Method and device for evaluating and predicting a shale oil enrichment areas of fault lacustrine basins

Abstract

A method is disclosed for evaluating and predicting a shale oil enrichment area of a fault lacustrine basin, comprising: obtaining materials and key data; determining a source-reservoir configuration relationship according to a longitudinal superposition relationship of different types of rock in a lithology profile and establishing a single-well lithofacies model; in the single-well lithofacies model, using a dolomite-to-formation ratio and a TOC average value to form a dolomite-to-formation ratio contour map and a TOC contour map, and superposing the dolomite-to-formation ratio contour map, the TOC contour map and a source-reservoir configuration relationship plane distribution map to form a lithofacies plane distribution map; on the basis of the lithofacies plane distribution map, superposing a vitrinite reflectance contour map and a dolomite thickness contour map to obtain a corresponding evaluation and prediction map of the shale oil enrichment area of the fault lacustrine basin.

Claims

1. A method for evaluating and predicting a shale oil enrichment area of a fault lacustrine basin, wherein the method comprising: Step 1, obtaining analytical test material for a key core well in a fine-grained facies region of the shale oil enrichment area of the fault lacustrine basin, and obtaining key data of the target stratum logging interpretation based on the analytical test material, wherein the key data of the target stratum logging interpretation includes a dolomite-to-formation ratio, dolomite thickness, a lithology profile, a total organic carbon (TOC) average value, and effective source rock thickness; Step 2, determining a source-reservoir configuration relationship according to a longitudinal superposition relationship of different types of rock in the lithology profile, and establishing a single-well lithofacies mode in conjunction with the dolomite-to-formation ratio and the TOC average value; Step 3, in the single-well lithofacies mode, forming a dolomite-to-formation ratio contour map, a TOC contour map and a source-reservoir configuration relationship plane distribution map respectively by using the dolomite-to-formation ratio, the TOC average value and the source-reservoir configuration relationship, and superposing the dolomite-to-formation ratio contour map, the TOC contour map and the source-reservoir configuration relationship plane distribution map to form a lithofacies plane distribution map; and Step 4: on the basis of the lithofacies plane distribution map, superposing a vitrinite reflectance contour map and a dolomite thickness contour map formed through the dolomite thickness to obtain a corresponding evaluation and prediction map of the shale oil enrichment area of the fault lacustrine basin.

2. The method for evaluating and predicting a shale oil enrichment area of a fault lacustrine basin according to claim 1, wherein the analytical test material comprises an X-diffraction whole rock analysis main mineral component and TOC, and in Step 1, obtaining the key data of the target stratum logging interpretation based on the analytical test material comprises: establishing a first quantitative relationship between an ACDEN distance and the X-diffraction whole rock analysis main mineral component and a second quantitative relationship between the ACDEN distance and the TOC respectively; and applying the first quantitative relationship and the second quantitative relationship to each single well in the fine-grained facies region to obtain the key data of the target stratum logging interpretation.

3. The method for evaluating and predicting a shale oil enrichment area of a fault lacustrine basin according to claim 1, wherein the different types of rock include dolomite, argillaceous dolomite, dolomitic mudstone and argillaceous shale.

4. The method for evaluating and predicting a shale oil enrichment area of a fault lacustrine basin according to claim 1, wherein Step 2 further comprises: determining the lithofacies type of each single well in conjunction with the dolomite-to-formation ratio and the TOC average value.

5. The method for evaluating and predicting a shale oil enrichment area of a fault lacustrine basin according to claim 1, wherein Step 4 further comprises: dividing the sweet spots of shale oil and distribution areas based on the evaluation and prediction map of the shale oil enrichment area of the fault lacustrine basin.

6. A comprehensive evaluation device for a shale oil enrichment area of a fault lacustrine basin, wherein the device comprises: a processor, configured to: obtain analytical test material for a key core well in a fine-grained facies region of the shale oil enrichment area of the fault lacustrine basin, and obtain key data of the target stratum logging interpretation based on the analytical test material, wherein the key data of the target stratum logging interpretation includes a dolomite-to-formation ratio, dolomite thickness, a lithology profile, a TOC average value, and effective source rock thickness; determine a source-reservoir configuration relationship according to a longitudinal superposition relationship of different types of rock in the lithology profile, and establish a single-well lithofacies mode in conjunction with the dolomite-to-formation ratio and the TOC average value; in the single-well lithofacies mode, form a dolomite-to-formation ratio contour map, a TOC contour map, and a source-reservoir configuration relationship plane distribution map respectively by using the dolomite-to-formation ratio, the TOC average value, and the source-reservoir configuration relationship, and superpose the dolomite-to-formation ratio contour map, the TOC contour map and the source-reservoir configuration relationship plane distribution map to form a lithofacies plane distribution map; and on the basis of the lithofacies plane distribution map, superpose a vitrinite reflectance contour map and a dolomite thickness contour map formed through the dolomite thickness to obtain a corresponding evaluation and prediction map of the shale oil enrichment area of the fault lacustrine basin.

7. The comprehensive evaluation device for a shale oil enrichment area of a fault lacustrine basin according to claim 6, wherein the analytical test material comprises an X-diffraction whole rock analysis main mineral component and TOC, and obtaining the key data of the target stratum logging interpretation based on the analytical test material comprises: establishing a first quantitative relationship between an ACDEN distance and the X-diffraction whole rock analysis main mineral component and a second quantitative relationship between the ACDEN distance and the TOC respectively; and applying the first quantitative relationship and the second quantitative relationship to each single well in the fine-grained facies region to obtain the key data of the target stratum logging interpretation.

8. The comprehensive evaluation device for a shale oil enrichment area of a fault lacustrine basin according to claim 6, wherein the different types of rock include dolomite, argillaceous dolomite, dolomitic mudstone and argillaceous shale.

9. The comprehensive evaluation device for a shale oil enrichment area of a fault lacustrine basin according to claim 6, wherein the processor is further configured to: determine the lithofacies type of each single well in conjunction with the dolomite-to-formation ratio and the TOC average value.

10. The comprehensive evaluation device for a shale oil enrichment area of a fault lacustrine basin according to claim 6, wherein the processor is further configured to: divide the sweet spots of shale oil and distribution areas based on the evaluation and prediction map of the shale oil enrichment area of the fault lacustrine basin.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is an overall flow chart of a method for evaluating and predicting a shale oil enrichment area of a fault lacustrine basin according to an embodiment of the present invention.

(2) FIG. 2 is a schematic diagram of source-reservoir configuration relationship according to an embodiment of the present invention.

(3) FIG. 3 is a schematic diagram of lithofacies types according to an embodiment of the present invention.

(4) FIG. 4 is a diagram of an exemplary lithofacies plane distribution map according to an embodiment of the present invention.

(5) FIG. 5 is an evaluation and prediction map of an exemplary shale oil sweet spots according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(6) The present invention will be further described in detail with reference to the accompanying drawings and specific embodiments.

(7) The Ek2 of Cangdong Sag of Huanghua Depression in the Bohai Bay Basin is the main formation for Hydrocarbon layer system in the area. The core and logging mainly shows dark gray and gray-black (oil) lacustrine shales. This area, featuring a wide horizontal distribution range and large longitudinal formation thickness, has geological conditions for forming large-area contiguous distribution of shale oil. In recent years, many oil wells in the middle part of the Palaeo-lacustrine basin at the lower part of the slope of the Ek2 of Cangdong Sag have obtained industrial oil flow in the fine-grained sedimentary area, which has become an important replacement for future oil and gas exploration. Hereinafter, the method and device of the present invention will be described in detail by taking the fifth-order sequence Ek22SQ{circle around (6)} of the Ek2 of Cangdong Sag as an exemplary implementation object.

Embodiment 1

(8) As shown in FIG. 1, the present embodiment provides a method for evaluating and predicting a shale oil enrichment area of a fault lacustrine basin, generally comprising the following steps:

(9) Step S1 is to obtain analytical test material for a key core well in a fine-grained facies region of the shale oil enrichment area of the fault lacustrine basin, and obtain key data of the target stratum logging interpretation based on the analytical test material.

(10) Herein, the key data of the target stratum logging interpretation includes a dolomite-to-formation ratio, dolomite thickness, a lithology profile, a TOC average value, and effective source rock thickness.

(11) Step S2 is to determine a source-reservoir configuration relationship according to a longitudinal superposition relationship of different types of rock in the lithology profile, and establish a single-well lithofacies mode in conjunction with the dolomite-to-formation ratio and the TOC average value.

(12) Step S3 is to, in the single-well lithofacies mode, form a dolomite-to-formation ratio contour map, a TOC contour map, and a source-reservoir configuration relationship plane distribution map respectively by using the dolomite-to-formation ratio, the TOC average value, and the source-reservoir configuration relationship, and superpose the dolomite-to-formation ratio contour map, the TOC contour map and the source-reservoir configuration relationship plane distribution map to form a lithofacies plane distribution map.

(13) Step S4 is to, on the basis of the lithofacies plane distribution map, superpose a vitrinite reflectance contour map and a dolomite thickness contour map formed through the dolomite thickness to obtain a corresponding evaluation and prediction map of the shale oil enrichment area of the fault lacustrine basin.

(14) Specifically, for Step S1: the key core well, Well G108-8, is located at the lower part of the west slope of the Ek2 of the Cangdong Sag. The Ek2 of the Cangdong Sag of the well is continuously cored for nearly 500 m, and is divided into 10 fifth-order sequences from bottom to top, such as Ek24SQ{circle around (1)} and Ek24SQ{circle around (2)}. The core material reveals that Ek24SQ{circle around (1)} and Ek22SQ{circle around (8)} are tight sandstone sections, and the non-sandstone sections are mainly gray-black and dark-gray shale (oil shale) with a small amount of thin-layer pure taupe and brown dolomite in which local enrichment of sandy strips and sandy masses can be seen.

(15) The rich and detailed analytical test material is available for the core section. It is designed so that there are more than 1000 samples for whole rock X-diffraction and TOC testing. By establishing quantitative relationships between ACDEN distance and X-diffraction whole rock analysis main mineral components and between the ACDEN distance and the TOC, fitting formulas are respectively formed to interpret the lithology and TOC based on the ACDEN distance; the ACDEN distance fitting formulas are applied to all single wells in the fine-grained sedimentary area (more than 70 wells in the drilling target stratum); on a geological work platform (for example, the Reform GeoOffice), the logging interpretation lithology profiles and the TOC changing curves (formed by connecting the scatter points at intervals of 0.125 m) of all single wells Ek22SQ{circle around (6)} are obtained and based on this, the dolomite-to-formation ratios, dolomite thicknesses, TOC average values, effective source rock thicknesses and other key data of all the single wells Ek22SQ{circle around (6)} can be obtained through statistics.

(16) For Step S2, the longitudinal superposition combination relationships of dolomite and mudstone are observed according to the logging interpretation lithology profiles, source-reservoir ratios and dolomite-to-formation ratios of the single wells Ek22SQ{circle around (6)}, and finally three source-reservoir configuration relationships (multi-layer type, inter-bedded type, and sandwich type) are defined.

(17) As shown in FIG. 2, multi-layer type: the source-reservoir ratio is 0.7-1.5, the dolomite-to-formation ratio is 40-60%, and the thin-layer reservoir and the thin-layer source rock frequently intersect each other, and hydrocarbons generated by the thermal evolution of the source rock move to adjacent reservoirs; these types of reservoirs are thin and large in quantity, small in scale for each single layer, and have a single layer thickness distribution less than 1 m, but large cumulative thickness.

(18) Inter-bedded type: the source-reservoir ratio is 0.7-1.5, the dolomite-to-formation ratio is 40-60%, medium-thick source rock and medium-thick reservoirs are in longitudinal superimposed distribution; hydrocarbons generated by the thermal evolution of the source rocks can also easily move to adjacent reservoirs, and have a single layer thickness distribution of 1-2 m.

(19) Sandwich type can be subdivided into two categories. The first category: the source-reservoir ratio is less than 0.7, and the dolomite-to-formation ratio is greater than 60%; the medium-thin shale is sandwiched between massive dolomite and argillaceous dolomite (single-layer thickness is greater than 2 m); due to relatively thin source rock, the amount of hydrocarbons generated is small; although the dolomite reservoirs are relatively well developed, they can only form lean or even oil-free dry formations; the small amount of oil and gas produced by the thin source rock is only charged into the adjacent reservoirs. The second category: the source-reservoir ratio is greater than 1.5, and the dolomite-to-formation ratio is less than 40%; the medium-thin shale is sandwiched in massive mudstone (single-layer thickness is greater than 2 m); hydrocarbons generated are abundant, but good reservoirs are in shortage; even though the thin reservoirs have good oil-bearing properties, they have less thickness, resulting in considerable residual hydrocarbons in the shale, and locally meeting conditions for forming shale oil sweet spots.

(20) The division rules and standards of the lithofacies are shown in Table 1. According to the dolomite-to-formation ratio, the main-class lithofacies of a stratigraphic unit or sequence are named by the dominant lithofacies. On the basis of the main-class lithofacies, in conjunction with the abundance of organic matter, a subfacies is formed, namely: organic facies+dominant facies, such as: high-organic-matter dolomitic mudstone facies. On the basis of subfacies division, in conjunction with the source-reservoir configuration relationship, a small-class facies is formed, namely: stratigraphic facies+organic facies+dominant facies, such as: multi-layer type medium-high organic matter thin-layer argillaceous dolomite facies. According to the needs of actual research accuracy, drawings are plotted according to different facies such as main-class facies, subfacies or small-class facies. Taking the small-class facies with the highest drawing accuracy as an example, from the Ek22SQ{circle around (6)} in the Ek2 of Cangdong Sag of Huanghua Depression, 10 types of lithofacies such as the medium-high organic matter thin-layer mudstond-dolomite mixed phase, inter-bedded high-medium organic matter medium-layer mudstond-dolomite mixed facies, inter-bedded medium-low organic matter medium-layer argillaceous dolomite, can be identified, and the lithofacies mode of this area is finally established, as shown in FIG. 3.

(21) TABLE-US-00001 TABLE 1 Lithofacies type Small class Sub Stratigraphic Dominant facies Organic facies Stratigraphic facies class facies + Dolomite- Abundance Source- Logging Main Organic organic to- of reservoir interpretation class facies + facies + formation organic configuration single-layer Dominant dominant dominant No. Rock type ratio/% matter TOC/% relationship thickness facies facies facies 1 Dolomite >75 High >4 Sandwich Medium-thin Such as: Such Such as: facies organic type layer dolomite as: high multi-layer matter sandwiched facies, organic medium-high 2 Argillaceous 50-75 in thick argillaceous matter organic dolomite layer dolomite dolomitic matter facies (>2 m) facies, mudstone thin-layer Medium 2-4 Inter-bedded Medium dolomitic facies argillaceous 3 Dolomitic 25-50 Organic type layer mudstone dolomite mudstone matter (1-2 m) facies, facies facies Low <2 Multi-layer Thin layer argillaceous 4 Mudstone <25 organic type (<1 m) shale facies matter facies

(22) For Step S3, all the calculated single-well dolomite-to-formation ratio data of the Ek22SQ{circle around (6)} is applied to the plane graph to form a dolomite-to-formation ratio contour map, and the calculated TOC average values of all single wells are applied to the plane graph to form a TOC contour map. At the same time, all the calculated source-reservoir configuration relationships of the single wells are applied to the plane graph to form a source-reservoir configuration plane distribution map. The dolomite-to-formation ratio contour map, the TOC contour map and the source-reservoir configuration relationship plane distribution map are superimposed. According to the different plane combinations of the dolomite-to-formation ratio, TOC, and source-reservoir configuration in Table 1 and FIG. 3, the plane distribution map of small-class facies is formed, as shown in FIG. 4, for example, in the plane distribution area of inter-bedded medium-low organic matter middle-layer argillaceous dolomite facies, the dolomite-to-formation ratio contours are mainly distributed in the range of 50-75%, the TOC contours are distributed in the range of less than 4%, and the source-reservoir configuration relationships are dominated by inter-bedded type. Ek22SQ{circle around (6)} is mainly composed of six facies types such as inter-bedded medium-low organic matter medium-layer argillaceous dolomite facies and inter-bedded high-medium organic matter medium-layer mudstond-dolomite mixed facies. The facies plane distribution map can reflect the plane distribution of the main reservoirs (dolomite) and the plane distribution of the main source rock (mudstone), and can reflect the distribution rule of different source-reservoir configuration relationships in the plane.

(23) For Step S4, based on the plane distribution map of Ek22SQ{circle around (6)} in FIG. 4, a thermal evolution maturity Ro contour map is superimposed on it to obtain the corresponding evaluation and prediction map of the shale oil enrichment area of the fault lacustrine basin in conjunction with the dolomite thickness contour map, so as to evaluate and predict the shale oil enrichment area. Considering the various control factors of shale oil enrichment, Ek22SQ{circle around (6)} can be divided into 3 classes (I, II and III) of shale oil sweet spots (FIG. 5): sweet spots of Class I belong to the source/reservoir neighboring shale oil, with the main lithofacies type of inter-bedded medium-low organic matter medium-layer argillaceous dolomite facies, in which reservoirs are mainly dolomite, the dolomite-to-formation ratio is mainly distributed in the range of 50-75%, Ro is above 0.5%, and the average TOC is mainly distributed in the range of 1-3%, the average thickness of dolomite is more than 15 m, and the distribution area is about 106 km.sup.2; the sweet spots of Class II also belong to the source/reservoir neighboring shale oil, with the main lithofacies type of inter-bedded medium-high organic matter medium-layer dolomitic mudstone facies, in which reservoirs are mainly dolomitic mudstone, the dolomite-to-formation ratio is mainly distributed in the range of 25-50%, Ro is above 0.5%, and the TOC is mainly distributed in the range of 2-3.5%, the average thickness of dolomitic mudstone is 12 m, and the distribution area is about 165 km.sup.2; the sweet spots of Class III also belong to the source/reservoir neighboring shale oil and source/reservoir integrated shale oil, with relatively low thermal evolution maturity, in which Ro is basically distributed in the range above 0.5%, reservoirs are mainly dolomite and argillaceous shale with relatively low maturity, the dolomite-to-formation ratio is mainly distributed in the range of 15-70%, the TOC is mainly distributed in the range of 2-4%, and the distribution area is about 35 km.sup.2.

(24) According to the research results of the present invention, multiple pre-exploration wells are deployed in the class I sweet spot, and industrial oil flows are obtained in wells such as G108-8, KN9, GD61, which further confirms the reliability of the comprehensive evaluation and prediction method of the shale oil enrichment area of the fault lacustrine basin. Under the current economic and technical conditions, the prediction accuracy of the method can meet the needs of shale oil exploration.

Embodiment 2

(25) This embodiment provides a comprehensive evaluation and prediction device for a shale oil enrichment area of a fault lacustrine basin, comprising: a processor. The processor is configured to: obtain analytical test material for a key core well in a fine-grained facies region of the shale oil enrichment area of the fault lacustrine basin, and obtain key data of the target stratum logging interpretation based on the analytical test material, wherein the key data of the target stratum logging interpretation includes a dolomite-to-formation ratio, dolomite thickness, a lithological profile, a TOC average value, and effective source rock thickness; determine a source-reservoir configuration relationship according to a longitudinal superposition relationship of different types of rock in the lithological profile, and establish a single-well lithofacies mode in conjunction with the dolomite-to-formation ratio and the TOC average value; in the single-well lithofacies mode, form a dolomite-to-formation ratio contour map, a TOC contour map, and a source-reservoir configuration relationship plane distribution map respectively by using the dolomite-to-formation ratio, the TOC average value, and the source-reservoir configuration relationship, and superpose the dolomite-to-formation ratio contour map, the TOC contour map and the source-reservoir configuration relationship plane distribution map to form a lithofacies plane distribution map; and on the basis of the lithofacies plane distribution map, superpose a vitrinite reflectance contour map and a dolomite thickness contour map formed through the dolomite thickness to obtain a corresponding evaluation and prediction map of the shale oil enrichment area of the fault lacustrine basin.

(26) The processor is also configured to: based on the comprehensive evaluation and prediction of the shale oil enrichment area, divide the sweet spot types of shale oil and distribution areas.

(27) The processor is also configured to: based on the evaluation and prediction map of the shale oil enrichment area of the fault lacustrine basin, divide the sweet spot types of shale oil and distribution areas.

(28) It should be noted that the specific implementation details of Embodiment 2 can be referred to the foregoing Embodiment 1, and its details are not described herein again.

(29) Those skilled in the art can understand that all or part of the steps for implementing the methods in the above embodiments may be completed by related hardware under the instructions of a program, and the program is stored in a storage medium, and includes a plurality of instructions for enabling a single-chip processor, a chip, or a processor to perform all or part of the steps of the methods described in the various embodiments of the present application. The foregoing storage medium includes: a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk, and the like, which can store program codes.

(30) The above embodiments are not intended to limit the present invention, and the present invention is not limited to the above examples, and variations, modifications, additions or substitutions made by those skilled in the art within the scope of the technical solutions of the present invention also fall within the scope of protection of the present invention.