涠西南凹陷低倾角断层封堵能力分析  

Analysis on sealing capacity of low-angle faults in Weixi'nan sag

作　　者：王立锋 李文龙 沈利霞 刘云芝 曾超 Wang Lifeng;Li Wenlong;Shen Lixia;Liu Yunzhi;Zeng Chao(Hainan Branch of CNOOC(China)Ltd.,Haikou,Hainan 570311,China)

机构地区：[1]中海石油(中国)有限公司海南分公司

出　　处：《天然气勘探与开发》2022年第3期34-40,共7页Natural Gas Exploration and Development

基　　金：中海石油中国有限公司重大科技项目“南海西部油田上产2000万方关键技术研究”(编号:CNOOC-KJ 135 ZDXM 38ZJ)。

摘　　要：涠西南凹陷发育大量断块圈闭及断块+岩性圈闭,但断裂复杂、断块破碎,单个断块圈闭面积多小于0.3 km^(2),断层封堵性好坏决定了圈闭的有效性。为此,根据地质、地震资料和钻探成果综合分析了断层封堵性的主控因素,明确了影响断层封堵性的最关键因素是断层倾角,并依托断面正应力断层封堵性进行了半定量计算。研究结果表明:①低倾角断层往往断层位移更长、泥岩涂抹作用更强、封堵作用更强;②断面正应力和控圈断层的封堵能力正相关,在相同埋深下低倾角断层断面正应力更大,形成的圈闭保存条件更好;③断面正应力大于20 MPa时,成藏概率高,这类圈闭多位于花状断层外缘的花瓣断层,以平缓的铲式断层为主,断层断距较大,而断面正应力小于9 MPa时,为成藏的高风险区,这类圈闭多位于花状断层靠近花心的部位,断面陡而直,断距小,断面正应力大于9 MPa而小于20 MPa时,成藏风险介于以上两者之间,这类圈闭多位于花状断层的中部,即花瓣断层与花心断层之间。根据以上研究结果,在低倾角断层发育区优选了3个有利的勘探目标,钻探的6眼井均获得厚油气层发现。There develops a large number of fault block traps and fault block with lithologic traps in Weixi'nan sag.Due to complex faults and highly fragmented fault blocks,a single fault block trap is mostly less than 0.3 km^(2)in area,and the fault sealing capacity decides the trap effectiveness.Based on geologic,seismic and drilling data,the main factors controlling fault sealing in the study area were analyzed,indicating that the angle of fault is the most crucial factor.The sealing capacity of fault was calculated semi-quanti-tatively with the normal stress on the fault surface.The results show that,(1)the low-angle faults usually have longer displacement,stronger mudstone smear effect,and stronger sealing capacity;(2)the normal stress on fault surface is positively correlated with the sealing capacity of the fault that controls trap;at the same burial depth,the low-angle fault has larger normal stress on fault surface,and thus forms trap with better preservation conditions;and(3)the normal stress more than 20 MPa can cause high probability of reservoir forming,this kind of traps are often located in the petal faults at the outer edge of flower-shaped faults,which are mostly smooth listric faults with large fault throw;when the normal stress is less than 9 MPa,the reservoir forming is at high risk,this kind of traps are mostly near the center of flower-shaped faults,with steep and straight fault surface and small fault throw;when the normal stress is between 9 MPa and 20 MPa,the reservoir forming probability is between those above mentioned,this kind of traps are mostly located in the middle flower-shaped faults,namely between the petal and flower center.According to the study,three favorable explo-ration targets in the area of low-angle faults were selected.Thick oil layers have been discovered by 6 wells drilled in these targets.

关 键 词：涠西南凹陷 背形负花状断裂 低倾角断层 断面正应力 烃柱高度 

分 类 号：P618.13[天文地球—矿床学]