METHODS FOR IDENTIFYING COMPOUNDS USEFUL FOR PRODUCING HEAVY OILS FROM UNDERGROUND RESERVOIRS

Described herein are methods for identifying compounds useful for producing heavy oil from an underground reservoir. The methods facilitate the development of chemicals with improved physicochemical features. The methods generally involve first identifying a physicochemical property of a compound that needs to be improved in order to increase the efficiency of heavy oil removal from underground reservoirs. Next, the physicochemical property is calculated by molecular modeling using semi-empirical or ab-initio calculations. By modifying the molecular model of the compound, the targeted physicochemical property can be optimized. After a suitable compound has been identified, the compound can be synthesized and evaluated.

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Description
CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application No. 60/985,316, filed Nov. 5, 2007, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The number of steam assisted gravity drainage (SAGD) wells drilled in countries such as Canada is expected to increase in view of current demands for oil and fuels. In view of this, improving the production rate and/or increasing the total recovery from SAGD wells, and by Huff and Puff and cyclic steam stimulation (CSS) of wells, through the use of chemicals is highly desirable. Chemistry that can enhance the sweeping efficiency of the injected steam or hot water in the heavy oil reservoir is particularly desirable. When this approach is used globally in a reservoir, the production rate and total recovery is enhanced. Alternatively, when it is used locally, the use of chemicals can increase the local sweeping efficiency in reservoir regions having reduced permeability or poor quality. In SAGD operations, where a number of horizontal wells are used to reach every part of the producing reservoir segment, the underperforming regions may be identified by measuring the temperature distribution along the injection wells with distributed temperature sensing (DTS) systems. These regions can then be treated with targeted coiled tubing (CT) delivery of chemicals. Optimally, the CT delivery should be performed during steam injection, although treatment in the steam interruption periods can also be considered. Integrated CT services may be delivered, which include both the recognition and chemical mitigation of problems stemming from reduced permeability or poorer quality reservoirs.

2. Description of Related Art

In practice, SAGD and CSS is unlikely to reach 100 percent recovery of swept zones, which would require significant time and energy consumption to recover all the contained oil. The hindered recovery of heavy oils can be attributed to both the unfavorable wetting properties of the solid matrix and the high interfacial tension between the organic and aqueous phases. The oil is trapped in narrow capillaries, where the gravitational and hydrodynamic driving forces cannot overcome the resisting capillary forces. The Laplace pressure difference keeps the oil phase trapped in the capillaries. When the oil-water (O/W) interfacial tension (IFT) is sufficiently reduced, it is possible to remove most of the trapped oil. However, a fraction of the oil phase remains trapped in the capillaries because of the oil-wet condition of the reservoir. The oil can also be trapped when there are narrow passes in the capillaries, even in case of a water-wet reservoir. This is due to the Laplace pressure difference. High oil-water interfacial tension can also prevent the release of the organic phase from dead-capillary ends.

The reduced O/W IFT and the altered reservoir wetting during SAGD or CSS operations improve the useful transport processes within the steam chamber and in the water condensation region. These techniques, when applied locally, provide a number of advantages, including increased water flux through the solid matrix, homogeneous temperature distribution along the horizontal well, and homogeneous steam input into the formation along the horizontal well. When applied globally in a reservoir, an increase in oil production rate and steam chamber dimensions can be achieved, resulting in a reduced number of wells. Additionally, the life cycle is reduced and less residual oil remains in the reservoir after the total life cycle of the operation.

It follows from the above that the reduction of the O/W IFT is an important consideration for increasing efficiency. Surfactants can be used to reduce interfacial tension. For the high temperature conditions under which SAGD, CSS, and thermal recovery processes operate, surfactants of high thermal stability are needed. Surfactants are not intended to be used within the 150-350° C. range, which is the temperature range of SAGD, CSS, and other thermal recovery processes. Hence, there is a need for surfactants and other compounds possessing desirable properties (e.g., high thermal stability) that can effectively remove heavy oils from underground reservoirs.

BRIEF SUMMARY OF THE INVENTION

Described herein are methods for identifying compounds useful for producing heavy oil from an underground reservoir. The methods facilitate the development of chemicals with improved physicochemical properties. The method generally involves first identifying a physicochemical property of a compound that needs to be improved in order to increase the efficiency of heavy oil removal from underground reservoirs. Next, the physicochemical property is calculated by molecular modeling using semi-empirical or ab-initio calculations. By modifying the molecular model of the compound, the targeted physicochemical property can be optimized. After a suitable compound has been identified, the compound can be synthesized and evaluated.

The advantages of the materials, methods, and articles described herein will be set forth in part in the description which follows, or may be learned by practice of the aspects described below. The advantages described below will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying Figures, which are incorporated in and constitute a part of this specification, illustrate several aspects described below.

FIG. 1 shows a flow diagram for a process for optimizing a physicochemical property of a compound.

FIG. 2 shows the geometrically optimized 3D model of the neutral sodium dodecyl sulfate (SDS) molecule.

FIG. 3 shows the structurally optimized 3D model of neutral sodium dodecylbenzene sulfonate (SDBS) molecule.

FIG. 4 shows the temperature distribution after 240 days of steam injection during a SAGD recovery process, where the horizontal color-bar makes it possible to read the temperatures at different locations of the steam chamber in ° C.

FIG. 5 shows the flow rate distribution of the water phase in the vertical direction after 240 days of steam injection during a SAGD recovery process. The positive value of flow rate indicates downward flow toward the producing well while the negative value of flow rate indicates upward flow from the injection well.

FIG. 6 shows the air/aqueous interfacial tension of SDBS solutions at 20° C. and atmospheric pressure as a function of solute mole fraction (X).

FIG. 7 shows the air/aqueous interfacial tension of SDBS solutions at 20° C. and atmospheric pressure as a function of solute mole fraction (X).

FIG. 8 shows the air/aqueous interfacial tension of SDS at 20° C. and atmospheric pressure as a function of solute mole fraction (X).

FIG. 9 is a flow diagram showing the recursive improvement of multiple physicochemical properties.

 DETAILED DESCRIPTION OF THE INVENTION

Before the present materials, articles, and/or methods are disclosed and described, it is to be understood that the aspects described below are not limited to specific compounds, synthetic methods, or uses, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

In this specification and in the claims that follow, reference will be made to a number of terms that shall be defined to have the following meanings:

Throughout this specification, unless the context requires otherwise, the word “comprise,” or variations such as “comprises” or “comprising,” will be understood to imply the inclusion of a stated integer or step or group of integers or steps, but not the exclusion of any other integer or step or group of integers or steps.

It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “an oil” includes a single oil or mixtures of two or more oils.

“Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

Described herein are methods for identifying compounds useful for producing heavy oil from an underground reservoir. Techniques for producing heavy oils include, but are not limited to, steam foams, foams formed with noncondensable gas, steam assisted gravity drainage (SAGD), cyclic steam stimulation (CSS), or steam flooding processes. However, other applications such as enhanced oil recovery or flow assurance can also be considered. In general, the compounds will be used under harsh conditions (e.g., high temperature and pressure). Thus, compounds possessing physicochemical properties that are compatible with these techniques can be useful in increasing the removal efficiency of heavy oils.

In one aspect, the method comprises:

selecting a starting compound useful in producing heavy oil from an underground reservoir and a physicochemical property of the starting compound to be improved;

constructing a molecular model of the starting compound;

constructing a combined property associated with the physicochemical property of the starting compound using one or more sub-properties of a sub-property set of the starting compound;

calculating the combined property of the molecular model of the starting compound;

altering the molecular model of the starting compound to produce a modified molecular model;

calculating the combined property of the modified molecular model;

comparing the combined property of the modified molecular model with the combined property of the molecular model of the starting compound; and

determining if the combined property of the modified molecular model is improved relative to the combined property of the molecular model of the starting compound.

The first step involves selecting a starting compound useful in a process for producing heavy oil that has at least one physicochemical property that can be improved upon. By improving at least one physicochemical property of the starting compound, the efficiency of heavy oil removal is ultimately increased. A number of different types of compounds are used to remove heavy oils from underground reservoirs. For example, surfactants, polymers, emulsifiers, demulsifiers, corrosion inhibitors, asphaltene inhibitors, gas hydrate inhibitors, foam forming compounds, and any combination thereof can be injected into a reservoir.

Using the methods described herein, the starting compound can be modified and evaluated in order to determine if one or more physicochemical properties of the modified compound have improved. The term “physicochemical property” is defined herein as any inherent property of a compound that can be altered by modifying the compound. The selection of the physicochemical property can vary depending upon the end use of the compound. For example, when high temperature processes are used to remove heavy oil, the physicochemical property of the compound of interest (e.g., a surfactant or polymer) can be thermal stability or reduction in coke formation.

In another aspect, the physicochemical property is the performance of the compound. The term “performance” is defined herein as the ability of the compound to improve oil recovery. In the case when the compound is a surfactant, there are different ways to measure the improved recovery. For example, improved oil recovery occurs when the surfactant increases the total recovered oil (i.e., integrated recovery) over time compared to the absence of surfactant. Alternatively, the increase of the oil recovery rate in the presence of surfactant can be measured. For example, core flooding experiments in the presence and absence of surfactant can be performed and the total amounts of recovered oil can be compared.

Other physicochemical properties include, but are not limited to, (1) increasing the solubility of molecules belonging to a specific molecular class; (2) improving the dielectric permittivity of molecules; (3) improving the interfacial activity of surfactants; (4) improving the oil solubilization capability of surfactants; (5) improving the emulsion breaking capabilities of demulsifiers; (6) improving the corrosion inhibition capability of corrosion inhibitors; (7) increasing the adsorption of molecules on solid/liquid, liquid/liquid, or liquid/gas interfaces, (8) improving the performance of gas hydrate inhibitors (i.e., capability to prevent gas hydrate formation or deposition), (9) improving the performance of asphaltene inhibitors (i.e., prevent asphaltene association, precipitation or deposition), (10) improving the thermal stability and/or foam stability of steam or noncondensable gas foams, (11) increasing the viscosity of foams, (12) reducing the oil-water interfacial tension of surfactants, (13) enhancement of microemulsion formation, (14) reduction in the wetting angle that water forms in contact with the reservoir rock surface when the incorporating liquid is crude oil, or any combination thereof.

After a starting compound has been selected, a molecular model of the starting compound is produced. Generally, molecular modeling studies involve three stages. In the first stage, a model is selected to define the intra- and inter-molecular interactions in the system. The two most common models that are used in molecular modeling are quantum mechanics and molecular mechanics. These models enable the energy of any arrangement of the atoms and molecules in the system to be calculated, and allow the modeler to determine how the energy of the system varies as the positions of the atoms and molecules change. The second stage of the study is the calculation itself, such as an energy minimization, a molecular dynamics or Monte Carlo simulation, or a conformational search. Finally, the calculation is analyzed, not only to calculate properties but also to check that it has been performed properly.

Molecular modeling programs known in the art for designing and quantifying certain features of the compound can be used herein. In one aspect, Materials Studio 4.2 software, available from Accelrys, Inc. of San Diego, Calif., USA, can be used herein. The selection of the molecular modeling program can be based partially on the physicochemical property and sub-property of the physicochemical property to be evaluated. For example, if the physicochemical property to be evaluated is thermal stability, the sub-property associated with thermal stability that can be evaluated may be, but is not limited to, decomposition energy, decomposition rate, enthalpy of formation, enthalpy of decomposition, flash point, bond dissociation energy of the bond having the smallest bond order, hydrolysis energy of the bond having the smallest bond order, hydrolysis energy in the presence of silica of the bond having the smallest bond order, hydrolysis energy in the presence of clays of the bond having the smallest bond order, or any combination thereof. Once the sub-property is selected, the molecular modeling program evaluates the sub-property. The term “evaluate” as used herein involves qualitatively and/or quantitatively determining the sub-property. For example, if the physicochemical property is thermal stability, and the sub-property is bond dissociation energy, the bond dissociation energy of several bonds in the starting compound can be provided by the molecular modeling program. Moreover, if the physicochemical property is thermal stability, the sub-property set may include the reaction rate and/or the activation energy of the decomposition reaction. One can approach these terms by considering the energy changes during the decomposition process. Spontaneous processes have a negative free energy (G) change. The free energy change ΔG=ΔH−TΔS (where ΔH is the enthalpy change, T is the absolute temperature, and ΔS is the entropy change). When ΔG calculated for the difference between the reactants and product, is negative, the chemical reaction is naturally occurring without outside intervention. Therefore, it is crucial to know the free energy change to decide whether or not a reaction will proceed spontaneously. Under given conditions, a molecule is thermally unstable if the G of the (assumed) decomposition products is smaller than the G of the original molecule. When a molecule is thermally unstable, it is important to know the reaction rates of the decomposition. The decomposition rates are important because, although a selected molecule could be thermodynamically unstable, its application is still feasible if the decomposition rate is low enough. There may be a considerable difference between the decomposition rates of two molecules having the same decomposition ΔG. The reaction energy path determines reaction rates. The reaction should overcome the activation energy barrier. The higher the barrier, the slower is the reaction. The activation energy barrier is associated with the energy of the activated complex. The reaction rates are also dependent on temperature, because for a chemical reaction to have a significant rate there must be a noticeable number of molecules with the energy equal or greater than the activation energy. The most common way to increase the population of higher energy molecules is to increase the temperature. One can calculate the activation energy from the structure of the activated complex using molecular modeling software. In a further example, if the compound is an asphaltene inhibitor, the physicochemical property may comprise prevention of asphaltene association, precipitation, or deposition, and the sub-property set will comprise the association energy between asphaltene molecules and the association energy between the asphaltene inhibitor and asphaltene molecules.

In other aspects, two or more sub-properties (designated herein as P(combined)) can be used to evaluate a physicochemical property. For example, if the physicochemical property is the solubility of the molecule in a specific solvent, the P(1), . . . , P(N) sub-property set could be the solute-solute interaction energy (EUU), solvent-solvent interaction energy (EVV), and the solvent-solute interaction energy (EVU). In this example, P(combined) can be expressed by the following equation: (nVU×EVU)−(nVV×EVV)−(nUU×EUU), where nVU is the number of solvent molecules in the first solvation layer surrounding the solute; and nVV and nUU are the coordination numbers in the pure solvent and solute, respectively. If the solute is an electrolyte, then the Born energy is also included in the sub-property set.

In another aspect, when the physicochemical property is the frequency dependent dielectric permittivity, then the P(1), . . . , P(N) sub-property set can be the molar volume, dipole moment, and the rotational diffusion coefficient. In this aspect, P(combined) can be calculated based upon these sub-properties. In a further aspect, when the physicochemical property is the interfacial activity of a surfactant, the sub-property includes the Hydrophile-Liphophile Balance (HLB) number (i.e., balance between the oil soluble and water soluble moieties in a surface active molecule), adsorption enthalpy, and critical micelle concentration (CMC) value (i.e., the concentration above which the formation of micelles is observable) of the surfactant.

After a particular sub-property of the starting material has been evaluated, the molecular model of the starting compound is modified. The modification of the starting compound is intended to improve the selected sub-property of the starting compound. The term “improve” is defined herein as any enhancement of the sub-property of the modified compound relative to the starting compound. For example, the bond dissociation energy of a selected bond in the modified compound can be higher when compared to the same or similar bond in the starting compound. Alternatively, the bond dissociation energy of the weakest bond in the modified compound can be higher when compared to the bond dissociation energy of the weakest bond of the starting compound. The improvement can also be the reduction of a desired property. For example, the modified compound can exhibit reduced hydrophilicity compared to the starting compound (i.e., increased hydrophobicity).

The methods described herein can be applied sequentially to improve more than one physicochemical property. During the improvement of the second physicochemical property, the first one might be altered. In the event this occurs, a recursive application of the design process can be introduced as depicted in FIG. 9. For example, when a surfactant is evaluated, the F(j) physicochemical property of the surfactant can be thermal stability and the F(j+1) physicochemical property is the ability of the surfactant to remove heavy oil from the reservoir (i.e., performance). Alternatively, if a sub-property was improved but the experimental physicochemical property (i.e., the thermal stability) was not improved, another sub-property associated with thermal stability such as, for example, hydrolysis energy in the presence of silica, can be evaluated. This is depicted in FIG. 1 (arrow from Step 14 to Step 3). Alternatively, if the calculated P(combined) value of the modified compound was not improved (Step 8 in FIG. 1), Step 5 in FIG. 1 can be repeated by modifying the starting compound differently.

After the physicochemical property(ies) of the modeled compound have been optimized, the modeled compound is synthesized and the physicochemical properties are evaluated experimentally. In the case when it is not feasible or economic to synthesize the modified compound (Step 9 in FIG. 1), Step 5 in FIG. 1 can be repeated by modifying the starting compound differently to produce a modified compound that is easier to synthesize. In the case when the modeled compound is commercially available, it is not necessary to synthesize the compound. When experimentally evaluating the modeled compound, it is desirable to reproduce the conditions in the underground reservoir. For example, when evaluating the thermal stability of the compound, SAGD process conditions can be used.

EXAMPLES

The following examples are set forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, and methods described and claimed herein are made and evaluated, and are intended to be purely exemplary and are not intended to limit the scope of what the inventors regard as their invention. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.) but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in ° C. or is at ambient temperature, and pressure is at or near atmospheric. There are numerous variations and combinations of reaction conditions, e.g., component concentrations, desired solvents, solvent mixtures, temperatures, pressures, and other reaction ranges and conditions that can be used to optimize the product purity and yield obtained from the described process. Only reasonable and routine experimentation will be required to optimize such process conditions.

Below is an exemplary procedure for improving one or more physicochemical properties of compounds useful for producing heavy oil. The procedure is shown schematically in FIG. 1.

Example 1 Improve the Thermal Stability of Surfactants Useful in SAGD Applications

  • 1) Define a physicochemical property. F(j), of existing chemical compound (CC) to be improved.

In this example, sodium dodecyl sulfate (SDS) surfactant is CC and the physicochemical property (F(j)) is thermal stability.

  • 2) Construct a molecular model of CC (MM-CC).

From the known chemical structure, construct the three-dimensional (3D) molecular model of SDS.

Geometrical optimization was used to fine-tune the structure of the model. The resulting 3D structure is presented in FIG. 2. This structure is the molecular model of the SDS chemical compound, which is designated as MM-CC. Spheres 13-37 represent hydrogen (H), spheres 1-12, carbon (C), spheres 38 and 40-42, oxygen (O), sphere 39, sulfur (S), and sphere 43, sodium (Na), atoms. The small numbers on the atoms identify the specific atoms. Materials Studio 4.2 software was used for the structure construction and the geometrical optimization.

  • 3) Construct a combined property, designated as P(combined), by using P(1), P(2), . . . , P(N) sub-property set.

The sub-properties for evaluating thermal stability are defined as follows: P(1)=enthalpy of formation, P(2)=flash point, etc. P(combined)=bond dissociation energy of the bond having the smallest bond number, P(combined+1)=hydrolysis energy, P(combined+2)=hydrolysis energy in the presence of silica, etc. The combined property in this specific example is defined as follows: P(combined)−bond dissociation energy of the bond having the smallest bond number.

  • 4) Calculate the P(combined) property of MM-CC (P(combined){MM-CC}).

Determination of the bond numbers of the bonds of the molecular model (i.e., FIG. 2) of SDS. The results are presented in Table 1.

TABLE 1 Bond orders of the different bonds in both the neutral SDS molecule and the anion. Neutral Anion (as a result of the molecule dissociation of Na+) Bond Bond orders Bond orders Na43—O42 0.28 O42—S39 1.01 1.09 O40—S39 1.20 1.12 S39—O38 0.56 0.44 O38—C12 0.94 1.00

Selection of the bond with the smallest bond order. From Table 1 the Na43-O42 bond has the smallest bond order in the neutral molecule. This bond will require the smallest energy to break. This conclusion is in line with ionic dissociation. SDS is a salt that dissociates in water. Since SDS is going to be used in the SAGD process where water is abundant, anion formation will occur. In fact, the SDS anions are responsible for the surfactant behavior in water. Therefore, the properties of the SDS anion were investigated only. Referring to Table 1, the bond with the smallest bond order in the SDS anion is the S39-O38 sulfur-oxygen bond.

Calculating the bond dissociation energy of the bond having the smallest bond order. Having identified the weakest bond in the SDS anion, the bond dissociation energy of this bond was calculated. The calculated bond dissociation energy of the S39-O38 sulfur-oxygen bond is 32.73 kcal/mol. This quantity was calculated by the VAMP-DMol3 routines of the Materials Studio 4.2 software. This quantity is P(combined) {MM-CC}.

  • 5) Alter the chemical structure of the molecular model MM-CC.

The chemical structure of MM-CC was altered. A benzyl ring was attached to the C12 chain and replaced the S39-O38 sulfur-oxygen bond with a S38-C46 sulfur-carbon bond as indicated in FIG. 3. Spheres 13-37 and 49-52 represent hydrogen (H), spheres 1-12 and 43-48, carbon (C), spheres 39-41, oxygen (O), sphere 38, sulfur (S), and sphere 42, sodium (Na), atoms. The small numbers on the atoms identify the specific atoms. This new molecule is the sodium dodecylbenzene sulfonate (SDBS) which is designated as N-MM-CC.

  • 6) Calculate the P(combined) property of N-MM-CC (P(combined){N-MM-CC}).

Determination of the bond numbers of the bonds of the molecular model (i.e., FIG. 3) of SDBS. The results are shown in Table 2.

TABLE 2 Bond orders of the different bonds in both the neutral SDBS molecule and the anion. Neutral Anion (as a result of the molecule dissociation of Na+) Bond Bond orders Bond orders Na42—O41 0.38 O41—S38 0.98 1.11 O39—S38 1.22 1.11 S38—C46 0.55 0.42 C43—C12 0.99 0.99

Selection of the bond with the smallest bond order. Table 2 indicates that the smallest bond order in the neutral molecule is the Na42-O41 bond. This bond will require the smallest energy to break. As discussed above, since SDBS is going to be used in the SAGD process where water is abundant, anion formation will occur. Similar to SDS, the properties of the SDBS anion were evaluated. The bond with the smallest bond order in the SDBS anion is the S38-C46 sulfur-carbon bond as indicated in Table 2.

Calculate the bond dissociation energy of the bond having the smallest bond order. The bond dissociation energy of S38-C46 in SDBS was calculated. The bond dissociation energy of the S38-C46 sulfur-carbon bond is 81.24 kcal/mol. This quantity was calculated by the VAMP-DMol3 routines of the Materials Studio 4.2 software. This quantity is P(combined){N-MM-CC}.

  • 7) Compare P(combined){MM-CC} with P(combined){N-MM-CC}.

The bond dissociation energy of the S39-O38 sulfur-oxygen bond in SDS is 32.73 kcal/mol. This is smaller than the bond dissociation energy of the S38-C46 sulfur-carbon bond in SDBS, which is 81.24 kcal/mol. Consequently, it is more difficult to break the weakest bond in SDBS than in SDS.

  • 8) Evaluate P(combined) property of the new molecular model.

Because the bond dissociation energy of the weakest bond of the SDBS molecular model is higher than the bond dissociation energy of the weakest bond of the SDS molecular model, the P(combined) property (i.e., the bond dissociation energy of the bond having the smallest bond number) was improved. In other words, it is more difficult to break the weakest bond in SDBS than in SDS, which implies that F(j) (i.e., the thermal stability) was improved.

  • 9) Evaluate synthesis of the new molecule (N—CC).

Since SDBS is an industrially produced surfactant, the synthesis of the new molecule is feasible and economic. However, in the event the compound is not commercially available, the feasibility of synthesizing the new compound will be evaluated.

  • 10) Chemical synthesis of the new molecule (N—CC).

Due to the commercial availability of SDBS, this step is not necessary. However, in the case of new compounds, chemical synthesis will be required.

  • 11) Experimental measurement of either the physicochemical property (F(j)), or measurement and calculation of P(combined), or a sub-property associated with P(combined) of SDBS (designated as F(j){N—CC}).

F(j) was defined in Step 1 of FIG. 1 as the thermal stability of the chemical compound (CC). The thermal stability and the actual thermal conditions of the SAGD process for evaluating the thermal stability were evaluated.

a) Thermal Stability

Thermal instability of a compound can be characterized by the decomposition rate of the compound under the given conditions. This rate is temperature dependent. Sophisticated instrumentation is necessary to measure reaction rates. It is easier to measure the percentage of the activity decay of the chemical compound after holding the material at a specified temperature for a given time i.e., after heat treatment. The surface activity decrease of the compound is the most relevant, because this property is related to the intended usage of surfactants in the SAGD process for the removal of heavy oil.

The surface activity of the surfactant by interfacial tension measurements was characterized. The air-water interfacial tension as a function of the natural logarithm of the mole fraction of the surfactant was plotted. From this plot, the Gibbs adsorption excess can be calculated. This plot is also instrumental in obtaining the critical micellar concentration (CMC) from the break point of the curve. Assuming that the thermal decomposition process produces compound(s) of negligible interfacial activity, the shift of the CMC value of the heat treated material as compared to the original one is related to the amount of the missing (decomposed) surfactant molecules (i.e., it is only possible to plot the apparent concentration of the surfactant since the amount of the decomposed fraction is not known). The CMC (original surfactant)/CMC (partially decomposed surfactant) ratio is equivalent to the concentration of the active (non-decomposed) compound in the heat treated compound/total concentration of the initially present compound. The ratio quantitatively characterizes the amount of decomposed surfactant and, thus, the thermal stability. There is no decomposition if the ratio is 1, with increasing decomposition as the ratio decreases.

In addition to the CMC shift, the concentration shift of any pre-selected interfacial tension (IFT) value can be used to characterize the thermal stability, because the decomposition is equivalent to a transformation (division with a constant) of the concentration axis. Other experimental techniques such as, for example, the determination of the dissolved number of moles by osmometry, can also be used to detect the thermal decomposition. However, this technique is qualitative. Thus, CMC (original surfactant)/CMC (partially decomposed surfactant) was used to evaluate F(j){N—CC}.

(b) Actual Thermal Conditions of the SAGD Process

To evaluate thermal decomposition, the thermal strain the surfactant experiences when it is used under SAGD conditions was determined. There are two components of the thermal strain: the temperature and the time the material is exposed to this temperature. Reservoir simulation was used to obtain these parameters at different stages of the production. The ECLIPSE reservoir simulation program, available from Schlumberger Technology Corporation of Sugar Land, Tex., USA, was used for the calculations.

(i) Simulation Parameters

    • 90 percent quality steam was injected at 45 bar (652.8 psia), which corresponds to 258° C. for 240 days.
    • After 240 days, 90 percent quality steam was injected at 25 bar (362.7 psia), which corresponds to 224° C.
    • The shortest residence time was calculated from the flow of the water phase in all directions through the shortest distance between injector and producer (5 meters straight down from injector to producer).
    • The longest residence time was calculated from the flow of the water phase in all directions through the longest distance at the outer edge of the steam chamber where the highest water saturation was observed.
    • Horizontal permeability: 6000 mDarcy.
    • Vertical permeability: 3000 mDarcy.
    • Porosity: 0.34.
    • Initial oil saturation: 85 percent.
    • Irreducible water saturation: 15 percent.
    • Initial reservoir conditions: P=13.5 bar (195.8 psia), T=10° C.

(ii) Obtained Temperature Distribution

FIG. 4 shows the temperature distribution after 240 days of steam injection during a SAGD recovery process.

(iii) Obtained Water Flow Rate Distribution

FIG. 5 shows the flow rate distribution of the water phase in the vertical direction after 240 days of steam injection during a SAGD recovery process.

(iv) Thermal Strain on an Injected Water Soluble Chemical

Table 3 shows the residence times of a water soluble material in the steam chamber of the SAGD process along with the corresponding temperatures at different stages of production. The residence times together with the corresponding temperatures determine the thermal strain. The results indicate that the injected surfactant should survive about 250° C. for 1 day at least.

TABLE 3 Longest Time from Shortest Corre- residence Corre- beginning residence sponding time sponding (days) Phase time (days) T (C.) (days) T (C.) 100 Early 7 258 15 234 steam rise 145 Steam rise 6 258 34 226 240 Steam 1 258 53 219 reaching top of formation 430 Steam 2 224 62 209 spread

c) Thermal Testing of the New Chemical Compound (N—CC)

(i) Experimental Procedure for Cleaning and Charging a 25 ml High Pressure Reaction Vessel

Prior to performing the experiment, the reaction vessel such as a Parr 4791 25 ml reactor was thoroughly cleaned to prevent contamination. If there was any discoloration/oxidation present from previous heating on the interior of the vessel, the metal was exposed with a mild abrasive such as Scotch-Brite pads. The entire interior of the vessel was first cleaned with warm water, concentrated laboratory soap, and a soft brush. Care must be taken to vigorously rinse the vessel to remove all traces of soap. The interior of the vessel was then rinsed with high purity de-ionized (DI) water (resistivity of 18.2 MΩ) to remove any contamination from the tap water. Finally, a high purity volatile water soluble solvent such as HPLC Grade acetone was used to remove excess water in the vessel. Solvent that does not completely evaporate is removed by using compressed nitrogen.

The reactor is loaded with the sample in an oxygen-free environment, such as a nitrogen atmosphere glovebox, to simulate downhole conditions. Oxygen-free high purity DI water was used to make solutions and limit the amount of oxygen present. Oxygen-free water was made by boiling water for 30 minutes in an oxygen-free environment. The container must be sealed after boiling to prevent oxygen in the atmosphere from dissolving back into the water.

The glovebox has all of the components necessary to charge the vessel before nitrogen purging begins. This includes the reaction pressure vessel, tools to seal the vessel, oxygen-free water, pipettes to transfer water, and the surfactant sample. The surfactant sample having a known mass between 0.5-1.5 grams is placed in a sealed container of known mass. Once the oxygen level in the glovebox was measured below 50 ppm, the oxygen free DI water was added to the reactor. The solubility of each surfactant in water at 20° C. should be checked prior to charging so that enough oxygen free DI water is added to the vessel to ensure that the surfactant powder completely dissolves. The liquid volume in the pressure vessel does not exceed more than half of the total volume of the vessel to allow for expansion. After adding the DI water the surfactant powder is slowly added to create a solution. Once the components were added, the reactor was sealed with the appropriate tools and removed from the glovebox. The mass of the empty container that held the surfactant was measured again to determine the residual mass of surfactant, and accordingly the mass of surfactant added to the reactor.

Once sealed, the reaction vessel was heated with an apparatus such as a heating jacket that is coupled with a controller to regulate the fluid temperature, which is measured by a thermocouple inside the vessel. The interior of the vessel is at atmospheric pressure before heating. Upon heating, the pressure inside the vessel is approximately equal to the vapor pressure of pure water at the temperature of the fluid. Insulation, such as aramid tape, was wrapped around the reaction vessel to prevent excessive heat loss at higher temperatures. The time that the fluid takes to reach the temperature setpoint and the time that the fluid remains at the setpoint was recorded. Once the desired time interval at the setpoint was reached, the power to the heater was disengaged, any insulation was removed, and the vessel was left to cool unaided.

(ii) Removing Surfactant Sample from 25 ml High Pressure Reaction Vessel After Heating

Prior to extracting the solution from the reaction vessel, an Erlenmeyer flask with lid and a large funnel were cleaned using the same procedure as for the reaction vessel. The weight of the dry Erlenmeyer flask and lid was determined before the solution was added. The reaction vessel was disassembled cautiously so as to not spill any solution condensed on the walls. The solution was poured into the Erlenmeyer flask using a large funnel and all interior parts of the vessel were rinsed into the flask with a wash bottle containing DI water. Care was taken not to spill any solution outside of the flask. The total mass of the flask and water solution was determined. The mass concentration (grams surfactant/grams total) was determined using the recorded surfactant powder mass in the vessel and the total mass of solution. The mass of DI water and surfactant required was considered in advance so that the rinsed solution is not too dilute for the forthcoming air/aqueous interfacial tension measurements.

(iii) Making Dilutions of the Solution and Testing Air/Aqueous Interfacial Tension of the Chemical Compound (CC)

Approximately 10-12 dilutions were created from the original solution obtained from the reaction vessel. Half of the dilutions were above and the other half below the reference critical micelle concentration (CMC) of the surfactant in question. The reference CMC was determined by creating dilutions of a non-thermal treated surfactant solution and plotting the air/aqueous interfacial tension of each dilution as a function of the molar fraction of the dilutions on a logarithmic scale. When lines of best fit were drawn for each curve, the intersection point provides the CMC. When analyzing air/aqueous interfacial tension, at least six individual drops were measured for interfacial tension from one dilution to ensure repeatability and to ascertain the standard deviation of the data. More than six points of data were taken if the data seemed unnaturally skewed or inconsistent.

(iv) Experimental Results

SDBS was tested by thermally treating the compound at various time intervals and temperatures. The thermal stability of the compound was evaluated by comparing the plot of the air/aqueous interfacial tension as a function of the molar fraction of surfactant in solution on a logarithmic scale. FIGS. 6 and 7 show the air/aqueous interfacial tension of SDBS as a function of solute mole fraction after thermal treatment at various temperatures. There was no evident shift in the CMC after the SDBS was thermally treated at three different temperatures for varying time intervals, which indicates that there was no decomposition during thermal treatment.

  • 12) Experimental measurement of either the physicochemical property (F(j)), or measurement and calculation of P(combined), or a sub-property associated with P(combined) of SDS (designated as F(j){CC}).

Using the techniques described above in Step 11, the thermal stability of SDS under SAGD process conditions was evaluated. FIG. 8 shows the Air/Aqueous Interfacial Tension of SDS at 20° C. and atmospheric pressure as a function of Solute Mole Fraction (X).

  • 13) Comparison of F(j){CC} with F(j){N—CC)}.

CMC (original surfactant)/CMC (partially decomposed surfactant)=1 for SDBS at each set of conditions at which it was tested. With respect to SDS, the ratio was 1.4×10−4/5.0×10−4=0.28 after two hours at 250° C. and 600 psi.

  • 14) Evaluate improvement of the physicochemical property F(j) of the newly synthesized or selected molecule N—CC.

The property F(j) of the newly synthesized or selected molecule, N—CC (SDBS) was improved.

  • 15) Conclusion.

SDBS has improved thermal stability when compared to SDS and may be suitable for producing heavy oil using SAGD process conditions.

Various modifications and variations can be made to the compounds, compositions, and methods described herein. Other aspects of the compounds, compositions, and methods described herein will be apparent from consideration of the specification and practice of the compounds, compositions and methods disclosed herein. It is intended that the specification and examples be considered as exemplary.

Claims

1. A method for identifying a chemical compound useful for producing heavy oil from an underground reservoir comprising:

(a) selecting a starting compound useful in producing heavy oil from an underground reservoir and a physicochemical property of the starting compound to be improved;
(b) constructing a molecular model of the starting compound;
(c) constructing a combined property associated with the physicochemical property of the starting compound using one or more sub-properties of a sub-property set of the starting compound;
(d) calculating the combined property of the molecular model of the starting compound;
(e) altering the molecular model of the starling compound to produce a modified molecular model;
(f) calculating the combined property of the modified molecular model;
(g) comparing the combined property of the modified molecular model with the combined property of the molecular model of the starting compound; and
(h) determining if the combined property of the modified molecular model is improved relative to the combined property of the molecular model of the starting compound.

2. The method of claim 1, wherein the combined property of the modified molecular model is improved relative to the combined property of the molecular model of the starting compound, and further comprising determining if synthesis of a new chemical compound according to the modified molecular model is feasible and economic.

3. The method of claim 2, wherein synthesis of a new chemical compound according to the modified molecular model is feasible and economic, and further comprising synthesizing a new chemical compound according to the modified molecular model.

4. The method of claim 3, further comprising determining if the physicochemical property of the new chemical compound is improved relative to that of the starting compound.

5. The method of claim 4, wherein determining if the physicochemical property of the new chemical compound is improved relative to that of the starting compound comprises experimental measurement of the physicochemical properties of the starting compound and the new compound.

6. The method of claim 1, wherein the combined property of the modified molecular model is not improved relative to the combined property of the molecular model of the starting compound, and further comprising repeating steps (e)-(h) of claim 1.

7. The method of claim 2, wherein synthesis of a new chemical compound according to the modified molecular model is not feasible or economic, and further comprising repeating steps (e)-(h) of claim 1.

8. The method of claim 4, wherein the physicochemical property of the new chemical compound is not improved relative to that of the starting compound, and further comprising repeating steps (c)-(h) of claim 1.

9. The method of claim 1, wherein the physicochemical property comprises thermal stability, coke formation, ability of the compound to improve oil recovery, solubility, dielectric permittivity, interfacial activity, oil solubilization capability, emulsion breaking capability, corrosion inhibition capability, adsorption of molecules on solid/liquid, liquid/liquid, or liquid gas interfaces, prevention of gas hydrate formation or deposition, prevention of asphaltene association, precipitation, or deposition, thermal stability and/or foam stability of steam or noncondensable gas foams, viscosity of foams, oil-water interfacial tension, microemulsion formation, wetting angle that water forms in contact with the reservoir rock surface when the incorporating liquid is crude oil, or any combination thereof.

10. The method of claim 1, wherein the compound comprises a surfactant, a polymer, an emulsifier, a demulsifier, an asphaltene inhibitor, a gas hydrate inhibitor, a corrosion inhibitor, or a foam forming compound.

11. The method of claim 1, wherein the physicochemical property comprises thermal stability, and the sub-property set comprises decomposition energy, decomposition rate, enthalpy of formation, enthalpy of decomposition, flash point, bond dissociation energy of the bond having the smallest bond order, hydrolysis energy of the bond having the smallest bond order, hydrolysis energy in the presence of silica of the bond having the smallest bond order, hydrolysis energy in the presence of clays of the bond having the smallest bond order, or any combination thereof.

12. The method of claim 1, wherein the physicochemical property comprises solubility, and the sub-property set comprises the solute-solute interaction energy (EUU), solvent-solvent interaction energy (EVV), and the solvent-solute interaction energy (EVU).

13. The method of claim 1, wherein the physicochemical property comprises dielectric permittivity, and the sub-property set comprises the molar volume, dipole moment, and the rotational diffusion coefficient.

14. The method of claim 1, wherein the physicochemical property comprises interfacial activity of a surfactant, and the sub-property set comprises the HLB number, adsorption enthalpy, CMC value, or any combination thereof.

15. The method of claim 1, wherein the physicochemical property comprises thermal stability, and the sub-property set comprises the reaction rate and/or the activation energy of the decomposition reaction.

16. The method of claim 1, wherein the compound is an asphaltene inhibitor, the physicochemical property comprises prevention of asphaltene association, precipitation, or deposition, and the sub-property set comprises the association energy between asphaltene molecules and the association energy between the asphaltene inhibitor and asphaltene molecules.

Patent History
Publication number: 20090114387
Type: Application
Filed: Jan 16, 2008
Publication Date: May 7, 2009
Applicant: SCHLUMBERGER TECHNOLOGY CORP. (SUGAR LAND, TX)
Inventors: Geza Horvath Szabo (Edmonton), Michael Longpre (Edmonton), Fuenglarb Zabel (Edmonton)
Application Number: 12/015,229
Classifications
Current U.S. Class: Prospecting (166/250.16)
International Classification: E21B 49/00 (20060101);