Research status of Hefei Basin

(1) History of oil and gas exploration in the Hefei Basin

Since oil and gas exploration began in the Hefei Basin in 1958, the basin has had a history of oil and gas exploration for more than 40 years. Despite great efforts, However, due to the constraints of various factors such as the complex surface conditions of the Hefei Basin, the Hefei Basin is still a basin in the early stages of exploration. The exploration history of the basin can be roughly divided into the following research stages:

1. The first stage (1958-1964) of gravity, magnetic and geochemical exploration and survey stage

This stage We have completed 1:200,000 aeromagnetic, ground gravity, and magnetic surveys, conducted a small amount of vertical electrical sounding surveys in the northern part of the basin, and conducted geochemical exploration in some areas. In this stage, 43 shallow geological wells (well depth within 1000 m) were drilled in the basin, with a total footage of 25172 m. Through the above work, the structural units in the basin were initially divided, and more than 30 meters thick dark mudstone of the Lower Cretaceous Zhuxiang Formation was discovered for the first time in Well Zhu 1 in the northern part of the basin, which was analyzed as a possible oil source rock.

2. The second stage (1970-1985) light point mode seismic survey stage

From the summer of 1964 to the autumn of 1970, the oil and gas survey and exploration work in the Hefei Basin was temporarily suspended. In 1970, after the Anhui Petroleum Exploration Office was established, a new round of exploration started focusing on the Hefei Basin. 6 deep wells were drilled with a total footage of 16511 m, 14 shallow geological wells with a footage of 12293 m were drilled, and 1520.25 km of seismic survey lines were completed. , including more than 500 kilometers of light-point seismic profiles. No direct oil and gas shows were found in the drilling, and the seismic data were of poor quality and could only be used to study regional geological structures. Through the work at this stage, we have a further understanding of the basin's basement, geological structure, Mesozoic and Cenozoic stratigraphic sedimentary development, and source-reservoir-caprock combinations. In addition to confirming that the Lower Cretaceous Zhuxiang Formation oil source rocks are relatively developed in the eastern Daqiao Depression, two new sets of possible oil source rocks were discovered: the lower section of the Upper Cretaceous Xiangdaopu Formation and the Lower Tertiary Dingyuan Formation, and pointed out the basin The east is a favorable area for exploration.

With the end of light point mode seismic exploration in 1976, the oil and gas exploration work in the Hefei Basin was suspended for another 11 years.

3. The third stage (1988-1996) two-dimensional digital seismic survey stage

In this stage, oil and gas survey and exploration work represented by digital seismic survey was carried out. From 1988 to 1989 and 1991 to 1992, the Second Division of the Geophysical Prospecting Bureau of China National Petroleum Corporation completed 13 digital seismic survey lines with a length of 694 km in the eastern part of the basin, focusing on the Cretaceous and Paleogene strata. Among them, there are 2 large regional sections (89-50 and 89-212), but no reliable local structures were found. During this period, the Fifth Division of the Geophysical Exploration Bureau of China National Petroleum Corporation and the University of Science and Technology of China completed five large MT regional sections in the basin. From 1992 to 1993, the Second Division of the Petroleum Geophysical Exploration Bureau continued to complete three digital seismic survey lines with a length of 261 km, two of which were regional large sections (92-L23, 93-212). Starting from the second half of 1993, the Oil and Gas Exploration Management Department of the Southern New Area took over the oil and gas survey and exploration work in the Hefei Basin. Based on the north-south HF93-L23 seismic section through the central part of the basin made by the Petroleum Geophysical Exploration Bureau, possible seismic profiles were discovered in the upper part of the Lower Jurassic. There may be thicker Paleozoic under the coal-bearing structures and the Indosinian surface. From 1993 to 1996, 19 seismic survey lines were deployed in the target area in the central part of the basin and 5 large regional profiles (94-135, 94-80, 95-50, 96-150, 96- 40) A total of 24 lines***1285 km.

4. The fourth phase (1999 to present) comprehensive basin survey phase

This phase is mainly undertaken by Shengli Oilfield. From 1999 to 2000, Shengli Oilfield Geophysical Exploration Company completed the first There are 9 regional seismic profiles covering the entire basin, with a total length of 1366.75 km. And 9 sections were explained. Subsequently, an exploratory well, Well Ancan 1, was deployed on the newly discovered Shuangdunji structure.

At the same time, from 1999 to 2000, the Exploration Division of Shengli Petroleum Administration also carried out research work on the "Preliminary Evaluation of Oil and Gas Geology in the Hefei Basin" to conduct a planar exploration of the two main source rocks of the Lower Jurassic, Carboniferous and Permian. The distribution and thermal evolution history were analyzed and evaluated in depth, and oil and gas resources were estimated, and favorable exploration zones and local structures were pointed out.

(2) Current status of research on the Hefei Basin

Research on the Hefei Basin has a long history. As early as the early 20th century, Chinese and foreign scholars began sampling the strata exposed around the Hefei Basin. Research. After the founding of New China, many geologists have conducted research on the Hefei Basin. In the early 1950s, Zhu Tingku, Zhang Zu and others conducted geological surveys in the Dabie area and divided the stratigraphic units. In the 1960s, Zheng Wenwu and Yang Zhijian studied the Foziling Group in the northern Dabie Mountains and successively identified the Meishan Group and the Sanjianpu Formation. The research during this period mainly focused on stratigraphic sequences. After the 1980s, Wang Hongzhen, Zhu Xia, Zhu Guang, Xu Zhiqin, Wang Qingchen, Xue Aimin, Xu Chunhua and others conducted a series of special studies on the formation and evolution of Hefei and the relationship between the basin, the Dabie orogen and the Tanlu fault. Large-scale and detailed basin geological research began with petroleum geological exploration research for the purpose of searching for oil and gas.

Since 1958, there have been 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 Exploration Brigade of the Ministry of Geology, the Anhui Petroleum Exploration Office and the Petroleum Geophysical Exploration Bureau. More than a dozen exploration teams have conducted oil and gas exploration. Based on these data, predecessors have conducted a certain degree of research on the Hefei Basin. In addition to the division of strata and basement characteristics in the basin, some research has also been conducted on structural geological characteristics. For example, the Compilation Group of China Petroleum Geology (1992) has conducted a relatively comprehensive study. He studied the structural evolution history and structural unit characteristics of the Hefei Basin, and pointed out more favorable exploration areas. They believe that based on the basin's basement, caprock, faults, and Mesozoic and Cenozoic sedimentary distribution characteristics, the Hefei Basin can be divided into Yingshang Sag, Wabu-Wushanmiao Uplift, Dingyuan Sag, Daqiao Sag, and Lu'an Uplift and seven secondary structural units in the Shucheng Depression. Regarding the history of tectonic evolution, they divided the geological development process of the Hefei Basin into the following three stages: the pre-Sinian geological development stage, the Sinian to Triassic stage, and the Mesozoic and Cenozoic stages, and considered it as a As far as the sedimentary basin, the basic unit of oil and gas survey, is concerned, the Hefei Basin only formed a unified sedimentary basin during the Mesozoic Era. During the Mesozoic and Cenozoic periods, the Hefei Basin experienced filling sedimentation in the Early Jurassic—comprehensive depression in the Middle Jurassic—strong faulting in the Late Jurassic and Cretaceous—and shrinkage in the Tertiary. Until the whole process of the occurrence and development of death. However, in terms of regional tectonic properties, they belong to two geotectonic units with different properties. Bounded by the Feixi-Liu'an deep fault, its north belongs to the North China Platform, and its south is developed on the basis of the North Huaiyang geosynclinal fold belt. In addition, they also conducted some research on the main faults of the Hefei Basin.

Of course, some scholars have also studied the Hefei Basin from other aspects. For example, Wang Rong and Shen Hou used pollen data to study the climate of the Hefei Basin in various periods; Xue Aimin and Yang Xiaomao (1994) used apatite fission track data to invert the ancient geothermia of the Hefei Basin and estimate the subsidence. rate and denudation rate; Liao Jingjuan and Xue Aimin used open system pyrolysis experiments in 1994 to analyze three oil source rock samples of the Cretaceous Zhuxiang Formation, Xiangdaopu Formation and Paleogene Dingyuan Formation in the Hefei Basin, and concluded studied the dynamic parameters of oil source rocks in different eras in the Hefei Basin; Wang Xin (1996) used thin-section observation, cathodoluminescence and scanning electron microscopy to study the Jurassic low-permeability tight sandstone, not only discussing its origin, but also combining Studies such as organic geochemistry and seismic stratigraphy believe that the Jurassic strata in the Hefei Basin have the potential to develop high-quality sandstone reservoirs, and high-quality reservoirs may exist in areas where fault systems are developed, in the direction of oil and gas migration, and adjacent to the development of oil source rocks.