Method of excavation of oil and gas-producting wells

Abstract

A method of opening oil- and gas productive layers has the steps of cutting of two slots in one plane so as to form a partition of rock between them and so that stresses from surfaces of slots are redistributed onto the partition and create in it additional pressure, and selecting widths of the slots and the partition such that the partition becomes so stressed that it self-destructs, and as a result a single slot is formed with a length which is equal to lengths of both initial slots and the partition.

Description

BACKGROUND OF THE INVENTION

The present invention relates to oil and gas industry, and in particular to methods of opening of oil- and gas productive layers. It relates to reliable determination and opening of oil- and gas-productive deposits, with reduction of loses for such works.

Methods of determination of oil- and gas- productive layers are known, that include detailed investigation of geological-geophysical and exploration materials over an area and cuts through the wells. However, very often, because of complicated structure and specifics of saturation of rock-collector, this objective can not be properly achieved (see V. A. Kosterina, T. V. Sokolova “Non-traditional Approach to Determination of Productive Terrigenic Collectors and Evaluation of Their Saturation”, Geophysics No. 2, 2005, EAGO). For this case it is necessary to carry out special investigations for determination of gas-oil regions.

On the other hand in some cuts through the wells water-containing layers directly adjoin gas-oil parts of the cut. Existing methods of opening (cumulative perforation) in this case creates cracks and causes a flow of water, that penetrates into a productive layer. This leads to a reduction of flow and closing of the water-filled well.

A method for increasing productivity of wells due to an increase of permeability of a near-well zone is known, in which stresses generated there are reduced due to cutting of slots along the productive layer and the slots are located in one plane symmetrically relative to the well (SU Inventor's Certificate No. 10472234 “Method of Excavation of Oil and Gas Deposits, I. M. Petukhov, L. M. Marmoshtein, et al, 1976). For cutting of shots, a significant time is needed—about 3 hours to cut through 1 meter.

A method is also known with the use of solvents simultaneously with cutting of slots. However, this method requires high energy consumption (U.S. Pat. No. 3,966,992). Slots are cut in an upper part of the productive layer along the well from 2 sides symmetrically to its axis. The device for cutting of slots is displaced along the well at a distance of h, m. Slots are cut in succession with remaining partitions of the width 1 that does not exceed the well diameter. Then the formed partition is destroyed, and the operation of slot cutting is repeated over the whole thickness of a working interval. The distance is determined in accordance with the following formula:

h>σd/2σ³{1+|1+4(σ³/σ|^1/2},

where d—is diameter; σ—is horizontal stress at a depth of location of the layer MPa; σ³ is a cubic strength of rocks of the productive layer, MPa.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to increase productivity of opening of oil- and gas-productive layers due to reliable determination of productive layers, isolation of water flows, reduction of expenses for opening of effective areas, and increase of permeability of a near-well zone of layers.

In keeping with this objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a method of opening of oil- and gas-productive layers, comprising the steps of cutting of two slots in one plane so as to form a partition of rock between them and so that stresses from surfaces of slots are redistributed-onto the partition and create in it additional pressure; and selecting widths of the slots and the partition such that the partition becomes so stressed that it self-destructs, and as a result a single slot is formed with a length which is equal to lengths of both initial slots and the partition.

The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The single FIGURE of the drawings is a schematic view illustrating a method of excavation in oil and gas-producing wells.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The method in accordance with the present invention includes cutting of two slots in one plane so as to form a partition of rock between them and so that stresses from surfaces of slots are redistributed onto the partition and create in it additional pressure; and selecting widths of the slots and the partition such that the partition becomes so stressed that it self-destructs, and as a result a single slot is formed with a length which is equal to lengths of both initial slots and the partition.

In accordance with the invention values have been determined of sizes of the slots and distances between them for self-destruction of the partitions. The partition is in extreme stressed condition with the size:

h=½·σ/σ³{1+}1+4|σ³/σ1}^1/2

The parameters in this formula take into consideration sizes of contour slot, strength characteristic of the layer (σ3) and a value of stresses taken from the slots (σ). The formula is obtained as follows.

Extreme load P_st on the partition is

P_str=C_s·σ³·h

where C_s=h/m is a coefficient of shape (since later on it is accepted that 1=m˜d, then (C_s=h/1).

Load P acting on the partition is P=σ(1+h).

Equating P and Pstr it is obtained

h/d·h σ³=(d+h)·σ

From it

$h=\frac{d}{2}·\sigma /{\sigma }^3{\left\{1+(1+4·{\sigma }^3·\sigma 1\right\}}^{1/2}$

σ and σ³ are in Mpa.

Measures of values σ and σ³ are in Mpa.

Measure of h is the same as of d, namely in mm, since the values of σ and σ³ are in measureless combinations. In the given example h is in mm.

The method in accordance with the present invention includes the following operations.

In accordance with the formula

$h=\frac{d}{2}·\sigma /{\sigma }^3\left\{1+|1+4({\sigma }^3/\sigma 1^{1/2}\right\}$

a width of self-destructive partitions is determined. In an upper part of the productive layer 1 along the well 2 slots 3 are cut from two sides symmetrically relative to the axis of the well by a known method, for example by sand-blasting perforation. The device for cutting the slots is moved along the well over a distance h. Then, a next slot 3 is cut. The operations are repeated: the slots 3 are cut with formation of the partitions 4 with a width along the axis of the well over the whole extent of the productive layer 1.

After self-destruction of the partitions 4 two symmetrical vertical shots are formed, equal to the extent of the productive layer 1. The width of the shots can be not less than 2 diameters of the well, and the thickness—not less than 30 mm. The present invention is illustrated by the following example.

Length of the slots 1 is selected to be equal to a diameter of the well d=200 mm. Then the length of the self-destructing partitions h is determined.

H=200/2·40/120{1+(1+4·120)40)^1/2=153 mm˜150 mm.

The number of slots in the productive interval is calculated, and the obtained value is determined to an integral number toward a lower side

H+(5000+h)/(d+h)=(5000+150)/(200+150)=14.7˜14.

A sand-blasting perforator with a motor adjusted to the speed of 5 mm/min is introduced into the well, and attachments of the sand-blasting perforator are installed at a depth 2005.8 m. A working liquid with quarts sand and having a fraction 0.6-1.0 mm is supplied into the perforator with pressure at the mouth 20 Mpa for 40 min. During this time a slot with the length 200 mm will be cut through. Then the tool is lifted by 550 mm without rotation, and second slot is cut through. Similarly remaining 12 slots are cut through. After cutting through of the last slot the well is washed to clean water.

The method in accordance with the present invention allows determining borders of productive layers, reliably open productive layers, and significantly reduced expenses for forming unloading slots.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of methods differing from the type described above.

While the invention has been illustrated and described as embodied in a method of excavation in oil and gas-producing wells, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.

Claims

1. A method of opening oil-and gas productive layers, comprising the steps of cutting of two slots in one plane so as to form a partition of rock between them and so that stresses from surfaces of slots are redistributed onto the partition and create in it additional pressure; and selecting widths of the slots and the partition such that the partition becomes so stressed that it self-destructs, and as a result a single slot is formed with a length which is equal to lengths of both initial slots and the partition.

2. A method as defined in claim 1, wherein the slot is cut over a height 1 not less than a diameter of a well, a cutting device is moved along the well over a distance determined as follows: Where d is a diameter of the well, in m, then cutting a next slot over the same height; destroying the formed partition; and repeating the steps of cutting and destroying over a whole thickness of an interval of work.

H>(σ·d)/2/β3{1+|1+4(σ3/σ|1/2}

σ—is a horizontal stress at a depth of the layer, Mpa,

σ3—is a cubic strength of rocks of productive layer, Mpa,

h—is a distance, m;