A method for predicting dynamic permeability pressure in shale formations

Abstract

The present application relates to a kind of shale formation dynamic permeation pressure prediction method, comprising the following steps: based on shale cylinder sample, obtain shale porosity, density and cation exchange capacity, calculate to obtain the solute concentration parameter inside and outside shale, to obtain shale initial membrane efficiency;Test and obtain the activity of drilling fluid and shale, on this basis, carry out drilling fluid and shale soaking experiment, test and obtain the porosity and density of shale under the action of drilling fluid at different times, and then calculate the shale membrane efficiency deterioration coefficient under different drilling time;Comprehensive drilling fluid activity, shale activity, initial membrane efficiency and membrane efficiency deterioration coefficient, establish the shale formation dynamic permeation pressure prediction method considering the influence of drilling fluid.The present application can reflect the shale membrane efficiency deterioration law and permeation pressure dynamic change law under the influence of drilling fluid, and then determine the driving characteristics of drilling fluid invasion shale in drilling process, which is helpful to establish shale formation safe drilling technology.

Description

Technical Field

[0001] This invention relates to the field of drilling engineering in shale formations, and more particularly to a method for predicting dynamic permeability pressure in shale formations. Background Technology

[0002] Shale formations are typical high-temperature formations for drilling, leading to severe wellbore instability. The high water sensitivity of shale is a major contributing factor to this instability. Due to this sensitivity, when aqueous media in drilling fluid infiltrate shale, they undergo hydration with the internal clay, causing hydration damage. This damage results in structural fracturing and reduced mechanical strength of the shale, ultimately leading to wellbore instability. Osmotic pressure is one of the primary driving forces behind the infiltration of aqueous media into shale. Therefore, clarifying the osmotic pressure of shale is crucial for controlling shale hydration and ensuring wellbore stability.

[0003] Current research on the osmotic pressure of shale mainly relies on the semi-permeable membrane theory, which assumes that shale is a non-ideal semi-permeable membrane (membrane efficiency less than 1), considering the concentration difference across the membrane to calculate osmotic pressure. However, current calculation methods are all based on a constant semi-permeable membrane efficiency. In reality, due to the strong water sensitivity of shale, its structure is dynamically changing under the influence of drilling fluid, leading to membrane efficiency degradation. Therefore, the osmotic pressure of shale is in a dynamic adjustment process under the influence of drilling fluid. However, no research on dynamic osmotic pressure has been found to date. Summary of the Invention

[0004] To address the aforementioned technical issues, this application combines indoor experiments and theoretical calculations to establish a dynamic osmotic pressure prediction method for shale formations by obtaining the shale membrane efficiency degradation coefficient. This method helps to deepen the understanding of the driving mechanism of drilling fluid intrusion into shale and is of great significance for preventing shale hydration and establishing stable wellbore technology for shale formations.

[0005] This application is achieved through the following technical solution:

[0006] A method for predicting dynamic permeability of shale formations includes the following steps:

[0007] Obtain mudstone and shale samples from the target formation;

[0008] Based on mudstone and shale samples from the target formation, the porosity, density, and cation exchange capacity of the mudstone and shale were obtained.

[0009] Based on the porosity, density, and cation exchange capacity of shale, the solute concentration parameters inside and outside the shale were calculated.

[0010] The initial film efficiency of the shale was calculated based on the solute concentration parameters inside and outside the shale.

[0011] Tests were conducted to obtain the activity of drilling fluid and shale.

[0012] We conducted drilling fluid immersion experiments on mudstone and shale to obtain the porosity and density of the target formation under different drilling fluid treatment times.

[0013] The degradation coefficient of shale film efficiency is calculated based on the porosity and density of shale under different drilling fluid action times.

[0014] Based on the initial membrane efficiency of shale, drilling fluid activity, shale activity, and membrane efficiency degradation coefficient, the dynamic osmotic pressure of shale during the drilling process is obtained, thereby establishing a method for predicting the dynamic osmotic pressure of shale formations that considers the influence of drilling fluid.

[0015] Compared with the prior art, this application has the following beneficial effects:

[0016] This application can demonstrate the degradation law of shale film efficiency and dynamic change law of osmotic pressure under the influence of drilling fluid during the drilling process, thereby clarifying the driving characteristics of drilling fluid intrusion into shale during the drilling process, which is helpful to establish safe drilling technology for shale formations. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of the embodiments of this application and form part of this application, do not constitute a limitation on the embodiments of the present invention.

[0018] Figure 1 This is a flowchart of the dynamic permeability prediction method for shale formations in the embodiments;

[0019] Figure 2 These are porosity diagrams of mudstone and shale under different drilling fluid action times in the embodiments;

[0020] Figure 3 This is a diagram showing the density of mudstone and shale at different times of drilling fluid application in the embodiments;

[0021] Figure 4 This is a graph showing the degradation coefficient of shale film efficiency under the action of drilling fluid in the embodiments;

[0022] Figure 5 This is a dynamic osmotic pressure diagram under the action of drilling fluid in the embodiment. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0024] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. It should also be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments; similar or identical parts between embodiments can be referred to interchangeably.

[0026] This case study uses an actual drilling operation in a shale formation of an oilfield in China as an example, with shale rock samples from that formation used as test samples. Figure 1 As shown in this embodiment, the method for predicting dynamic permeability pressure in shale formations includes the following steps:

[0027] Step 1: Using an indoor core drilling rig, sample the outcrops or downhole core columns of the target formation to obtain cylindrical rock samples.

[0028] Step 2: Obtain the porosity and density of the target formation based on shale cylindrical rock samples.

[0029] This embodiment uses the gas measurement method to test porosity. Specifically, the volume V of the rock sample is first measured using vernier calipers. f Then, the shale was placed in the sample chamber to begin gas analysis. When the pressure at both ends of the sample chamber was balanced, the volume V of the rock sample skeleton was obtained. s .

[0030] Based on the rock sample volume V f and skeleton volume V s The porosity φ of the rock sample is calculated using the following formula:

[0031]

[0032] Density testing: The mass m of the cylindrical rock sample was weighed using a balance, and then the sample volume V was determined based on the undisturbed rock sample. f Thus, the rock sample density ρ is obtained:

[0033]

[0034] The porosity of mudstone and shale was obtained through testing. It has a content of 5.22% and a density ρ of 2.35 g / cm³. 3 .

[0035] Step 3: Obtain the cation exchange capacity of the target formation.

[0036] This embodiment uses methylene blue titration to obtain the cation exchange capacity of the target formation. Specifically, the cylindrical rock sample is ground into powder using a grinder; the shale powder is mixed with distilled water to prepare a shale slurry, then 3% hydrogen peroxide solution and 2.5 mol / L sulfuric acid solution are added, and the mixture is slowly boiled and diluted with water to form the titration solution. A 0.01 mol / L methylene blue solution is prepared, and 0.5 mL of the prepared methylene blue solution is added to the titration solution each time. After stirring with a glass rod, a drop of methylene blue is placed on filter paper. This process is repeated until a blue ring appears on the filter paper, at which point the experiment is stopped, and the cation exchange capacity of the shale is calculated.

[0037]

[0038] In the above formula, CEC represents the cation exchange capacity of shale, in mmol / kg; d ro Total amount of methylene blue consumed in titration, ml; m clay The weight in grams (g) of shale used in the titration.

[0039] The cation exchange capacity of the mudstone and shale was found to be 78.8 mmol / kg.

[0040] Step 4: Based on the cation exchange capacity, density, and porosity of shale, calculate and obtain the solute concentration parameters inside and outside the shale.

[0041] Among them, the solute concentration parameter includes the anion concentration C inside the shale. a Cation concentration C inside mudstone and shale c Average solute concentration on both the inner and outer sides of the mudstone and shale

[0042] Among them, the anion concentration C inside the mudstone and shale a The calculation equation is as follows:

[0043]

[0044] In the above formula, CEC is the cation exchange capacity of mudstone and shale, ρ is the density of the rock sample, and φ is the porosity of the rock sample.

[0045] Among them, the average solute concentration on both the inner and outer sides of the mudstone and shale It mainly depends on the concentration of dissolved substances in the formation water within the mudstone and shale, and is calculated using the following formula:

[0046]

[0047] In the above formula, C out The solute concentration of the external fluid of the shale is expressed in mol / cm³. 3 C foThe solute concentration of the fluid (formation water) inside the mudstone and shale is 435.2 mmol / L.

[0048] Among them, the cation concentration C inside the mudstone and shale c It equals the total number of anions in the shale plus the inherent negative charge, as shown below:

[0049] C c =C a +CECρ(1-φ)

[0050] In the above formula, CEC is the cation exchange capacity of mudstone and shale, ρ is the density of the rock sample, and φ is the porosity of the rock sample.

[0051] Step 5: Calculate and obtain the initial membrane efficiency of the mudstone and shale.

[0052] Assuming shale is a semi-permeable membrane, the membrane efficiency calculation equation is as follows:

[0053]

[0054] In the above formula, η is the membrane efficiency. When the input parameters are the initial state parameters of the shale, the calculated membrane efficiency is the initial membrane efficiency η. o ;R w R m R wm These represent the ratio of cation to anion friction coefficient in water, the ratio of cation to anion friction coefficient in shale, and the ratio of anion friction coefficient in shale to anion friction coefficient in water.

[0055] Among them, R m and R w Using empirical coefficients of 1.8 and 1.63, R0 wm Distribution is closely related to porosity, as shown below:

[0056] R wm =52.106φ -1.737

[0057] Based on the membrane efficiency calculation equation, by substituting the above parameters of cation exchange capacity, porosity, density, and solute concentration inside and outside the shale, the initial membrane efficiency of the shale was calculated to be 0.34.

[0058] Step 6: Obtain the activity values ​​of drilling fluid and shale.

[0059] This embodiment uses the saturated humidity method to obtain the activity values ​​of drilling fluid and shale. Specifically, based on the correlation equation between humidity and activity, the humidity of drilling fluid and shale is measured using a humidity meter, and then the drilling fluid activity 'a' is calculated. nw Activity a of mudstone and shale mw The correlation equation between humidity and activity is as follows:

[0060] a w =0.0099R h -0.0038

[0061] In the above formula, a w For activity, R h Humidity.

[0062] Test results show that the drilling fluid activity a nw Activity a of mudstone and shale mw The values ​​are 0.64 and 0.22 respectively.

[0063] Step 7: Conduct drilling fluid and shale immersion experiments to further test the porosity and density of the shale under the action of drilling fluid, and obtain the porosity φ(t) and density ρ(t) of the target formation at different times of drilling fluid action, such as... Figure 2 , Figure 3 As shown.

[0064] Step 8: Based on the porosity and density of shale under the action of drilling fluid, the following formula is used to calculate the degradation coefficient of shale film efficiency at different times:

[0065]

[0066] In the above formula, η(t) represents the membrane efficiency under different drilling fluid treatment times. Based on the membrane efficiency equation, η(t) can be calculated by substituting the porosity φ(t) and density ρ(t) under different drilling fluid treatment times. o The initial membrane efficiency is given by δ(t); δ(t) represents the degradation coefficient of the shale membrane efficiency at different times, ranging from 0 to 1. A degradation coefficient of 1 indicates the greatest damage to membrane efficiency, signifying a complete loss of membrane efficiency. A degradation coefficient of 0 indicates no damage to membrane efficiency. The calculation results of the degradation coefficient are as follows: Figure 4 As shown.

[0067] Step 9: Based on the initial membrane efficiency of the shale, the membrane efficiency degradation coefficient, and the activity of the drilling fluid and shale, obtain the dynamic osmotic pressure of the shale during the drilling process. The equation for calculating the osmotic pressure is:

[0068]

[0069] In the above formula, P π (t) represents the dynamic osmotic pressure; R is the ideal gas constant, with a value of 0.00831 L / (K·mol); T is the temperature, using the target formation temperature of 110℃; V is the molar volume of water, with a value of 0.018 L / mol.

[0070] The calculated dynamic permeability variation law of shale is as follows: Figure 5As shown, it can be observed that with increasing drilling time, the membrane efficiency deteriorates more severely, the osmotic pressure gradually decreases, and the ability of the drilling fluid to penetrate the shale is weakened.

[0071] The dynamic osmotic pressure prediction method for shale formations provided in this application can reflect the degradation law of shale film efficiency and dynamic change law of osmotic pressure under the influence of drilling fluid during the drilling process, thereby clarifying the driving characteristics of drilling fluid intrusion into shale during the drilling process, which helps to establish safe drilling technology for shale formations.

[0072] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for predicting dynamic permeability pressure in shale formations, characterized in that: Includes the following steps: Obtain mudstone and shale samples from the target formation; Based on mudstone and shale samples from the target formation, the porosity, density, and cation exchange capacity of the mudstone and shale were obtained. Based on the porosity, density, and cation exchange capacity of shale, the solute concentration parameters inside and outside the shale were calculated. The initial film efficiency of the shale was calculated based on the solute concentration parameters inside and outside the shale. To obtain the activity of drilling fluid and shale; We conducted drilling fluid immersion experiments on mudstone and shale to obtain the porosity and density of the target formation under different drilling fluid treatment times. The degradation coefficient of shale film efficiency is calculated based on the porosity and density of shale under different drilling fluid action times. Based on the initial membrane efficiency of shale, drilling fluid activity, shale activity, and membrane efficiency degradation coefficient, the dynamic osmotic pressure of shale during the drilling process is obtained, thereby establishing a method for predicting the dynamic osmotic pressure of shale formations that considers the influence of drilling fluid; The formula for calculating membrane efficiency is: ； In the above formula, For membrane efficiency, when the input parameters are the initial state parameters of the shale, the calculated membrane efficiency is the initial membrane efficiency. ; , , These are the ratios of anion and cation friction coefficients in water, the ratio of anion and cation friction coefficients in mudstone and shale, and the ratio of anion friction coefficients in mudstone and anion friction coefficients in water. This represents the concentration of anions within the mudstone and shale. This refers to the cation concentration inside the mudstone and shale. This represents the average solute concentration on both the inner and outer sides of the mudstone and shale. This refers to the porosity of the rock sample.

2. The method for predicting dynamic permeability pressure in shale formations according to claim 1, characterized in that: The specific method for obtaining mudstone and shale samples from the target formation is as follows: using an indoor core drilling rig, sampling is carried out on outcrops or downhole core columns of the target formation to obtain cylindrical rock samples.

3. The method for predicting dynamic permeability pressure in shale formations according to claim 1, characterized in that: The porosity of the rock sample is calculated using the following formula. : ； In the above formula, For the volume of the rock sample, For the volume of the skeleton; The density of the rock sample is calculated using the following formula. : ； In the above formula, m is the mass of the rock sample.

4. The method for predicting dynamic permeability pressure in shale formations according to claim 1, characterized in that: The solute concentration parameters inside and outside the shale include the anion concentration inside the shale. Cation concentration inside mudstone and shale Average solute concentration on both the inner and outer sides of mudstone and shale .

5. The method for predicting dynamic permeability pressure in shale formations according to claim 4, characterized in that: The anion concentration inside mudstone and shale is calculated using the following formula. : ； In the above formula, CEC represents the cation exchange capacity of shale. The density of the rock sample, Porosity of the rock sample; The following formula is used to calculate the cation concentration inside mudstone and shale. : ； The average solute concentration is calculated using the following formula. : ； In the above formula, This represents the solute concentration of the fluid outside the mudstone and shale formation. ; This represents the solute concentration of the fluid inside the mudstone and shale.

6. The method for predicting dynamic permeability pressure in shale formations according to claim 1, characterized in that: The activity of drilling fluid and shale was obtained using the saturated humidity method.

7. A method for predicting dynamic permeability pressure in shale formations according to claim 1 or 6, characterized in that: The following formula was used to calculate the degradation coefficient of shale membrane efficiency at different times: ； In the above formula, The membrane efficiency under different drilling fluid treatment times can be calculated based on the membrane efficiency equation by substituting the porosity and density under different drilling fluid treatment times. Initial membrane efficiency; The coefficients representing the degradation of shale membrane efficiency at different times are distributed in the range of 0-1.

8. The method for predicting dynamic permeability pressure in shale formations according to claim 1, characterized in that: The dynamic permeability pressure of shale is calculated using the following formula: ； In the above formula, For dynamic osmotic pressure, The coefficients representing the degradation of shale membrane efficiency at different times are given. R is the initial membrane efficiency; R is the ideal gas constant; T is the temperature. This is the molar volume of water; This refers to drilling fluid activity. The activity of mudstone and shale.

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