塔里木盆地下寒武统微生物礁储集性研究及油气勘探意义

通过塔北西部-柯坪地区大量的野外露头观测及室内薄片观察与物性分析,对塔里木盆地下寒武统肖尔布拉克组上二亚段微生物礁白云岩储集性进行了精细研究。该层微生物礁仅在研究区南部三个剖面有发现,其中在昆盖阔坦剖面发育数量最多、体积最大,呈近东西向带状、串珠状分布;英尔苏和苏盖特布拉克两剖面发育数量和体积皆较小,呈现由南到北逐减趋势。微生物礁白云岩具有粒内孔、晶间孔、溶孔、格架孔、微裂缝和缝合线6种储集空间,但储集性能远低于预期目标,平均孔隙度与渗透率分别仅有1.84%和0.91×10-3 μm2,属于特低孔特低渗储集体。结合前人工作不难发现,塔里木盆地下寒武统甚至更老地层的微生物礁不应再作为台缘带油气勘探的重点对象,而台缘微生物颗粒滩更具有勘探潜力。

Reservoirs of the Lower Cambrian Microbial Reefs and Its Significance on Petroleum Exploration,Tarim Basin,NW China

The microbial reef reservoirs of the 2nd submember in the upper part of the Lower Cambrian Xiaoerbulak Formation have been researched based on outcrop section, thin section identification and experiment analysis in the west of North Tarim to Kelpin area. The microbial reefs were found in south of the study area, of which the largest number and volume growth in Kungaikuotan section, showing a nearly E-W distribution, while less development in Yingersu and Sugaitebulak sections. 6 kinds of reservoir space developed in the microbial reef dolostones:intragranular pores, intergranular pores, dissolved pores, fenestral pores, micro-fractures and stylolites. But the reservoir characteristics are far from expectative goals, the average porosity and permeability are only 1.84% and 0.91×10-3 μm2, belongs to ultra-low porosity and ultra-low permeability reservoirs. It's difficult to the effective reservoirs of Lower Cambrian in Tarim Basin. Combined with previous work, the microbial reefs should not be used as the key objects of hydrocarbon exploration in Lower Cambrian and even older strata, whereas the microbial bank can be used as the next major explorative horizon.