each layer in each block.

10. The apparatus for predicting performance profile of multi-layered oil reservoirs according to claim 9, wherein the processor is configured to:

determine performance profile of each layer in each block according to the relation between water cut and oil recovery efficiency, the relation between Kh and well injection rate, the relation between Kh and well production rate, and the reservoir type, Kh and the reserves of each layer in each block;

accumulate the performance of each layer in each block to obtain an performance of each block;

accumulate the performance of each block to obtain a total performance of the multi-layered oil reservoirs.

11. The apparatus for predicting performance profile of multi-layered oil reservoirs according to claim 10, wherein the processor is configured to:

determine individual well injection rate of all water injection wells in each block according to the relation between Kh and well injection rate, and individual well Kh value; determine individual well production rate of all production wells in each block according to the relation between Kh and well production rate, and individual well Kh value;

obtain injection rate of each layer of an individual water injection well by multiplying the individual well injection rate by a ratio of Kh of each layer of the individual well to Kh of the individual well; obtain production rate of each layer of an individual production well by multiplying the individual well production rate by a ratio of Kh of each layer of the individual well to Kh of the individual well;

obtain injection rate of each layer in each block by accumulating injection rates of layers of all water injection wells at the same layer in each block; obtain production rate of each layer in each block by accumulating production rates of layers of all production wells at the same layer in each block;

determine the relation between water cut and oil recovery efficiency of each layer according to the reservoir type and the development strategies of each layer;

predict the performance profile of each layer in each block according to the relation between water cut and oil recovery efficiency, the injection rate, the production rate and the reserves of each layer.

12. The apparatus for predicting performance profile of multi-layered oil reservoirs according to claim 9, wherein the processor is configured to: represent the relation between water cut and oil recovery efficiency of different reservoir types under different development strategies in the form of type curve, of which the horizontal axis indicates the oil recovery efficiency and the vertical axis indicates the water cut.

13. The apparatus for predicting performance profile of multi-layered oil reservoirs according to claim 9, wherein the processor is configured to: when dividing multi-layered oil reservoirs into a plurality of blocks, causing in each block, each layer to have one reservoir type, or layers more than a preset number to have one reservoir layer type; and/or, causing the boundary line of each block to be matched with the deployed well pattern.

14. The apparatus for predicting performance profile of multi-layered oil reservoirs according to claim 9, wherein the processor is configured to: determine the relation between Kh and well injection rate, and the relation between Kh and well production rate of the individual production well in the multi-layered oil reservoirs under different restrictive conditions in an inflow and outflow performance evaluation method.