阿北区块A井区构造特征及油气地质条件

Study on Structural Feature and its Oil and Gas Geologic Conditions of A Well Area,North of Awati Sag,Tarim Basin

环阿瓦提凹陷区(环阿区)的油气勘探一直没有重大突破,近年来随着钻探技术及认识程度的提高,对环阿区油气勘探前景,尤其是对潜在有利构造带进行重新评估显得十分迫切。基于前人研究成果,利用A井区已有钻探及新旧地震资料,通过开展系统的地层、构造解释与关键层位(第三系底、中上奥陶灰岩顶)构造图编制,揭示该井区中新生界为一完整的、轴向NW—SE的线状挤压背斜,古生界则为一个大型的冲断盐丘穹隆状背斜,古生界盐构造的解释与前期认识有较大差异。在此基础之上,通过分析其油气地质条件,得出该井区具有构造圈闭规模大、毗邻中上奥陶统闭塞海湾相烃源岩、裂缝性储层发育、盖层条件好、海西晚期(二叠纪末)形成古构造圈闭、印支—喜山期继承性隆起且处于油气运移和充注中心等较为有利的油气地质条件。其不利因素为埋藏较深(达6 400～7 500 m),且可能受到东北部大型火山侵入体的影响。

Few large oil and gas fields have been presently discovered around the Awati Sag in western Tarim Basin. However, in recent years, with both the improvements of drilling technology and level of understanding, it is obviously urgent to carry out related re-evaluation upon those potential favorable structural traps or zones. In this paper, based on previous studies, using both pre-existing and newly-obtained 2D seismic data covering the A structure together with drilling data, we firstly conduct seismic data interpretation and delineate structural maps of key reflector layers （the bottom surface of the Tertiary and the top surface of the mid-upper Ordovician limestones）. The results show that the A structure is an integrated compressional anticline trending NW-SE within the Mesozoic-Cenozoic interval, but within Palaeozoic interval it is a large-scale thrust-diapir domal anticline structure, which is quietly different from previous understanding. Further analysis on oil and gas conditions indicate that the thrust-diapir domal structure possesses some essential elements for forming potential giant reservoir, including： 1） a large-scale trap with an area of 260 km2 and a closure height of 1 100m; 2） location beside available source rocks of the mid-upper Ordovician blocked-trough; 3） fractured reservoir of the Upper Cambrian-Middle Ordovician carbonate rocks; 4） late Hercynian paleostructural trap condition together with continuous hydrocarbon charging from Cretaceous to the present; 5） massive shale sealing condition as well as the fault sealing condition within the shale beds. The adverse factors for this structure are its depth of burial with target layers up to 6 400-7 500 m, and may be affected by the neighboring large-scale volcanic intrusion to its northeast.