A method for extracting anisotropic resistivity of shale oil reservoir in horizontal wells

Abstract

The present invention discloses a method for extracting anisotropic resistivity of horizontal well shale oil reservoirs, comprising: obtaining adjacent well information, as well as the apparent resistivity curves of N sub-arrays of horizontal well array induction logging and the synthesized ones; dividing the formation interfaces of the horizontal well based on the short-spacing sub-array curve and the measured GR curve; establishing an interpretation model, and constructing a layered isotropic processing model M1 and a homogeneous anisotropic processing model M2; inversely calculating the curve of the i-th sub-array to obtain the formation resistivity profile, and using it as the initial value for the next long-spacing sub-array; inversely calculating the apparent resistivity curves of each sub-array in sequence to obtain the corresponding formation resistivity profiles; for the j-th formation, using the model M2 to inversely calculate the anisotropic resistivity R hj and R vj ; repeating the above steps to obtain the anisotropic resistivity of each formation. This method can accurately extract the anisotropic resistivity information of shale oil reservoirs, effectively eliminate the influence of well deviation, surrounding rock and anisotropy on logging response, and ensure the accuracy of reservoir oil saturation calculation.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum exploration and development, belongs to the category of electric logging methods, and in particular to a method for extracting anisotropic resistivity of shale oil reservoirs in horizontal wells. Background Art

[0002] Array induction logging is widely used in oil and gas resource exploration. It has significant characteristics for shale oil reservoirs, has small invasion anomalies, and is widely used in oil-based mud. However, the separation of curves in inclined wells and horizontal wells leads to inaccurate saturation parameters, and the synthetic curve cannot reflect the true formation information under the influence of layer thickness. However, the simulation of array induction logging response in horizontal wells usually adopts a three-dimensional processing method, which has low calculation accuracy and slow speed. At the same time, it is seriously affected by multiple factors such as instrument tilt and mud filtrate invasion in horizontal wells, and cannot accurately reflect the true formation conditions. At present, there are few methods for accurately extracting resistivity of horizontal wells. It is urgent to develop new methods for extracting anisotropic resistivity of horizontal wells to effectively measure the anisotropic resistivity information of shale oil reservoirs in horizontal wells. Summary of the invention

[0003] In order to solve the above technical problems, the present invention discloses a method for extracting anisotropic resistivity of shale oil reservoirs in horizontal wells. The method is based on the original signal of array induction logging, in order to provide accurate formation information for shale oil reservoir evaluation.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for extracting anisotropic resistivity of a horizontal well shale oil reservoir comprises the following steps:

[0006] s1. Obtaining the formation thickness, horizontal resistivity, and natural GR curve information of adjacent wells, as well as the measured N subarrays of horizontal well array induction logging and the synthesized apparent resistivity curve, wherein the horizontal well array induction logging subarray includes a short source distance subarray and a long source distance subarray;

[0007] s2. Divide the horizontal well formation interface based on the short source distance subarray curve and the measured horizontal well GR curve;

[0008] s3. Establish an interpretation model, construct a layered isotropic processing model M1 and a homogeneous anisotropic processing model M2;

[0009] s4. Invert the i-th subarray curve to obtain the formation resistivity profile Rts i , and use the result as the initial value of the next long source distance subarray;

[0010] s5. Invert the apparent resistivity curves of each subarray in turn to obtain the corresponding formation resistivity profiles Rts i , i=1,…,N;

[0011] s6. For the jth stratum in the layered isotropic processing model M1, combined with the inversion results of step s5, the homogeneous anisotropic processing model M2 is used to invert the anisotropic resistivity R of the current layer. hj and R vj ;

[0012] s7. Repeat step s6 in sequence to process each layer in the layered isotropic processing model M1, and then obtain the anisotropic resistivity of each stratum.

[0013] Optionally, step s3 includes the following steps:

[0014] s3.1. According to the electrical characteristics of shale oil reservoirs and the drilling environment, the actual formation model is established by considering the influence of wellbore, formation folds, layer thickness and well deviation;

[0015] s3.2. Ignore the influence of formation folds, perform borehole correction on the N sub-array signals in step s1, and establish the corresponding interpretation model;

[0016] s3.3. Considering the influence of layer thickness and anisotropy respectively, the strata are equivalent to strata with layer thickness influence but no anisotropy influence and strata with anisotropy but no layer thickness influence, and then constructing layered isotropic processing model M1 and homogeneous anisotropic processing model M2 in turn;

[0017] s3.4. Layered isotropic processing model M1 includes the parameter Rts i , θ and H j , where Rts i is the equivalent isotropic resistivity, H j is the formation thickness, θ is the well deviation, i represents the i-th subarray, j represents the j-th formation, and the layered isotropic processing model M1 is used to eliminate the influence of layer thickness;

[0018] s3.5. Homogeneous anisotropic processing model M2 includes parameters R hj , θ and R vj , where R hj is the horizontal resistivity, R vj is the vertical resistivity, θ is the well deviation, j represents the jth formation, and the homogeneous anisotropic processing model M2 is used to obtain anisotropic information.

[0019] Optionally, step s4 includes the following steps:

[0020] s4.1. Use the reference resistivity of adjacent wells, the measured subarray curves of horizontal wells and the synthetic curves to provide the initial value of inversion;

[0021] s4.2. For the first subarray curve, combine the inversion initial value provided in step s4.1 with the layered isotropic processing model M1 constructed in step s3 to obtain the formation resistivity profile Rts i , and use the result as the initial value of the next long source distance subarray;

[0022] s4.3. For the i-th subarray curve, the formation resistivity profile Rts obtained by inversion of the previous subarray is i-1 As the initial value of inversion, the formation resistivity profile Rts is obtained by inversion. i , and use the result as the initial value of the next long source distance subarray.

[0023] Optionally, step s6 comprises the following steps:

[0024] s6.1. The homogeneous anisotropic processing model M2 established in step s3 includes the parameter R h and R v , where R h is the horizontal resistivity, R v is the vertical resistivity, and the model ignores the effect of layer thickness;

[0025] s6.2. For the jth stratum in the layered isotropic processing model M1, the N resistivity profiles of the current layer obtained in step s5 are used as inversion input information. Combined with the homogeneous anisotropic processing model M2 constructed in step s3, the interpretation result of step s5 is inverted to obtain the anisotropic resistivity R of the current layer. hj and R vj ;

[0026] s6.3. Invert all layers in the layered isotropic processing model M1 layer by layer, repeat the above process, and obtain the anisotropic resistivity of each stratum.

[0027] The beneficial effects of the present invention are as follows: the present invention provides a method for extracting anisotropic resistivity of shale oil reservoirs in horizontal wells based on raw signals of array induction logging, which makes full use of information from adjacent wells, determines the position of layer interfaces, and provides initial values ​​for subsequent processing; two equivalent processing strategies are adopted for complex three-dimensional formations, and multiple groups of initial values ​​are provided for each equivalent model, so that the speed and accuracy of the inversion process are greatly improved; in the later interpretation and evaluation, the oil saturation, movable oil saturation, etc. of the reservoir can be accurately calculated through the inversion results of the anisotropic resistivity of each layer, providing reliable parameters for reservoir evaluation.

[0028] The method proposed in the present invention can effectively eliminate the influence of well deviation, surrounding rock and anisotropy on logging response, and effectively extract the anisotropic resistivity information of horizontal well shale oil reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a flow chart of a method for extracting anisotropic resistivity of shale oil reservoirs in horizontal wells based on original signals of array induction logging in the present invention;

[0030] Figure 2 It is a schematic diagram of an equivalent explanation model of the present invention;

[0031] Figure 3 It is a schematic diagram of the layered isotropic processing model of the present invention;

[0032] Figure 4 It is a schematic diagram of the homogeneous anisotropic processing model of the present invention;

[0033] Figure 5 The three-layer formation model of 65° and 80° of the present invention, wherein (a) is a three-layer formation model of 65°, and (b) is a three-layer formation model of 80°;

[0034] Figure 6 for Figure 5 The original responses of each sub-array of the model array induction logging, where (a) is the original response of each sub-array of the 65° formation model array induction logging, and (b) is the original response of each sub-array of the 80° formation model array induction logging;

[0035] Figure 7 The inversion results of the layered isotropic processing model corresponding to each subarray of the present invention, wherein (a) is the inversion result of the 65° layered isotropic processing model, and (b) is the inversion result of the 80° layered isotropic processing model;

[0036] Figure 8 These are the inversion results of the homogeneous anisotropic processing model of the present invention, wherein (a) is the inversion result of the 65° homogeneous anisotropic processing model, and (b) is the inversion result of the 80° homogeneous anisotropic processing model. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] A method for extracting anisotropic resistivity of shale oil reservoir in horizontal wells, such as Figure 1 As shown, the following steps are included:

[0039] s1. Obtain the formation thickness, horizontal resistivity, natural GR curve information of adjacent wells, and the measured horizontal well array induction logging N sub-arrays (SGM0, SGM1...SGM N-1) and a synthesized apparent resistivity curve, wherein the horizontal well array induction logging subarray includes a short source distance subarray and a long source distance subarray;

[0040] s2. Divide the horizontal well formation interface based on the short source distance subarray curve and the measured horizontal well GR curve;

[0041] s3. Establish an interpretation model, construct a layered isotropic processing model M1 and a homogeneous anisotropic processing model M2;

[0042] Step s3 specifically includes the following steps:

[0043] s3.1. According to the electrical characteristics of shale oil reservoirs and the drilling environment, the actual formation model is established by considering the influence of wellbore, formation folds, layer thickness and well deviation;

[0044] s3.2. Figure 2 As shown, due to the limited detection range, the influence of formation folds is ignored, and the corresponding interpretation model is established after the borehole correction is performed on the N sub-array signals in step s1;

[0045] s3.3. Considering the influence of layer thickness and anisotropy respectively, the strata are equivalent to strata with layer thickness influence but no anisotropy influence and strata with anisotropy but no layer thickness influence, and then constructing layered isotropic processing model M1 and homogeneous anisotropic processing model M2 in turn;

[0046] s3.4. Figure 3 As shown, the layered isotropic processing model M1 includes the parameter Rts i , θ and H j , where Rts i is the equivalent isotropic resistivity, H j is the formation thickness, θ is the well deviation, i represents the i-th subarray, j represents the j-th formation, and the layered isotropic processing model M1 is used to eliminate the influence of layer thickness;

[0047] s3.5. Figure 4 As shown, the homogeneous anisotropic processing model M2 includes the parameter R hj , θ and R vj , where R hj is the horizontal resistivity, R vj is the vertical resistivity, θ is the well deviation, j represents the jth formation, and the homogeneous anisotropic processing model M2 is used to obtain anisotropic information.

[0048] s4. Invert the i-th subarray curve to obtain the formation resistivity profile Rts i , and use the result as the initial value of the next long source distance subarray;

[0049] Step s4 specifically includes the following steps:

[0050] s4.1. Figure 5 Taking the formation model shown in the figure as an example, the reference resistivity of adjacent wells, the measured subarray curves of horizontal wells and the synthetic curves are used to provide the initial inversion value for data processing;

[0051] s4.2. For the first subarray curve, such as Figure 6 As shown, combining the inversion initial value provided in step s4.1 with the layered isotropic processing model M1 constructed in step s3, the formation resistivity profile Rts is obtained by inversion. i , and use the result as the initial value of the next long source distance subarray;

[0052] s4.3. For the i-th subarray curve, the formation resistivity profile Rts obtained by inversion of the previous subarray is i-1 As the initial value of inversion, the formation resistivity profile Rts is obtained by inversion. i , and use the result as the initial value of the next long source distance subarray.

[0053] s5. Figure 7 As shown in the figure, the apparent resistivity curves of each subarray are inverted in turn to obtain the corresponding formation resistivity profiles Rts i , i=1,…,N;

[0054] s6. For the jth stratum in the layered isotropic processing model M1, combined with the inversion results of step s5, the homogeneous anisotropic processing model M2 is used to invert the anisotropic resistivity R of the current layer. hj and R vj ;

[0055] Step s6 specifically includes the following steps:

[0056] s6.1. The homogeneous anisotropic processing model M2 established in step s3 includes the parameter R h and R v , where R h is the horizontal resistivity, R v is the vertical resistivity, and the model ignores the effect of layer thickness;

[0057] s6.2. Figure 8 As shown in the figure, for the jth stratum in the layered isotropic processing model M1, the N resistivity profiles of the current layer obtained in step s5 are used as the inversion input information, and the interpretation result of step s5 is inverted in combination with the homogeneous anisotropic processing model M2 constructed in step s3 to obtain the anisotropic resistivity R of the current layer. hj and R vj ;

[0058] s6.3. Invert all layers in the layered isotropic processing model M1 layer by layer, repeat the above process, and obtain the anisotropic resistivity of each formation.

[0059] s7. Repeat step s6 in sequence to process each layer in the layered isotropic processing model M1, and then obtain the anisotropic resistivity of each stratum.

[0060] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for extracting anisotropic resistivity of shale oil reservoirs in horizontal wells, characterized in that: The steps include: s1. Obtaining the formation thickness, horizontal resistivity, and natural GR curve information of adjacent wells, as well as the measured N subarrays of horizontal well array induction logging and the synthesized apparent resistivity curve, wherein the horizontal well array induction logging subarray includes a short source distance subarray and a long source distance subarray; s2. Divide the horizontal well formation interface based on the short source distance subarray curve and the measured horizontal well GR curve; s3. Establish an interpretation model, construct a layered isotropic processing model M1 and a homogeneous anisotropic processing model M2; s4. Invert the i-th subarray curve to obtain the formation resistivity profile Rts i , and use the result as the initial value of the next long source distance subarray; s5. Invert the apparent resistivity curves of each subarray in turn to obtain the corresponding formation resistivity profiles Rts i , i=1,…,N; s6. For the jth stratum in the layered isotropic processing model M1, combined with the inversion results of step s5, the homogeneous anisotropic processing model M2 is used to invert the anisotropic resistivity R of the current layer. hj and R vj ; s7. Repeat step s6 in sequence to process each layer in the layered isotropic processing model M1, and then obtain the anisotropic resistivity of each stratum.

2. A method for extracting anisotropic resistivity of a horizontal well shale oil reservoir according to claim 1, characterized in that: Step s3 includes the following steps: s3.

1. According to the electrical characteristics of shale oil reservoirs and the drilling environment, the actual formation model is established by considering the influence of wellbore, formation folds, layer thickness and well deviation; s3.

2. Ignore the influence of formation folds, perform borehole correction on the N sub-array signals in step s1, and establish the corresponding interpretation model; s3.

3. Considering the influence of layer thickness and anisotropy respectively, the strata are equivalent to strata with layer thickness influence but no anisotropy influence and strata with anisotropy but no layer thickness influence, and then constructing layered isotropic processing model M1 and homogeneous anisotropic processing model M2 in turn; s 3.

4. Layered isotropic treatment model M1 including parameter Rts i , θ and H j , where Rts i is the equivalent isotropic resistivity, H j is the formation thickness, θ is the well deviation, i represents the i-th subarray, j represents the j-th formation, and the layered isotropic processing model M1 is used to eliminate the influence of layer thickness; s3.

5. Homogeneous anisotropic processing model M2 includes parameters R hj , θ and R vj , where R hj is the horizontal resistivity, R vj is the vertical resistivity, θ is the well deviation, j represents the jth formation, and the homogeneous anisotropic processing model M2 is used to obtain anisotropic information.

3. A method for extracting anisotropic resistivity of a horizontal well shale oil reservoir according to claim 1, characterized in that: Step s4 comprises the following steps: s4.

1. Use the reference resistivity of adjacent wells, the measured subarray curves of horizontal wells and the synthetic curves to provide the initial value of inversion; s4.

2. For the first subarray curve, combine the inversion initial value provided in step s4.1 with the layered isotropic processing model M1 constructed in step s3 to obtain the formation resistivity profile Rts i , and use the result as the initial value of the next long source distance subarray; s4.

3. For the i-th subarray curve, the formation resistivity profile Rts obtained by inversion of the previous subarray is i-1 As the initial value of inversion, the formation resistivity profile Rts is obtained by inversion. i , and use the result as the initial value of the next long source distance subarray.

4. A method for extracting anisotropic resistivity of a horizontal well shale oil reservoir according to claim 1, characterized in that: Step s6 comprises the following steps: s6.

1. The homogeneous anisotropic processing model M2 established in step s3 includes the parameter R h and R v , where R h is the horizontal resistivity, R v is the vertical resistivity, and the model ignores the effect of layer thickness; s6.

2. For the jth stratum in the layered isotropic processing model M1, the N resistivity profiles of the current layer obtained in step s5 are used as inversion input information. Combined with the homogeneous anisotropic processing model M2 constructed in step s3, the interpretation result of step s5 is inverted to obtain the anisotropic resistivity R of the current layer. hj and R vj ; s6.

3. Invert all layers in the layered isotropic processing model M1 layer by layer, repeat the above process, and obtain the anisotropic resistivity of each stratum.

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