番禺低隆起—白云凹陷北坡断层封闭性研究

Study on fault sealability of Panyu Low Massif and north slope of Baiyun Sag

张忠涛 施和生 秦成岗 高 鹏 屈 亮

中海石油（中国）有限公司深圳分公司研究院，广东 广州 510240

Research Institute of Shenzhen Company, CNOOC, Guangzhou 510240, China

对南海北部珠江口盆地番禺低隆起—白云凹陷北坡地区的断层特征及封闭性主控因素作了初步归纳和总结，并对断层封闭性与油气成藏的关系进行了分析。研究区长期处于张应力场背景之中，反向正断层发育。这些断层都在晚期（10 Ma左右）形成，控制了该区圈闭的形成与分布，同时，也影响和控制了油气的运移、聚集及油气分布范围。断层封闭性影响因素较多，侧向封闭性主要影响因素为地层砂岩质量分数，其次是断距。纵向封闭性影响因素有断层性质、断层活动强度及构造应力场等。该区研究认为，所处地层砂岩质量分数小于30%，断层断距适宜（500 m以下且未断穿上部盖层），且走向上延伸较短的，具有较好的侧向封闭性。该区气藏在纵向上能够得以封闭的原因主要在于断层晚期形成，平面上呈雁行式排列组合，具有扭性特征，纵向封闭条件相对较好，且该区天然气属晚期充注，气藏受构造运动影响小，使得油气得以保存。同时，由于研究区的烃源供给非常充足，在局部地区，即使断层在纵向上泄露了油气，但只要天然气的充注速度大于散失速度，圈闭仍可使油气聚集成藏。封闭有利地区为研究区的南部及东部，其珠江组上段砂质质量分数小于30%，属古珠江三角洲前缘—浅海陆棚相的区域。

The paper sums up the characteristics of faults on Panyu Low Massif and north slope of Baiyun Sag in Eastern Pearl River Mouth Basin and the main control factors of its sealability, analyzes the relationship of fault sealability and hydrocarbon accumulation. In the research area, the antithetic normal faults are developed for it was in background of tensile stress for a long term. The faults were all formed in the late period(about 10 Ma), not only control formation and distribution of the traps, but also affect and control the migration and accumulation of oil and gas and their distributing range. Fault sealability is controlled by many factors. Controlling factors of lateral sealing are mainly sand content rate of formation, and secondly fault throw. And the affecting factors of vertical sealing are fault properties, active intensity and tectonic stress field, etc. The faults whose lateral sealing is best are those antithetic normal faults that sand content rate of formation less than 30%, proper fault throw(below 500 m and not break the sealing) and their length on strike is relatively short; faults whose vertical sealing is best are the wrench faults, formed lately and in echelon array on the plane and also with twisting properties. Meanwhile, the gas reservoirs are the late hydrocarbon accumulation with less effect of tectonic movement, so plenty of gas could be preserved. For supplies of hydrocarbon is quite sufficient in the research area, although gas can be lost by fault on vertical in local part, the velocity of gas charging is faster than its losses and gas still accumulates in fault traps. The favorable sealing zone is in the south and east part of the research zone, where sand content rate in the upper section of Zhujiang Formation less than 30%, and belongs to ancient Pearl River delta front- continental shelf zone.