Hydrocarbon Accumulation Pattern and Main Control Factor Analysis of Sandstone Reservoirs in the Kungurian Stage Salt Domes of K Oilfield

Salt dome formations are commonly recognized as high-quality regional cap rocks in petroleum-rich basins, but there has been limited discussion on the accumulation patterns of oil and gas within these formations. In K Oilfield, the Kungurian Stage salt has an average thickness of 3 km. However, due to a lack of understanding of hydrocarbon accumulation within the salt dome, exploration and development have not been carried out. This paper aims to analyze the formation mechanism of sandstone reservoirs within the salt dome, and characterize the shape and distribution of these sand bodies. The research combines regional tectonic evolution analysis with drilling, logging, seismic, and test data. The results show that: 1) During the upward movement of the salt, the internal sand bodies underwent squeezing, rolling, and peristaltic movements due to plastic deformation of the salt formation, resulting in blocky lenticular sand bodies that are the main reservoir rocks within the salt; 2) Sand bodies with faults in the lower part of the salt are filled with oil, while those without faults in the upper part are dry. Faults that connect the lenticular sand bodies and source rocks provide migration pathways for hydrocarbons and are the main controlling factor for oil and gas accumulation; 3) The oil reservoir has the characteristics of “lower source and upper reservoir, fault connection, and one sand body, one reservoir”; 4) The lenticular sand bodies in the middle-lower part of the salt dome are the most favorable position for oil and gas accumulation. Based on this accumulation pattern, well X-6 was drilled in the lower part of the salt dome, resulting in high oil production. The study provides a theoretical basis for the development of Kungurian geological reserves and a reference for the discovery of similar intra-salt reservoirs.