Oil and gas exploration history in Hefei Depression

1. Oil and gas survey and exploration stage (1958-1964)

In 1958, the First Petroleum Survey Brigade of the Ministry of Geology and Mineral Resources conducted a 1:200,000 petroleum geological survey in the Hefei Depression , drilled 43 geological shallow wells with a total footage of 25172m, and discovered the possible source rock of the Lower Cretaceous Zhuxiang Formation in Zhu 1 Well - dark mudstone; the 304th and 305th Wings of the East China Petroleum Bureau of the Ministry of Petroleum completed the entire basin in 1:20 All ground gravity and magnetic surveys. In 1964, the Anhui District Team of the First Petroleum Survey and Exploration Brigade was cancelled, and oil and gas exploration in the Hefei Depression was interrupted.

2. Light spot - simulated seismic oil and gas survey and exploration stage (1970-1976)

Since 1970, the Anhui Provincial Geological Bureau has completed a 1:200,000 basin-wide regional geological survey. Subsequently, the Anhui petroleum survey team was reorganized and the Anhui Petroleum Exploration Office was established. The exploration office has completed 559km of spot seismic and 961km simulated seismic in the Hefei Depression; drilled 6 deep wells (Well Heshen 1 to Well Heshen 6) in local structural highs and deep depressions in the eastern and central parts of the basin, with a total footage of 16511m ; Drilled 57 shallow geological survey wells, with a footage of 12,293m. Although oil and gas indications have been seen during drilling, their reliability is still questionable. In this stage, in addition to confirming the source rocks of the Lower Cretaceous Zhuxiang Formation, it was also newly discovered that varying amounts of dark mudstone were intercalated in the middle and upper parts of the Upper Cretaceous Xiangdaopu Formation and the middle and upper Paleogene Dingyuan Formation, revealing that the basin The east is a favorable area for exploring the Cretaceous-Paleogene system.

Beginning in 1976, the focus of oil exploration work in Anhui Province shifted to the Tianchang area, and the oil and gas survey and exploration work in the Hefei Depression was suspended for another 11 years.

3. Digital seismic oil and gas survey exploration stage (1988-1996)

During the period from 1988 to 1996, the Second Geological Survey Office of the former China National Petroleum Corporation’s Geophysical Prospecting Bureau was in Hefei Ao Seismic exploration work was carried out again. Among them, from 1988 to 1989 and 1991 to 1992, the Cretaceous and Paleogene in the eastern part of the basin were the main target layers, and 13 digital survey lines covering 694km were completed, but no reliable local structures were found. During this period, Section 5 of the Petroleum Geophysical Exploration Bureau and the University of Science and Technology of China completed five large MT regional sections in the central, northern and northeastern parts of the basin. From 1992 to 1993, the Second Division of the Petroleum Geophysical Exploration Bureau continued to complete three digital seismic survey lines, 257km in length, two of which were regional large sections deployed in the central and western parts of the basin, especially the SN-directed H F93-L23 survey line that ran through the central part of the basin. , due to the discovery of possible coal measure reflection combinations and inner Paleozoic anticline structural indications in the upper part of the Lower Jurassic, the main target layer for oil and gas exploration in the Hefei Depression was shifted downward to the Carboniferous-Permian and Jurassic systems.

In the second half of 1993, the Southern New Area Exploration Management Department of the New Area Division was established. While conducting seismic surveys in the target area west of Hefei, two large regional seismic profiles were deployed. By the end of 1994, China had completed 11 digital seismic survey lines, covering a total length of 568km. In order to further implement the Paleozoic inner fault anticline structure, Xiaomiao and Wushanmiao Jurassic fault nose structures in the target area west of Hefei, and to identify the geological structure in the western part of the basin, the Southern New Area Exploration Management Department implemented the project west of Hefei in 1995. There are 8 census seismic lines with a total length of 172km and 1 large north-south regional seismic profile in the western part of the basin with a length of 140km. In order to clarify the structure of the western part of the Hefei Depression and its relationship with the eastern part, the Exploration Management Department of the Southern New Area deployed three regional seismic survey lines in 1996, totaling approximately 285km. To sum up, from the establishment of the Southern New Area Exploration Management Department in 1993 to 1996, it completed 23 digital seismic survey lines covering 1165km (Figure 1-3).

Figure 1-3 Early exploration extent map of the Hefei Depression

During this period, the Hangzhou Institute of Petroleum Geology completed the early trap evaluation of the Hefei Depression, and the University of Petroleum (Beijing) completed In order to study hydrocarbon generation and preservation conditions, the Institute of Geophysics of the Chinese Academy of Sciences completed a comprehensive study of oil and gas geology and two-dimensional basin simulation, and the Hefei Chemical Exploration Center of the former Ministry of Geology and Mineral Resources completed a study of organic geochemistry of oil source rocks.

Due to the reorganization of petroleum and chemical industry organizations from 1997 to 1999, no work was put into it.

4. Comprehensive oil and gas survey and exploration stage (1999 to present)

At the end of 1998, Shengli Oilfield Co., Ltd. obtained the oil and gas exploration rights in the Hefei Depression and started a new round of exploration. It has successively carried out comprehensive exploration research on seismic, gravity, aeromagnetic, electrical, geochemical prospecting, remote sensing, geoelectrochemistry, hydrochemistry, regional geological survey and drilling. Two-dimensional seismic coverage area is 3374.75km2; gravity coverage area is 27686km2; geochemical exploration is 24645km2; 5 electrical EMAPs are 707.3km and 3 MT are 484km; aeromagnetic 30416km2; ground geological survey 330km2; 7 pre-stack depth migration processing sections, ***1015.25km; 7 restored balance profiles (Figure 1-4); 1 parameter well has been drilled - Well Ancan 1, with a footage of 5200m.

Through the drilling of Well Ancan 1, it was discovered that the Lower Jurassic Fanghushan Formation contains 80m thick source rock, and the Carboniferous-Permian source layer was also encountered, preliminarily establishing the northern part of the basin. of stratigraphic sequences. Through two-dimensional seismic exploration, seismic acquisition and processing technology under complex surface conditions has been initially accumulated, and a number of local structures have been discovered and implemented; through gravity exploration, the gravity field of the depression has been established and the distribution characteristics of the main fault systems have been determined; Through chemical exploration, the geochemical field of the depression was established, and it was found that the depression has 4 types and 3 zones of oil and gas properties. Through the analysis of electrical exploration data, it was found that the depression has 2 electrical marker layers and three divisions between north and south. The electric field characteristics are divided into east and west; through aeromagnetic detection, it was found that the depression has a double-layer magnetic structure and a group of volcanic rock structures; through ground geological surveys, the coupling relationship between the depression and the Dabie orogenic belt was studied, as well as the impact of the Tanlu fault activity on Influenced by the evolution of the depression, two oil seeps were also discovered, revealing the fact that effective source rocks exist in the depression. In particular, through gravity-magnetic-electricity-seismic joint inversion, we studied the intrinsic relationships of various geophysical fields, obtained the first gravity-magnetic-electricity-seismic joint inversion structural map of the depression, and determined the fault system. and the distribution of hidden structures. At the same time, through research on a large number of topics, we have deepened our geological understanding and laid a solid foundation for further evaluating the oil and gas prospects of the Hefei Depression and formulating exploration plans.

Figure 1-4 Exploration extent map of Hefei Depression

A—Seismic; B—Electrical method; C—Well location; D—Geochemical prospecting

However , as far as the current level of exploration is concerned, the Hefei Depression is still in the regional exploration stage. The main source rock layers of the basin have not yet been determined. The conditions of the Paleozoic and Lower Jurassic source rocks underlying the basin are not well understood yet. Although the Jurassic The deep lacustrine source rocks in this system have undergone hydrocarbon generation and accumulation processes, but the degree of evolution is too high; the Paleogene system in the Shucheng Sag may be the layer with the most exploration potential, but its resource potential needs to be further realized. The oil and gas geological characteristics, accumulation patterns and preservation conditions of the basin need to be further studied, resulting in a lack of clear understanding of the favorable areas for oil and gas exploration in the basin.