库车坳陷中新生界天然气成藏动力学研究

A STUDY OF DYNAMIC PROCESS OF GAS RESERVOIRING IN MESOZOIC AND CENOZOIC IN KUQA DEPRESSION

库车坳陷是塔里木盆地北部一近东西走向的狭长坳陷,以中新生代地层为主。地层压实排出水离心流区位于拜城凹陷和阳霞凹陷,克拉苏—依奇克里克构造带、东秋里塔克构造带和塔北前缘隆起带为越流泄水区。库车坳陷在早第三纪—库车早期主要为油藏、凝析油气藏形成时期;库车晚期—第四纪西域期是气藏的主要形成时期。天然气经短距离侧向汇聚,通过沟通源岩和圈闭的断裂垂向富集。在强烈的构造挤压和气体充注条件下,被具有很好封闭性的下第三系膏盐岩严密封闭,形成异常高压气藏。下伏三叠系—侏罗系源岩的沉积埋藏水、粘土矿物脱出水沿断裂带伴随天然气向浅部越流,在构造顶部形成相对低矿化度的地下水化学特征。

Kuqa depression is a near latitudinally-trending long and narrow depression located in the north of the Tarim Basin and is dominated by Meso-Cenozoic strata. Centrifugal flow of discharge water from compaction occurs in Baicheng sag and Yangxia sag. While discharge areas of cross flow are located in Kelasu-Yiqikelike tectonic belt, eastern Qiulitake tectonic belt and Tabei frontal uplift zone. In Kuqa depression, oil reservoirs and condensate oil/gas reservoirs were mainly formed in Early Tertiary-Early Kuqa Age, while gas reservoirs were mainly formed in Late Kuqa Age-Quaternary Xiyu Age. Natural gas would have gathered laterally in a short distance and then enriched vertically along fractures that linked up source rocks with traps. The gas was tightly sealed by the Eogene halite with good sealing ability under strong tectonic compression and gas charging conditions, leading to the formation of abnormal high pressure gas reservoirs. The sedimentary fossil water in the underlying Triassic-Jurassic source rocks and water of dehydration from clay minerals flowed to shallow layers along with gas, resulting in relatively low salinity of water in the top structure.