Geological Control Mechanism of Various Types of Oil and Gas Reservoirs Coexistence Around K Block in South Turgay Basin, Kazakhstan

Abstract

The South Turgay Basin is one of the important petroliferous basins in Kazakhstan. K Block is located in the north of the South Turgay Basin. Kumkol oilfield is the biggest one in the South Turgay Basin until now. Kumkol oilfield has been developed for more than 30 years, and water content is very high. The replacement reserve of K Block is not enough, so it is urgent to find the reserve replacement in K Block. Through the fine seismic data interpretation, reservoir inversion, and log interpretation, the three types of oilfield were identified in the periphery of the K Block. The formation mechanism of different types of oil and gas reservoirs and the coexistence mechanism of various types of oil and gas reservoirs are revealed. The results show that there are three types of oil and gas reservoirs developed in the K Block, buried hill oil reservoir, lithological-stratigraphic oil reservoir, and fault block oil reservoir. Comprehensive research points out that different reservoir types are directly controlled by different tectonic sedimentation. The formation of buried hill oil reservoirs is mainly controlled by the palaeo-geomorphology of the pre-Jurassic basement and two-stage tectonic movements at the end of Jurassic and Cretaceous. The slope background of the pre-Jurassic and the lithostromes of J2ds formation control the distribution of the lithological-stratigraphic reservoir in the western K Block. The formation of fault block traps and a wide range of oil and gas migration in the Late Jurassic control the formation of fault block reservoirs. The coexistence of the three types of reservoir is controlled by a variety of tectonic background-buried hill, slope, and depression. The diverse tectonic setting controls the diversification of the sediments-delta, lake, and river. The multistage tectonic movements in the Late Jurassic and the Late Cretaceous controlled the diversity of traps. The three factors control the coexistence of various types of oil and gas reservoirs.