北部湾盆地海中凹陷勘探思路创新及H3X井钻后认识

Innovative exploration and post-drilling insights from H3X well in Haizhong Sag of Beibuwan Basin

江东辉 杨鹏程 程雪彤 曹倩 余永琪 牛华伟

JIANG Donghui YANG Pengcheng CHENG Xuetong CAO Qian YU Yongqi NIU Huawei

1. 中国石化 上海海洋油气分公司, 上海 200120; 2. 中国石化 石油勘探开发研究院 无锡石油地质研究所, 江苏 无锡 214126

1. Shanghai Offshore Oil & Gas Company, SINOPEC, Shanghai 200120, China; 2. Wuxi Research Institute of Petroleum Geology, SINOPEC, Wuxi, Jiangsu 214126, China

北部湾盆地海中凹陷前期历经几十年油气勘探，一直未取得商业发现，分析认为受“优质烃源岩不落实、规模储层发育区不清以及有利成藏区带不明”3个方面问题的制约。为了实现该地区的勘探突破，按照盆地分析的思路，重新开展了关键成藏要素的落实，基于原型盆地恢复以及“三古”特征明确了海中凹陷发育始新统流沙港组优质烃源岩；重新厘定了源—汇体系，发现在涠西南低凸起倾末端的海中陡坡带地貌平缓地区发育三角洲—滩坝有利沉积体系；按照“近大型导油气断裂带和储层发育区”的勘探思路，优选了海中陡坡带作为下步勘探的最有利区带。按照该思路部署的H3X井取得了高产突破，证实了海中凹陷为富生烃凹陷，油气主要来自于流沙港组，早油晚气，两期成藏；证实了海中陡坡带发育三角洲—滩坝砂沉积体系，滩坝砂虽单层薄但累厚大，深层储层受裂缝的有效改造物性变好；进一步明确了海中凹陷陡坡带是涠西探区规模增储的重要方向，划分为“上部常压构造圈闭”和“下部超压构造—岩性圈闭”2套成藏系统，断砂输导的匹配和有效储层的发育是成藏的关键要素，海三构造高部位是重点扩储方向，海四构造是首要的突破方向。

The Haizhong Sag of the Beibuwan Basin has undergone decades of oil and gas exploration, but no commercial achievements have been made. Previous analysis suggested that this is primarily constrained by three key issues: indefiniteness of high-quality source rocks, unclear large-scale reservoir developing zone, and unknown profitable hydrocarbon accumulation. To achieve exploration breakthroughs in the region, key factors controlling reservoir formation were reexamined and confirmed based on basin analysis methodologies. By reconstructing the prototype basin and analyzing the characteristics of paleobathymetric, paleogeomorphology, and paleo-provenance, the study identified that the Haizhong Sag developed high-quality source rocks of the Eocene Liushagang Formation. The source-to-sink system was redefined, revealing the presence of a favorable delta-beach bar sedimentary system in the relatively flat areas of the steep slope zone of the Haizhong Sag at the distal end of the Weixinan low uplift. Guided by the exploration strategy of exploring reservoirs near major fault zones of hydrocarbon transport and reservoir development areas, the steep slope zone in the Haizhong Sag was selected as the most favorable area for future exploration. The H3X well, deployed based on this strategy, achieved production breakthrough, confirming the Haizhong Sag as a hydrocarbon-rich sag with favorable conditions for dual-source hydrocarbon supply. The oil and gas mainly originated from the deeply buried Liushagang Formation of the Haizhong Sag. Oil formed in early stage and gas formed in late stage, with two periods of accumulation. The study also confirmed that the Haizhong steep zone developed a delta-beach bar sand sedimentary system. The single layer of beach-bar sand is thin, but the accumulated thickness is large. The deep reservoirs have been significantly improved by the crack modification with better physical property. Furthermore, it clarified that the steep slope zone in the Haizhong Sag is a critical target for large-scale reserve increase in Weixi area. Two hydrocarbon accumulation systems were identified, including the upper normal-pressure structural traps as well as the lower overpressure structural and lithologic traps. The connections between sand body and fault and the development of effective reservoirs are key elements for accumulation. The high position of the Hai-3 structure is the key target for reserve expansion, while the Hai-4 structure is the priority for new breakthroughs.

中国石化先导项目“海域重点增储与突破目标勘探潜力及评价”(YTBXD-CGKT-2024-002-011-SH)资助。

https://doi.org/10.11781/sysydz2025020223