Fine description method for microfacies of riverway

Abstract

The invention discloses a riverway microfacies fine depicting method which is used for a shallow water braided river delta of a dense-rich sandstone stratum. The depicting method comprises the steps of basic data collection and arrangement, single-well sand body identification, sand body thickness calculation, sand system number calculation, single-well sedimentary microfacies division, single-well primary and secondary river channel division, sand system number lower limit determination, sand system number contour map drawing, fine depicting of river channel microphases and the like. The method is based on single well sand body identification, the thickness, granularity, logging curve form and other characteristics of the river channel sand body are analyzed, and the river channel microfacies are further divided into a main river channel with concentrated reservoir development and a secondary river channel with less reservoir development. The determination of the main river channel sand system number lower limit and the sand system number plane distribution characteristics is beneficial to fine description of the main river channel, so that the high-quality sand body plane distribution characteristics are determined, and a favorable reservoir development zone is predicted.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum exploration and development, and in particular relates to a method for finely characterizing river channel microfacies in a shallow braided river delta rich in dense sandstone strata. Background Art

[0002] The braided river delta facies has a well-developed source-reservoir-cap combination in the vertical direction, which can be used as a key target for oil and gas exploration. Compared with the river mouth bar sand body and sheet sand body, the river channel sand body is thicker, extends farther, and has less matrix and cement. It is the most important skeleton sand body in the braided river delta facies, providing a good material basis for the development of reservoirs and is conducive to the formation and enrichment of subsequent oil and gas reservoirs. Due to the differential distribution of river channel sand bodies, there are differences in the enrichment of tight sandstone gas reservoirs in braided river deltas.

[0003] At present, the research on braided river deltas is mostly found in conventional oil and gas reservoirs. A large number of studies are based on core observation, thin section analysis and scanning electron microscopy, analyzing the division and combination of lithofacies, combining well logging data to analyze the electrical characteristics of the target layer, dividing sedimentary microfacies, identifying the distribution characteristics of river sand bodies, and characterizing the macroscopic distribution of braided river delta channels according to the "sand-to-formation ratio" (sand body thickness / formation thickness) data.

[0004] At present, most of the technologies for finely depicting river channel microfacies are based on the analysis of the "sand-to-land ratio" or the planar distribution characteristics of sand body thickness in the study area. According to the principle of dominant phase, the area with a "sand-to-land ratio" greater than 0.5 is divided into river channel development areas, and the river channel microfacies are depicted. However, there are strata with large-scale development of dense sandstone at the basin scale. Most areas of such dense sandstone-rich strata have a "sand-to-land ratio" value of more than 0.5, and river channel microfacies are developed over a large area. The existing technology only depicts the river channel development area, and it is difficult to further finely depict high-quality river channel sand bodies. Summary of the invention

[0005] In order to solve the above-mentioned problems existing in the prior art, the present invention provides a method for fine characterization of river channel microfacies of shallow braided river deltas in dense sandstone formations. The method effectively solves the problem of fine characterization of river channel microfacies of shallow braided river deltas in widely developed dense sandstone formations, and is helpful to finely analyze the planar distribution characteristics of high-quality sand bodies and predict favorable reservoir development zones.

[0006] The technical solution adopted by the present invention is:

[0007] A method for fine characterization of river channel microfacies, which is used for shallow braided river deltas rich in dense sandstone formations, comprises the following steps:

[0008] S1. Collection and collation of basic data: Collect data of the study area, including geological overview, core data, thin section data, conventional logging data, and stratified data;

[0009] S2. Single well sand body identification: Based on conventional logging data, core data and thin section data, the lithology and electrical characteristics of the single well sand body are comprehensively identified to determine the development characteristics of the single well sand body;

[0010] S3. Calculation of sand body thickness: Based on the identification results of the sand body in a single well, the sand body thickness of the single well is counted according to the formation stratification data, and the sand-to-formation ratio is calculated; the sand-to-formation ratio is the total sand body thickness divided by the formation thickness.

[0011] S4. Calculation of sand body coefficient: Calculate the sand body coefficient of a single well based on the value of the sand body thickness and the sand-to-ground ratio of the single well;

[0012] S5. Single well sedimentary microfacies division: Based on the geological overview, the core data and conventional logging data are combined to determine the characteristics of different sedimentary microfacies and logging curves, and divide the single well sedimentary microfacies;

[0013] S6. Division of main and secondary channels of single wells: Analyze the sedimentary microfacies characteristics of single wells, and further divide the channel microfacies of braided river delta into main channels and secondary channels according to the characteristics of channel sand body thickness, sand body grain size, logging curve morphology, etc.

[0014] S7. Determine the lower limit of the sand system number: Analyze the sand system numbers corresponding to the main river channel and the secondary river channel respectively, and determine the lower limit of the sand system number of the main river channel;

[0015] S8. Draw a sand system number contour map: Based on the sand system number of a single well, combined with geological overview and paleo-geomorphology during the sedimentary period, draw a sand system number contour map;

[0016] S9. Detailed characterization of river channel microfacies: According to the lower limit of the sand system number of the main river channel, characterize the main river channel based on the sand system number contour map, analyze the sand body development zones of the main river channel, and predict the favorable reservoir development zones.

[0017] Furthermore, in step S2, the single well lacking lithology data can refer to the GR curve, and define the part with a GR value less than 65 as sandstone; the GR curve is a natural gamma logging curve, which records the natural gamma ray intensity of underground rocks.

[0018] Furthermore, in step S3, based on the stratification data and in accordance with the sandstone division results, the total thickness of sandstone in a single well within the study layer is calculated, and the total thickness of the sand body is divided by the formation thickness to obtain the sand-to-formation ratio.

[0019] Furthermore, in step S4, the sand body thickness of the single well is multiplied by the sand-to-formation ratio to obtain the sand body coefficient of the single well.

[0020] Furthermore, in step S7, the main channel and the secondary channel are compared with the corresponding sand system coefficients to determine the lower limit of the sand system coefficient of the main channel.

[0021] Furthermore, in step S8, based on the sedimentary background such as the provenance direction and the settlement center during the stratum deposition period, the planar distribution trend of the sand system number is determined, and a contour map of the sand system number is drawn.

[0022] Furthermore, in step S9, the zone with a sand system coefficient lower limit higher than the main channel in the sand system coefficient contour map is defined as the main channel development zone, and a fine-detailed plan view of the channel microfacies of the target layer section in the study area is obtained to predict the favorable reservoir development zone.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention proposes a method for fine characterization of river channel microfacies in shallow braided river deltas in dense sandstone formations. It effectively solves the problem that existing river channel characterization methods are difficult to characterize high-quality river channel sand bodies inside dense sandstone formations, and enriches the theoretical basis for predicting favorable reservoir development zones.

[0025] 2. This invention is based on the research on the identification of sand bodies in single wells in dense sandstone formations and the characteristics of river channel sand bodies, combined with the single well sedimentary microfacies performance of shallow braided river delta phase, to analyze the development characteristics of the main and secondary channels, clarify the numerical differences of the sand systems in the main and secondary channels, and characterize the development zones of the main channels. It provides theoretical support for clarifying favorable reservoir development zones and predicting favorable exploration zones in shallow braided river deltas with dense sandstone formations, which has important practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a flow chart of the method of the present invention.

[0027] Figure 2 It is a typical main and secondary river channel single well histogram in an embodiment of the present invention.

[0028] Figure 3 It is a numerical contour diagram of the sand system according to an embodiment of the present invention.

[0029] Figure 4 It is a schematic diagram of the lower limit division of the number of sand systems in the main river channel according to an embodiment of the present invention.

[0030] Figure 5 It is a plan view of the fine depiction of the river channel microfacies according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying 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 present invention, that is, the embodiments described are only part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0032] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0033] Combine the following Figure 1-5 A specific embodiment of the present invention will be described.

[0034] like Figure 1 As shown, a method for fine characterization of river channel microfacies is used for shallow braided river delta rich in dense sandstone strata, comprising the following steps:

[0035] S1. Collection and collation of basic data: Collect data of the study area, including geological overview, core data, thin section data, conventional logging data, and stratified data;

[0036] S2. Single well sand body identification: Based on conventional logging data, core data and thin section data, the lithology and electrical characteristics of the single well sand body are comprehensively identified to determine the development characteristics of the single well sand body;

[0037] S3. Calculation of sand body thickness: Based on the identification results of the sand body in a single well, the sand body thickness of the single well is counted according to the formation stratification data, and the sand-to-formation ratio is calculated; the sand-to-formation ratio is the total sand body thickness divided by the formation thickness.

[0038] S4. Calculation of sand body coefficient: Calculate the sand body coefficient of a single well based on the value of the sand body thickness and the sand-to-ground ratio of the single well;

[0039] S5. Single well sedimentary microfacies division: Based on the geological overview, the core data and conventional logging data are combined to determine the characteristics of different sedimentary microfacies and logging curves, and divide the single well sedimentary microfacies;

[0040] S6. Division of main and secondary channels of single wells: Analyze the sedimentary microfacies characteristics of single wells, and further divide the channel microfacies of braided river delta into main channels and secondary channels according to the characteristics of channel sand body thickness, sand body grain size, logging curve morphology, etc.

[0041] S7. Determine the lower limit of the sand system number: Analyze the sand system numbers corresponding to the main river channel and the secondary river channel respectively, and determine the lower limit of the sand system number of the main river channel;

[0042] S8. Draw a sand system number contour map: Based on the sand system number of a single well, combined with geological overview and paleo-geomorphology during the sedimentary period, draw a sand system number contour map;

[0043] S9. Detailed characterization of river channel microfacies: According to the lower limit of the sand system number of the main river channel, characterize the main river channel based on the sand system number contour map, analyze the sand body development zones of the main river channel, and predict the favorable reservoir development zones.

[0044] In step S2, the single well lacking lithology data can refer to the GR curve, and define the part with a GR value less than 65 as sandstone; the GR curve is a natural gamma logging curve, which records the natural gamma ray intensity of underground rocks.

[0045] In step S3, based on the stratification data and in accordance with the sandstone division results, the total thickness of sandstone in a single well within the study layer is calculated, and the total thickness of the sand body is divided by the formation thickness to obtain the sand-to-formation ratio.

[0046] In step S4, the sand body thickness of the single well is multiplied by the sand-to-formation ratio to obtain the sand body coefficient of the single well.

[0047] In step S5, the channel facies is dominated by sandy deposits, mainly fine sandstone, medium sandstone, and gravel-bearing sandstone. Vertically, it has a discontinuous positive rhythm of coarse at the bottom and fine at the top. The sedimentary structure is dominated by plate-like and trough-like cross-bedding and parallel bedding. The logging GR curve is mainly box-shaped or bell-shaped.

[0048] In step S6, the main channel has stable sedimentation, with a large set of thick fine-medium sandstone and a small amount of thin mudstone, good sand body sorting, and large channel thickness and single sand body thickness; the secondary channel migrates frequently, mainly manifested as thin and medium-thick fine sandstone intercalated with a small amount of thin siltstone and mudstone, and the channel thickness and single sand body thickness are relatively small.

[0049] In step S7, the main channel and the secondary channel are compared with the corresponding sand system numbers to determine the lower limit of the sand system number of the main channel. The sand system numbers of single wells with developed main channels are all higher than 90, and the sand system numbers of single wells with developed secondary channels are all lower than 90, that is, the lower limit of the sand system number of the main channel is 90.

[0050] In step S8, based on the sedimentary background such as the provenance direction and the settlement center during the stratum deposition period, the planar distribution trend of the sand system number is determined, and a contour map of the sand system number is drawn.

[0051] In step S9, the zone with a sand system number lower limit higher than the main channel in the sand system number contour map is defined as the main channel development zone (i.e., the main channel with a sand system number greater than 90 in the sand system number contour map), and a detailed plan view of the channel microfacies of the target layer in the study area is obtained to predict the favorable reservoir development zone.

[0052] like Figure 2 As shown, identifying sand bodies, clarifying single well sedimentary microfacies and distinguishing between main and secondary channels are the basic conditions for the fine characterization of the channel in the present invention.

[0053] like Figure 3As shown, by comparing the number of sand systems in the main and secondary channels with the corresponding single wells, the lower limit of the number of sand systems in the main channel can be determined.

[0054] like Figure 4 As shown, the depiction of the plane distribution of the sand body is the basic condition for the fine depiction of the river channel in the present invention.

[0055] like Figure 5 As shown in the figure, based on the sand system coefficient contour map combined with the lower limit of the main channel sand system coefficient, the main channel is finely portrayed, and the sedimentary microfacies fine portrayal plane map is obtained to clarify the high-quality sand body development zone and predict the plane development of favorable reservoirs.

[0056] The above contents are merely examples and explanations of the structure of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for fine characterization of river channel microfacies, characterized in that: The method is used for shallow braided river delta rich in dense sandstone formations, and comprises the following steps: S1. Collection and collation of basic data: Collect data of the study area, including geological overview, core data, thin section data, conventional logging data, and stratification data; S2. Single well sand body identification: Based on the conventional logging data, the core data and the thin section data, the lithology and electrical characteristics of the single well sand body are comprehensively identified to determine the development characteristics of the single well sand body; S3. Calculation of sand body thickness: Based on the identification result of the sand body in the single well, the sand body thickness of the single well is counted according to the formation stratification data, and the sand-to-formation ratio is calculated; the sand-to-formation ratio is the total sand body thickness divided by the formation thickness. S4, calculation of sand body coefficient: based on the sand body thickness of the single well and the value of the sand-to-ground ratio, calculate the sand body coefficient of the single well; S5. Single well sedimentary microfacies division: Based on the geological overview, and in combination with the core data and the conventional logging data, the characteristics of different sedimentary microfacies, logging curve characteristics, etc. are determined, and the single well sedimentary microfacies are divided; S6. Division of main and secondary channels of single wells: Analyze the sedimentary microfacies characteristics of single wells, and further divide the channel microfacies of braided river delta into main channels and secondary channels according to the characteristics of channel sand body thickness, sand body grain size, logging curve morphology, etc. S7, determining the lower limit of the sand system number: analyzing the sand system numbers corresponding to the main river channel and the secondary river channel respectively, and determining the lower limit of the sand system number of the main river channel; S8. Drawing a sand system number contour map: Based on the sand system number of a single well, combined with the geological overview and the paleo-geomorphology of the sedimentary period and other data, a sand system number contour map is drawn; S9. Detailed characterization of channel microfacies: According to the lower limit of the sand system coefficient of the main channel, characterize the main channel based on the sand system coefficient contour map, analyze the sand body development zones of the main channel, and predict favorable reservoir development zones.

2. A method for fine characterization of river channel microfacies according to claim 1, characterized in that: In step S2, the single well lacking lithology data can refer to the GR curve, and define the part with a GR value less than 65 as sandstone; the GR curve is a natural gamma logging curve, which records the natural gamma ray intensity of underground rocks.

3. A method for fine characterization of river channel microfacies according to claim 1, characterized in that: In the step S3, based on the stratification data and in accordance with the sandstone division result, the total thickness of sandstone in a single well in the studied layer section is calculated, and the total thickness of the sand body is divided by the formation thickness to obtain the sand-to-formation ratio.

4. A method for fine characterization of river channel microfacies according to claim 1, characterized in that: In the step S4, the sand body thickness of the single well is multiplied by the sand-to-ground ratio to obtain the sand body coefficient of the single well.

5. A method for fine characterization of river channel microfacies according to claim 1, characterized in that: In the step S7, the main channel and the secondary channel are compared with the corresponding sand system coefficients to determine the lower limit of the sand system coefficient of the main channel.

6. A method for fine characterization of river channel microfacies according to claim 1, characterized in that: In the step S8, based on the sedimentary background such as the provenance direction and the settlement center during the stratum deposition period, the planar distribution trend of the sand system number is determined, and the sand system number contour map is drawn.

7. A method for fine characterization of river channel microfacies according to claim 1, characterized in that: In step S9, the zone in the sand system coefficient contour map that is higher than the lower limit of the sand system coefficient of the main channel is defined as the main channel development zone, and a fine-detailed plan view of the channel microfacies of the target layer section in the study area is obtained to predict the favorable reservoir development zone.

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