北部湾盆地涠西南凹陷涠洲组断裂—岩性复合圈闭发育模式与勘探实践

Development model and exploration practice of fault-lithologic composite traps in Oligocene Weizhou Formation, Weixinan Sag, Beibuwan Basin

胡德胜 孙文钊 满晓 陈奎 陈丽君 宫立园 李珊珊

HU Desheng SUN Wenzhao MAN Xiao CHEN Kui CHEN Lijun GONG Liyuan LI Shanshan

1. 中海石油(中国)有限公司 湛江分公司, 广东 湛江 524057; 2. 中海石油(中国)有限公司 海南分公司, 海口 570300

1. Zhanjiang Branch of CNOOC(China) Co., Ltd., Zhanjiang, Guangdong 524057, China; 2. Hainan Branch of CNOOC(China) Co., Ltd., Haikou, Hainan 570300, China

为了解决北部湾盆地涠西南凹陷勘探目标搜索和油田可持续开发难度大的问题，对该区二号断裂带渐新统涠洲组三段构造圈闭发育层段开展了断裂—岩性复合圈闭研究。通过对控洼断裂演化与涠三段沉积特征关系的研究，发现涠三段沉积期二号断裂带活动性较弱，凹陷长轴方向辫状河三角洲水下分流河道向洼中持续推进；涠二段、涠一段沉积期区域构造活动强烈，产生一系列雁列式断裂，辫状河三角洲前缘形成的相对孤立的水下分流河道与呈雁列式断裂形成角度交错相互切割，从而形成了NE—SW向靠断层封堵、NW—SE向靠砂体尖灭的特色河道型构造—岩性圈闭群。研究表明：(1)涠三段发育“二号断裂带洼中断隆背景、低频摆动水道、雁列张扭断裂”三因素耦合的断裂—岩性型圈闭模式，辫状河三角洲水下分流河道主流线与二号断裂带的交会区是构造—岩性圈闭有利发育区带；(2)近物源交会区主要发育复合型构造—岩性圈闭，远物源交会区主要发育孤立型构造—岩性圈闭，建立了凹陷轴向河道控砂，断裂、砂体复合控藏的成藏模式。断裂—岩性型圈闭模式和成藏模式应用效果好，搜索了一批NE—SW向靠断层封堵、NW—SE向靠砂体尖灭的有利断裂—岩性复合圈闭群，并在涠B-E构造得到很好的应用，WB-E 1井钻遇油层近100 m，后续多口井钻探成功，新增油气探明地质储量超千万立方米，证实二号断裂带涠三段断裂—岩性复合圈闭是重要的勘探领域。

In order to address the challenges related to exploration target search and sustainable development of oilfields in the Weixinan Sag of Beibuwan Basin, this study focused on fault-lithologic composite traps within the structural trap development section of the third member of Oligocene Weizhou Formation in the No.2 fracture zone of Weixinan Sag. By examining the relationship between the evolution of depression-controlling faults and the sedimentary characteristics of the third member of Weizhou Formation, it was observed that the No.2 fault zone exhibited weak activity during the sedimentary period of the third member, facilitating the continuous transportation of underwater distributary channels of the braided river delta along the long axis direction of the sag towards the depression. Conversely, the regional tectonic activities were intense during the sedimentary periods of the second and first members of Weizhou Formation, leading to the formation of a series of en-echelon faults. The interaction between relatively isolated underwater distributary channels of the braided river delta front and en-echelon faults resulted in angled staggered formations and intersecting channels, ultimately creating a distinctive channel-type structural-lithologic trap group characterized by NE-SW trending fault sealing and NW-SE trending sand body pinching. The research findings indicate the development of a three-factor coupling fault-lithologic trap model in the third member of the Weizhou Formation. This model includes the depression faulted uplift background of the No.2 fracture zone, low-frequency oscillating channel, and en-echelon tension-torsion fault. The intersection area of the main stream line of underwater distributary channel in a braided river delta and the No.2 fracture zone is identified as a favorable zone for structural-lithologic traps. Additionally, composite structural-lithologic traps are predominantly found in the near-source intersection area, while isolated structural-lithologic traps are more common in the far-source intersection area, leading to the formation of an accumulation model involving axial channel sand control, fault, and sand body composite control. The fault-lithologic trap model and accumulation model have demonstrated effective application in practice. Several favorable fault-lithologic composite trap groups with distinct fault sealing and sand body pinching orientations have been identified, particularly in the Wei B-E structure. Notably, well WB-E 1 has successfully drilled nearly 100 meters of oil layer, with subsequent wells yielding positive results. The exploration efforts in the third member of the Weizhou Formation within the No.2 fault zone of the Weixinan Sag have led to the discovery of geological reserves exceeding 10 million cubic meters, underscoring the significance of fault-lithologic composite traps in this region.

中国海洋石油有限公司“十四五”重大科技专项“地层岩性油气藏高效识别与精细评价技术(KJGG2022-0303)”资助。

https://doi.org/10.11781/sysydz202402215