Potentials and favorable directions for new fields, new types of oil-gas exploration in Jizhong depression, Bohai Bay Basin

Jizhong depression is rich in oil-gas resources. After more than 40 years of exploration and development, it has been the main oil-gas production base and a crucial area for increasing reserves and production in Huabei oilfield. In recent years, multiple important breakthroughs have been made in new fields and new types of hydrocarbon exploration, showing good exploration prospects. However, it still faces problems such as unclear understanding of hydrocarbon accumulation conditions, as well as undetermined replacement areas and plays. Based on systematically analyzing the hydrocarbon accumulation conditions and their controlling factors in Jizhong depression, the paper summarizes the oil-gas enrichment regularities, recognizes the hydrocarbon accumulation characteristics and exploration potentials of the depression, and further points out the prospects and directions for new fields and new types of future exploration in the depression. Comprehensive assessment indicates that Jizhong depression has developed the Paleogene and Carboniferous-Permian source beds, forming two main reservoirs including marine carbonate rocks and Paleogene clastic rocks. Moreover, it has four types of hydrocarbon plays, i. e., new-generation and paleo-reservoir, self-generation and self-reservoir, lower generation and upper reservoir, paleo-generation and paleo-reservoir, constituting four types of composite hydrocarbon accumulation belts dominated by paleo-buried hills, i. e., central uplift, steep slope, slope, and trough, for which the proved rates of oil-gas resources are 45.7% and 11.0% respectively, and where the remaining hydrocarbon resources are abundant. The holistic research suggests that the five major fields of deep buried-hills and their inners, deep Paleogene layers, shale oil, deep coalbed methane, and new sags generally have good accumulation conditions, great resource potentials, and broad exploration prospects. Thirteen favorable targets, as favorable plays for natural gas exploration in Jizhong depression, have been implemented in the buried-hills and inners, such as Hexiwu buried-hill of Langgu sag, Wuqing sag, and Wen'an slope in northern Jizhong depression, with the predicted natural gas resources of 1453×108 m3. Twelve favorable structures, as the main plays for the exploration of deep Paleogene layers in Jizhong depression, are developed in the Liuchu-Huangfucun area of Raoyang sag, Wuqing anticline belt of Wuqing sag, Yuke-Shennan anticline belt of Shenxian sag, inner belt of Wen'an slope, Langgu sag, and steep slope of Jinxian sag, with the predicted oil resources of 2.4×108 t. The predicted trap resources of 2.3×108 t in two favorable tectonic belts in Baoding sag and the remaining natural gas resources of 836×108 m3 in Wuqing sag demonstrate that they are realistic areas achieving exploration breakthroughs in new wellblocks of sags. The available shale oil resources in the lower submember of Member 3 of Shahejie Formation in Shulu sag and the lower submember of Member 1 of Shahejie Formation in Raoyang sag are estimated to be 9.1×108 t, and the total resources of the favorable exploration area for deep coalbed methane in the outer blet of Wen'an slope amount to 1.53×1012 m3, indicating the favorable exploration targets for strategic replacement in unconventional fields in Jizhong depression. © 2024 Science Press. All rights reserved.