A method for evaluating the seepage characteristics of shale oil based on lamination density

Abstract

The present invention discloses a method for evaluating the seepage characteristics of shale oil according to the lamination density. Based on the comprehensive analysis of geological and logging data, the top and bottom depths and thicknesses of the main sub-layers in the research block are determined. Key logging curves are screened, and the number of laminations is determined by using the method of taking the second derivative. The change of the corresponding lamination density is determined according to the ratio of the number of laminations to the thickness. The regional seepage characteristics are evaluated through the change law of the lamination density of different sub-layers in the target area, providing a practical technical method for the development of shale oil.

Description

Technical Field

[0001] The present invention relates to the technical field of unconventional oil and gas development, and particularly to a method for evaluating the seepage characteristics of shale oil according to the lamination density. Background Art

[0002] Lamination refers to the smallest or thinnest original sedimentary layer that can be distinguished in sediments or sedimentary rocks, and it is a sedimentary structure widely developed in shale. The development of lamination affects the distribution of shale pore types and pore size ratios. Generally speaking, under the same conditions such as thickness and lithology, the more developed the lamination is, the higher its lamination density value is, indicating that its total organic carbon content and organic matter pores both relatively decrease, while the inorganic pores are relatively developed. Therefore, the lamination development characteristics are a reflection of the change of seepage characteristics of shale reservoirs. A large lamination density means good reservoir seepage characteristics. At present, the research on lamination development characteristics generally adopts methods such as laboratory analysis. This method is limited by the number of drilling cores and well sections. How to quickly and effectively carry out the analysis of lamination density of shale oil reservoirs is one of the difficult problems that geologists urgently need to solve. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for finely dividing the lamination density based on logging data and evaluating the seepage characteristics of shale oil according to the lamination density.

[0004] In order to solve the above technical problem, the technical solution adopted by the present invention is: A method for evaluating the seepage characteristics of shale oil according to the lamination density, comprising the following steps:

[0005] 1) Through the statistical analysis of the logging series of the target block, determine the main logging series of the completed wells, and determine the compensated density logging curve or the compensated acoustic logging curve as the key logging curve in combination with the vertical resolution characteristics of conventional logging data. Among them, first select the compensated density logging curve as the key logging curve. If the compensated density logging curve is not recorded in the completed wells, then select the compensated acoustic logging curve as the key logging curve;

[0006] 2) For the logging data of all completed wells in the target block, determine the top and bottom depths of the sub-layers in combination with geological data, use the second derivative derivative method to analyze the number of laminations of the key logging curve, determine the lamination density, and conduct seepage characteristic analysis according to the change characteristics of the lamination density.

[0007] Step 2) includes the following steps:

[0008] ① Divide the top, bottom depths and thicknesses of the target layers in the research block, and in combination with the core analysis and geological information of the target block, use the logging data to determine the top depth, bottom depth and thickness of the sub-layers by using the methods of stratigraphic correlation and logging response characteristic analysis;

[0009] ②Select key logging curves. By using the second derivative derivation method and counting the number of positive and negative features of the second derivative of the key logging curves, the number of laminations developed in the corresponding interval can be determined.

[0010] ③Use the key logging curves to determine the number of laminations in the target layer. The number of laminations divided by the lamination thickness is the lamination density.

[0011] ④Conduct lamination density analysis on the completed wells in the target block. On this basis, establish an isogram of the lamination density distribution of different sub-layers. A high lamination density value indicates good seepage characteristics, while a low lamination density value indicates poor seepage characteristics. Use the variation characteristics of the lamination density in different well areas to reflect the variation characteristics of the seepage properties of shale oil reservoirs.

[0012] The beneficial effects of the present invention are as follows: It effectively improves the accuracy of analyzing the seepage characteristics of shale oil using logging data. It can quickly carry out the division of shale oil lamination density and the analysis of seepage characteristics, effectively improving the development efficiency of shale oil and the oil and gas production. Description of the Drawings

[0013] Figure 1 It is the logging curve of Well G108-8 in the embodiment adopting the method of the present invention.

[0014] Figure 2 It is the isogram of the lamination density of Sub-layer 19 in Well Area G108-8 in the embodiment adopting the method of the present invention. Detailed Embodiment

[0015] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0016] The method for evaluating the seepage characteristics of shale oil according to the lamination density of the present invention includes the following steps:

[0017] 1) Through the statistical analysis of the logging series in the target block, determine the main logging series of the completed wells. Combine the vertical resolution characteristics of the conventional logging data to determine the compensated density logging curve or the compensated acoustic logging curve as the key logging curve. Among them, first select the compensated density logging curve as the key logging curve. If the compensated density logging curve is not recorded in the completed well, then select the compensated acoustic logging curve as the key logging curve.

[0018] 2) For the logging data of all completed wells in the target block, combine the geological data to determine the top and bottom depths of the sub-layers. Use the second derivative derivation method to conduct lamination number analysis on the key logging curves, determine the lamination density, and conduct seepage characteristic analysis according to the variation characteristics of the lamination density.

[0019] Step 2) includes the following steps:

[0020] ① Divide the top, bottom depths and thickness of the target layer in the research block. Combine the core analysis and geological information of the target block, and use well logging data to determine the top depth, bottom depth and thickness of the sub-layers by using the methods of stratigraphic correlation and well logging response characteristic analysis;

[0021] ② Select key well logging curves. By using the second derivative method, the number of laminations developed in the corresponding layer section can be determined by counting the number of positive and negative characteristics of the second derivative of the key well logging curves;

[0022] ③ Use the key well logging curves to determine the number of laminations in the target layer. The number of laminations divided by the lamination thickness is the lamination density.

[0023] ④ Conduct lamination density analysis on the completed wells in the target block. On this basis, establish the isogram of lamination density distribution of different sub-layers. A high lamination density value indicates good seepage characteristics, while a low lamination density value indicates poor seepage characteristics. Use the variation characteristics of lamination density in different well areas to reflect the variation characteristics of the seepage properties of shale oil reservoirs.

[0024] Based on the comprehensive analysis of well logging and geological data, the present invention determines the key well logging curves, analyzes the number of laminations by using the second derivative method, determines the lamination density, and conducts seepage property analysis, effectively improving the accuracy of using well logging data for shale oil seepage property analysis. It can quickly carry out the division of shale oil lamination density and seepage property analysis, effectively improving the development efficiency of shale oil and the oil and gas production. It is applicable to the development of shale oil and gas, improving the oil and gas production and development efficiency.

[0025] Embodiment

[0026] Use the method of the present invention to design the evaluation scheme for shale oil seepage properties in Well Area G108-8 of the second member of Kongdian Formation in Cangdong Sag. The specific method is as follows:

[0027] 1) Determine the key well logging curves in combination with the vertical resolution characteristics of conventional well logging data

[0028] Through the analysis of the performance indicators of well logging instruments, it can be known that the vertical resolution of dual laterolog data is 0.61 m, the vertical resolution of compensated acoustic wave is 0.61 m, the vertical resolution of compensated density is 0.48 m, and the resolution of compensated neutron is 0.69 m. By statistically analyzing the well logging series of 132 completed wells in the second member of Kongdian Formation in Cangdong Sag, and combining the well logging data acquisition situation in the block and different instrument performance indicators, it is determined that the key well logging curve is compensated density. If the compensated density well logging data is not acquired in the analyzed well, the seepage property evaluation is carried out by using the compensated acoustic wave data.

[0029] 2) Combine geology and well logging data to determine the top and bottom depths of the sub-layers, and use the second derivative method to conduct lamination number analysis to determine the lamination density;

[0030] ①Divide the top depth, bottom depth and thickness of the target layer in the research block;

[0031] Combined with the core analysis and geological information of the target block, use well logging data and methods such as stratigraphic correlation and response characteristic analysis to determine the top and bottom depths of the sub-layers. Through the analysis of geological and well logging data, the shale oil reservoir in the second member of the Kong Formation is divided into 21 sub-layers. Among them, the stratification data of the 19th sub-layer of Well G108-8 is 3,233.0 - 3,251.5 m, and the thickness is 18.5 m.

[0032] ②Select key well logging curves and use the second derivative method to determine the number of laminations;

[0033] The basic principle of the second derivative method is as follows: perform the second derivative on the discrete data of the key well logging curves. Among them, f″(key curve) < 0 represents that the curve shows a convex state, and f″(key curve) > 0 represents that the curve shows a concave state; use the positive and negative characteristics of the second derivative to characterize the convexity and concavity of the key well logging curves. The change in convexity and concavity of the curve indicates the existence of obvious lamination change characteristics. By counting the number of positive and negative characteristics of the second derivative of the key curve in the target layer section, the number of laminations developed in the corresponding layer section can be determined. By performing the second derivative on the 19th sub-layer of Well G108-8, it can be known that this sub-layer has a total of 25 laminations, and the lamination thickness is between 0.5 - 1.2 m (see Figure 1 ).

[0034] ③Determine the lamination density according to the sub-layer thickness and the number of laminations;

[0035] From the above analysis, it can be known that using the compensated density well logging curve to determine that the number of laminations developed in the 19th sub-layer is 25, and the thickness is 18.5 m. According to the ratio of the number of laminations in the sub-layer to the sub-layer thickness, the lamination density of the 19th sub-layer is determined to be 1.35.

[0036] ④Determine the lamination density for all completed wells in the target block, and conduct seepage characteristic analysis according to the change characteristics of the lamination density.

[0037] Use this method to determine the lamination density of the 19th sub-layer of 132 wells in the G108-8 well area, draw an isogram of the lamination density distribution, and reflect the change characteristics of the seepage properties of the shale oil reservoir according to the change characteristics of the lamination density in the well area ( Figure 2 ). The higher the lamination density of the corresponding layer section in the figure, the better the seepage characteristics of the reservoir, providing technical support for regional sweet spot analysis and well location deployment.

[0038] Using this method can quickly and effectively carry out the evaluation of the seepage characteristics of shale oil reservoirs, provide guidance for the deployment of shale oil well locations, and effectively improve the development process of shale oil and gas reservoirs.

[0039] In summary, the content of the present invention is not limited to the above embodiments. Those skilled in the art can easily propose other embodiments within the technical guiding ideology of the present invention, but such embodiments are all included within the scope of the present invention.

Claims

1. A method for evaluating the seepage characteristics of shale oil according to the lamination density, characterized in that, It includes the following steps: 1) Through the statistical analysis of the logging series of the target block, determine the main logging series of the completed wells. Combining with the vertical resolution characteristics of the conventional logging data, determine the compensated density logging curve or the compensated acoustic logging curve as the key logging curve. Among them, first select the compensated density logging curve as the key logging curve. If the compensated density logging curve is not recorded in the completed wells, then select the compensated acoustic logging curve as the key logging curve; 2) For the conventional logging data of all completed wells in the target block, determine the top and bottom depths of the sub-layers in combination with the geological data. Use the second derivative derivative method to analyze the number of laminations of the key logging curve, determine the lamination density, and conduct seepage characteristic analysis according to the change characteristics of the lamination density, including the following steps: ① Divide the top, bottom depths and thicknesses of the target layers in the research block. Combining with the core analysis and geological information of the target block, use the conventional logging data and the formation correlation and logging response characteristic analysis methods to determine the top depth, bottom depth and thickness of the sub-layers; ② Select the key logging curve, and use the second derivative derivative method. By counting the positive and negative characteristic numbers of the second derivative of the key logging curve, the number of developed laminations in the corresponding layer section can be determined; ③ Use the key logging curve to determine the number of laminations in the target layer. The number of laminations divided by the lamination thickness is the lamination density; ④ Conduct lamination density analysis on the completed wells in the target block. On this basis, establish the isogram of the lamination density distribution of different sub-layers. If the lamination density value is high, the seepage characteristics are good; if the lamination density value is low, the seepage characteristics are poor. Use the change characteristics of the lamination density in different well areas to reflect the change characteristics of the seepage properties of the shale oil reservoir.

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