莺歌海盆地东方区高温超压气藏盖层封盖机制  

Caprock sealing mechanism of high-temperature and overpressure gas reservoirs in the Dongfang Block,Yinggehai Basin,South China

作　　者：汪洋 裴健翔 刘亿 WANG Yang;PEI Jian-Xiang;LIU Yi(Hubei Geological Bureau,Wuhan 430022, Hubei, China;Zhanjiang Branch of CNOOC China Co., Ltd., Zhanjiang 524057, Guangdong,China)

机构地区：[1]湖北省地质局,湖北武汉430022 [2]中海石油(中国)有限公司湛江分公司,广东湛江524057

出　　处：《华南地质与矿产》2016年第4期397-405,共9页Geology and Mineral Resources of South China

基　　金：国家重大专项“莺琼盆地高温高压天然气成藏主控因素及勘探方向”(编号:2011ZX05023-004)

摘　　要：莺歌海盆地是一个典型的高温超压盆地,盖层能否及如何有效封闭该盆地内中深层高温超压气藏是一个值得探讨的重要问题。为此,以该盆地东方区为例,通过气田实际资料及理论分析盖层的宏观地质特征及微观封闭能力。研究表明:该区高温超压气藏盖层的封盖机制包括低构造倾角、厚层泥岩封闭、浅海泥岩盖层中泥质粉砂岩与粉砂质泥岩频繁互层、超压间接封闭、高温超压引起的高突破压力与排替压力比值;其中前3者是决定该区高温超压气藏盖层对天然气封闭能力的主导因素和先决条件,后两者则是中深层浅海相泥质碎屑岩盖层具备优质封盖条件的基础。进而对比剖析了DF-A、DF-B超压气田及DF-C含气构造等典型实例,认为:DF-B气田气体充满度高的原因在于上述五个要素的最优配置;而高构造倾角的岩性气藏储层能量相对较高,对盖层封闭能力的要求高,在其他盖层条件相似甚至更差的情况下,气藏遭到破坏的风险大,这也是DF-C含气构造尚未取得商业性突破的重要原因。The effective sealing of caprocks plays an essential role in the formation of high-temperature and overpressure gas reservoirs in the middle and deep strata of the Yinggehai Basin. In this case study of the Dongfang exploration block in this basin, we analyzed the macroscopic geological characteristics and microscopic sealing capability of caprocks.We found that the following five factors contribute to the caprock sealing mechanismin this study area: (1) there were lithologic traps with low structure angles; (2) the thick mudstone cap rock has hindered gas diffusion upward; (3) the frequently interbeded silty mudstones and argillaceous siltstones made the capillary force doubled and redoubled, so the breakthrough pressure of caprock was multiply increased; (4) the abnormally high carbonate content on the top surface of caprocks formed overpressure sealing indirectly, and the sealing ability of caprocks on free natural gas increased tremendously; and (5) the reservoir physical property was improved under high-temperature and overpressure environment, which reduced the displacement pressure. Thus the breakthrough pressure of caprocks is much higher than the displacement pressure of a gas reservoir, and the gas pool is sealed with high efficiency by the caprocks. The former three factors will help decide if the caprock is effective for a high-temperature and overpressure gas reservoirs; the latter two will help determine the basic conditions for thegood quality of neritic facies argillaceous clastic caprocks in the middle and deep strata. Through a comparisonanalysis on three typical examples of the DF-A gas field, DF-B gas field and DF-C gas-bearing structure, wefound that the reason for the DF-B gas field with high gas-filled degree is the optimal allocation of all of the abovefive factors.A lithologic gas reservoir with a huge structure angle is usually accompanied by a high reservoir energy,which thus requires a higher quality of the caprock. Under the similar or even worse sealing conditions, such a reservoir w

关 键 词：莺歌海盆地高温超压浅海泥岩盖层封盖机制宏观地质特征微观封闭能力低构造倾角 

分 类 号：P618.130.22[天文地球—矿床学]