Accumulation model and exploration direction of medium-large gas fields in Yinggehai Basin

With the in-depth exploration of high-temperature and high-pressure natural gas in Yinggehai Basin, the longitudinal and transverse distribution of natural gas is becoming increasingly complex, and the direction of subsequent expanded exploration is still unclear. It is urgent to deeply analyze the accumulation model of natural gas in different belts from the perspective of reservoiring process. providing a guide for the further exploration of natural gas. Based on the newly acquired 2D wide-line and 3D ocean bottom node seismic data, the paper studies the key accumulation factors such as the hydrocarbon source conditions, transportation system, and reservoir sand body of the basin, and systematically summarizes the differences in tectonic activities in different belts and their control on hydrocarbon accumulation. The research shows that two sets of source rocks, l. e., the Miocene marine source rocks and the Oligocene transitional source rocks, are developed in Yinggehai Basin, providing the material basis for the formation of medium- large gas fields in Ymgzhong anticlinal belt and Yingdong fault-step belt, respectively. Two types of natural gas transport systems are developed in the basin, and the inherited tectonic ridges, formed under sinistral strike-slip compression deformation in early stage and dextral strike-slip tension fracturing in late stage, as well as migration channels by faulted fractures and faults can provide an efficient hydrocarbon transport system for the large-scale oil-gas accumulation. Low-stand submarine fans, axial waterways, and delta sand bodies are developed under the condition of low accommodation space, by which the large tectonic-lithological combination traps are formed and provide reservoir space for oil and gas. On this basis, the differences in natural gas accumulation in different belts are analyzed, and two types of accumulation models have been established, l. e., "continuous charging of Miocene marine source rocks, dynamic adjustment of oil-gas decompression, multi-stage three-dimensional accumulation" in the medium-deep strata of Ymgzhong anticlinal belt, and "hydrocarbon supply by Oligocene transitional source rocks, convergence of deep tectonic ridges, vertical transport of overpressure-driven fracture in late stage, and complex accumulation in medium-deep strata" in Yingdong fault-step belt. The medium-deep large-scale tectonic traps in Ymgzhong anticlinal belt and its surrounding large-scale Miocene submarine fan-channel li- thological traps, as well as the medium-deep "tectonic + lithological + buried hill" traps in Yingdong fault-step belt are the targets for petroleum exploration in medium-large gas fields, showing great resource potential. © 2023 Science Press. All rights reserved.