琼东南盆地深水区天然气成藏过程及动力机制研究

琼东南盆地深水区中央峡谷已连续发现多个大中型气田，但天然气成藏过程、动力机制一直存有疑问,制约勘探新领域的拓展。综合应用有机地球化学、构造地质学及成藏动力学分析方法，对比剖析中央峡谷气田群莺歌海组 黄流组储层展布、天然气成熟度、母质来源及运聚特征。地球化学及地质分析表明天然气主要来自乐东 陵水凹陷深部的崖城组前三角洲- 浅海相泥岩，莺歌海组- 黄流组浊积水道纵横向展布、储盖组合及压力特征控制了天然气多期有序充注、聚集 逸散动平衡的过程，局部构造高点控制了成藏规模；中央拗陷带深部异常高压为规模成藏提供了充足动力和运移通道，垂向压力封存箱及区域盖层控制了天然气的富集层位，中央峡谷天然气成藏具备“垂向+侧向运移、常压—压力过渡带复式聚集”特征；强烈构造变形区有利于压力和流体的集中释放，峡谷下方的底辟上拱与峡谷下切呈现“似镜像”关系，导致剩余压力梯度大，形成天然气的高效输导体系。根据这一新的成藏模式，提出中央峡谷下方的梅山组构造圈闭及陵南斜坡、松南低凸起等是大中型气田的勘探新领域。

On Accumulation Process and Dynamic Mechanism of Natural Gas in the Deep Water Area of Central Canyon, Qiongdongnan Basin

Several medium to large gas fields have been discovered in the deep- water area of the Qiongdongnan Basin, but their accumulation mechanism and dynamic process are still in dispute and have constrain oil and gas exploration in this area. Through organic geochemical and structural geology methods this study analyzed and investigated the distribution of Yinggehai and Huangliu Formation reservoirs, gas maturity/origin and possible accumulation mechanisms in the central canyon gas fields. Geochemical and geological results show that natural gases are mainly derived from type III kerogens, and their possible source rocks are the prodelta and neritic mudstones of Yacheng Formation in Ledong- Lingshui sag. Extensive distribution of turbidite channels of Yinggehai and Huangliu formations, accumulation and cap assemblages and pressure features effectively control multiple sequential charging process and accumulation- escape balance, with local structure highs controlling the scale of the gas pool. Anomalous high- pressure in the deep part of Ledong and Lingshui sags provides adequate driving force and migration channels for large accumulation, and the vertical pressure compartment and regional cap rock have controlled the sequences for gas accumulation. The natural gas accumulation in the central canyon is characteristic of vertical- lateral migration and composite accumulation of average pressure and excess pressure zone. Strong structural deformation is favorable for rapid releasing of pressure and fluids. Diapir uplifting and canyon incision shows a mirror- like relationship, resulting in a big remnant pressure gradient and thus forming high efficient migration pathways. Based on this new accumulation model, this study proposes that the structural traps of the Meishan Formation below the central canyon, the traps in the Lingnanslope and the low uplift of Songnan could be new exploration targets for large to medium gas fields in the deep- water area.