Ancient karsts and hydrocarbon accumulation in the middle and western parts of the North Tarim uplift, NW China

Ordovician karsts are well developed in the Yingmaili and Halahatang areas of the North Tarim Basin. The ancient karsts are an important factor for forming Ordovician hydrocarbon reservoirs in the central and western regions of the North Tarim Basin. They are distributed, like successive broad belts, along the south side of the North Tarim uplift and constitute a large complex ancient karst reservoir system together with the Lunnan bulge. The main controlling factors of the Ordovician karsts are uplift, interlamination parallel unconformity, fault systems, rock physical properties and high-energy sedimentary phases. The Ordovician karsts can be divided into uplift-controlled karst areas, the strata- and fault-controlled karst areas and limited karst areas while karsts of different origins can overlay each other. The ancient karsts are developed mainly in four periods: the Caledonian, Hercynian, Indo-China Yanshan, and Yanshan, and karsts of different periods overlay each other, too. The condition for developing large-scale ancient karst reservoirs exists in the area and the complex ancient karst systems can be rich in oil and gas. Along both sides of the Middle-Upper Ordovician clastic pinch-outs are the more favorable areas for large ancient karst reservoirs.

摘 要塔里木盆地北部哈拉哈塘和英买力地区的奥陶系古岩溶非常发育，随着勘探程度的提高和地质认识的深入开始引起重视。研究认为，古岩溶是塔北中西部地区奥陶系油气成藏的重要控制因素，沿塔北隆起南翼呈宽幅带状连片分布，与轮南凸起一起构成一套大型复合古岩溶储集体系。奥陶系岩溶发育的主要控制因素有隆升作用、层间平行不整合、断裂系统、岩石物理性质和高能相区等，平面上可以划分出隆控岩溶区、层控-断控岩溶区及局限岩溶区，多种成因的岩溶彼此之间可以复合叠置。此外，该区古岩溶具有分期多次发育的特点，主要期次有四个：加里东、海西、印支—燕山和燕山等，并存在多期叠置的特征。塔北隆起中西部地区具备形成大型古岩溶油气藏的条件，塔北复合古岩溶体系有望整体连片含油，沿中上奥陶统碎屑岩尖灭线两侧是寻找大规模古岩溶油气藏群的有利地区。