Prediction method for favorable blank area of multi-section, multi-convex and multi-depression petroliferous basin

Abstract

The invention relates to a method for predicting favorable blank areas of a multi-section, multi-convex and multi-depression petroliferous basin, and belongs to the technical field of oil-gas exploration. The prediction method comprises the following steps: 1) under a multi-fracture, multi-convex and multi-depression oil-gas-containing basin structure pattern of a target series of strata, taking a distribution range of each high-quality hydrocarbon source rock of the target series of strata in different deposition periods as a center, and taking an oil-gas accumulation period paleostructure and oil-gas accumulation period fluid difference of the target series of strata as boundaries; carrying out oil-gas system division of the target strata series of the petroliferous basin; and 2) in each oil gas system of the divided target series of strata, superposing key reservoir forming elements of the target series of strata of the petroliferous basin, and determining a superposing area outside an oil gas explored reserve area range as a favorable exploration blank area. According to the method, oil and gas system division performed in combination with other key elements under the construction of a macroscopic pattern is more reasonable, superposition analysis of multiple reservoir forming elements is performed on the basis, a favorable exploration blank area is predicted, and a direction is indicated for fine exploration.

Description

Technical Field

[0001] The present invention relates to a method for predicting favorable blank areas in multi-fault, multi-convex and multi-depressed oil and gas bearing basins, belonging to the technical field of oil and gas exploration. Background Art

[0002] At present, most oil and gas bearing basins have entered the stage of high exploration degree. The exploration targets are becoming increasingly complex and hidden, the reserve scale is getting smaller and smaller, and the reserve grade is constantly deteriorating, which are the new exploration characteristics faced by oil and gas exploration workers in old areas with high exploration degree. However, judging from the reserve growth of oil and gas bearing basins at home and abroad, the reserve blank areas in the main oil-bearing formations in high exploration degree areas are still important reserve-increasing fields in the coming long period. However, due to the large number of oil and gas bearing formations and the uneven distribution of oil and gas reserves within the formations, how to carry out fine exploration in high exploration degree areas to achieve the goals of commercial oil and gas discovery and finding large-scale high-quality reserves has become a difficult problem faced by oil and gas exploration workers in old areas.

[0003] In view of the increasing difficulty in exploring the reserve blank areas in the main oil-bearing formations in mature exploration areas, Xiang Lihong et al. disclosed a method for optimizing exploration targets for reserve blank areas in the main oil-bearing formations in mature exploration areas, taking the third member of Shahejie Formation in the southern slope of Bonan Sag in Jiyang Depression as an example, in the article "Method for Optimizing Exploration Targets for Reserve Blank Areas in the Main Oil-bearing Formations in Mature Exploration Areas - Taking the Third Member of Shahejie Formation in the Southern Slope of Bonan Sag as an Example" (Oil & Gas Geology and Recovery Efficiency, 2020, 27(02): 53-61). Based on the premise of using mathematical geology methods to predict the remaining resource potential of blank areas, this method is guided by the theory of the orderliness of oil and gas reservoir distribution to determine the possible types of oil reservoirs and the key research directions in blank areas. By carefully analyzing and dissecting the original geological data such as drilling, logging, well logging, oil testing and testing, studying the main controlling factors of oil reservoir formation in the reserve area, establishing a fine geological model and an oil reservoir formation model in the study area, and under the guidance of this model, combined with the analysis of failed wells in reserve blank areas, clarifying the differences in reservoir formation elements, oil and gas distribution and reservoir formation mechanisms between the reserve area and the blank area, and determining the main reasons for the formation of blank areas. This method is mainly limited to the research on blank areas within the explored reserve areas, conducting exploration for expanding the oil-water boundary in order to achieve continuous oil-bearing, but insufficient in the exploration research on blank areas in non-reserve areas.

[0004] With the development of the theory of hydrocarbon accumulation and the improvement of exploration practice understanding, the exploration idea has been transformed in recent years, and lithostratigraphic hydrocarbon reservoirs are searched in the flanks of structures. The exploration technical methods for lithostratigraphic hydrocarbon reservoirs include the technical method for optimizing and evaluating favorable zones of lithostratigraphic hydrocarbon reservoirs, the technical method for implementing and evaluating lithostratigraphic traps, and the technical method for preliminary exploration and evaluation of lithostratigraphic oil reservoirs. The continental faulted sag trough area is the deep depression area except the positive tectonic belt in the fault depression and the middle and lower parts of the slope, which is in a weakly tectonically active area and is a favorable development area for lithostratigraphic traps. In the process of realizing the exploration of lithostratigraphic hydrocarbon reservoirs, sequence stratigraphic division technology is used to establish the sequence stratigraphic framework of the target series, and key geophysical technologies such as fine time-depth conversion, joint analysis of stratigraphic slices and seismic attributes, and comprehensive reservoir prediction are comprehensively applied to achieve a major breakthrough in the exploration of lithostratigraphic hydrocarbon reservoirs. For example, the Songfangtun concave slope zone is an inherited nose-shaped structural slope formed during the occurrence and development of the Sanzhao Sag in the Songliao Basin. The Putaohua oil layer is the most important oil-bearing target layer in the upper, middle and lower oil-bearing combinations in the study area. For a long time, the understanding of the hydrocarbon accumulation law of the Putaohua oil layer has been unclear. Liu Zongbao publicly disclosed in "Hydrocarbon Accumulation Model and Prediction of Favorable Blocks in the Putaohua Oil Layer of the Songfangtun Concave Slope Zone" (Master's Degree Thesis, Daqing Petroleum Institute) that starting from the paleotectonic evolution of the Sanzhao Sag and its surrounding areas, a detailed study of the paleotectonic evolution of the Songfangtun concave slope zone was carried out, and the large Songfangtun-Mofantun paleo-nose structure was discovered for the first time, and the controlling effect of the paleotectonic on hydrocarbon accumulation was recognized; based on the paleotectonic research, the provenance of the study area was determined by analyzing the formation thickness and sandstone thickness; the Putaohua oil layer was finely stratigraphically divided and correlated by applying the theories of sedimentology and sequence stratigraphy, and a high-resolution sequence stratigraphic framework was established; through the study of sedimentary microfacies in key sedimentary time units, the sedimentary microfacies of the Putaohua oil layer were obtained; through the study of the burial history of the source rock, the primary migration period of hydrocarbons and the key period of hydrocarbon accumulation were known, and a new understanding of the hydrocarbon migration field was obtained. Based on the research on the structure, sandstone, static, dynamic, perforation, abandoned wells and oil-water interface of the Putaohua oil layer, 31 typical single traps were analyzed, 4 hydrocarbon accumulation models in the Songfangtun concave slope zone were summarized, and the main oil-controlling factors of single local structures were pointed out. Under the guidance of the hydrocarbon accumulation law, the favorable proven areas and favorable blank areas around the development area were predicted. Although the above methods can predict the favorable proven areas and favorable blank areas around the development area, there are still deficiencies in the study of the hydrocarbon accumulation law and favorable blank areas in the multi-convex and multi-sag pattern controlled by syndepositional faults in different periods. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for predicting favorable blank areas in a multi-fault, multi-convex and multi-sag hydrocarbon-bearing basin, so as to solve the problem that the existing technology has inaccurate research and prediction of favorable blank areas in the multi-convex and multi-sag pattern controlled by syndepositional faults in different periods.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0007] A prediction method for favorable blank areas in a multi-fault, multi-convex and multi-sag hydrocarbon-bearing basin, comprising the following steps:

[0008] 1) Under the structural pattern of a multi-fault, multi-convex and multi-sag hydrocarbon-bearing basin in the target strata, taking the distribution ranges of high-quality source rocks in different sedimentary periods of the target strata as the centers and the paleo-structures during the hydrocarbon accumulation period and the fluid differences during the hydrocarbon reservoir formation period in the target strata as the boundaries, divide the hydrocarbon systems of the target strata in the hydrocarbon-bearing basin;

[0009] 2) In each hydrocarbon system of the divided target strata, superimpose the key hydrocarbon accumulation elements of the target strata in the hydrocarbon-bearing basin, and determine the superimposed area outside the range of the explored hydrocarbon reserves as the favorable exploration blank area.

[0010] The prediction method for favorable blank areas in a multi-fault, multi-convex and multi-sag hydrocarbon-bearing basin of the present invention attaches importance to the fact that the structure is the main controlling factor for hydrocarbon accumulation and plays a controlling role in each element of hydrocarbon accumulation. The division of hydrocarbon systems combined with other key elements under the macroscopic structure pattern is more reasonable. On this basis, the superimposed analysis of multiple hydrocarbon accumulation elements is carried out to predict favorable exploration blank areas, indicating the direction for fine exploration.

[0011] In the present invention, a sag that simultaneously satisfies the following three conditions is a multi-fault, multi-convex and multi-sag hydrocarbon-bearing basin: ① The total extension length of secondary faults in the sag (unit: km) / the total area of the sag (unit: km 2 ) ≥ 0.14; ② The total area of the sag (unit: km 2 ) / the number of convexes in the sag (unit: pieces) ≤ 160; ③ The total area of the sag (unit: km 2 ) / the number of sags in the sag (unit: pieces) ≤ 450.

[0012] Furthermore, the distribution ranges of high-quality source rocks in different sedimentary periods are obtained by a method comprising the following steps: According to the occurrence of syndepositional faults, fault activities and sag distributions in different sedimentary periods of the target strata in the study area, and in combination with the source rock indexes of the target strata, determine the distribution ranges and thicknesses of high-quality source rocks in different sedimentary periods of the target strata. This method combines macroscopic and microscopic aspects and the research results of structural disciplines and hydrocarbon generation disciplines for analysis, that is, under the macroscopic pattern of the occurrence of syndepositional faults, fault activities and sag distributions, comprehensive analysis is carried out in combination with the microscopic indexes of source rocks, and the results obtained are more reliable and reasonable than those from single-discipline analysis. At the same time, it emphasizes and highlights the importance of key elements such as faults and sags in the study of high-quality source rocks in a multi-fault, multi-convex and multi-sag hydrocarbon-bearing basin.

[0013] Furthermore, a method for determining the paleo-structure during the hydrocarbon accumulation period includes the following steps: Based on the current structural profile characteristics of the target formation in the study area, obtain the structural maps and structural outline maps of the target formation in different sedimentary periods, and then conduct the division of structural units in different sedimentary periods of the target formation to determine the planar distribution characteristics of the paleo-structure during the hydrocarbon accumulation period.

[0014] Furthermore, the occurrence, fault activity, and sag distribution of syndepositional faults in different sedimentary periods of the target formation are determined by a method including the following steps: Based on the current structural profile characteristics of the target formation in the study area, obtain the isopach maps of strata and fault growth indices in different periods, and then, in combination with the principle of balanced section restoration, obtain the occurrence, fault activity, and sag distribution of syndepositional faults in different sedimentary periods.

[0015] Furthermore, a method for determining the current structural profile characteristics of the target formation includes the following steps: Conduct structural analysis based on seismic profiles, drilling and logging data, etc. in the study area to obtain the geological interpretation map of the seismic profile in the study area, and then convert it into a geological profile through the velocity formula to further determine the current structural profile characteristics of the Paleogene.

[0016] Furthermore, the key hydrocarbon accumulation elements include the distribution area of high-quality source rocks, the distribution area of sand body lithofacies, and the depth range of the lower limit of buoyancy hydrocarbon accumulation in the target formation of the study area. The advantage of using the distribution area of high-quality source rocks, the distribution area of sand body lithofacies, and the depth range of the lower limit of buoyancy hydrocarbon accumulation as the key hydrocarbon accumulation elements for superposition is that under the multi-convex and multi-sag pattern controlled by the difference in the activity intensity of syndepositional faults (synsedimentary faults), within each subdivided hydrocarbon-bearing system, the distribution area of high-quality source rocks and sand body lithofacies are superposed, emphasizing the near-source accumulation of hydrocarbons under the vertical conduction of faults; at the same time, the depth range of the lower limit of buoyancy hydrocarbon accumulation is superposed, and classification and grading are carried out in combination with the guidance of benefit exploration to optimize the favorable exploration blank areas within different depth ranges and conduct optimization and ranking. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of the prediction method for exploring favorable blank areas in hydrocarbon-bearing basins of the present invention;

[0018] Figure 2 It is the regional seismic time section interpretation scheme (taking the large section 7 of a certain eastern sag as an example) in the embodiment of the present invention;

[0019] Figure 3 It is the regional depth geological section interpretation scheme (taking the large section 7 of a certain eastern sag as an example) in the embodiment of the present invention;

[0020] Figure 4 It is the distribution map of the intensity of syndepositional faults (synsedimentary faults) and sags in different sedimentary periods (taking the sedimentary period of the 1st - 4th sand members in the middle submember of the third member of the Paleogene in a certain eastern sag as an example) in the embodiment of the present invention;

[0021] Figure 5 This is the isopach map of high-quality source rocks in different sedimentary periods in the embodiment of the present invention (taking the sedimentary period of the lower sub-member of the third member of the Paleogene in a certain eastern sag as an example);

[0022] Figure 6 This is the tectonic unit division map in different sedimentary periods in the embodiment of the present invention (taking the bottom surface of the 1st-4th sand groups of the middle sub-member of the third member of the Paleogene in a certain eastern sag as an example);

[0023] Figure 7 This is the oil and gas system division map in the embodiment of the present invention (taking the Paleogene in a certain eastern sag as an example);

[0024] Figure 8 This is the superposition prediction blank area of key hydrocarbon accumulation elements in the embodiment of the present invention (taking the superposition of high-quality source rocks, sand bodies, buoyancy hydrocarbon accumulation lower limit values, and explored hydrocarbon reserves areas in the lower sub-member of the third member of the Paleogene in a certain eastern sag as an example);

[0025] Figure 9 This is the optimization of favorable exploration zones in the embodiment of the present invention (taking the upper sub-member of the third member of the Paleogene in a certain eastern sag as an example). Detailed implementation manners

[0026] Taking a certain eastern sag in China as the research area and the Paleogene in the research area as the target stratigraphic series below, the technical solution of the present invention will be further described in combination with the detailed implementation manners.

[0027] Example 1

[0028] The prediction method for the favorable blank area of a multi-fault, multi-convex, and multi-sag hydrocarbon-bearing basin in this embodiment has a process as Figure 1 shown and includes the following steps:

[0029] 1) Conduct structural analysis based on the regional seismic profiles, drilling and logging data, etc. of a certain eastern sag to obtain the geological interpretation map of the regional seismic profiles of a certain eastern sag (as Figure 2 shown), and then convert it into a geological profile through the velocity formula (as Figure 3 shown) to determine the current structural profile characteristics of the Paleogene.

[0030] Taking the seismic profile in the middle area of a certain eastern sag as an example, the Lanliao Fault is steep at the top and gentle at the bottom, with a listric fault plane as its basic feature. The displacement of the basement fault changes strongly, resulting in differences in the basin structure. In the middle area, there are many second- and third-order faults such as the Lanliao Fault, Duzhai Fault, Xulou Fault, Wenxi Fault, Wendong Fault, Changyuan Fault, Shijiaji Fault, and Wuxingji Fault, which control the Wenliu low bulge and the Mazhai sag, Liutun sag, Haitongji sag, Qianliyuan sag, and Wennan sag, etc. In the Paleogene basement of a certain eastern sag, there are many but small-scale bulges and sags in the northern part of the middle area, indicating many but weak faults; from north to south, the number of faults decreases and the intensity increases, while the number of bulges and sags decreases and the amplitude increases.

[0031] 2) According to the present tectonic profile characteristics of the Paleogene in a certain eastern sag, the isopach maps and fault growth indices of the strata in different periods of the Paleogene are obtained. Then, combined with the principle of balanced section restoration, the attitudes of syndepositional faults, fault activities, and sag distributions in different sedimentary periods of the Paleogene are obtained.

[0032] During the sedimentary period of the Paleogene in a certain eastern sag, there were multiple stages of tectonic activities. According to the analysis results of seismic profiles, the isopach maps and fault growth indices of the strata in different periods are obtained. Combining with the principle of balanced section restoration, it is considered that the main syndepositional faults in the Paleogene of a certain eastern sag began to be active in the sedimentary period of Member 4 of the Shahejie Formation, the lower sub-member of Member 3 of the Shahejie Formation, the 1st - 4th sand groups in the middle section of Member 3 of the Shahejie Formation, and the upper sub-member of Member 2 of the Shahejie Formation, which are the initial rifting period, strong rifting period, multi-fault rifting period, and weakening rifting period respectively. The attitude of the Lanliao Fault controlling the sag in the southern area of the sag is slope-ramp type, the attitude of the Lanliao Fault controlling the sag in the northern area of the sag is domino type, and the middle area of the sag is a transition area, where the attitude of the Lanliao Fault controlling the sag is listric.

[0033] Taking the sedimentary period of the 1st - 4th sand groups in the middle sub-member of Member 3 of the Shahejie Formation in the Paleogene of a certain eastern sag as an example (as Figure 4 shown), the intensity of synsedimentary faults (syndepositional faults) and sag distributions in different sedimentary periods are analyzed. The overall distribution range of the stratum thickness is 100 - 300m, and the maximum thickness in the sag reaches 500m. The overall range of the fault growth index is 1.1 - 1.5. This period is a multi-fault rifting period, mainly developing faults such as the Changyuan Fault, Huanghe Fault, and Wendong (east branch) Fault, etc. East-dipping and west-thickening or west-dipping and east-thickening faulted half-grabens are widely developed, and faulted depression-grabens are only developed in the southern and northern parts of the Lanliao Fault. The sedimentation-subsidence center is mainly located in the Liutun - Haitongji sag, followed by the north depression of Gegangji. Fault activities are the main controlling factors for the formation of sags. Faults such as the Huanghe, Changyuan, and Wendong faults were generated and were highly active. The western sag belt was divided into multiple small sags, the central uplift belt was gradually formed, the southwestern sag began to develop, and a "multi-convex and multi-sag" tectonic pattern gradually took shape in a certain eastern sag, and 12 sags were basically formed.

[0034] 3) Based on the occurrence of syndepositional faults, fault activities, and sag distributions during different sedimentary periods of the Paleogene in a certain eastern sag, combined with the source rock indicators of the Paleogene, determine the distribution range and thickness of high-quality source rocks during different sedimentary periods of the Paleogene.

[0035] Based on the analysis of the geochemical characteristics, lithological characteristics, logging response characteristics, and layer and facies control laws of source rocks, logging evaluations of high-quality source rocks were carried out for different tectonic units, different strata, and different lithological combination types. The results show that the high-quality source rocks in the Paleogene of a certain eastern sag are mainly developed in the late transgressive system tract (the upper submember of the fourth member of the Shahejie Formation) and the early highstand system tract (the lower submember of the third member of the Shahejie Formation, the middle submember of the third member of the Shahejie Formation, and the bottom of the upper submember of the third member of the Shahejie Formation). Among them, the high-quality source rocks in the upper submember of the fourth member of the Shahejie Formation and the lower submember of the third member of the Shahejie Formation are relatively developed, with a maximum thickness of 400 m, and the maximum thickness of the other strata is 150 - 300 m.

[0036] The extensional activity in the southern part of the sag is strong. Magma intrudes upward and bakes, resulting in a decrease in the competence of crustal rocks and making it easy to slip and deform. As a result, the occurrence of the Lanliao Fault is slope-ramp type, controlling the structure of the southern part of the sag to be wide basin and shallow depression, with kerogen types of III and II2, and poor-quality source rocks, which are freshwater lacustrine facies. The rocks in the northern part of the sag have strong competence and are prone to brittle deformation, resulting in the occurrence of the Lanliao Fault being domino type, controlling the structure of the northern part of the sag to be narrow and shallow, with many highs and lows, with kerogen types of II1 and II2, and medium-quality source rocks, which are salt-free lacustrine facies. The middle part of the sag is a transition zone, with the occurrence of the Lanliao Fault being shovel type, controlling the structure of the middle part of the sag to be high convex and deep depression, with kerogen types of I and II1, and high-quality source rocks, which are salt lake facies.

[0037] Taking the sedimentary period of the lower submember of the third member of the Shahejie Formation in the Paleogene of a certain eastern sag as an example (as Figure 5 shown), this period is a strong fault-depression period. Due to the successive generation of secondary and tertiary faults such as Shijiaji, Weixi, and Wenxi, a subsidence center also appears in the west, with many highs and lows. Salt rocks are developed in the northern part of a certain eastern area, the climate is humid, with a strong reducing environment, and the source rock quality is excellent. The thick values of high-quality source rocks are mainly distributed in the sedimentation center (the Xinwei 12 well area) and the surrounding salt-distributed areas (Pucheng - Hubuzhai, Weicheng - Mazhai, Huqing, Wennan Duzhai). From the salt lake center to the basin margin, the thickness decreases from thick to thin, and the abundance decreases from high to low. Differences in hydrocarbon generation units begin to appear due to the strong activity of faults.

[0038] 4) Based on the characteristics of the present tectonic profiles in the Paleogene of a certain eastern sag, obtain the tectonic maps and tectonic outline maps of different sedimentary periods of the Paleogene, and then carry out the division of tectonic units in different sedimentary periods of the Paleogene to determine the planar distribution characteristics of paleo-structures during the hydrocarbon accumulation period of the Paleogene.

[0039] According to research data and literature, the criteria and basis for dividing tectonic units are major faults, isobaths, and the pinch-out lines of strata, etc. Combining with the structural maps and structural outline maps of the structural analysis results, the Paleogene tectonic units of a certain eastern sag are divided (as Figure 6 shown), and the sub-secondary tectonic units are divided into the Lanliao fault step zone, the eastern sub-sag zone, the central low uplift, the western sub-sag zone, and the western slope zone. The activities of the late caprock faults transform the early faults and structures, forming 35 positive structures and 12 negative structures controlled by 43 secondary and tertiary faults, and the specific situation is shown in Table 1.

[0040] Table 1 Division Table of Tectonic Units in a Certain Eastern Sag

[0041]

[0042] In Table 1, (1) to (35) are positive structures (uplifts), and [1] to

[12] are negative structures (depressions).

[0043] Based on the theory of hydrocarbon accumulation and exploration practice, it is concluded that: the total extension length of the secondary faults in the sag (unit: km) / the total area of the sag (unit: km 2 ) ≥ 0.14 is considered to have many faults; the total area of the sag (unit: km 2 ) / the number of uplifts in the sag (unit: pieces) ≤ 160 is considered to have many uplifts; the total area of the sag (unit: km 2 ) / the number of depressions in the sag (unit: pieces) ≤ 450 is considered to have many depressions.

[0044] There are a total of 37 secondary faults in the Paleogene of a certain eastern sag (1 in Sha 4, 18 in the lower part of Sha 3, 9 in the middle part of Sha 3 (1 - 4), and 9 in the upper part of Sha 2); the total extension length of the secondary faults in the sag is 797 km / the total area of the sag is 5300 km 2 = 0.15, and the fault development density ranks among the top in the Bohai Bay Basin, showing the characteristics of many faults. The total area of the Paleogene sag in a certain eastern sag (km 2 ) / the number of uplifts in the sag (5300 / 35) = 151, that is, one uplift develops per 151 km 2 , showing the characteristics of many uplifts. The total area of the Paleogene sag in a certain eastern sag (km 2 ) / the number of depressions in the sag (5300 / 12) = 442, that is, one depression develops per 442 km 2 , showing the characteristics of many depressions. Generally speaking, the Paleogene of a certain eastern sag has a basin structure pattern with many faults, many uplifts, and many depressions.

[0045] In the Paleogene system of a certain eastern sag, 14 positive structures such as Wenliu, Machang, Huazhuangji and Qingzuji are mainly developed, accounting for about 45% of the exploration area of the sag, and are mainly distributed in the central low convex zone and the western slope zone. The positive structures in the Paleogene system are characterized by large uplift amplitude and steep structural slope, with excellent configuration of source rock, cap rock and reservoir. The high-quality source rocks are mainly distributed in the main body of the structure and the surrounding slopes, and the maximum distance from the top of the structure to the center of the sag does not exceed 14 km. The traps of the positive structures developed in the Paleogene system have large amplitude and steep slope. The oil and gas migrate and accumulate to the high positions sufficiently and with strong driving force. The excellent source-reservoir-cap configuration is conducive to the enrichment and preservation of oil and gas.

[0046] 5) Under the structural pattern of an oil and gas bearing basin with multiple faults, multiple highs and multiple sags in the Paleogene system, taking the distribution range of each high-quality source rock in different sedimentary periods of the Paleogene system as the center and the paleo-structure in the oil and gas accumulation period of the Paleogene system and the fluid difference in the oil and gas reservoir accumulation period as the boundary, the oil and gas system of the Paleogene system in a certain eastern sag is divided.

[0047] Under the structural pattern of the Paleogene basin with multiple faults, highs and lows, through oil-source correlation, the fluid difference characteristics of oil and gas reservoirs in various structures of the Paleogene in a certain eastern sag are analyzed, which can be specifically divided into the following 10 categories: ① In Wenmingzhai, Weicheng, Guyunji, Hubuzhai, Pucheng, the main oil source of the main structure comes from the upper sub-member of the fourth member of the Shahejie Formation - the lower sub-member of the third member of the Shahejie Formation, the main oil source of the near-sag structure comes from the middle sub-member of the third member of the Shahejie Formation, and the coal-derived gas comes from the Carboniferous - Permian. ② In Pucheng and Chenying, the main oil source of the main structure comes from the upper sub-member of the fourth member of the Shahejie Formation - the lower sub-member of the third member of the Shahejie Formation, the main oil source of the near-sag structure comes from the middle sub-member of the third member of the Shahejie Formation, and the coal-derived gas comes from the Carboniferous - Permian. ③ In Mazhai and north of Mazhai, the oil source mainly comes from the upper sub-member of the fourth member of the Shahejie Formation - the lower sub-member of the third member of the Shahejie Formation. ④ In Xingzhuang, north of Huazhuangji, and northwest of Wen, the oil source mainly comes from the middle sub-member of the third member of the Shahejie Formation, and secondly from the upper sub-member of the fourth member of the Shahejie Formation - the lower sub-member of the third member of the Shahejie Formation. ⑤ In Huazhuangji, Qingzuji, west of Wen, and west of Liuzhuang, the oil source mainly comes from the upper sub-member of the fourth member of the Shahejie Formation - the lower sub-member of the third member of the Shahejie Formation, and secondly from the middle and upper sub-members of the third member of the Shahejie Formation, and the coal-derived gas comes from the Carboniferous - Permian. ⑥ In the east of Wen, south of Wen, Liuzhuang, north of Baimiao, and north of Qiaokou, the oil source mainly comes from the upper sub-member of the fourth member of the Shahejie Formation - the lower sub-member of the third member of the Shahejie Formation, and secondly from the middle, upper sub-members of the third member of the Shahejie Formation and the first member of the Shahejie Formation, and the coal-derived gas comes from the Carboniferous - Permian. ⑦ In the south of Qiaokou, Xinhuo, Tangzhuang, and south of Baimiao, the oil source mainly comes from the upper sub-member of the fourth member of the Shahejie Formation - the lower sub-member of the third member of the Shahejie Formation, and secondly from the middle and upper sub-members of the third member of the Shahejie Formation, and the coal-derived gas comes from the Carboniferous - Permian. ⑧ In Machang, Xuji, and Sanchunji, the oil source mainly comes from the upper sub-member of the fourth member of the Shahejie Formation - the lower sub-member of the third member of the Shahejie Formation, and secondly from the middle and upper sub-members of the third member of the Shahejie Formation, and the coal-derived gas comes from the Carboniferous - Permian. ⑨ In Zhaozhuang, Fanglij, Mengju, Nanhejia, and Linzhai, the oil source mainly comes from the middle sub-member of the third member of the Shahejie Formation, and secondly from the lower sub-member of the third member of the Shahejie Formation and the first member of the Shahejie Formation, and the coal-derived gas comes from the Carboniferous - Permian. ⑩ In Guancheng, the upper sub-member of the fourth member of the Shahejie Formation - the lower sub-member of the third member of the Shahejie Formation has a certain hydrocarbon generation capacity. Under the structural pattern of the Paleogene oil and gas-bearing basin with multiple faults, highs and lows, with the distribution range of each high-quality hydrocarbon source rock in different sedimentary periods of the Paleogene as the center, and the paleo-structure in the oil and gas accumulation period of the Paleogene and the fluid difference in the oil and gas reservoir accumulation period as the boundary, the oil and gas systems in the Paleogene of the oil and gas-bearing basin are divided, and the Paleogene in a certain eastern sag is divided into 10 oil and gas systems, namely ① Puwe, ② Pucheng, ③ Mazhai, ④ Liutun, ⑤ Haitongji, ⑥ Qianliyuan, ⑦ north of Gegangji, ⑧ south of Gegangji, ⑨ southwest sag, and ⑩ Guancheng oil and gas systems (as Figure 7 shown). Each oil and gas system has an independent hydrocarbon source rock area. The distribution of oil and gas is controlled by the adjacent oil-generating sags around, and the lateral migration distance of oil and gas is relatively short, serving as the basic unit for the next calculation of oil and gas resource volume and exploration evaluation.

[0048] 6) Within the oil and gas systems in the Paleogene of the divided eastern sag, the key accumulation elements in the Paleogene of the oil and gas-bearing basin are superimposed, and the superimposed area outside the range of the explored oil and gas reserves is determined as the favorable exploration blank area.

[0049] In the Paleogene of a certain eastern sag, high-quality hydrocarbon source rocks developed in the lower sub-member of the third member of the Shahejie Formation - the upper sub-member of the fourth member of the Shahejie Formation. 3750m is the depth of the lower limit of buoyancy accumulation. Under the pattern of multiple highs and lows controlled by the difference in the activity intensity of syndepositional faults (synsedimentary faults), the depth ranges of the high-quality hydrocarbon source rock distribution area + sand body lithofacies distribution area + buoyancy accumulation lower limit value are superimposed to determine that the superimposed areas with burial depths shallower than 3000m, burial depths of 3000m - 3750m, burial depths of 3750m - 4250m, and burial depths deeper than 4250m outside the range of the already explored hydrocarbon reserves area are favorable exploration blank areas (as Figure 8 shown). Combining with the guidance of benefit exploration, favorable exploration blank areas are selected and prioritized in the depth intervals shallower than 3750m and 3750 - 4250m in different hydrocarbon systems (as Figure 9 ). Taking the upper sub-member of the third member of the Shahejie Formation in a certain eastern sag as an example, the first-class favorable exploration areas selected from 10 hydrocarbon systems are the Puwei, Haitongji, Qianliyuan, and Pucheng hydrocarbon systems in sequence, and the second-class favorable exploration area of the upper sub-member of the third member of the Shahejie Formation is the Qianliyuan hydrocarbon system.

Claims

1. A method for predicting favorable blank areas in a multi-fault, multi-convex and multi-depressed hydrocarbon-bearing basin, characterized in that: It includes the following steps: 1) Under the structural pattern of a multi-fault, multi-convex and multi-depressed hydrocarbon-bearing basin in the target series, with the distribution ranges of high-quality source rocks in different sedimentary periods of the target series as the center and the paleo-structures during the hydrocarbon accumulation period and the fluid differences during the hydrocarbon reservoir formation period of the target series as the boundaries, the hydrocarbon systems of the target series in the hydrocarbon-bearing basin are divided; 2) In each hydrocarbon system of the divided target series, the key hydrocarbon accumulation elements of the target series in the hydrocarbon-bearing basin are superimposed, and the superimposed area outside the range of the explored hydrocarbon reserves is determined as the favorable exploration blank area.

2. The method for predicting favorable blank areas in a multi-fault, multi-convex and multi-depressed hydrocarbon-bearing basin according to claim 1, characterized in that: The distribution ranges of high-quality source rocks in different sedimentary periods are obtained by a method including the following steps: According to the occurrence of syn-sedimentary faults, fault activities and depression distributions in different sedimentary periods of the target series in the study area, combined with the source rock indexes of the target series, the distribution ranges and thicknesses of high-quality source rocks in different sedimentary periods of the target series are determined.

3. The method for predicting favorable blank areas in a multi-fault, multi-convex and multi-depressed hydrocarbon-bearing basin according to claim 1, characterized in that: The key hydrocarbon accumulation elements include the distribution areas of high-quality source rocks, the distribution areas of sand body lithofacies and the depth ranges of the lower limits of buoyancy hydrocarbon accumulation in the target series of the study area.

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