Sea area oil-gas exploration feasibility evaluation method and evaluation system

Abstract

The embodiment of the invention provides a sea area oil-gas exploration feasibility evaluation method and evaluation system, and belongs to the field of geological exploration. The evaluation method comprises the steps of determining a first score related to a reservoir forming probability according to hydrocarbon supply intensity, reservoir capacity, a hydrocarbon supply window and a capping condition of an exploration target; determining a second score related to the resource reserves according to the well control oil and gas scale of the exploration target; determining a third score related to constructability according to an engineering index of a pre-exploration well point of the exploration target; and performing first weighting processing on the first score, the second score and the third score to determine a target score. The method fully considers the oil and gas reservoir forming probability of the exploration target, gives consideration to the economy of sea area oil and gas exploration, reasonably evaluates the resource scale and economic value of the exploration target, and can make accurate quantitative evaluation on the feasibility of sea area exploration in combination with the difficulty and cost of sea area exploration engineering. The method has the advantages of high reliability, strong operability and quantification.

Description

Technical Field

[0001] This invention relates to the field of geological exploration technology, and more specifically to a method and system for evaluating the feasibility of offshore oil and gas exploration. Background Technology

[0002] As onshore oil and gas exploration deepens and resources dwindle, offshore oil and gas exploration efforts are intensifying. Due to the extremely high drilling costs in offshore oil and gas exploration, various factors need to be comprehensively considered during actual exploration. Currently, research on the feasibility of offshore oil and gas exploration is relatively weak, and quantitative evaluation standards are rather simplistic, especially lacking research related to economic costs. New, effective, and accurate methods are urgently needed. Summary of the Invention

[0003] This invention provides a method and device for evaluating the feasibility of offshore oil and gas exploration. It can conduct integrated geological and engineering analysis of exploration targets in the sea area. In particular, it adopts economic indicators to make a quantitative evaluation of their exploration feasibility, which indirectly improves the success rate of oil and gas exploration and the subsequent oil and gas recovery rate. It has the advantages of high reliability, strong operability and quantification.

[0004] The purpose of this invention is to provide a method for evaluating the feasibility of offshore oil and gas exploration. The method includes: determining a first score related to the probability of hydrocarbon accumulation for the exploration target based on its hydrocarbon supply intensity, storage capacity, hydrocarbon supply window, and capping conditions; determining a second score related to the resource reserves of the exploration target based on the well-controlled oil and gas scale of the exploration target; determining a third score related to the workability of the exploration target based on the engineering indicators of the pre-exploration well points of the exploration target; and performing a first weighting process on the first score, the second score, and the third score to determine a target score for the drillability of the exploration target.

[0005] Optionally, determining the first score related to the hydrocarbon accumulation probability of the exploration target based on its hydrocarbon supply intensity, reservoir capacity, hydrocarbon supply window, and capping conditions includes: determining a first sub-score for the hydrocarbon supply intensity based on the source strata, source rock quality, hydrocarbon generation threshold, and distance between the exploration target and the hydrocarbon generation center; determining a second sub-score for the reservoir capacity based on the reservoir thickness, fracture area, and porosity of the exploration target; determining a third sub-score for the hydrocarbon supply window based on the range and area of ​​the hydrocarbon supply window of the exploration target; determining a fourth sub-score for the capping conditions based on the lithological assemblage, thickness, and pressure coefficient of the overlying strata of the exploration target; and performing a second weighting process on the first, second, third, and fourth sub-scores to determine the first score.

[0006] Optionally, the second weighting process for the first sub-score, the second sub-score, the third sub-score, and the fourth sub-score includes: setting the weighting coefficient of the second sub-score to the maximum and setting the weighting coefficient of the fourth sub-score to the minimum.

[0007] Optionally, determining the second score related to resource reserves of the exploration target based on the well-controlled oil and gas scale of the exploration target includes: determining the well-controlled oil and gas resource quantity of the pre-exploration well points using the volumetric method based on the target reservoir thickness, oil and gas-bearing area, and porosity of the exploration target; determining the benchmark equilibrium production of the exploration target based on the construction cost, production ratio, and standard unit price of oil and gas in the area where the exploration target is located; determining the second score as 100% when the well-controlled oil and gas resource quantity is greater than or equal to the benchmark equilibrium production; and determining the ratio of the well-controlled oil and gas resource quantity to the benchmark equilibrium production as the second score when the well-controlled oil and gas resource quantity is less than the benchmark equilibrium production.

[0008] Optionally, determining the third score related to the workability of the exploration target based on the engineering indicators of the pre-exploration well points of the exploration target includes: assigning a value to each engineering indicator based on the engineering indicators and the corresponding operational capability threshold for each engineering indicator; and performing a third weighting process on the assigned values ​​of each engineering indicator to determine the third score.

[0009] Optionally, the engineering indicators include the water depth of the exploratory well and the target layer burial depth of the exploratory well. Assigning values ​​to each engineering indicator based on the engineering indicators and the corresponding operational capability thresholds includes: determining the seafloor time depth and the main target layer time depth at the exploratory well using the seismic profile of the exploration target; determining the water depth and the target layer burial depth of the exploratory well using the velocity model, the seafloor time depth, and the main target layer time depth; assigning a value to the water depth of the exploratory well based on the water depth and water depth operational capability thresholds; and assigning a value to the target layer burial depth of the exploratory well based on the target layer burial depth and drilling depth operational capability thresholds.

[0010] Optionally, the engineering indicators also include the pressure coefficient encountered at the exploratory well point. Assigning a value to each engineering indicator based on the engineering indicators and the corresponding operational capability threshold includes: determining the pressure change curve of the exploratory well point based on the pressure gradient of the area where the exploration target is located; determining the internal pressure coefficient of the exploration target based on the pressure change curve and the maximum pressure of the exploratory well point during the drilling process; and determining the value assigned to the pressure coefficient encountered at the exploratory well point based on the internal pressure coefficient of the exploration target and the pressure operational capability threshold.

[0011] Optionally, the first weighting process for the first score, the second score, and the third score includes: setting the weighting coefficient of the first score to be greater than the weighting coefficient of the third score, and setting the weighting coefficient of the second score to be less than the weighting coefficient of the third score.

[0012] Optionally, the exploration targets include: structural traps, lithological traps, stratigraphic traps, and structural-lithological composite traps.

[0013] On the other hand, the present invention also provides an evaluation system for the feasibility of offshore oil and gas exploration. The evaluation system includes: a first determining device for determining a first score related to the probability of hydrocarbon accumulation of the exploration target based on the hydrocarbon supply intensity, reservoir capacity, hydrocarbon supply window, and capping conditions of the exploration target; a second determining device for determining a second score related to the resource scale of the exploration target based on the estimated target well-controlled resource scale of the exploration target; a third determining device for determining a third score related to the workability of the exploration target based on the engineering indicators of the pre-exploration well points of the exploration target; and a weighted processing device for performing a first weighted processing on the first score, the second score, and the third score to determine a target score for the drillability of the exploration target.

[0014] Through the above technical solution, the present invention provides a method for evaluating the feasibility of marine oil and gas exploration. Compared with existing methods such as multi-exploration element evaluation, it fully considers the probability of oil and gas accumulation of the exploration target, takes into account the economics of marine oil and gas exploration, reasonably evaluates the resource scale and economic value of the exploration target, and combines the difficulty and cost of marine exploration engineering. It can make a more accurate quantitative evaluation of the feasibility of marine exploration, and has the advantages of high credibility, strong operability, and quantification.

[0015] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings:

[0017] Figure 1 This is a flowchart illustrating a method for evaluating the feasibility of offshore oil and gas exploration according to an embodiment of this application;

[0018] Figure 2 This is a schematic diagram illustrating marine tectonic evolution according to an embodiment of this application;

[0019] Figure 3 This is a schematic diagram of the development of drill cores and thin-section fractures of an exploration target according to an embodiment of this application;

[0020] Figure 4 This is a schematic diagram of the core filling of an exploration target according to an embodiment of this application;

[0021] Figure 5 This is a schematic diagram illustrating the hydrocarbon accumulation model of an exploration target according to an embodiment of this application;

[0022] Figure 6 This is a schematic diagram of a marine oil and gas exploration feasibility evaluation system according to an embodiment of this application. Detailed Implementation

[0023] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0024] The applicant discovered that in the process of oil and gas exploration of offshore targets, the economic scale benefits of oil and gas and the exploration and construction costs have a significant impact on the feasibility of exploration. Based on this, embodiments of the present invention provide a method for quantitatively evaluating the exploration feasibility of offshore targets. Specifically, through comprehensive analysis of petroleum geological conditions, the probability of reservoir formation of the exploration targets in the study area is quantitatively evaluated and assigned a value; through oil and gas resource calculation, the resource quantity of the exploration targets in the study area is obtained, and compared with the minimum economic scale reserves obtained under the economic evaluation of the offshore engineering conditions, thereby evaluating and assigning a value to the resource scale; based on the water depth of the pre-exploration well points, the burial depth of the target layer, and pressure conditions of the exploration targets, the difficulty of the project is quantitatively evaluated and assigned a value; after weighting and summing the scores of the assigned values ​​of each indicator, the final score of the exploration feasibility of the offshore target is obtained.

[0025] Method Implementation Examples

[0026] Specifically, this invention first provides a method for evaluating the feasibility of offshore oil and gas exploration, such as... Figure 1 As shown, the evaluation method may include steps S110-S140.

[0027] Step S110: Determine the first score of the exploration target related to the probability of hydrocarbon accumulation based on the hydrocarbon supply intensity, storage capacity, hydrocarbon supply window and capping conditions of the exploration target.

[0028] In one embodiment, exploration targets may include: structural traps, lithological traps, stratigraphic traps, and structural-lithological composite traps. Stratigraphic traps, for example, are ancient buried hills. Ancient buried hills are a type of ancient landform where the Earth's crust, after long-term weathering and erosion following crustal movements, creates an uneven surface. Later, this surface subsided and was covered by Cenozoic sedimentary layers, with the resulting hillocks being called ancient buried hills. The first buried hill oil and gas reservoir discovered worldwide was the Moore County buried hill oil and gas reservoir, accidentally discovered in 1909 during exploration of Cenozoic oil-bearing strata in the Cincinnati Uplift in central Ohio, USA. It featured well-developed fractures and caverns with good connectivity, and the well initially produced approximately 20 tons of oil per day. Subsequently, in Prudhoe Bay, the United States, exploration was conducted using Cretaceous mudstone and shale as caprocks, Mississippian and Pennsylvanian limestone as reservoirs, and Triassic and Permian deltaic sandstone as exploration directions, discovering buried hill oil and natural gas oil-bearing zones with geological reserves exceeding 10 billion barrels each. In 1928, over 1,800 wells were drilled in the Oklahoma region, leading to the discovery of several large and medium-sized ancient buried hill oil fields, more than 30 oil and gas reservoirs of varying sizes, and an estimated oil-bearing area of ​​56 km². 2 .

[0029] For ancient buried hills in the study area, evaluation and assignment can be carried out on four aspects: hydrocarbon supply intensity, reservoir capacity of weathering crust and fractures, hydrocarbon supply window, and capping conditions. In other words, the quantitative evaluation and assignment of the hydrocarbon accumulation probability of ancient buried hills can include: analyzing the hydrocarbon generation and expulsion capacity of hydrocarbon supply centers around the ancient buried hill, determining the reservoir capacity of the weathering crust and fractures of the ancient buried hill, identifying the hydrocarbon supply window between the ancient buried hill and the hydrocarbon generation center, and studying the capping conditions of the ancient buried hill. These constitute the hydrocarbon accumulation probability elements of the ancient buried hill target. The final score of the hydrocarbon accumulation probability is obtained by summing these elements, thus obtaining the first score.

[0030] Specifically, step S110 may include the following steps S111-S115.

[0031] Step S111: Determine the first sub-score of hydrocarbon supply intensity based on the source strata, source rock quality, hydrocarbon generation threshold, and distance between the exploration target and the hydrocarbon generation center.

[0032] Specifically, hydrocarbon supply intensity, also known as hydrocarbon generation intensity, refers to the hydrocarbon generation and expulsion capacity of the hydrocarbon supply center around the exploration target. It can be used to evaluate whether a region has the potential to generate sufficient oil and gas reservoirs.

[0033] For the source strata of the exploration target, stratigraphic tracing can be conducted to construct a sequence stratigraphic framework, thereby clarifying the source strata. In one embodiment, the structural features of the study area are characterized by a graben controlled by reverse faults. Before the Eocene, the paleotectonic setting was characterized by a deep depression and high uplift, with a sedimentary environment of a tidal delta-tidal flat symbiotic sedimentary system under a semi-enclosed bay, forming the coal-bearing source rocks of the Baoshi Formation and Pinghu Formation. Regarding the quality of the source rocks of the exploration target, source rock evaluation can be conducted to clarify the source rock composition, abundance, type, and maturity, as well as the thickness, area, hydrocarbon generation, and intensity, thereby clarifying the source rock quality of the hydrocarbon generation center. For the hydrocarbon generation threshold of the exploration target, basin simulation can be conducted to estimate the hydrocarbon generation and expulsion volume and intensity of the hydrocarbon generation center, thereby calculating the hydrocarbon generation threshold. Furthermore, the distance between the paleohill target and the hydrocarbon generation center can be measured to estimate the hydrocarbon migration and charging efficiency. Using the above parameters and indicators, the hydrocarbon supply intensity of the source rocks can be calculated directly or indirectly.

[0034] For example, a hydrocarbon supply intensity in the range of 1000-2000 is assigned 20 points; 2000-3000 is assigned 30 points; 3000-4000 is assigned 40 points; 4000-5000 is assigned 50 points; 5000-6000 is assigned 60 points; 6000-7000 is assigned 70 points; 7000-8000 is assigned 80 points; 8000-9000 is assigned 90 points; and a hydrocarbon supply intensity greater than 9000 is assigned 100 points.

[0035] In one embodiment, drilling revealed well-developed coal seams and dark mudstone in the Pinghu and Baoshi Formations, with a cumulative thickness of 317-528m for the gray mudstone, and even greater thickness in the upper Pingxia section. Although no large-scale oil and gas discoveries were found in the buried hills of the study area, oil and gas have been discovered in the overlying Eocene Baoshi and Pinghu Formations, and these are already under development, indicating the coexistence of oil and gas. Specifically, the cumulative thickness of single-well coal seams ranges from 17-51m, with widespread distribution from the upper Pingxia section to the Baoshi Formation, and the upper and lower Pingxia sections showing more developed coal seams. The mudstone of the Pinghu Formation is mostly of medium to good quality source rock. The organic matter abundance of the Pinghu Formation source rocks is rated as good to excellent, with TOC mostly greater than 1%. The high organic matter abundance of the Pinghu Formation source rocks in the well area indicates good source rocks. Therefore, it is determined that the oil and gas source is sufficient, the source conditions are good, the hydrocarbon supply intensity is greater than 9000, and there is ample hydrocarbon supply potential. Therefore, a score of 100 can be assigned.

[0036] Step S112: Determine the second sub-score of the reservoir capacity based on the reservoir thickness, fracture distribution area, and porosity of the exploration target.

[0037] For buried hills, their reservoir capacity refers to the reservoir capacity of the weathering crust and fractures. First, it is necessary to analyze the regional tectonic history and stratigraphic evolution history to estimate the time when the buried hill was exposed to the surface. Then, geophysical methods can be used to analyze and predict the reservoir of the buried hill, including the thickness of the weathering crust, the area of ​​fractures, and porosity. Finally, combining the regional stress field and its evolution process, geophysical methods such as ant tracking can be used to predict the degree of fracture development and analyze the fracture development characteristics of the buried hill.

[0038] Specifically, reservoir thickness actually calculates the degree of interlayer development within the buried hill. The greater the reservoir thickness, the more stable the lateral distribution of the interlayers, and the greater the probability that the reservoir being evaluated is a layered reservoir. Statistical analysis of reservoir thickness development in over a dozen developed oilfields in China shows that reservoirs thicker than 5m have a larger lateral distribution of interlayers, increasing the probability of a layered reservoir (30 points); reservoirs thicker between 2-5m have a moderate probability of being layered (60 points); and reservoirs thinner than 2m have a limited lateral distribution area in non-reservoir sections, failing to provide vertical isolation, thus increasing the probability of a blocky reservoir (90 points). Furthermore, the study assigns scores to different porosity indices. For example, a porosity range of 0-5 is assigned a score of 40; a porosity range of 5-10 is assigned a score of 60; a porosity range of 10-15 is assigned a score of 80; and a porosity range of 15-20 is assigned a score of 100. Furthermore, cracks developing into tectonic cracks are assigned a score of 90, weathering cracks are assigned a score of 60, and no cracks are assigned a score of 30.

[0039] In one embodiment, such as Figure 2 As shown, the tectonic evolution indicates that the area roughly went through the Indosinian orogeny, the Yanshanian orogeny, and the Cenozoic alteration and burial stage. The ancient buried hills in the study area have a relatively short exposure time, and the weathering crust is underdeveloped. Drilling has confirmed that the weathering crust is thin and not a primary reservoir space. Geophysical analysis suggests that fractures are well-developed and widely distributed in the ancient buried hills of the study area, such as... Figure 3 As shown, well-developed fractures are also revealed in the drill core and thin sections. However, as... Figure 4 As shown, core samples from wells in the eastern part of the study area reveal that some fractures are filled with calcite, reducing reservoir space. Therefore, the reservoir capacity of the weathering crust and fractures is moderate to poor. Overall, based on the above scoring criteria, a value of b = 60 is assigned.

[0040] Step S113: Determine the third sub-score of the hydrocarbon supply window based on the range and area of ​​the oil and gas supply window of the exploration target.

[0041] Specifically, clarifying the hydrocarbon supply window between ancient buried hills and hydrocarbon generation centers requires analyzing the source-reservoir configuration relationship between the ancient buried hill reservoirs and hydrocarbon generation centers. For example, based on the relationship between the ancient buried hill target and the hydrocarbon generation center, the oil and gas transport channels between them can be studied to clarify the direction and channels of oil and gas migration, thereby determining the range and area of ​​the oil and gas supply window and evaluating the oil and gas transport efficiency.

[0042] In another embodiment, hydrocarbon supply methods can be categorized and scored. The criteria can be as follows: Category a: Direct contact between the source rock and the buried hill reservoir with bidirectional hydrocarbon supply, scored 100 points; Category b: Direct contact between the source rock and the buried hill reservoir with unidirectional hydrocarbon supply via faults and unconformities, scored 90 points; Category c: Direct contact between the source rock and the buried hill reservoir with unidirectional hydrocarbon supply via faults or unconformities, scored 80 points; Category d: Indirect contact between the source rock and the buried hill reservoir with bidirectional hydrocarbon supply, scored 40 points; Category e: Indirect contact between the source rock and the buried hill reservoir with unidirectional hydrocarbon supply via faults and unconformities, scored 30 points; Category f: Indirect contact between the source rock and the buried hill reservoir with unidirectional hydrocarbon supply via faults or unconformities, scored 20 points.

[0043] In one embodiment, the ancient buried hill in the study area is sandwiched between two faults, which are both tectonic control faults and oil source faults. The eastern fault extends to the basement, dips NE-D at an angle of approximately 120°, has a displacement of 40–180 m, and an extension length of approximately 11 km. The northern fault, at a greater depth, extends to the basement, dips NE-D at an angle of approximately 80°, has a displacement of 20–180 m, and a planar extension length of approximately 10.4 km. Figure 5 As shown, due to the presence of the large fault, the ancient buried hill is directly connected to the hydrocarbon generation system, with a large hydrocarbon supply window area and relatively high oil and gas transmission efficiency, and the assigned score c = 90.

[0044] Step S114: Determine the fourth sub-score of the capping condition based on the lithological combination, thickness, and pressure coefficient of the overlying strata of the exploration target.

[0045] The conditions of the overlying strata of the exploration target are another important evaluation factor. Specifically, the study of the capping conditions of ancient buried hills needs to clarify the lithological assemblage, thickness, and pressure coefficient of the overlying strata, characterize the main faults surrounding the ancient buried hill target, and clarify the capping and preservation conditions of the ancient buried hill. For example, the classification criteria for reservoir-caprock combinations are as follows: Type I is a red bed cover below the source, where the source rock and the buried hill reservoir are not in direct contact, resulting in poor hydrocarbon supply conditions, and is therefore assigned a score of 50; Type II is a self-capped source rock, where the overlying strata are effective source rocks, and the buried hill is in direct contact with the source rock, which is most conducive to buried hill hydrocarbon accumulation, and is therefore assigned a score of 90; Type III is an upper Paleocap, mainly covered by Carboniferous-Permian coal-bearing strata, where the Paleogene source rock and the buried hill reservoir are separated, resulting in worse hydrocarbon supply conditions compared to Type I, and is therefore assigned a score of 40; Type IV is an immature mudstone cap above the source, covered by immature mudstone, resulting in poor hydrocarbon supply and preservation conditions, and is less conducive to buried hill hydrocarbon accumulation compared to Type III, and is therefore assigned a score of 20.

[0046] In one embodiment, regarding the top cover layer, two sets of cover layers develop above the buried hill: high-density volcanic clastic sediments and an overlying mudstone layer. The volcanic clastic rocks are inferred to be tuff, tuffaceous mudstone, tuffaceous sandstone, breccia, etc., with dense lithology and a thickness of 20–380 m. The overlying mudstone cover layer has a thickness of 17 m–359 m, gradually increasing in thickness from southwest to northeast, and its sealing capacity gradually strengthens. Therefore, the ancient buried hill in the study area has relatively good sealing conditions, with an assigned score d = 90.

[0047] Step S115: Perform a second weighting process on the first sub-score, the second sub-score, the third sub-score, and the fourth sub-score to determine the first score.

[0048] In the aforementioned hydrocarbon accumulation probability A, the weights of hydrocarbon supply intensity a, weathering crust and fracture storage capacity b, hydrocarbon supply window c, and capping conditions d can be adjusted according to actual production conditions.

[0049] In one embodiment, step S115 may include: setting the weighting coefficient of the second sub-score to the maximum and the weighting coefficient of the fourth sub-score to the minimum. For example, setting the weighting coefficient of the second sub-score to 0.4, the weighting coefficient of the fourth sub-score to 0.1, and the weighting coefficients of the fourth sub-score to 0.2 and 0.3 respectively. Then, multiplying the scores of the four indicators by their respective weights to obtain the evaluation formula for the first score:

[0050] A = 0.2a + 0.4b + 0.3c + 0.1d

[0051] Then, combining the weighting assignments mentioned above, calculations are performed to determine the first score related to the probability of hydrocarbon accumulation in the ancient buried hill: A = 0.2*100 + 0.4*60 + 0.3*90 + 0.1*90 = 80. The final score after weighting is then calculated.

[0052] It is worth noting that there is a considerable amount of research on hydrocarbon accumulation probability in this field, so other methods of existing technology can also be used to assign values ​​to the first score. Specifically, for the evaluation criteria of the four parameters—hydrocarbon supply intensity, reservoir capacity, hydrocarbon supply window, and capping conditions—different methods of assigning values ​​can be used according to actual geological conditions, referring to existing technologies. This invention is only used as an example and is not intended to limit the scheme.

[0053] Step S120: Determine the second score of the exploration target related to resource reserves based on the well-controlled oil and gas scale of the exploration target.

[0054] In one embodiment, step S120 may include:

[0055] Step S121: Based on the target reservoir thickness, oil and gas area and porosity of the exploration target, determine the well-controlled oil and gas resources of the pre-exploration well points using the volumetric method.

[0056] Specifically, the size of the fracture reservoir can be estimated by predicting the thickness, area, and porosity of the weathering crust, and then the volumetric method can be used to estimate the well-controlled oil and gas resources at the exploratory wells.

[0057] Step S122: Determine the baseline equilibrium production of the exploration target based on the construction cost, production ratio, and standard unit price of oil and gas in the area where the exploration target is located.

[0058] Specifically, based on existing facilities, a reasonable development project plan can be formulated, and the investment costs for drilling and completion during the exploration and development phases, i.e., construction costs, can be calculated. Then, based on the predicted cumulative oil and gas production and future gas prices, the internal rate of return can be calculated, the benchmark equilibrium production can be estimated, and the minimum economic scale reserves can be calculated.

[0059] Step S123: If the well-controlled oil and gas resources are greater than or equal to the benchmark balanced production, the second score is set to 100%.

[0060] Step S124: When the well-controlled oil and gas resources are less than the benchmark balanced production, the ratio of the well-controlled oil and gas resources to the benchmark balanced production is determined as the second score.

[0061] In other words, the resource quantity of the exploration target in the study area is obtained through the oil and gas resource calculation in step S121, and compared with the minimum economic scale reserve obtained from the economic evaluation under marine engineering conditions in step S122. Next, based on the relative size relationship between the well-controlled oil and gas resource quantity at the exploratory well points and the minimum economic scale reserve, the resource scale is evaluated and assigned a value, and the target oil and gas resource scale of the exploration target is scored to obtain a second score.

[0062] In one embodiment, geophysical methods are first used to predict the thickness, area, and porosity of the weathering crust, and the size of the fracture reservoir space is estimated. The volumetric method is then used to estimate the well-controlled oil and gas resources at the exploratory well sites. For example, it is estimated that the resource reserves in a certain ancient buried hill area exceed 80 billion cubic meters. Then, based on existing platforms, pipelines, and constructed facilities, an integrated exploration and development evaluation is conducted. A baseline balanced production of 4.5 billion cubic meters of natural gas can cover economic costs. Assuming a recovery rate of 55%, the minimum economically viable reserve needs to reach 8.2 billion cubic meters.

[0063] Therefore, the estimated oil and gas reserves of 80 billion cubic meters for this ancient buried hill area far exceed the lower limit of 8.2 billion cubic meters for economic development. Thus, the second score related to resource reserves for the buried hill resource scale in this study area is assigned a value of 100%, i.e., a maximum score of 100 points.

[0064] Step S130: Determine the third score related to the constructability of the exploration target based on the engineering indicators of the pre-exploration well points of the exploration target.

[0065] In one embodiment, step S130 may include:

[0066] Step S131: Assign a value to each engineering indicator based on the engineering indicator and the corresponding operational capability threshold.

[0067] In one embodiment, the engineering parameters may include the water depth of the exploratory well and the burial depth of the target layer at the exploratory well. In this case, step S131 may include:

[0068] 1) Determine the seabed time depth at the pre-exploration well point and the time depth of the main target layer at the pre-exploration well point by using the seismic profile of the exploration target.

[0069] 2) Determine the water depth of the exploratory wells and the burial depth of the target layer by using the velocity model, seabed time depth and the time depth of the main target layer.

[0070] 3) Determine the water depth value for the exploratory wells based on the water depth and water depth operation capability threshold.

[0071] 4) Determine the target layer burial depth of the pre-exploration well point based on the target layer burial depth and drilling depth operation capability threshold.

[0072] Specifically, in step S131, firstly, the seabed time depth at the pre-exploration well point can be obtained using seismic profiles, and converted into seawater depth using a velocity model, thereby determining whether the well is a shallow or deep-water exploration well. Secondly, again using seismic profiles, the time depth of the main target layer at the pre-exploration well point can be obtained, and converted into depth values ​​using a velocity model, thus clarifying the burial depth of the target layer.

[0073] In one embodiment, the water depth at the location of the exploratory well in the buried hill in the study area is 90m, which is a shallow water area. Based on the current operational capabilities of marine exploration vessels, the water depth operation threshold is set at 100m. Therefore, the operational technology at this water depth is mature, and a full score w = 100 is assigned. If the water depth at the exploratory well location exceeds 100m, the construction depth assignment needs to be calculated based on the extreme construction water depth threshold, for example, 150m. In the case of depths exceeding 150m, the assignment is 0, meaning that construction is not possible or requires more resources. Between 100-150m, the assignment w can be calculated based on the detected water depth H according to the following formula:

[0074]

[0075] Where H2 is the limit water depth threshold for construction and H1 is the water depth operation capability threshold.

[0076] Meanwhile, the exploratory well encountered the top of an ancient buried mountain at a depth of 4600m, which is relatively deep, about 200m deeper than the industry's conventional drilling depth of 4400m. Therefore, the value of h is assigned as 80. The specific calculation can be based on the top surface depth M, using the following formula to calculate the assigned value of h:

[0077]

[0078] Where M2 is the ultimate drilling depth threshold, for example, 5400m, and M1 is the drilling depth operation capacity threshold, for example, 4400m.

[0079] In one embodiment, the engineering parameters may further include the pressure coefficient encountered at the exploratory well site, and step S131 may include:

[0080] 1) Determine the pressure change curve of the pre-exploration well point based on the pressure gradient of the area where the exploration target is located.

[0081] 2) Determine the internal pressure coefficient of the exploration target based on the pressure change curve and the maximum pressure at the exploratory well point during the drilling process.

[0082] 3) Determine the value of the pressure coefficient encountered at the pre-exploration well point based on the internal pressure coefficient of the exploration target and the pressure operation capacity threshold.

[0083] Specifically, in step S131, the pressure gradient of the area can be calculated using the surrounding drilled wells, the pressure change curve of the exploratory well can be estimated, and the maximum pressure during the drilling process can be read to determine whether it belongs to the high-pressure exploratory well.

[0084] In one embodiment, the prediction results show that the formation begins to pressurize at 4000m, and the pressure coefficient at 4600m exceeds 1.5, falling into the overpressure category. Specifically, the pressure coefficient P inside the buried hill drops to around 1.2. The specific calculation can be performed by assigning a value to p using the following formula:

[0085] p = (2-P) × 100

[0086] Therefore, the pressure index is assigned a value of p = 80.

[0087] Step S132: Perform a third weighting process on the assigned values ​​of each engineering indicator to determine the third score.

[0088] Furthermore, the water depth, target layer burial depth, and pressure conditions can be studied and understood, and evaluated and assigned values ​​based on industry experience. For example, the weight of the water depth at the exploratory well point can be set to 0.2, the weight of the target layer burial depth at the exploratory well point to 0.3, and the weight of the pressure coefficient encountered at the exploratory well point to 0.5, thereby determining the calculation formula as follows:

[0089] E = 0.2 * w + 0.3 * h + 0.5 * p

[0090] Then, combining the assigned scores mentioned above, the third score related to constructability of the ancient buried hills in the study area is calculated to be: E = 0.2*100 + 0.3*80 + 0.5*80 = 84.

[0091] Step S140: Perform a first weighted processing on the first score, the second score, and the third score to determine the target score for the drillability of the exploration target.

[0092] In this process, based on the importance of each indicator to oil and gas exploration and development, the target accumulation probability, resource scale, and total engineering difficulty score of the exploration target should be assigned values ​​respectively.

[0093] In one embodiment, step S140 may include:

[0094] Step S141: Set the weighting coefficient of the first score to be greater than the weighting coefficient of the third score, and set the weighting coefficient of the second score to be less than the weighting coefficient of the third score.

[0095] For example, the weighting coefficient for the first score is greater than that for the third score, and the weighting coefficient for the second score is less than that for the third score. Specifically, based on the importance of each indicator to oil and gas exploration and development, the total scores for the probability of formation (A), resource size (R), and engineering difficulty (E) of the ancient buried hill target are assigned 50, 20, and 30 points, respectively. Then, the scores for the probability of formation, resource size, and engineering difficulty of the ancient buried hill target are added together to obtain the final score, thus completing the quantitative evaluation of the drillability of the ancient buried hill target in the sea area.

[0096] In summary, in the embodiments provided in this application, the weighted scores of each indicator are accumulated as follows: In the hydrocarbon accumulation probability A, the weights of the four indicators—hydrocarbon supply intensity (a), weathering crust and fracture storage capacity (b), hydrocarbon supply window (c), and capping conditions (d)—are 20%, 40%, 30%, and 10%, respectively. Each indicator's score is multiplied by its respective weight, and the final score is calculated after weighting. The calculation formula is:

[0097] A = 0.2a + 0.4b + 0.3c + 0.1d

[0098] In the engineering difficulty E, the weights of seawater depth w, target layer burial depth h, and pressure condition p are 20%, 30%, and 50%, respectively. The scores of each indicator are multiplied by their respective weights to calculate the final score after weighting. The calculation formula is:

[0099] E = 0.2 * w + 0.3 * h + 0.5 * p

[0100] Preferably, the scores for the probability of reservoir formation, resource scale, and engineering difficulty of the ancient buried hill target are added together to obtain the final score G, thus completing the quantitative evaluation of the drillability of the ancient buried hill target in the sea area. The calculation formula is:

[0101] G = 0.5 * A + 0.2 * R + 0.3 * E

[0102] =0.5*(0.2*a+0.4*b+0.3*c+0.1*d)+0.2*R+0.3*(0.2*w+0.3*h+0.5*p)

[0103] = 0.5*80 + 0.2*100 + 0.3*84

[0104] =85.2

[0105] That is, the final score for the drillability of the ancient buried hill target in the study area was 85.2.

[0106] Furthermore, when there is only one marine exploration target, a higher evaluation score indicates stronger drillability. The specific limits of drillability need to be defined based on actual exploration experience. When there are multiple marine exploration targets, the scores of both can serve as important references, with the target with the higher score being preferred for drilling. Therefore, this invention can be applied to more scenarios.

[0107] Through the above technical solution, the present invention provides a method for evaluating the feasibility of offshore oil and gas exploration. Compared with existing methods such as multi-exploration element evaluation (e.g., considering porosity assignment, permeability assignment, weathering and leaching time assignment, hydrocarbon supply method assignment, reservoir-seal combination type assignment, source rock hydrocarbon generation intensity assignment, and determining the height of the hydrocarbon supply window), the present invention not only fully considers the probability of oil and gas accumulation of the exploration target, but also takes into account the economics of offshore oil and gas exploration, reasonably evaluates the resource scale and economic value of the exploration target, and combines the difficulty and cost of offshore exploration engineering to make a more accurate quantitative evaluation of the feasibility of offshore exploration. It has the advantages of high credibility, strong operability, and quantification.

[0108] Therefore, this invention enables integrated geological and engineering analysis of exploration targets in marine areas. Taking the feasibility analysis of ancient buried hill exploration in a certain marine area as an example, the specific technical solution of this invention is illustrated, and its exploration feasibility is quantitatively evaluated. This provides an important reference when selecting the best exploration target from multiple options. This invention can indirectly improve the success rate of oil and gas exploration and the subsequent oil and gas recovery rate, effectively overcoming various shortcomings of existing technologies and possessing high industrial application value.

[0109] Device Examples

[0110] On the other hand, the present invention also provides an evaluation system 200 for the feasibility of offshore oil and gas exploration, such as... Figure 6 As shown, the evaluation system 200 may include:

[0111] The first determining device 210 is used to determine a first score related to the hydrocarbon accumulation probability of the exploration target based on the hydrocarbon supply intensity, storage capacity, hydrocarbon supply window and capping conditions of the exploration target.

[0112] The second determining device 220 is used to determine a second score related to the resource size of the exploration target based on the target well-controlled resource size estimate of the exploration target.

[0113] The third determining device 230 is used to determine a third score related to the workability of the exploration target based on the engineering indicators of the pre-exploration well points of the exploration target.

[0114] The weighted processing device 240 is used to perform a first weighted processing on the first score, the second score, and the third score to determine the target score of the drillability of the exploration target.

[0115] Optionally, the first determining device 210 may further include: a first sub-score determining module, used to determine a first sub-score of hydrocarbon supply intensity based on the source strata, source rock quality, hydrocarbon generation threshold, and distance between the exploration target and the hydrocarbon generation center; a second sub-score determining module, used to determine a second sub-score of reservoir capacity based on the reservoir thickness, fracture distribution area, and porosity of the exploration target; a third sub-score determining module, used to determine a third sub-score of the hydrocarbon supply window based on the range and area of ​​the oil and gas supply window of the exploration target; a fourth sub-score determining module, used to determine a fourth sub-score of capping conditions based on the lithological assemblage, thickness, and pressure coefficient of the overlying strata of the exploration target; and a sub-score weighting processing module, used to perform a second weighting processing on the first sub-score, second sub-score, third sub-score, and fourth sub-score to determine the first score.

[0116] Optionally, the sub-score weighting processing device can also be used to: set the weighting coefficient of the second sub-score to the maximum and the weighting coefficient of the fourth sub-score to the minimum.

[0117] Optionally, the second determining device 220 may further include: a resource quantity determining module, used to determine the well-controlled oil and gas resources of the pre-exploration well point using the volumetric method based on the target reservoir thickness, oil and gas-bearing area and porosity of the exploration target; a balanced production determining module, used to determine the benchmark balanced production of the exploration target based on the construction cost, production ratio and standard unit price of oil and gas in the area where the exploration target is located; and a second score determining module, used to perform the following functions: when the well-controlled oil and gas resources are greater than or equal to the benchmark balanced production, the second score is determined as 100%; and when the well-controlled oil and gas resources are less than the benchmark balanced production, the ratio of the well-controlled oil and gas resources to the benchmark balanced production is determined as the second score.

[0118] Optionally, the third determining device 230 can also be used to: assign a value to each engineering indicator based on the engineering indicator and the corresponding operational capability threshold; and perform a third weighting process on the assigned value of each engineering indicator to determine a third score.

[0119] Optionally, if the engineering indicators include the water depth of the exploratory well and the burial depth of the target layer at the exploratory well, then the third determining device 230 can also be used to: determine the seafloor time depth and the time depth of the main target layer at the exploratory well using the seismic profile of the exploration target; determine the water depth of the exploratory well and the burial depth of the target layer at the exploratory well using the velocity model, the seafloor time depth, and the time depth of the main target layer; determine the water depth assignment of the exploratory well based on the water depth of the exploratory well and the water depth operation capability threshold; and determine the target layer burial depth assignment of the exploratory well based on the burial depth of the target layer and the drilling depth operation capability threshold.

[0120] Optionally, the engineering indicators also include the pressure coefficient encountered at the exploratory well point. In this case, the third determining device 230 can also be used to: determine the pressure change curve of the exploratory well point based on the pressure gradient of the area where the exploration target is located; determine the internal pressure coefficient of the exploration target based on the pressure change curve and the maximum pressure of the exploratory well point during the drilling process; and determine the value assigned to the pressure coefficient encountered at the exploratory well point based on the internal pressure coefficient of the exploration target and the pressure operation capability threshold.

[0121] Optionally, the weighting processing device 240 can also be used to: set the weighting coefficient of the first score to be greater than the weighting coefficient of the third score, and set the weighting coefficient of the second score to be less than the weighting coefficient of the third score.

[0122] Optionally, exploration targets include: structural traps, lithological traps, stratigraphic traps, and structural-lithological composite traps.

[0123] Through the above technical solution, the present invention provides a method for evaluating the feasibility of marine oil and gas exploration. Compared with existing methods such as multi-exploration element evaluation, it fully considers the probability of oil and gas accumulation of the exploration target, takes into account the economics of marine oil and gas exploration, reasonably evaluates the resource scale and economic value of the exploration target, and combines the difficulty and cost of marine exploration engineering. It can make a more accurate quantitative evaluation of the feasibility of marine exploration, and has the advantages of high credibility, strong operability, and quantification.

[0124] Therefore, this invention enables integrated geological and engineering analysis of targets within a marine area. Taking the feasibility analysis of ancient buried hill exploration in a certain marine area as an example, the specific technical solution of this invention is illustrated, and its exploration feasibility is quantitatively evaluated. This provides an important reference when selecting the best exploration target from multiple options. This invention can indirectly improve the success rate of oil and gas exploration and the subsequent oil and gas recovery rate, effectively overcoming various shortcomings of existing technologies and possessing high industrial application value.

[0125] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0126] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A method for evaluating the feasibility of offshore oil and gas exploration, characterized in that, The evaluation methods include: Based on the hydrocarbon supply intensity, storage capacity, hydrocarbon supply window and capping conditions of the exploration target, determine the first score of the exploration target related to the probability of hydrocarbon accumulation; Based on the well-controlled oil and gas scale of the exploration target, a second score related to the resource reserves of the exploration target is determined; Based on the engineering parameters of the pre-exploration well points of the exploration target, determine the third score related to the constructability of the exploration target; and The first score, the second score, and the third score are subjected to a first weighting process to determine the target score for the drillability of the exploration target.

2. The evaluation method according to claim 1, characterized in that, The determination of the first score related to the hydrocarbon accumulation probability of the exploration target based on its hydrocarbon supply intensity, reservoir capacity, hydrocarbon supply window, and capping conditions includes: The first sub-score of the hydrocarbon supply intensity is determined based on the source strata, source rock quality, hydrocarbon generation threshold, and distance between the exploration target and the hydrocarbon generation center. The second sub-score of the reservoir capacity is determined based on the reservoir thickness, fracture spread area, and porosity of the exploration target. The third sub-score of the hydrocarbon supply window is determined based on the range and area of ​​the oil and gas supply window of the exploration target. The fourth sub-score of the capping condition is determined based on the lithological combination, thickness, and pressure coefficient of the overlying strata of the exploration target. A second weighting process is applied to the first sub-score, the second sub-score, the third sub-score, and the fourth sub-score to determine the first score.

3. The evaluation method according to claim 2, characterized in that, The second weighting process for the first sub-score, the second sub-score, the third sub-score, and the fourth sub-score includes: Set the weighting coefficient of the second sub-score to the maximum and the weighting coefficient of the fourth sub-score to the minimum.

4. The evaluation method according to claim 1, characterized in that, The determination of the second score related to resource reserves of the exploration target based on the well-controlled oil and gas scale of the exploration target includes: Based on the target reservoir thickness, oil and gas area and porosity of the exploration target, the well-controlled oil and gas resources of the pre-exploration well points are determined using the volumetric method. The baseline equilibrium production of the exploration target is determined based on the construction cost, recovery rate, and standard unit price of oil and gas in the area where the exploration target is located. When the well-controlled oil and gas resources are greater than or equal to the benchmark balanced production, the second score is determined to be 100%; and When the amount of well-controlled oil and gas resources is less than the benchmark balanced production, the ratio of the amount of well-controlled oil and gas resources to the benchmark balanced production is determined as the second score.

5. The evaluation method according to claim 1, characterized in that, The determination of the third score related to the workability of the exploration target based on the engineering indicators of the pre-exploration well points of the exploration target includes: Each engineering indicator is assigned a value based on the engineering indicator and the corresponding operational capability threshold; and The values ​​of each engineering indicator are then subjected to a third weighting process to determine the third score.

6. The evaluation method according to claim 5, characterized in that, The engineering indicators include the water depth of the exploratory wells and the burial depth of the target layer at the exploratory wells. Assigning values ​​to each engineering indicator based on the engineering indicators and the corresponding operational capability thresholds includes: The seafloor time depth at the pre-exploration well point and the time depth of the main target layer at the pre-exploration well point are determined by the seismic profile of the exploration target. The water depth of the pre-exploration well and the burial depth of the target layer of the pre-exploration well are determined by using the velocity model, the seabed time depth, and the time depth of the main target layer. Based on the water depth and water depth operation capability threshold of the pre-exploration well points, determine the assigned water depth value for the pre-exploration well points; and The target layer burial depth of the pre-exploration well point is assigned a value based on the target layer burial depth and drilling depth operation capability threshold of the pre-exploration well point.

7. The evaluation method according to claim 6, characterized in that, The engineering indicators also include the pressure coefficient encountered at the exploratory well points. Assigning values ​​to each engineering indicator based on the engineering indicators and the corresponding operational capability threshold includes: Based on the pressure gradient of the area where the exploration target is located, determine the pressure change curve of the pre-exploration well point; Based on the pressure change curve and the maximum pressure at the pre-exploration well point during drilling, the internal pressure coefficient of the exploration target is determined; and The pressure coefficient encountered at the pre-exploration well point is assigned a value based on the internal pressure coefficient of the exploration target and the pressure operation capacity threshold.

8. The evaluation method according to claim 1, characterized in that, The first weighting process for the first score, the second score, and the third score includes: The weighting coefficient of the first score is set to be greater than the weighting coefficient of the third score, and the weighting coefficient of the second score is set to be less than the weighting coefficient of the third score.

9. The evaluation method according to claim 1, characterized in that, The exploration targets include: structural traps, lithological traps, stratigraphic traps, and structural-lithological composite traps.

10. A feasibility evaluation system for offshore oil and gas exploration, characterized in that, The evaluation system includes: The first determining device is used to determine a first score of the exploration target related to the probability of hydrocarbon accumulation based on the hydrocarbon supply intensity, storage capacity, hydrocarbon supply window and capping conditions of the exploration target. The second determining device is used to determine a second score related to the resource size of the exploration target based on the target well-controlled resource size estimate of the exploration target; The third determining device is used to determine a third score related to the workability of the exploration target based on the engineering indicators of the pre-exploration well points of the exploration target; and A weighted processing device is used to perform a first weighted processing on the first score, the second score, and the third score to determine the target score of the drillability of the exploration target.

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