(China Petroleum Exploration and Development Research Institute, Beijing 100083)
Based on the observation, measurement and sampling analysis of outcrop profiles of Lower Cambrian in Meitan County, Zunyi City, Leshan City, Guizhou Province, Yanwanqiao Town, Hefeng County, Hubei Province, and Yonghe County, Guizhou Province, as well as the review of old wells such as Shenfang 1 Well and Xian 2/Well and the analysis of drilling effect of Huangye 1 Well, the black shale of Lower Cambrian in southeast Sichuan, western Hubei and eastern Chongqing was studied. According to the Evaluation of Shale Gas Resources Potential and Optimization Method of Favorable Areas issued by the Oil and Gas Resources Strategic Research Center of the Ministry of Land and Resources, it is predicted that the favorable development zones of Lower Cambrian shale gas reservoirs are mainly located in the southwest and northeast of the study area. The former is located in the south of Xuyong-Gu Lin-Xishui-Dingshan 1 line, mainly including Renhuai block in northern Guizhou and Qijiangnan block, while the latter mainly refers to the southeast of An-Daozhen-Pengshui-Lichuan line, mainly including Hunan. The geological resources in favorable areas are (1.06 ~ 6.47) ×10/2m3 (median is 3.09 ×10/2m3), and the recoverable resources are (0.12m3).
Shale gas accumulation conditions, favorable resource potential areas, Lower Cambrian in southeastern Sichuan, western Hubei and eastern Chongqing.
Shale gas accumulation conditions of Lower Cambrian in southeastern Sichuan, western Hubei and eastern Chongqing.
Nie Haikuan, Bao, Bian, Yu Chuan (China Petrochemical Exploration and Development Research Institute, Beijing 100083)
Based on the observation, sampling and laboratory analysis of black shale outcrops and drilling in southeastern Sichuan, western Hubei and eastern Chongqing, the sedimentary facies, organic matter type and content, maturity, distribution, porosity and gas content of lower CAMBRIAN black shale are studied. Compared with the main gas-producing shales in the United States, the Lower Cambrian shales in southeastern Sichuan, western Hubei and eastern Chongqing have great thickness, high organic carbon content, high maturity and high gas content, and have good geological conditions for shale gas reservoir development. According to the Method of Shale Gas Resource Potential Evaluation and Favorable Area Optimization issued by the Oil and Gas Resources Strategic Research Center of the Ministry of Land and Resources, it is considered that the most favorable areas for shale gas accumulation in Lower Cambrian shale are the southwest and northeast of the study area by using the method of comprehensive information superposition. According to the measured gas content, the geological resources of shale gas in Lower Cambrian are calculated by volume method as (1.06 ~ 6.47) ×10/2m3 (the median value is 3.09×10/2m3), and the recoverable resources are.
Keywords Lower Cambrian; Shale gas; Accumulation conditions; Resource potential; Shale gas favorable area; Southeast of Sichuan, west of Hubei and east of Chongqing
Fund projects: national special projects "National Survey and Evaluation of Strategic Selection of Oil and Gas Resources" and "National Survey and Evaluation of Shale Gas Resources Potential and Optimization of Favorable Areas" (No.:2009 GYXQ- 15).
The geological conditions of Lower Paleozoic in Sichuan Basin and its surrounding areas are unique, comparable to those in the eastern basin of the United States, and it is a key area for shale gas exploration in southern China [1-3]. The Lower Cambrian black shale in Sichuan Basin and its surrounding areas has the characteristics of large thickness, high organic carbon content and high maturity, and has good shale gas development conditions. Different scholars have done some research in this field [1 ~ 7]. The author thinks that the most favorable development areas of Lower Cambrian shale gas reservoirs in Sichuan Basin and its surrounding areas are located in southern Sichuan-northern Guizhou-central Guizhou, western Hubei-eastern Chongqing and northeastern Sichuan [8]. On the basis of the previous period, this study studied the combination of two favorable areas for shale gas development in southeastern Sichuan-western Hubei and eastern Chongqing according to the principle of predicting favorable areas from large to small, so as to achieve the purpose of more accurately predicting favorable areas for shale gas development and provide reference suggestions for exploration.
1 shale development characteristics
1. 1 shale distribution
The Lower Cambrian black shale mainly developed in Meishucun and Qianzhusi periods, corresponding to the low-energy environment corresponding to the maximum flooding surface, including Jiulao Cavern Formation in southern Sichuan, Qianzhusi Formation in northern Sichuan, Niutitang Formation in Guizhou-western Hunan, Shuijingtuo Formation in western Hubei and Tianzhu Mountain Formation in western Hunan. The distribution is stable, and the lithology is mainly black shale, carbonaceous shale, carbonaceous shale, nodular phosphorite and silty sand.
The shale development characteristics of 1. 1. 1 in the vertical direction.
Lithology changes greatly in the vertical direction. From bottom to top, the thickness of siliceous shale and carbonaceous shale decreases, while the thickness of gray-black shale and silty shale increases until it is completely transformed into gray silty shale and gray shale. Meiziwan section, Meitan County, Guizhou Province, is 27.9 meters thick (figure 1), with siliceous rocks at the bottom and carbonaceous shale and silty shale at the upper transition. In the Qingkou section of Jinsha, Guizhou, the measured thickness of black shale is 65m. The section of Yonghe Niutitang Formation in Weng 'an County, Guizhou Province has siliceous rocks at the bottom and carbonaceous shale and silty shale at the upper part, with the measured thickness of15438+07.5438+0m; The measured thickness of the section of Shuijingtuo Formation of Lower Cambrian in Yanwanqiao, Wuli Town, Hefeng County, Hubei Province is 87.6m (Figure 2).
1) The black shale profile of Niutitang Formation of Lower Cambrian in Meiziwan, Meitan County, Guizhou Province is as follows:
Oil and gas accumulation theory and exploration and development technology: Proceedings of Postdoctoral Academic Forum of China Petrochemical Petroleum Exploration and Development Research Institute 20 1 1. 4
Figure 1 Black shale profile of Niutitang Formation of Lower Cambrian in Meiziwan, Meitan County, Guizhou Province (measured thickness is 27.9 meters)
2) The profile of Shuijingtuo Formation of Lower Cambrian in Yanwanqiao, Wuli Town, Hefeng County, Hubei Province is as follows:
Oil and gas accumulation theory and exploration and development technology: Proceedings of Postdoctoral Academic Forum of China Petrochemical Petroleum Exploration and Development Research Institute 20 1 1. 4
The plane distribution characteristics of 1. 1.2
Planarly, shale is mainly developed in southern Sichuan-northern Guizhou-central Guizhou-western Hunan and Hubei-eastern Chongqing. This set of black shale is not developed in the Middle Paleozoic uplift area of Sichuan, but widely distributed in other areas, with the thickness generally between 20- 120m, and most areas are larger than 100m (Figure 3). The thickness of Zigong-Yibin-Luzhou-Weixin area in southern Sichuan-northern Guizhou is between 40 ~ 100 m, the thickness center is in Gongxian-Weixin area, and the thickness near the uplift in central Guizhou is between 40 ~120 m. For example, the measured thickness of the black shale section of Yonghe Niutitang Formation in Weng 'an County, Guizhou Province is 16544. The thickness of Enshi-Xiushan-Sangzhi area in western Hubei-eastern Chongqing is more than100m ... Specific to the study area, the lower CAMBRIAN black shale is mainly developed in the southwest and northeast of the study area, that is, Gu Lin-Bijie-Renhuai area, with a thickness of more than 60m and Enshi-Qianjiang area with a thickness of more than 80m. Generally speaking, the Lower Cambrian black shale in the study area has the characteristics of large thickness and wide distribution.
Fig. 2 Black shale profile of Shuijingtuo Formation of Lower Cambrian in Yanwanqiao, Wuli Town, Hefeng County, Hubei Province (measured thickness is 87.6m).
1.2 Types and contents of organic matter
The experimental results show that the values of IH and H/C are less than 50 and 0.5, respectively, which makes it difficult to accurately calibrate kerogen with different parent materials. Kerogen δ 13C can reflect the characteristics of primitive biological parent material, and the isotope mark of primitive biological parent material will not be seriously covered by the secondary isotope fractionation effect, which is generally considered as an effective index to classify the organic matter types of high-over mature source rocks [9 ~ 1 1]. According to the isotopic analysis of 22 samples, the δ 13C of lower CAMBRIAN black shale is -35.9 ‰ ~-29.5 ‰, with an average of -32.6‰. According to the standard that kerogen carbon isotope less than -28‰ is sapropelic type (type I), the organic matter type of Lower Cambrian black shale is sapropelic type (type I).
On the plane, because the sedimentary environment is the main factor to control the organic carbon content, the area with the highest organic carbon content is usually the sedimentary center of shale, forming two areas with high organic carbon value: southern Sichuan-northern Guizhou-central Guizhou and western Hunan and Hubei. The Weixin-Bijie-Guiyang area in southern Sichuan-northern Guizhou-central Guizhou is a high-value area, and the maximum organic carbon content in some areas exceeds 5%. For example, the measured organic carbon content of black shale in Qingkou Village, Jinsha County, Guizhou Province is 5.35%. Yichang-Wufeng-Hefeng-Xianfeng-Longshan-Youyang-Dejiang area in western Hunan and Hubei is a high-value area, and the organic carbon content in some areas can reach more than 5%. For example, the measured organic carbon content of black shale in Songtao Shichang, Guizhou Province and Ying Tao, Jiangkou, Guizhou Province is as high as 8.55% and 6.37% respectively (Figure 4).
Fig. 3 Isothickness map of Lower Cambrian black shale in southeastern Sichuan, western Hubei and eastern Chongqing.
Fig. 4 Isograms of organic carbon content of Lower Cambrian black shale in southeastern Sichuan, western Hubei and eastern Chongqing.
1.3 maturity and thermal evolution history
The evolution degree of Lower Cambrian black shale is generally high. On the plane, the maturity forms two high-value areas, namely, near the Dingshan 1 well area at the junction of Chongqing and Guizhou and near Fangshan 1 well area in Dafang County, with the maturity exceeding 4% and the maturity exceeding 5% in some areas. In most other areas, the maturity is above 3%, which is in the late stage of over-maturity (Figure 5), reaching the metamorphic stage and losing the vitality. However, according to the experience of shale gas exploration in the United States, shale gas reservoirs can also be developed under high maturity conditions, but their reservoir-forming conditions are complex and need to be studied according to the structural evolution history and hydrocarbon generation and expulsion history of shale.
Fig. 5 Isograms of maturity of Lower Cambrian black shale in southeastern Sichuan, western Hubei and eastern Chongqing.
The study area can be divided into four structural units, namely, the high-steep fold area in eastern Sichuan, the middle-low structural belt in southern Sichuan, the uplift and Renhuai slope in central Guizhou, and the fold belt in western Hunan and Hubei. The buried history of shale in different structural units is quite different. The evolution history of shale should be analyzed according to the specific problems of different structural units. In view of the lack of data on Renhuai slope, the evolution history of shale should be determined with reference to the uplift in central Guizhou. Lichuan syncline, central syncline, Huaguoping syncline, Yidu-Hefeng syncline and Sangzhi-Shimen syncline in the western Hunan-Hubei fold belt are similar in evolution history, so they are classified into one category for study.
1.3. 1 high and steep fold area in eastern Sichuan
There are many wells in this area, taking well Chi 7 of Dachi dry well structure in the north of this area as an example. The thermal evolution of upper Ordovician-lower Silurian black shale is very slow from deposition to late Permian, and it is in immature-low mature stage (RO < 0.5%). The buried depth of Middle Permian made it enter the stage of liquid hydrocarbon generation. After the Middle Jurassic, the Silurian system was in a state of rapid burial, and the maturity (Ro) value rapidly evolved from 1.3% to 2.2%, and the organic matter evolved to high maturity, which was in the stage of water transformation. Since Cretaceous, the maturity (Ro) of Silurian shale in most areas has exceeded 3% [12], and it is in the late stage of over-maturity, mainly producing dry gas (Figure 6). It belongs to long-term shallow burial-rapid burial-long-term deep burial-rapid uplift type, which is similar to the evolution history of Barnett shale in Fort Worth Basin, where shale gas production is the largest in the United States at present.
Fig. 6 Silurian burial history of well Chi 7 in Dachiganjing structure, eastern Sichuan [12]
1.3.2 low-moderate structural belt in southern Sichuan.
Shale in this area belongs to the type of early long-term shallow burial-middle early long-term uplift-middle deep burial-late rapid uplift, that is, the Lower Cambrian shale reached its maximum burial depth at the end of Silurian, but the depth was basically less than 2000m, with low maturity and limited hydrocarbon generation and expulsion capacity. Then it experienced uplift and stopped hydrocarbon generation for a long time in the early Triassic. After the Middle Triassic, it experienced the second burial and reached the stage of gas generation. After the middle Cretaceous, it began to rise rapidly and hydrocarbon generation stopped. Long-term shallow burial and long-term uplift in the middle and early stage are beneficial to the preservation of organic matter, rapid burial in the middle stage is beneficial to the generation of natural gas, and rapid uplift in the later stage is not conducive to the discharge of natural gas and the accumulation of shale gas. For example, at the end of Silurian, the buried depth of the Cambrian bottom boundary of Well Wei 2 in southern Sichuan reached 2000m, and the Ro value reached 0.8%, resulting in a small amount of crude oil. Then, due to the overall uplift of the stratum, the hydrocarbon generation process stopped and it was quickly buried since Indosinian. Triassic was the second hydrocarbon generation stage. By the middle Cretaceous, the buried depth of the Cambrian bottom boundary was over 6000 m, and the Ro value was over 2%, which entered the early stage of over-maturity, and began to rise rapidly after the middle Cretaceous. The burial history and thermal evolution history of this type are similar to those of barnett shale gas reservoir in Fort Worth Basin, USA. Both the Lower Silurian black shale and the Lower Carboniferous Barnett shale have the characteristics of early hydrocarbon generation (even no hydrocarbon generation)-late hydrocarbon generation-long-term burial-rapid uplift. The former started hydrocarbon generation in the Middle Triassic, reaching the maximum maturity, and then continued until the Middle Cretaceous, after which hydrocarbon generation stopped, but the uplift was limited. The latter started hydrocarbon generation in the late Carboniferous, reached the peak of hydrocarbon generation in Permian, Triassic and Jurassic, and continued until the end of Cretaceous, then uplifted, stopped hydrocarbon generation, and the uplift range was limited. Considering the great success of Barnett shale gas reservoir exploration, it is necessary to pay special attention to the shale with such burial history and thermal evolution history in the study area. Compared with the basin, the burial history and thermal evolution history of well Dingshan 1 on the edge of the basin are characterized by large hydrocarbon generation in the early stage and large uplift in the later stage, and the overall evaluation and preservation conditions are worse than those of Weiyuan gas field and other areas in the basin.
Fig. 7 Buried history of Wei 2 well in southern Sichuan [13]
1.3.3 Central Guizhou Uplift and Renhuai Slope
The burial history and thermal evolution history of Lower Paleozoic in central Guizhou Uplift and Renhuai Slope are characterized by early hydrocarbon generation-multiple hydrocarbon generation and expulsion in the middle period-rapid uplift in the late period (earlier than the uplift in Sichuan Basin). The lower CAMBRIAN black shale began to enter the hydrocarbon generation period in the early Ordovician (RO > 0.5%), and reached the maximum buried depth (RO > 1%) at the end of Silurian, with a peak of oil generation. In the late Triassic, it reached the stage of gas generation and suffered uplift and erosion at the end of Triassic. Late Jurassic-Early Cretaceous further subsided and reached the stage of dry gas generation. After the middle Cretaceous, it rose and hydrocarbon generation stopped (Figure 8). Generally speaking, the burial history and thermal evolution history of this type of shale are worse than those of Sichuan basin, which are mainly manifested by unfavorable factors such as early hydrocarbon generation time, large hydrocarbon generation amount, repeated hydrocarbon generation and expulsion in the middle stage and large uplift in the early stage.
1.3.4 western Hunan-Hubei fold belt
The history of shale burial in this area belongs to long-term continuous burial-rapid uplift type. Lower CAMBRIAN shale reached the peak of oil generation at the end of CAMBRIAN, reached the over-mature stage in Middle Jurassic, and rose rapidly since Yanshan period, and hydrocarbon generation stopped (Figure 9). Compared with the first two types, the burial history and thermal evolution history of this type have the characteristics of long-term continuous hydrocarbon generation, early uplift time (Jurassic) and large uplift range. Because the uplift and denudation transformation lasted for a long time, it was characterized by fold uplift and the Lower Paleozoic was exposed. In Enshi-Pengshui Central anticlinorium Belt and Yidu-Hefeng anticlinorium Belt, the oldest stratum exposed by cores is Sinian, and the black shale of Lower Cambrian has suffered from different degrees of denudation, with serious exposure and poor preservation conditions, which is not conducive to shale gas accumulation and poor development conditions. In the northern part of Huaguoping syncline and Sangzhi-Shimen syncline, the distribution continuity of Lower Cambrian black shale is good, which is a region with great shale gas exploration potential in this area.
Comparing these three types of burial history curves, it is not difficult to find that the area represented by Weiyuan gas field in Sichuan Basin has the following characteristics. Signs: (1) There was basically no hydrocarbon generation before Caledonian, but a large amount of oil and gas was generated in the other two areas; (2) It has the characteristics of late gas peak. For conventional oil and gas reservoirs, the gas peaks of gas source rocks are mainly Paleogene, followed by Cretaceous and Neogene, and the older the gas peaks of gas source rocks, the smaller the gas field proportion [16, 17]. The author believes that shale gas is no exception. According to American shale gas exploration and development experience, the later the gas peak, the better. For example, the most successful shale gas exploration and development in the United States is the barnett shale gas reservoir in Fort Worth Basin. The peak of shale gas production in Weiyuan gas field is in the Middle Cretaceous, while the peak of shale gas production in the Central Guizhou Uplift and the western Hunan and Hubei regions is in the Early Cretaceous (there is another gas production peak in Triassic) and the Middle Jurassic respectively. (3) It has the characteristics of late uplift time, rising after the Middle Cretaceous, and rising in the other two areas in the Early Cretaceous and Middle Jurassic. These three characteristics show that the Lower Cambrian in Sichuan Basin has good conditions for shale gas accumulation from the perspective of shale burial history and thermal evolution history. ?
Fig. 8 Strata Burial History in Central Guizhou Uplift Area [14]
Fig. 9 Buried History of Well Xian 2 in Western Hubei [15]
1.4 depth
The structure of the study area is complex, the buried depth of strata changes greatly, the research degree is low and the data base is weak. The overall change of buried depth of black shale in Lower Cambrian is clear, but it is difficult to accurately predict and draw the isoline of buried depth. We can infer the approximate buried depth range according to the outcrop and stratum thickness. In this study, the buried depth of shale is estimated according to outcrops, and the buried depth of shale is described in detail in key blocks with drilling data and seismic data. The geological maps of Nanchuan Sheet, Qijiang Sheet, Tongzi Sheet, Zunyi Sheet, Fuling Sheet, Zhongxian Sheet, etc.1:200,000 are comprehensively analyzed, and the buried depth of shale can be preliminarily predicted by using the formation thickness of Tongzi Sheet. The calculation shows that the buried depth of the Cambrian bottom boundary in the Triassic coverage area is between 3759 and 5375 meters, while the minimum buried depth in the Jurassic coverage area exceeds.
Generally speaking, the buried depth of black shale in Niutitang Formation of Lower Cambrian mainly has the following characteristics:
1) generally increases from southeast to northwest, and the maximum buried depth is 7500m. In the southeast of the study area, it is exposed along the area to the south of the east of Qiyueshan fault, that is, along Jinsha Cave in Guizhou-Zunyi Pine Forest, Xishui Tuhechang-Runnan, Shizhu Taiyuan Dam in Chongqing, Xiushan-Songtao County in Chongqing, Wuli Town in Hefeng County in Hubei Province-zouma town, and two estuaries in Changyang County in Hubei Province. In the abdomen of Shizhu syncline in western Hubei and eastern Chongqing, 1 well drilling revealed that the top surface of Lower Cambrian shale in Shizhu syncline was buried to 6500m, and Li 1 well drilling revealed that the top surface of Lower Cambrian shale in Lichuan syncline was buried to 3500m to 3600m. However, the buried depth of the Lower Cambrian shale in the anticline area is between 200 m and 2,500 m [6,500 m], and the buried depth of the Cambrian black shale increases towards the Sichuan Basin, with the buried depth of 2,000 m to 5,000 m near the well Dingshan 1 in Xishui County and Qijiang County, and the buried depth/kloc-in northern Guizhou (Renhuai Block).
2) The burial depth is obviously controlled by the distribution of folds, and it is eroded in the anticline; In the syncline area, due to the existence of overlying strata, the buried depth is relatively large. In the plane, it deepens from southeast to northwest, and the buried depth in the northwest of the study area is greater than that in the southeast.
3) The development of the fault has obvious influence on the buried depth of the target layer, and the buried depth of the falling plate of the fault becomes larger. For example, on both sides of Qiyueshan fault, the rising plate on the east side of the fault is exposed and eroded, while the buried depth in the falling plate on the west side is larger, and the farther away from the fault, the greater the buried depth.
1.5 Lithology-Geochemistry-Physical Property-Gas-Bearing Comprehensive Profile
Through field observation, profile measurement and experimental analysis, a comprehensive profile of lithology-rock minerals-geochemistry-physical properties-gas-bearing of Lower Cambrian shale in the study area is established. From the bottom to the top of the profile, with the destruction of anoxic environment, lithology-rock ore-geochemistry-physical properties-gas content and other indicators change regularly on the profile. For example, in the section of Niutitang Formation of Lower Cambrian in Meiziwan, Meitan County, Guizhou Province, the seasonal content is mainly 52% ~ 69%, with an average of 62.3%; Clay mineral content is mainly 3 1% ~ 46%, with an average of 36.23%; The organic carbon content is between 2.1%and 6.2%, with an average of 4.08%. The maturity of the two samples is 4.78‰ and 5.52‰ respectively. From bottom to top, with the destruction of anoxic environment, the lithology changes greatly, the thickness of siliceous shale and carbonaceous shale is small, the thickness of gray black/gray shale and silty shale increases, and the corresponding organic carbon content decreases until it is completely transformed into gray silty shale, sandy shale or argillaceous siltstone. Due to the destruction of anoxic environment, seawater becomes shallow, which leads to the decrease of timely content in profile, the increase of clay mineral content, and the change of maturity, porosity and permeability. The main gas-producing shale in the United States also has this feature, that is, the gas-producing shale section is mainly developed in the lower part of shale [19,20]. Combined with the comprehensive analysis of controlling factors of shale gas accumulation in the study area, drilling gas logging display and lithologic-geochemical-physical-gas-bearing comprehensive profile, it is considered that the lower part of Lower Cambrian shale section has good shale gas development conditions and is a favorable part for shale gas reservoir development.
Figure 10 Schematic diagram of outcrop and burial depth of black shale in Niutitang Formation of Lower Cambrian in southeastern Sichuan, western Hubei and eastern Chongqing.
2. Optimizing favorable areas and calculating resources.
2. 1 Selection basis and method
The main basis for the optimization of favorable areas and the calculation of resource quantity is the National Shale Gas Resource Potential Investigation and Evaluation and Favorable Area Optimization Project-Shale Gas Resource Potential Evaluation and Favorable Area Optimization Method issued by the Oil and Gas Resources Strategic Research Center of the Ministry of Land and Resources.
Figure 1 1 comprehensive profile of shale lithology-rock ore-geochemistry-physical properties-gas bearing of Lower Cambrian Niutitang Formation in Meiziwan, Meitan County, Guizhou Province.
Selection basis: On the basis of investigation of geological conditions, seismic data, drilling (shallow well with parameters) and experimental test, on the basis of mastering shale sedimentary facies, structural model, shale geochemical indicators and reservoir characteristics, and according to key parameters such as shale development law, spatial distribution and gas content, the favorable areas are further optimized in the prospective area.
Selection method: Based on the study of shale distribution, geochemical characteristics and gas-bearing property, multi-factor superposition, comprehensive geological evaluation, geological analogy and other methods are adopted to optimize the favorable shale gas areas and evaluate the resources (Table 1).
Table 1 Reference Index for Optimization of Favorable Area of Marine Shale Gas
2.2 Favorable areas and resources
Based on the comprehensive analysis of organic carbon content, maturity, buried depth, surface and evolution history, it is considered that the favorable areas for the development of lower CAMBRIAN shale gas reservoirs in the study area are mainly located in the southwest and northeast. The former is located in the south of Xuyong-Gu Lin-Xishui-Dingshan 1 well line, mainly including Renhuai block in northern Guizhou and Qijiangnan block, while the latter mainly refers to the southeast of An-Daozhen-Pengshui-Lichuan line.
Figure 12 Favorable areas for shale gas development of Lower Cambrian in southeastern Sichuan, western Hubei and eastern Chongqing.
Through the calculation of the resource potential evaluation unit in the favorable area of shale gas development in the study area, the geological resources in the favorable area of shale gas development are1.06×1012 ~ 6.47×1012m3 (the median is 3.09×/kloc The recoverable resources are 0.13×1012 ~ 0.78×10/2m3 (median is 0.37×10/2m3).
Table 2 Calculation of Geological Resources in Favorable Area of Lower Cambrian Shale in the Study Area by Volumetric Method
sequential
3 Conclusion theory
1) The favorable development areas of Lower Cambrian shale gas reservoirs in the study area are mainly located in the southwest and northeast. The former is located in the south of Xuyong-Gu Lin-Xishui-Dingshan 1 well line, while the latter mainly refers to the southeast of Andaozhen-Pengshui-Lichuan line.
2) The volume method is used to calculate the geological resources in the favorable shale gas area of Lower Cambrian in the study area as (1.06 ~ 6.47) ×10/2m3 (the median is 3.09×10/2m3), and the recoverable resources are.
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