Since 1958 began oil and gas exploration in Hefei basin, it has been more than 40 years. Although a lot of work has been done in Hefei basin, it is still in the early stage of exploration due to complex surface conditions and other factors. The exploration history of this basin can be roughly divided into the following research stages:
1. The first stage (1958 ~ 1964) is the gravity, magnetic and geochemical prospecting stage.
At present,1∶ 200,000 aeromagnetic and surface gravity magnetic surveys have been completed, a small amount of vertical electrical sounding has been done in the northern part of the basin, and geochemical exploration has been carried out in some areas. At present, 43 shallow geological wells have been drilled in the basin (well depth 1000 m), with a total footage of 25 1 72 m. Through the above work, the structural units in the basin have been preliminarily divided, and dark mudstone with a thickness of more than 30 meters has been found for the first time in Zhu1well in the north of the basin, which may be a source rock.
2. The second stage (1970 ~ 1985) is the seismic prospecting stage of light spot mode.
From the summer solstice of 1964 to the autumn of 1970, the oil and gas exploration in Hefei basin was temporarily suspended. 1970, after the establishment of Anhui Petroleum Exploration Department, a new round of exploration was started, focusing on Hefei Basin. Six deep wells were drilled successively, with total footage1651m, shallow geological wells 14, and footage 12293 m, and one seismic line was completed. There is no direct oil and gas display in drilling, and the quality of seismic data is poor, so it can only be used to study regional geological structure. Through the work in this stage, we have a further understanding of the basement, geological structure, sedimentary development of Mesozoic and Cenozoic strata and source-reservoir-cap assemblage of the basin. In addition to confirming that the source rocks of the Lower Cretaceous Zhuxiang Formation in the eastern part of Da Qiao Depression are relatively developed, two sets of possible source rocks of the lower member of the Upper Cretaceous Xiangdaopu Formation and the lower tertiary Dingyuan Formation have been newly discovered, and it is pointed out that the eastern part of the basin is a favorable area for exploration.
Exploration in Hefei Basin 1976 With the end of light spot mode seismic exploration, the oil and gas exploration in Hefei Basin was interrupted 1 1 year.
3. Phase III (1988 ~ 1996) 2D digital seismic exploration phase.
At this stage, oil and gas exploration represented by digital seismic exploration has been carried out. The No.2 Geophysical Exploration Bureau of China Petroleum and Natural Gas Co., Ltd. took Cretaceous and Paleogene as the main exploration targets, and completed 1989 and1991992 digital seismic lines in the east of the basin, with a length of 694 km. There are 2 regional sections (89-50, 89-2 12), and no reliable local structure is found. During this period, five geophysical prospecting bureaus of China Petroleum and Natural Gas Corporation and China University of Science and Technology have successively completed five MT regional profiles in the basin. During the period from1992 to1993, the Second Division of Petroleum Geophysical Exploration Bureau continued to complete three digital seismic lines with a length of 26 1 km, of which two were large-area profiles (92-L23, 93-265, 438+02). 1993 Since the second half of the year, the oil and gas exploration management department of Southern New Area has taken over the oil and gas exploration in Hefei Basin. According to the north-south HF93-L23 seismic profile made by the Petroleum Geophysical Bureau, it is found that there may be coal-bearing strata in the upper part of the Lower Jurassic, and there may be a thick Paleozoic under the surface of the Indosinian period. From 1993 to 1996, 19 seismic lines were deployed in the target area in the middle of the basin, and five regional profiles (94- 135, 94-80, 95-50, 96-/kloc) were deployed in the west of the basin for three consecutive years.
4. The fourth stage (1999 to present) is the comprehensive prospecting stage of the basin.
This stage is mainly undertaken by Shengli Oilfield. 1999 to 2000, geophysical prospecting company of Shengli Oilfield completed 9 regional seismic profiles covering the whole basin for the first time, with a total length of 1366.75 km. And nine configuration files. Subsequently, an exploratory well-Ansan 1 was deployed on the newly discovered double pier structure. At the same time, 1999-2000, the exploration department of Shengli Petroleum Administration Bureau also carried out the research work of "pre-evaluation of oil and gas geology in Hefei Basin", deeply analyzed and evaluated the plane distribution and thermal evolution history of the two main source rocks of Lower Jurassic, Carboniferous and Permian, estimated the oil and gas resources, and pointed out the favorable exploration zones and local structures.
(B) Hefei Basin Research Status
Hefei basin has a long history of research. As early as the 20th century, foreign scholars conducted sampling research on the exposed strata around Hefei Basin. After the founding of New China, many geologists have studied Hefei Basin. In the early 1950s, Zhu Tingku, Zhang Zu and others made a geological survey in Dabie Mountains and divided the stratigraphic units. In the 1960s, Zheng and others studied the Foziling Group in the northern Dabie Mountains, and successively identified Meishan Group and Sanjianpu Group. The research in this period mainly focused on the stratigraphic sequence. After the 1980s,,,,,, Wang,, etc. made a series of special studies on the formation and evolution of Hefei and its relationship with Dabie orogenic belt and Tanlu fault. Large-scale and detailed basin geological research began with petroleum geological exploration, aiming at finding oil and natural gas.
Since 1958, more than a dozen exploration teams, including the Ministry of Geology, the Ministry of Petroleum Industry, the East China Petroleum Exploration Bureau, the Aeromagnetic Brigade of the Ministry of Geology, the East China Petroleum Geophysical Brigade of the Ministry of Geology, the Anhui Petroleum Exploration Office and the Petroleum Geophysical Bureau, have conducted oil and gas exploration. According to these data, predecessors have done some research on Hefei Basin. In addition to the division of stratigraphic and basement characteristics of the basin, they also studied some tectonic geological characteristics. For example, China Petroleum Geology Compilation and Research Group (1992) has made a comprehensive study on the structural evolution history and structural unit characteristics of Hefei Basin, and pointed out more favorable exploration blocks. They believe that according to the Mesozoic and Cenozoic basement, caprock, faults and sedimentary distribution characteristics, Hefei Basin can be divided into seven secondary structural units, namely Yingshang Depression, Wabu-Wushanmiao Uplift, Dingyuan Depression, Da Qiao Depression, Lu 'an Uplift and Shucheng Depression. As for the tectonic evolution history, they divided the geological history development process of Hefei Basin into the following three stages: pre-Sinian geological history development stage, Sinian-Triassic stage and Mesozoic-Cenozoic stage, and thought that Hefei Basin, as the basic unit of oil and gas survey, formed a unified sedimentary basin only in Mesozoic. The Mesozoic-Cenozoic Hefei Basin experienced the whole development process of filling deposition in the early Jurassic, comprehensive depression in the middle Jurassic, strong depression in the Cretaceous in the late Jurassic and atrophy and extinction in the Tertiary. But in terms of regional tectonic properties, they belong to two different tectonic units. Bounded by the Feixi-Lu 'an deep fault, its north belongs to the North China Platform, and its south is developed on the basis of the North Huaiyang geosyncline fold belt. In addition, they also studied the main faults in Hefei basin.
Of course, some scholars have studied Hefei Basin from other aspects. For example, Rollin Wang and Shen Hou used sporopollen data to study the climate of Hefei Basin in different periods. He Yang (1994) used apatite fission track data to retrieve the paleogeothermal of Hefei Basin, and estimated the subsidence rate and erosion rate of Hefei Basin. Liao Jingjuan and Xue Aimin analyzed three sets of source rocks of Cretaceous Zhuxiang Formation, Xiangdaopu Formation and Paleogene Dingyuan Formation in Hefei Basin by open system pyrolysis experiment in 1994, and obtained the dynamic parameters of source rocks in different periods in Hefei Basin. On the other hand, Wang Xin (1996) studied Jurassic low-permeability tight sandstone by means of thin section observation, cathodoluminescence and scanning electron microscope, which not only discussed its genesis, but also thought that Jurassic strata in Hefei Basin had the potential to develop high-quality sandstone reservoirs, which may exist in areas with developed fault systems, located in the direction of oil and gas migration and adjacent to the development of source rocks.