Low boiled oil favorable zone evaluation method

Abstract

The invention relates to a method for evaluating a favorable zone of low boiled oil, which comprises the following steps of: carrying out comprehensive research on petroleum geology, including lake basin structure research, sequence stratigraphy research, sedimentary system research, hydrocarbon source rock research and oil and gas accumulation condition research, and carrying out comprehensive oil and gas evaluation and favorable pre-exploration zone optimization; determining the reservoir forming mode and exploration potential of the low boiled oil; a favorable exploration zone is preferably selected; the method is used for solving the problems that stratum phase change of continental facies failure is fast, the sand body scale is small, the scale of a single lithologic stratum oil and gas reservoir is small, but the number of continental facies lithologic stratum oil and gas reservoirs is large, and large-area lithologic stratum oil and gas reservoirs which are grouped, zoned and distributed in a continuous mode can be formed by overlapping multiple strata systems; through parameter pricing, the oil and gas generation capacity of low-maturity dark mud and shale is determined, the conditions for forming a self-generation and self-storage type low-maturity oil and gas reservoir are judged, a lithologic stratum oil and gas reservoir enrichment zone is delineated, and technical support is provided for low-maturity zone low-maturity oil favorable zone optimization.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum geological exploration, and in particular relates to a method for evaluating a favorable zone of low-maturity oil. Background Art

[0002] Low-mature oil is a concept opposite to mature oil in the late kerogen oil generation theory. It has a lower degree of source rock evolution and organic geochemical characteristics different from mature oil. It is formed in the late stage of diagenesis, before the evolution of organic matter reaches the hydrocarbon generation threshold. The source rock vitrinite reflectance Ro is about 0.3% to 0.7%, which is equivalent to the low-mature or immature stage of the kerogen hydrocarbon generation model. Its crude oil properties are generally heavy oil, and there is also condensate oil.

[0003] With the continuous deepening of exploration and development, conventional oil and gas reservoirs have been proven to a high degree. Under the existing technical conditions, it is difficult to make greater breakthroughs in the main strata. The exploration of new areas has become the focus of oil and gas evaluation at this stage. Low-mature oil with relatively shallow burial depth and low maturity can serve as one of the important successor areas for conventional oil and gas resources.

[0004] At present, conventional oil and gas evaluation methods are still used to evaluate low-maturity oil. There is no relatively mature evaluation method for favorable zones of low-maturity oil. Most methods are still in the theoretical research stage, and the characteristics of low-maturity oil and gas reservoirs themselves are ignored in the evaluation process. The existing evaluation methods cannot quantify the industrial development potential of low-maturity oil in the target strata.

[0005] The patent "A method for accurately determining the formation period of oil and gas reservoirs" (publication number CN108227035A) uses fluid inclusion comprehensive technology, basin numerical simulation technology, and source rock geochemical technology to comprehensively identify the formation period of oil and gas reservoirs. The accuracy of the formation period has been improved compared with previous technologies. The patent only mentions the discrimination standard of crude oil maturity through saturated hydrocarbon colorimetric analysis, pointing out that C2920S / (20S+20R) ratio <0.35 is low-mature oil, and C2920S / (20S+20R) ratio >0.35~0.5 is mature oil. According to the different types of crude oil maturity, it is preliminarily judged how many times oil and gas have been charged, and the formation period of oil and gas is preliminarily judged based on this. However, it does not solve the relationship between source rocks and low-mature oil reservoirs, and thus it is impossible to determine the effective source rock belt, and it cannot provide a favorable zone evaluation method.

[0006] The patent "A method for evaluating key parameters of hydrocarbon generation potential of high-quality source rocks" (publication number CN105223340A) establishes an evaluation model for hydrocarbon generation (expulsion) amount and hydrocarbon generation (expulsion) rate to evaluate the plan view of hydrocarbon generation potential of high-quality source rocks, and then evaluates the key parameters of hydrocarbon generation potential of high-quality source rocks in the immature to low-maturity stage, filling the gap in hydrocarbon generation of high-quality source rocks in the immature to low-maturity stage that has been weakened in the past. However, the patent focuses on the study of hydrocarbon generation and expulsion indicators of high-quality source rocks, ignoring the comprehensive evaluation of low-maturity oil reservoirs from various aspects such as source rocks, reservoirs, cap rocks, closures, migration, and preservation. Therefore, it cannot be used as a comprehensive and complete method for evaluating favorable zones for low-maturity oil.

[0007] To this end, the present invention proposes a method for evaluating favorable zones for low-maturity oil. In the context that the field of low-maturity oil is currently only in the theoretical research stage, the innovation of this method lies in that a systematic and comprehensive study of single factor analysis and its relationship with low-maturity oil reservoirs is carried out, and by clarifying the main and secondary factors of low-maturity oil accumulation, the low-maturity oil accumulation conditions are determined and the oil and gas enrichment zones are optimized in combination with the spatio-temporal configuration pattern of the source, reservoir, caprock and transport protection. Summary of the invention

[0008] The invention discloses a method for evaluating favorable zones for low-maturity oil. The method comprises the following steps: obtaining a three-dimensional seismic data body, well logging and well logging data, and experimental analysis data of an evaluation target zone; conducting sedimentary microfacies analysis, planar sedimentary facies, sedimentary system and paleogeographic evolution research of key wells; and analyzing the relationship between single-factor conditions such as sequence, sedimentary facies belt, fault, reservoir, and oil source in the zone; evaluating the relationship between system domain and reservoir - favorable system domain, sedimentary facies belt and reservoir - favorable sedimentary facies belt, reservoir and reservoir - porosity and permeability development belt, source rock and reservoir - effective source rock belt, unconformity and reservoir - unconformity development belt, paleotopography (slope, bulge) and reservoir - stratigraphic pinch-out belt, and fault and reservoir - structural fault development belt; determining the relationship between low-maturity oil accumulation conditions and optimizing the oil and gas enrichment belt based on the main and secondary factors of oil and gas accumulation, combining the spatial and temporal configuration of source, reservoir, caprock, and transport protection.

[0009] The present invention solves the technical problem by adopting the following technical solutions:

[0010] A method for evaluating favorable zones of low-maturity oil comprises the following steps:

[0011] Conduct comprehensive research on petroleum geology, including lake basin structure, sequence stratigraphy, sedimentary system, source rock, and oil and gas reservoir conditions, and conduct comprehensive oil and gas evaluation and optimization of favorable prospecting zones;

[0012] Clarify the accumulation pattern and exploration potential of low-maturity oil;

[0013] Prefer favorable exploration areas.

[0014] Further, the method for comprehensive oil and gas evaluation and optimization of favorable pre-exploration zones is as follows:

[0015] In comprehensive oil and gas evaluation, it is necessary to evaluate: the relationship between system domain and reservoir, so as to obtain favorable system domain; the relationship between sedimentary facies belt and reservoir, so as to obtain favorable sedimentary facies belt; the relationship between reservoir and reservoir, so as to obtain porosity and permeability development belt; the relationship between source rock and reservoir, so as to obtain effective source rock belt; the relationship between unconformity surface and reservoir, so as to obtain unconformity development belt; the relationship between paleotopography and reservoir, so as to obtain stratigraphic pinch-out belt; the relationship between fault and reservoir, so as to obtain the relationship between structural fault development belt;

[0016] On the basis of clarifying the main and secondary factors controlling oil and gas accumulation, the conditions for low-maturity oil accumulation are determined and the oil and gas enrichment zones are optimized in combination with the spatiotemporal configuration of the source, reservoir, caprock and transport protection.

[0017] Furthermore, when conducting a comprehensive study of petroleum geology, the following steps are included:

[0018] Study on lake basin structure and evolution: obtain two-dimensional and three-dimensional seismic data, process them, obtain seismic profile interpretation, and thus obtain lake basin structure. By conducting balanced profile analysis and structural physical simulation analysis on the lake basin structure, obtain the structural evolution diagram of the lake basin structure.

[0019] Study the sequence and sedimentary system: obtain seismic attributes and seismic facies, divide the sequence stratigraphy of single wells and well-connected wells, and analyze the single well facies and well-connected facies to establish the sequence stratigraphic framework, obtain the distribution characteristics of the sedimentary system, and finally obtain the distribution characteristics of the dominant reservoir;

[0020] Evaluation of source rocks and analysis of resource potential: Statistics of source rock thickness and organic geochemical analysis of source rocks are conducted to obtain the distribution characteristics of source rocks, kerogen types, and organic matter abundance. Based on the source rock vitrinite reflectance Ro data, hydrocarbon generation centers, hydrocarbon generation thresholds, and resource quantities are calculated.

[0021] Furthermore, when the favorable sedimentary facies belt is determined by the relationship between sedimentary facies belt and low-maturity oil reservoir, the oil and gas show is controlled by the distribution range of the favorable sedimentary facies belt of Shahejie Formation. The oil and gas show is not distributed in the main part of the sand body, but in the marginal area of ​​the main sand body. The delta front facies belt is the most favorable sedimentary facies belt for low-maturity oil, and the sand-to-ground ratio between 0.2 and 0.4 is most conducive to reservoir formation.

[0022] Furthermore, when the relationship between reservoirs and low-maturity oil reservoirs is used to determine the porosity and permeability development zones, for lithologic oil and gas reservoirs, the porosity and permeability development zones mainly include primary (secondary) pores, unconformity surfaces (under conditions of high permeability and leaching) and other relatively developed layers, among which the formation and distribution of secondary solution pores in the reservoir are the key to determining the production capacity and scale of lithologic oil and gas reservoirs. The formation of secondary solution pores in the reservoir is the result of organic-inorganic interaction during diagenetic evolution.

[0023] Furthermore, when the relationship between source rocks and low-maturity reservoirs is used to determine the effective source rock belt, oil and gas mainly migrate vertically along faults, and the distribution of oil and gas is controlled by the effective oil-generating range. The oil and gas shows are not distributed in the center of the effective source rock, but in the marginal area of ​​the center of the effective source rock. The oil and gas shows are mainly distributed in the areas with thin effective source rocks on both sides of the bulge. In the evaluation of effective source rocks, both non-poor source rocks with low abundance and good source rocks that have not entered the maturity threshold should be deducted. Effective source rocks are the real oil and gas contributors. Special considerations are needed for source rocks in specific environments, such as the formation of immature and low-maturity crude oil.

[0024] Furthermore, when the unconformity development zone is determined based on the relationship between the unconformity and the low-maturity oil reservoir, the unconformity is mainly the result of atmospheric water leaching. The unconformity in the two regions is a porosity and permeability development zone, which is a favorable place for oil and gas accumulation.

[0025] Furthermore, when the stratigraphic pinch-out zone is determined based on the relationship between uplift or bulge and low-maturity reservoirs, stratigraphic overlap, unconformity shielding and sand layer updip pinch-out type oil and gas reservoirs are generally attached to the basin edge slope and the wing of the uplift area in the basin in a belt-like shape. Compared with the lens-shaped sandstone body lithologic reservoirs in the depression area, the oil column height and single well production are relatively high;

[0026] Furthermore, when the fault structure development zone is determined based on the relationship between faults and low-mature oil reservoirs, the large central uplift zone is the main direction of oil and gas migration, and the zonal distribution along the main faults is the main form of complex oil and gas accumulation.

[0027] The advantages and positive effects of the present invention are:

[0028] The method of the present invention is aimed at the continental fault depression where the stratigraphic phase changes quickly, the sand body is small in scale, and the scale of a single lithologic stratigraphic oil and gas reservoir is also relatively small, but the number of continental lithologic stratigraphic oil and gas reservoirs is large, and the superposition of multiple systems can form large-area lithologic stratigraphic oil and gas reservoirs distributed in groups, belts, and continuous areas; through parameter pricing, it is determined that low-mature dark mud and shale have the ability to generate oil and gas, and the conditions for forming self-generating and self-storing low-mature oil and gas reservoirs are judged. Local micro-amplitude anticlines and thin interlayers of small fault blocks under the background of a large set of lithologic stratigraphic formations are easier to form oil and gas reservoirs with large cumulative thickness than a large set of sandstones, and the lithologic stratigraphic oil and gas reservoir enrichment zone is delineated, providing technical support for the optimization of favorable zones for low-mature oil in low-mature areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments, but it should be understood that these drawings are designed only for explanation purposes and are not intended to limit the scope of the present invention. In addition, unless otherwise specified, these drawings are intended only to conceptually illustrate the structural configurations described herein and are not necessarily drawn to scale.

[0030] Figure 1 A flow chart of a low-maturity oil research method for a low-maturity oil favorable zone evaluation method provided by an embodiment of the present invention;

[0031] Figure 2 A technical roadmap for low-maturity oil research of a method for evaluating a favorable zone of low-maturity oil provided in an embodiment of the present invention;

[0032] Figure 3 A thermal evolution diagram of a source rock layer for a method for evaluating a favorable zone of low-maturity oil provided by an embodiment of the present invention;

[0033] Figure 4 A low-maturity oil reservoir evaluation flow chart of a low-maturity oil favorable zone evaluation method provided in an embodiment of the present invention;

[0034] Figure 5 A low-maturity oil reservoir model diagram of a low-maturity oil favorable zone evaluation method provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0035] First of all, it should be noted that the specific structure, features and advantages of the present invention will be specifically described below by way of example, but all descriptions are only for illustration and should not be understood as limiting the present invention in any way. In addition, any single technical feature described or implied in the embodiments mentioned herein, or any single technical feature displayed or implied in the drawings, can still be combined or deleted between these technical features (or their equivalents) to obtain more other embodiments of the present invention that may not be directly mentioned in this document. In addition, in order to simplify the drawings, the same or similar technical features may be marked only in one place in the same drawing.

[0036] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0037] Example 1

[0038] This embodiment provides a method for evaluating favorable zones of low-maturity oil, comprising the following steps:

[0039] Conduct comprehensive research on petroleum geology, including lake basin structure, sequence stratigraphy, sedimentary system, source rock, and oil and gas reservoir conditions, and conduct comprehensive oil and gas evaluation and optimization of favorable prospecting zones;

[0040] Clarify the accumulation pattern and exploration potential of low-maturity oil;

[0041] Prefer favorable exploration areas.

[0042] Specifically, the method for comprehensive oil and gas evaluation and optimization of favorable exploration zones is as follows:

[0043] In comprehensive oil and gas evaluation, it is necessary to evaluate: the relationship between system domain and reservoir, so as to obtain favorable system domain; the relationship between sedimentary facies belt and reservoir, so as to obtain favorable sedimentary facies belt; the relationship between reservoir and reservoir, so as to obtain porosity and permeability development belt; the relationship between source rock and reservoir, so as to obtain effective source rock belt; the relationship between unconformity surface and reservoir, so as to obtain unconformity development belt; the relationship between paleotopography (slope, bulge) and reservoir, so as to obtain stratigraphic pinch-out belt; the relationship between fault and reservoir, so as to obtain the relationship between structural fault development belt;

[0044] On the basis of clarifying the main and secondary factors controlling oil and gas accumulation, the conditions for low-maturity oil accumulation are determined and the oil and gas enrichment zones are optimized in combination with the spatiotemporal configuration of the source, reservoir, caprock and transport protection.

[0045] Specifically, the comprehensive study of petroleum geology includes the following steps:

[0046] Study on lake basin structure and evolution: obtain two-dimensional and three-dimensional seismic data, process them, obtain seismic profile interpretation, and thus obtain lake basin structure. By conducting balanced profile analysis and structural physical simulation analysis on the lake basin structure, obtain the structural evolution diagram of the lake basin structure.

[0047] Study the sequence and sedimentary system: obtain seismic attributes and seismic facies, divide the sequence stratigraphy of single wells and well-connected wells, and analyze the single well facies and well-connected facies to establish the sequence stratigraphic framework, obtain the distribution characteristics of the sedimentary system, and finally obtain the distribution characteristics of the dominant reservoir;

[0048] Evaluation of source rocks and analysis of resource potential: Statistical analysis of source rock thickness and organic geochemical analysis of source rocks are conducted to obtain the distribution characteristics of source rocks, kerogen types, and organic matter abundance. Based on the source rock vitrinite reflectance Ro data, the hydrocarbon generation center, hydrocarbon generation threshold, and resource volume are calculated;

[0049] Detailed and comprehensive collection of relevant data in the study area, including 3D seismic data, logging and well logging data, production reports, experimental analysis data, and previous scientific research results; select key coring wells, conduct systematic core description, sedimentary structure analysis, thin section identification, and grain size analysis, conduct sedimentary facies and sedimentary microfacies analysis, planar sedimentary facies, sedimentary system and paleogeographic evolution research of key wells, describe petrological characteristics, sedimentary structure, and grain size changes in detail, and conduct composition analysis, grain size analysis, sedimentary microfacies analysis and genetic analysis, and compile cross-sectional structural diagrams ; Collect core and cutting samples, sedimentary petrology, organic petrology, organic carbon, pyrolysis, chloroform asphalt "A", group components, saturated hydrocarbon chromatography, saturated hydrocarbon chromatography, kerogen separation, kerogen vitrine, high temperature hot pressure simulation experiment, simulated gas analysis, organic petrology; collect seismic data, carry out seismic profile interpretation, seismic phase analysis, seismic attribute interpretation, compile basin structure and tectonic evolution map, sequence stratigraphic analysis, sedimentary system, source rock evaluation and resource potential analysis, oil and gas accumulation conditions and accumulation model and other industrial maps;

[0050] When the favorable sedimentary facies belt is determined by the relationship between sedimentary facies belt and low-maturity oil reservoir, the oil and gas show is controlled by the distribution range of the favorable sedimentary facies belt of Shahejie Formation. The oil and gas show is not distributed in the main part of the sand body (fan delta, braided river delta, etc.), but distributed in the marginal area of ​​the main sand body. The delta front facies belt is the most favorable sedimentary facies belt for low-maturity oil, and the sand-to-ground ratio between 0.2-0.4 is most conducive to reservoir formation.

[0051] When the porosity and permeability development zones are determined by the relationship between reservoirs and low-maturity oil reservoirs, for lithologic oil and gas reservoirs, the porosity and permeability development zones mainly include primary (secondary) pores, unconformity surfaces (under conditions of high permeability and leaching) and other relatively developed layers. The formation and distribution of secondary dissolved pores in reservoirs are the key to determining the production capacity and size of lithologic oil and gas reservoirs. The formation of secondary dissolved pores in reservoirs is the result of organic-inorganic interaction during diagenetic evolution.

[0052] When the relationship between source rocks and low-maturity reservoirs is used to determine the effective source rock belt, oil and gas mainly migrate vertically along faults, and the distribution of oil and gas is controlled by the effective oil-generating range. The oil and gas shows are not distributed in the center of the effective source rock, but in the marginal area of ​​the center of the effective source rock. The oil and gas shows are mainly distributed in the areas with thin effective source rocks on both sides of the bulge. When evaluating the effective source rock, it is necessary to deduct both the non-poor source rocks with low abundance and the better source rocks that have not entered the maturity threshold. The effective source rock is the real oil and gas contributor. Special consideration is required for the source rock in a specific environment, such as the formation of immature-low-maturity crude oil.

[0053] When the unconformity development zone is determined based on the relationship between the unconformity and the low-maturity reservoir, the unconformity is mainly the result of atmospheric water leaching. The unconformity in the two regions is a porosity and permeability development zone, which is a favorable place for oil and gas accumulation.

[0054] When the stratigraphic pinch-out zone is determined based on the relationship between uplift (or bulge) and low-maturity reservoirs, a good oil-accumulating structural background is an important condition for the formation of rich and high-yield lithologic stratigraphic oil and gas reservoirs. The stratigraphic overlap, unconformity shielding and sand layer updip pinch-out and other types of oil and gas reservoirs are generally attached to the basin edge slope and the wing of the uplift area in the basin in a belt-like shape. Compared with the lens-shaped sandstone body lithologic reservoirs in the depression area, the oil column height and single well production are relatively high.

[0055] When the fault structure development zone is determined based on the relationship between faults and low-mature oil reservoirs, the large central uplift zone is the main direction of oil and gas migration, and the belt distribution along the main fault is the main form of compound oil and gas accumulation;

[0056] According to the constructed oil and gas accumulation model, the petroleum geological characteristics of different zones in the study area are evaluated from various aspects such as source rock, reservoir, cap rock, closure, migration and preservation, and favorable zones - enriched and high-yield "sweet spot" blocks - are selected to broaden geological understanding, break the exploration ideas around "deep depressions" and "mature areas", and enable the low-maturity oil accumulation model to jump out of the deep depressions, go up the slopes and low uplifts, thus achieving a breakthrough in the exploration of low-maturity oil and gas reservoirs.

[0057] Example 2

[0058] The drilling of a depression provided in this embodiment revealed 9 sets of oil-bearing strata and discovered two large oil fields of 100 million tons. It is one of the depressions with many types of oil reservoirs, large oil and gas reserves and great potential for remaining resources. It has broad exploration prospects, but faces the following 4 problems during the exploration process: 1) The exploration degree of the main strata and the exploration target strata is high, while the exploration degree of the reserve exploration strata is low, and the basic geological characteristics and potential are not yet clear; 2) The dark mudstone in the new stratum is thick and widely distributed, with oil-generating capacity, and is mainly composed of low-mature oil and gas resources; 3) The new strata have developed three types of sedimentary facies, namely fan delta, braided river delta and lake facies, belonging to multi-source and multi-sedimentary systems, and the reservoirs are very developed; 4) Low-mature oil and gas have been discovered in drilling, and industrial oil and gas flows have been obtained in many wells; the oil source comparison results show that the oil and gas shows all come from the Shahejie Formation itself, which has the conditions for forming self-generating and self-storing low-mature oil and gas reservoirs, and has certain exploration potential. Once a breakthrough is made, it can be used as a successor battlefield for exploration.

[0059] Comprehensive data on the study area were collected, including three-dimensional seismic data, mud logging and well logging data, production reports, experimental analysis data, and previous scientific research results. Among them, there were more than 800 comprehensive mud logging maps, 1 set of stratified data books, analytical test data of 150 wells, 10 analytical projects, 6,822 analytical data, and more than 140 references. We selected key coring wells, conducted systematic core description, sedimentary structure analysis, thin section identification, and grain size analysis; conducted sedimentary facies and sedimentary microfacies analysis, planar sedimentary facies, sedimentary system, and paleogeographic evolution research on key wells; observed and described 25 coring wells and 150 thin sections (19 wells), described the petrological characteristics, sedimentary structure, and grain size changes in detail, conducted composition analysis, grain size analysis, sedimentary microfacies analysis, and genetic analysis, and compiled a cross-sectional structure diagram; collected samples including core and cuttings samples, of which 36 core samples were used for sedimentary petrology, organic petrology, asphalt "A", color quality, chromatography, and other project analysis, and 142 core and cuttings small samples were collected; conducted organic carbon, pyrolysis, and chloroform asphalt analysis. A total of 100 samples were analyzed for 11 analysis projects, including Qing "A", group components, saturated hydrocarbon chromatography, saturated hydrocarbon chromatogram, kerogen separation, kerogen mirror coal, high-temperature hot pressure simulation experiment, simulated gas analysis, organic petrology, etc., 50 seismic profile interpretations, 2 seismic phase analyses, 12 seismic attribute interpretations, data collation and map compilation were completed. By stratifying the strata of the wells in the secondary depression and sorting and screening the existing data, data such as 906 dark mudstone thickness data, 1130 TOC data, and 1092 chloroform asphalt "A" data were selected. Based on these data, contour maps of dark mudstone thickness, TOC content, and contour maps of chloroform asphalt "A" content were drawn.

[0060] Using the rock-electricity combined method, the thickness of each single well and sub-concave source rock was identified and counted, and the source rock isopach map was compiled to mark out two main source rock development areas (the thickest point, the sedimentary center). Three layers of dark mudstone were identified: the first layer of dark mudstone is 27.5-493.5m thick, accounting for 79.43% of the formation thickness, mainly dark gray mudstone, with a small amount of red mudstone and gray sandstone. The dark mudstone is 27.5-372.5m thick, accounting for 41.58-88.95% of the formation thickness; the second layer of dark mudstone is 6.5-76m thick, mainly purple-red mudstone, gray sandstone, gray, and dark gray mudstone are interbedded in unequal thickness. The cumulative thickness of dark mudstone is 6.5-76m, accounting for 18.6-88.6% of the formation thickness; the thickness of the third layer of dark mudstone is 25-400m, and the cumulative thickness of dark mudstone is 6-46.5m, accounting for 20-65.18% of the formation thickness; the cumulative thickness of shale is 1.5-24m, accounting for 7.32-36.78% of the formation thickness, and the distribution range is relatively large.

[0061] Dark mudstone has good organic matter type, generally II 1-Type I kerogen is dominant, characterized by oil generation. The Ro value of immature oil ranges from 0.3% to 0.5%, and the Ro value of low-mature oil ranges from 0.5% to 0.9%. The maximum burial depth of the third layer is 3750m, the current maximum ground temperature is 97-135℃, and the Ro value is 0.6% to 0.9%. The low-mature source rock areas in the two oil-generating areas are 236.5km 2 and 341.7km 2 , the degree of thermal evolution of organic matter is at a low maturity stage. The first layer of source rock has the lowest heating temperature and the lowest degree of thermal change. The current maximum burial depth is 2500-2700m, the current maximum ground temperature is 84-96℃, and the Ro value is 0.46-0.5%, which is in an immature stage in the region. Vitrinite reflectance is an effective indicator for studying the maturity of source rocks and dividing them into maturity stages. The relationship diagram of Ro variation with well depth in the whole area shows that the Ro value is <0.5% above 2600m, and below 2600m, the Ro value of most samples is >0.5%, indicating that it has entered the maturity threshold. The comprehensive profile of thermal evolution of organic matter shows that below 2600m, T max The values ​​are all >435℃; asphalt "A" / TOC and HC / TOC both exceed the hydrocarbon expulsion thresholds of 5% and 3%, respectively. Although the asphalt "A" / TOC above is relatively high, the HC / TOC is mostly below 3%, which is not conducive to hydrocarbon expulsion. The maturity threshold of this area is around 2600m, 2600-3600m is the low maturity stage, and below 3600m enters the mature stage. From the perspective of the degree of conversion, the asphalt "A" / TOC begins to exceed the hydrocarbon expulsion threshold from the first layer, but the HC / TOC above the maturity threshold is mostly less than 3%, and the hydrocarbon expulsion rate is low. Although the HC / TOC value is low, the asphalt "A" / TOC is higher than other layers above the maturity threshold, and the type is relatively good, rich in algae that can generate hydrocarbons early, and has the ability to form immature to low-mature oil.

[0062] Through the analysis of the thermal evolution profile of the source rock, it is determined that the source rock in the shallow depression of the Shahejie Formation in the Cangdong Sag reaches the immature-low-mature hydrocarbon generation threshold at a burial depth of 1500m (Ro is approximately 0.3%), begins to expel a large amount of hydrocarbons at a burial depth of 2000m, and reaches the peak of hydrocarbon expulsion at a burial depth of 2400m. Although the degree of thermal evolution in this area is low, the shale still has a strong ability to generate and expel hydrocarbons. Figure 3As shown in the figure, through the thermal simulation experiment of source rock and the analysis of thermal evolution profile, it is determined that the source rock reaches the immature-low-mature hydrocarbon generation threshold when the burial depth is about 1500m (Ro is about 0.3%), starts to generate a lot of hydrocarbons when the burial depth reaches about 2100m (Ro is about 0.4-0.5%), and reaches the peak of hydrocarbon expulsion when the burial depth reaches about 2600m (Ro is about 0.6%). The corresponding asphalt "A", HC, asphalt "A" / TOC, HC / TOC have good correlation with each period. The third layer of dark mudstone has a wide distribution range and large thickness, but the burial depth is shallow, and most of the burial depth is concentrated in 1500-3000m. The degree of thermal evolution is low, and it is mainly composed of low-mature source rocks. Mature source rocks are only distributed in the central area. The overall burial depth of the first layer of source rock is not very large, and the bottom boundary burial depth is about 1400-2400m, which belongs to immature-low-mature source rock. Comprehensive research shows that the low-mature shale in the shallow sag of Shahejie Formation in Cangdong Sag can be used as an effective source rock.

[0063] From the perspective of conversion degree, the asphalt "A" / TOC of the first layer begins to exceed the hydrocarbon expulsion threshold of 5%, but the HC / TOC above the mature threshold is mostly less than 3%, and the hydrocarbon expulsion rate is low. Although the HC / TOC value of the first layer is low, the asphalt "A" / TOC is higher than other layers above the mature threshold, and the type is relatively good, rich in algae that can generate hydrocarbons early, and the first layer has the ability to form immature-low-mature oil. Most of the asphalt "A" / TOC and HC / TOC of the third layer exceed the hydrocarbon expulsion threshold of 5% and 3%, respectively, indicating that the third layer of source rocks has begun to expel hydrocarbons in large quantities. From the perspective of conversion degree, although the thermal evolution degree of this area is low, the mudstone still has a strong ability to generate and expel hydrocarbons.

[0064] According to the Ro contour map, the mature areas and hydrocarbon generation centers of source rocks on the plane are determined according to the main indicators of immature-low maturity division (the range of Ro values ​​for immature oil is 0.3%-0.5%; the range of Ro values ​​for immature oil is 0.5%-0.9%).

[0065] Example 3

[0066] In order to better understand the above-mentioned method for evaluating favorable zones for low-maturity oil, this embodiment provides an application example for illustration. In this embodiment, through analysis of favorable sedimentary facies, reservoir performance and reservoir influencing factors, it is determined that the favorable sedimentary facies for low-maturity oil is the sand-mud interbedded zone at the delta front.

[0067] Mainly the third layer and the first layer, and the third layer sand body is more developed than the first layer sand body. It includes 6 sets, including the third layer lower sand body, the third layer middle sand body, the third layer upper sand body, the first layer lower sand body, the first layer middle sand body and the first layer upper sand body. The third layer sand body type: braided delta and fan delta sand bodies are the main reservoir types of the third layer. Their distribution boundaries are controlled by the paleotopography of the basin margin. The sand body distribution is confirmed by using drilling data combined with seismic facies. The sand body has a narrow distribution range in the north, large thickness variations, poor sand and mud differentiation, and cannot form a good reservoir-cap combination.

[0068] The sand bodies in the gentle slope belt are widely distributed, and the thickness of the sandstone gradually decreases toward the center of the lake basin. The sandstone in the gentle slope belt is well developed, and the thickness changes slowly, forming 2-3 sets of reservoir-caprock combinations in the vertical direction. The third layer is mainly dark gray mudstone, and the middle and lower parts are interbedded with sandstone and mudstone. Oil and gas are mainly distributed in the reservoir layer about 100m thick in the lower part of the third layer. The second layer is interbedded with gray mudstone and sandstone, and the formation thickness varies greatly. The first layer is mainly gray mudstone interbedded with sandstone, and the bottom is biogenic limestone and oolitic limestone interbedded with oil shale.

[0069] This section of the stratum is divided into three parts: upper, middle and lower. It includes clastic sand bodies and carbonate beach-bar sediments, and has developed three reservoir types: sandstone, biogenic limestone and dolomite. The sandstone in the north is mainly distributed at the root of the fault downthrown disk, and the distribution range in the south is large. The distribution of biogenic limestone is obviously controlled by the ancient topography and is distributed in the ancient slope or underwater low uplift structure.

[0070] Through comprehensive analysis of sandstone thickness, sandstone percentage, porosity and permeability, reservoir evaluation maps of the lower third layer, middle third layer, upper third layer and first layer were obtained, and four types of reservoirs were divided. According to the interpretation of logging data, the effective porosity of the reservoir is 17-32%, with an average of 23%, and the permeability is 18-364mD, with an average of 226mD. The comprehensive evaluation is medium-high porosity and medium-high permeability reservoirs, and the reservoir properties of the granular beach and the third layer delta underwater distributary channel are good.

[0071] Example 4

[0072] In order to better understand the above-mentioned method for evaluating favorable zones of low-maturity oil, this embodiment provides an application example for illustration: controlled by the dual factors of structure and sedimentary reservoir, the relationship between sequence, sedimentary facies, unconformity, fault, reservoir, oil source and reservoir is studied to clarify the controlling factors of reservoir.

[0073] Method 1: Analysis of the relationship between single factors (sequence, sedimentary facies, faults, reservoirs, oil sources, etc.) and reservoirs. The stratigraphic phase of continental faults changes quickly, the sand body is small in scale, and the scale of a single lithologic stratigraphic oil and gas reservoir is also relatively small, but the number of continental lithologic stratigraphic oil and gas reservoirs is large, and the superposition of multiple systems can form large-scale lithologic stratigraphic oil and gas reservoirs that are distributed in groups and belts and in continuous areas. The reserve abundance and single-well production of lithologic stratigraphic oil and gas reservoirs are generally low, but there are also enriched and high-yield "sweet spot" blocks. Local micro-amplitude anticlines and thin interlayers of small fault blocks under the background of a large set of lithologic stratigraphic formations are easier to form oil and gas reservoirs with large cumulative thickness than large sets of sandstones. There are mainly five types of lithologic stratigraphic oil and gas reservoir enrichment zones. Single factor analysis of the relationship between faults, reservoirs, and oil sources and reservoirs was conducted to establish the correlation between the three and oil and gas reservoirs.

[0074] Method 2: Analysis of the relationship between multiple factors and reservoirs. The “ternary coupling” reservoir control believes that “target reservoir = oil source × physical property × trap closure amplitude. The main factor that determines the development of the trap is the matching of the paleo-tectonic background and the sediment source system”. Lake mudstone and shale have the ability to form low-maturity oil and gas. The sandstone lithology traps developed in the main depression area have the conditions to form self-generating and self-storage low-maturity oil and gas reservoirs. The anticline area develops reservoir types such as the first lower biogenic limestone, the third biogenic limestone, and marl. Oil testing found oil and gas points, proving that the anticline trap is favorable. Through comprehensive comparative studies, the reservoir type is determined by multi-factor superposition, the main and secondary factors that control the formation and preservation of the reservoir are clarified, and the reservoir type is determined. Favorable sedimentary facies belts are a prerequisite for determining the quality of reservoir physical properties. To find enriched and high-yield zones, it is first necessary to find favorable sedimentary facies belts. Oil and gas displays are controlled by the distribution range of favorable sedimentary facies belts of the Shahejie Formation. A low-maturity oil accumulation model is established based on typical seismic profiles, such as Figure 5 As shown, oil and gas shows are not distributed in the main part of the sand body (fan delta, braided river delta, etc.), but in the marginal area of ​​the main sand body. The thickness of the sand body in the favorable sedimentary phase belt is relatively thin, ranging from 10 to 40 m. There are few or no oil and gas shows in the main area of ​​the sand body greater than 40 m. The delta front subfacies and beach-bar microfacies are the most favorable sedimentary phase belts for low-maturity oil. The sand-to-ground ratio between 0.2 and 0.4 is most conducive to reservoir formation. The oil and gas generated by the source rock often migrate along the fault surface, unconformity surface, etc. to the favorable phase belt, forming self-generation and self-storage, lower generation and upper storage reservoirs, and the most oil and gas shows are found.

[0075] For lithologic oil and gas reservoirs, the porosity and permeability development zones mainly include relatively developed layers such as primary (secondary) pores and unconformity surfaces (under conditions of high permeability and leaching). Among them, the formation and distribution of secondary dissolved pores in the reservoir are the key to determining the production capacity and scale of lithologic oil and gas reservoirs. The formation of secondary dissolved pores in the reservoir is the result of organic-inorganic action during diagenetic evolution. The effective porosity of the reservoir is 17-32%, with an average of 23%, and the permeability is 18-364mD, with an average of 226mD. The comprehensive evaluation is medium-high porosity-medium-high permeability reservoir. Oil and gas are mainly distributed in the reservoir with a thickness of about 100m in the lower part of the third layer. It is one of the main oil-bearing target layers and a favorable place for oil and gas accumulation. The lower part of the first layer is biogenic limestone, oolitic limestone and oil shale, with a thickness of about 20-50m. It belongs to the beach-bar sand body, which is a porosity and permeability development zone, one of the main oil-bearing target layers, and a favorable place for oil and gas accumulation.

[0076] The oil and gas show is controlled by the distribution range of the effective source rock belt of the Shahejie Formation. Oil and gas mainly migrate vertically along the faults, and the distribution of oil and gas is controlled by the effective oil-generating range. The oil and gas show is not distributed in the center of the effective source rock, but in the marginal area of ​​the center of the effective source rock. The thickness of the effective source rock is relatively thin, ranging from 10 to 40 meters. There are few or no oil and gas shows in the central area of ​​the source rock greater than 40 meters. The oil and gas shows are mainly distributed in the gentle slope areas on the east and west sides of the central uplift and secondary uplift. The thickness of the effective source rock is relatively thin, ranging from 10 to 40 meters.

[0077] The study confirmed that the low-maturity oil in this area has certain exploration potential and is an important successor battlefield for conventional oil and gas exploration. The selected target area is used as a breakthrough to carry out the optimization of favorable zones. According to the constructed oil and gas accumulation model, the petroleum geological characteristics of different zones in the study area are evaluated from the aspects of source rock, reservoir, cap rock, trap, migration and preservation, and favorable zones - enriched and high-yield "sweet spot" blocks are selected. By analogy with the accumulation conditions of these four depressions, the main attack direction is selected. The exploration deployment ideas mainly based on lithologic reservoirs in the groove and slope areas are proposed. The third and first layers are the main source rock layers in the depression, and the north and south sides of the source rock thickness center are more favorable zones; the first layer has a lower maturity, and the favorable zones are mainly distributed around the source rock thickness center, especially near the center. Anticline traps, fault traps and lithologic traps are selected, and favorable pre-exploration targets are selected. The application of methods provides favorable support for the optimization of exploration targets.

[0078] The above embodiments describe the present invention in detail, but the contents are only preferred embodiments of the present invention and cannot be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A method for evaluating favorable zones of low-maturity oil, characterized in that: The steps include: Conduct comprehensive research on petroleum geology, including lake basin structure, sequence stratigraphy, sedimentary system, source rock, and oil and gas reservoir conditions, and conduct comprehensive oil and gas evaluation and optimization of favorable prospecting zones; Clarify the accumulation pattern and exploration potential of low-maturity oil; Prefer favorable exploration areas.

2. According to claim 1, a method for evaluating favorable zones of low-maturity oil is characterized by: The methods for comprehensive oil and gas evaluation and optimization of favorable prospecting zones are as follows: In comprehensive oil and gas evaluation, it is necessary to evaluate: the relationship between system tracts and reservoirs, so as to obtain favorable system tracts; The relationship between sedimentary facies and reservoirs, thus obtaining favorable sedimentary facies; The relationship between reservoir and oil reservoir, so as to obtain the porosity and permeability development zone; The relationship between source rocks and reservoirs, thus obtaining effective source rock belts; The relationship between unconformity and oil reservoir, thus obtaining the unconformity development zone; the relationship between paleotopography and oil reservoir, thus obtaining the stratigraphic pinch-out zone; the relationship between fault and oil reservoir, thus obtaining the relationship between structural fault development zones; By clarifying the main and secondary factors controlling oil and gas accumulation, the conditions for low-maturity oil accumulation are determined and the oil and gas enrichment zones are optimized in combination with the spatio-temporal configuration of the source, reservoir, caprock and transport protection.

3. The method for evaluating favorable zones of low-maturity oil according to claim 1, characterized in that: When conducting a comprehensive study of petroleum geology, the following steps are included: Study on lake basin structure and evolution: obtain two-dimensional and three-dimensional seismic data, process them, obtain seismic profile interpretation, and thus obtain lake basin structure. By conducting balanced profile analysis and structural physical simulation analysis on the lake basin structure, obtain the structural evolution diagram of the lake basin structure. Study the sequence and sedimentary system: obtain seismic attributes and seismic facies, divide the sequence stratigraphy of single wells and well-connected wells, and analyze the single well facies and well-connected facies to establish the sequence stratigraphic framework, obtain the distribution characteristics of the sedimentary system, and finally obtain the distribution characteristics of the dominant reservoir; Evaluation of source rocks and analysis of resource potential: Statistics of source rock thickness and organic geochemical analysis of source rocks are conducted to obtain the distribution characteristics of source rocks, kerogen types, and organic matter abundance. Based on the source rock vitrinite reflectance Ro data, hydrocarbon generation centers, hydrocarbon generation thresholds, and resource quantities are calculated.

4. The method for evaluating favorable zones of low-maturity oil according to claim 1, characterized in that: When the favorable sedimentary facies belt is determined by the relationship between sedimentary facies belt and low-maturity oil reservoir, the oil and gas show is controlled by the distribution range of the favorable sedimentary facies belt of Shahejie Formation. The oil and gas show is not distributed in the main part of the sand body, but in the marginal area of ​​the main sand body. The delta front facies belt is the most favorable sedimentary facies belt for low-maturity oil, and the sand-to-ground ratio between 0.2 and 0.4 is most conducive to reservoir formation.

5. The method for evaluating favorable zones of low-maturity oil according to claim 1, characterized in that: When the porosity and permeability development zones are determined by the relationship between reservoirs and low-maturity oil reservoirs, for lithologic oil and gas reservoirs, the porosity and permeability development zones mainly include the layers with relatively developed primary pores and unconformity surfaces. The formation and distribution of secondary solution pores in the reservoir are the key to determining the production capacity and scale of lithologic oil and gas reservoirs. The formation of secondary solution pores in the reservoir is the result of organic-inorganic interaction during diagenetic evolution.

6. The method for evaluating favorable zones of low-maturity oil according to claim 1, characterized in that: When the relationship between source rocks and low-maturity oil reservoirs is used to determine the effective source rock belt, oil and gas mainly migrate vertically along faults, and the distribution of oil and gas is controlled by the effective oil-generating range. However, oil and gas displays are not distributed in the center of the effective source rock, but in the marginal area of ​​the center of the effective source rock.

7. The method for evaluating favorable zones of low-maturity oil according to claim 1, characterized in that: When the unconformity development zone is determined based on the relationship between the unconformity and the low-maturity oil reservoir, the unconformity is mainly the result of atmospheric water leaching. The unconformity in the two regions is a porosity and permeability development zone, which is a favorable place for oil and gas accumulation.

8. The method for evaluating favorable zones of low-maturity oil according to claim 1, characterized in that: When the stratigraphic pinch-out zone is determined based on the relationship between uplift or bulge and low-maturity oil reservoirs, stratigraphic overlap, unconformity obstruction and sand layer updip pinch-out type oil and gas reservoirs are generally attached to the basin edge slope and the wing of the uplift area in the basin in a belt-like shape. Compared with the lens-shaped sandstone body lithologic oil reservoirs in the depression area, the oil column height and single well production are relatively high.

9. The method for evaluating favorable zones of low-maturity oil according to claim 1, characterized in that: When the fault structure development zone is determined based on the relationship between faults and low-mature oil reservoirs, the large central uplift zone is the main direction of oil and gas migration, and the zonal distribution along the main faults is the main form of complex oil and gas accumulation.

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