Abstract: Fault basins are the important oil-gas production bases in China. With the deepening of exploration work, the proven conventional oil-gas resources in the middle and shallow layers (depth<3 500 m) exceeds 70 %, the difficulty of discovering large-scale oil-gas reservoirs increased, and the exploration focus gradually shifted to deep sag area. Based on studying the genetic mechanisms, development conditions of lithologic reservoirs, and hydrocarbon generation conditions in the deep sag area of Huanghua depression, the paper systematically summarizes the accumulation conditions of tight oil and gas in the deep sag areas of fault basin. The research suggests that the fan delta plains, fan delta fronts, and nearshore underwater fans are developed near the provenance, as a result of being controlled by fault activities, lake level fluctuations, and source supply intensity. Multiple types of lithologic reservoirs are developed in the central part of the lake basin, including sublacustrine fans, slope fans, far-shore underwater fans, slump turbidites, and regressive delta fronts. When the burial depth is greater than 3 500 m, the reservoirs are gradually densified under the control of compaction. Deep sag areas have a large accommodation space during lake flooding, which is conducive to the formation and preservation of organic-rich shale, and thus has better source rock conditions. The accumulation models for Kongxi slope, Banqiao sag, and Qikou main sag are established, respectively, and it is proposed that the fan delta front in Member 2 of Kongdian Formation in Kongxi sag, the basin-floor fans and slope fans in Member 3 of Dongying Formation in Qikou main sag are favorable target areas. Well CT1 and Well HT1 were deployed and drilled in 2023, from which a high-yield industrial oil flow of 118.9 t/d and 33.2-35.7 t/d were obtained respectively, indicating two fields of hundred million ton scale for increasing reserves were discovered. This confirms the exploration potential of large-scale tight lithologic oil-gas reservoirs in the deep sag areas of Huanghua depression, providing a crucial resource base for the sustainable development of old oil fields.

Key words: Huanghua depression, Paleogene, deep sag area, genetic mechanism, lithologic oil-gas reservoir, hydrocarbon accumulation, exploration practice

摘要： 断陷盆地是中国重要的油气生产基地。随着勘探工作的日益深入,中浅层(深度<3 500 m)常规油气资源探明程度超过70 %,寻找大规模油气藏的难度增加,勘探重点逐步转向深凹区。基于黄骅坳陷深凹区成因机制、岩性储集体发育条件和生烃条件等研究,系统梳理了断陷盆地深凹区致密油气的成藏条件。研究认为:受断陷活动、湖平面升降和物源供给强度控制,近物源区发育扇三角洲平原、扇三角洲前缘和近岸水下扇,湖盆中部发育湖底扇、斜坡扇、远岸水下扇、滑塌浊积体和退积型三角洲前缘等多类型岩性储层;当埋深大于3500 m后,储层受压实作用控制而逐渐致密化;深凹区在湖泛期具有相对较大的可容纳空间,有利于富有机质页岩的形成和保存,具备更好的源岩条件。通过建立孔西斜坡、板桥次凹和歧口主凹区的油气成藏模式,提出了孔西次凹孔店组二 段扇三角洲前缘、歧口主凹东营组三段盆底扇—斜坡扇等有利目标区。2023年,部署实施的CT1井和HT1井分别获得118.9 t/d 和33.2~35.7 t/d的高产工业油流,即发现2个亿吨级规模增储战场,证实黄骅坳陷深凹区具备大型致密岩性油气藏勘探潜力,为老油田的可持续发展提供了重要的资源基础。

关键词: 黄骅坳陷, 古近系, 深凹区, 成因机制, 岩性油气藏, 油气成藏, 勘探实践