珠江口盆地白云—荔湾深水区油气成藏条件及勘探方向

珠江口盆地白云—荔湾深水区的天然气勘探已经历了5个阶段,经地质综合研究认为:①白云凹陷具备优越的烃源条件,经历了断陷—断坳—坳陷3大构造演化阶段,断陷期沉积的文昌组—恩平组具有巨大的生烃能力,断坳期和坳陷期受渐新世和中新世2个陆架坡折带的控制,形成的渐新世珠海组浅海三角洲—滨岸沉积体系和中新世珠江组—韩江组深水扇沉积体系,是深水区最有利的2套储盖组合;②该深水区油气的成藏规律不同于北部浅水区,陆架坡折带、构造脊+断裂+砂体+不整合+流体底辟复合油气输导体系及晚期构造运动是控制该区油气运移和成藏的3大要素;③荔湾3-1深水气田是上述成藏条件共同作用下的典型代表,优越的圈闭条件,受陆架坡折带控制的三角洲分流河道相优质储层,断层+底辟构造构成的垂向输导体系和上覆巨厚的海相泥岩盖层,是大气田形成的有利地质条件。进而指出近期该区天然气的勘探方向:①凹陷中央的深水扇体系;②白云凹陷主洼东西两侧的隆起区构造—地层复合圈闭群;③主洼西南侧断阶带上一系列的大型构造圈闭群;④南侧荔湾等一系列凹陷的超深水新区。

Hydrocarbon accumulation conditions and exploration direction of Baiyun Liwan deep water in the Pearl River Mouth Basin

A comprehensive geologic study was performed in the Baiyun Liwan deepwater area， Pearl River Mouth Basin, based on the achievements obtained during the former 5 exploration stages. The following understandings were obtained. (1) The Baiyun Sag has supreme source rock conditions and has experienced 3 tectonic evaluation stages, namely rifting, coupled faulting， downwarping, and downwarping. The Wenchang Enping Fms deposited during the rifting stage have large hydrocarbon generation potentials. During the coupled faulting and downwarping as well as downwarping stages, the deposition in the study area was controlled by the Oligocene and Miocene shelf slope break zone. The Oligocene Zhuhai Fm of shallow marine delta longshore facies and the Miocene Zhujiang Hanjiang Fms of deep fan facies are the most favorable two reservoir seal combinations in the study area. (2) Hydrocarbon accumulation pattern in the deep water is different from that in the northern shallow water. Shelf slope break zone, composite carrier system consisting of structural ridge, fault, sandbody, unconformity and fluid diapir as well as late tectonic movement are the three major factors controlling hydrocarbon migration and accumulation in the study area. (3) The Liwan 3 1 gas field is a typical example. The supreme trapping conditions, quality reservoirs of delta distributary channel facies under the control of shelf slope break zone, vertical carrier system consisting of fault and diapir, as well as the overlying very thick marine mudstone seal provided favorable geologic conditions for the formation of large gas fields. Four areas were identified as the targets of near term gas exploration, namely the composite structural stratigraphic trap cluster in the uplifted areas on both sides of the major structural low of the Baiyun Sag, a series of large structural traps on the fault terrace to the southwest of the major structural low, and ultra deep frontiers in sags such as Liwan to the south of major structural low.