Reduction-increase permeability method for evaluating enhanced permeability fluids in shale / tight reservoirs

Abstract

The present invention relates to a method for evaluating enhanced permeability fluid in shale / tight reservoirs by reducing volume and enhancing permeability. The essence of improving the recovery rate of shale gas reservoirs is to expand the seepage space of shale oil and gas. Microscopically, the improvement of the seepage space comes from the volume space released after the minerals in the shale are dissolved. Therefore, by calculating the volume reduction after the reaction of mineral components in the shale, the enhanced permeability fluid for shale reservoirs is optimized, the variation relationship between the seepage capacity and the seepage space of shale reservoirs is clarified, and it is interpreted that the "quantity" in the new idea of reducing volume and enhancing permeability is the mineral volume content, providing a theoretical basis for the optimization of enhanced permeability fluid in shale reservoirs.

Description

Technical Field

[0001] The invention relates to the field of oil and gas exploration and development, and to a reduction-increase permeability method for evaluating shale / tight reservoir permeability fluid. Background Art

[0002] Hydraulic fracturing creates a complex fracture network through rock mechanics, greatly improving the seepage capacity of shale gas at the macro and meso scales; shale is deposited in a reducing environment and is rich in reducing substances such as pyrite, chlorite and organic matter, which can be dissolved by oxidizing fluid to produce dissolution pores, thereby improving the seepage capacity of shale gas at the micro scale. Oxidation-coordinated hydraulic fracturing can build a more complete fracture network, thereby effectively improving the recovery rate of shale gas reservoirs.

[0003] The essence of improving the recovery rate of shale gas reservoirs is to expand the seepage space of shale oil and gas, and the increase in the seepage space at the microscopic level comes from the volume space released after the minerals in the shale are dissolved. However, not all fluids increase the volume of the seepage channel alone after the action. Some fluids are accompanied by precipitation after the action, thereby reducing the volume of the seepage channel. Therefore, by calculating the volume reduction of the mineral components in the shale after the reaction, the shale reservoir permeability fluid is selected, which is of great significance for the construction of the shale reservoir permeability oxidation fluid system. Summary of the invention

[0004] In view of the above problems, the present invention proposes a method for increasing permeability by reducing the amount of permeability fluid for evaluating shale / tight reservoirs, comprising the following steps:

[0005] (1) Test the mineral components of representative rock samples of the reservoir and correct the initial content of each mineral component;

[0006] (2) Select the experimental core, dry it and measure its mass Minitial;

[0007] (3) The selected reservoir permeability fluid is subjected to water-rock interaction with the core, and the changes in solution pH and conductivity are detected;

[0008] (4) The reaction ends when the pH value and conductivity of the solution fluctuate very little or no longer.

[0009] (5) After the reaction is completed, the core is taken out, dried and its residual mass Mresidual is measured;

[0010] (6) After the test, determine the mineral components of the rock sample, determine whether precipitation occurs, calculate and correct the remaining content of the main components involved in the reaction in the rock sample, and calculate the reduction in volume content of each mineral component based on the density of each mineral component and the rock density;

[0011] (7) Evaluate the effect of oxidation fracturing and permeability enhancement in shale reservoirs based on the reduction in mineral volume content.

[0012] Among them, the initial content of each mineral component in the shale reservoir is corrected according to the following formula:

[0013] W i = W i初 ×(1 - W TOC )

[0014] In the formula: W i refers to the initial content of the mineral component after correction, %; W i初 refers to the initial content of the mineral component in the whole-rock analysis, %; W TOC refers to the TOC content, %.

[0015] The residual content of each mineral component after the reaction is corrected according to the following formula:

[0016]

[0017] In the formula: W i ' refers to the remaining content of each mineral component after correction, %; W i剩余 refers to the remaining content of each component mineral, %; M 剩余 refers to the mass of the rock sample after the reaction, g; M 初始 refers to the mass of the initial rock sample, g; W TOC refers to the content of TOC, %.

[0018] The volume reduction of the mineral components in the rock sample after the water-rock interaction is calculated according to the following formula:

[0019]

[0020] In the formula: Wv refers to the volume reduction, %; W j refers to the percentage content of the precipitate, %; W i refers to the content of each mineral component after correction before the reaction, %; W i ' refers to the percentage content of each mineral component after correction after the reaction; ρ 岩石 refers to the density of the rock, g / cm 3 ; ρ i refers to the density of each mineral participating in the reaction, g / cm 3 ; ρ j refers to the density of the precipitate, g / cm 3 .

[0021] The beneficial effects are as follows:

[0022] (1) This method interprets that the "quantity" in the new idea of "quantity reduction and permeability increase" is the volume content of minerals, providing a theoretical basis for the selection of fluids for increasing the permeability of shale reservoirs.

[0023] (2) The relationship between the seepage capacity and the change of seepage space in shale reservoirs is determined. The method is simple, the calculation is fast, and the accuracy is high;

[0024] (3) It provides a direction for stimulation and transformation, dissolving low-density mineral components. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flowchart of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0026] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the invention.

[0027] (1) According to the whole-rock analysis and TOC test results of organic-rich shale in Block A, determine the initial content of each mineral component in shale, as shown in Table 1;

[0028] Table 1 Initial content of each mineral component in shale

[0029]

[0030] After correction, the content of each mineral component in shale is shown in Table 2;

[0031] Table 2 Initial content of each mineral component in shale after correction

[0032]

[0033]

[0034] (2) Select 6 shale cores of equal weight, and measure their masses to be 60 g each;

[0035] (3) Select experimental fluids as 1% hydrogen peroxide, 3% hydrogen peroxide, 5% hydrogen peroxide, 3% sodium persulfate, 6% sodium persulfate, and 9% sodium persulfate respectively, soak the cores, and end the soaking when the pH value and conductivity of the solution change little or no longer change.

[0036] (4) Take out the cores, dry them, and measure their masses, as shown in Table 3;

[0037]

[0038] (5) The test results of whole-rock analysis and TOC content of shale after the experiment are shown in Table 4;

[0039] Table 4 Remaining content of each mineral component in shale

[0040]

[0041] The remaining content of each component of the modified shale is shown in Table 5;

[0042] Table 5 Remaining content of each mineral component of the modified shale

[0043]

[0044] (6) It can be seen from the change in the content of mineral components that the main targets of hydrogen peroxide are calcite, dolomite, pyrite, chlorite and organic matter; the main targets of sodium persulfate are calcite, dolomite, pyrite, clay minerals and organic matter, and gypsum precipitation occurs after the action of sodium persulfate. Among them, the shale density is taken as 2.65 g / cm 3 ; the calcite density is taken as 2.71 g / cm 3 ; the dolomite density is taken as 2.86 g / cm 3 ; the pyrite density is taken as 4.9 g / cm 3 ; the gypsum density is taken as 2.31 g / cm 3 ; the illite-smectite interstratified mineral density is taken as 2.09 g / cm 3 ; the illite density is taken as 2.9 g / cm 3 ; the chlorite density is taken as 2.7 g / cm 3 ; the organic matter density is taken as 1.25 g / cm 3 .

[0045] (5) Calculate the change in the total volume content of the components participating in the reaction according to the following formula:

[0046]

[0047] In the formula: Wv refers to the volume reduction, %; W j refers to the percentage content of the precipitate, %; W i refers to the content of each mineral component after correction before the reaction, %; W i ' refers to the percentage content of each mineral component after correction after the reaction; ρ 岩石 refers to the density of the rock, g / cm 3 ; ρ i refers to the density of each mineral participating in the reaction, g / cm 3 ; ρ j refers to the density of the precipitate, g / cm 3 .

[0048] The calculation results are shown in Table 6;

[0049] Table 6 Total volume reduction of minerals

[0050]

[0051] From the total volume reduction of the minerals, it can be seen that 5% hydrogen peroxide has the largest volume reduction. Therefore, the 5% hydrogen peroxide solution has the best effect of oxidation-induced fracture and permeability enhancement.

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered by the scope of the claims and the description of the present invention.

Claims

1. The method for evaluating enhanced permeability fluid in shale / tight reservoirs by the method of reducing fluid volume and enhancing permeability, characterized in that It includes the following steps: (1) Test the mineral components of representative reservoir rock samples and correct the initial contents of each mineral component; (2) Select the experimental core and measure its mass M after drying 初始 ; (3) Conduct water-rock interaction between the selected reservoir permeability-increasing fluid and the core, and detect the changes in the pH value and conductivity of the solution; (4) When the fluctuations of the pH value and conductivity of the solution are very small or no longer fluctuate, the reaction ends; After the reaction is completed, take out the core, dry it and measure its remaining mass M 剩余 ; (6) Test the mineral components of the rock sample after the experiment, determine the main components participating in the reaction, judge whether precipitation occurs, calculate and correct the remaining contents of the main components participating in the reaction in the rock sample, and calculate the reduction amount of the volume content of each mineral component according to the density of each mineral component and the rock density; (7) Evaluate the oxidation-induced fracturing and permeability-increasing effect of the shale reservoir according to the reduction amount of the mineral volume content.

2. The method for evaluating the fluid for enhancing permeability in shale / tight reservoirs by reducing the amount of fluid and enhancing permeability according to claim 1, wherein: Correct the initial contents of each mineral component according to the following formula: W i = W i初 × (1 - W TOC ) where: W i refers to the initial content of the modified mineral components, %; W i初 refers to the initial content of mineral components in whole-rock analysis, %; W TOC refers to the TOC content, %.

3. The reduced permeability increase method for evaluating shale / tight reservoir permeability increasing fluid according to claim 1, characterized in that: Correct the remaining contents of each mineral component after the reaction according to the following formula: Where: W i ' refers to the remaining content of each mineral component after correction, %; W i剩 refers to the remaining content of each component mineral, %; M 剩余 refers to the mass of the rock sample after reaction, g; M 初始 refers to the mass of the initial rock sample, g; W TOC refers to the content of TOC, %.

4. The method for evaluating the fluid for enhancing permeability in shale / tight reservoirs by reducing the amount of fluid and enhancing permeability according to claim 1, wherein: Calculate the reduction amount of the volume of each mineral component in the rock sample after water-rock interaction according to the following formula: Where: Wv refers to the volume reduction, %; W j refers to the percentage content of the precipitate, %; W i refers to the content of each mineral component after pre - reaction correction, %; W i ' refers to the percentage content of each mineral component after post - reaction correction; ρ 岩石 refers to the density of the rock, g / cm 3 ; ρ i refers to the densities of the various minerals participating in the reaction, g / cm 3 ; ρ j refers to the density of the precipitate, g / cm 3 .

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