塔里木盆地柯坪地区下寒武统吾松格尔组岩性组合及其成因和勘探意义——亚洲第一深井轮探1井突破的启示

Lithological combination,genesis and exploration significance of the Lower Cambrian Wusonggeer Formation of Kalpin area in Tarim Basin: Insight through the deepest Asian onshore well-Well Luntan 1

作为紧邻中寒武统膏岩层的第一套白云岩地层,下寒武统吾松格尔组的岩性组合及其成因认识对塔里木盆地寒武系盐下油气勘探由"近源"转向"盐间和盐相关"具有重要的战略意义。以夏特等野外露头为主,结合典型井位,梳理了柯坪地区吾松格尔组的岩性组合、储集空间类型,讨论了沉积相演化与储层成因,结果表明:(1)柯坪地区吾松格尔组以潮坪相为主,主要发育混积坪、云坪、膏云坪和颗粒滩沉积,对应岩性有含陆源碎屑泥质泥晶白云岩、泥质泥粉晶白云岩、颗粒白云岩、粉晶藻白云岩、叠层石白云岩及膏质白云岩等;(2)储层主要发育于藻相关的颗粒白云岩、粉晶藻白云岩、藻叠层白云岩,储集空间分别为粒间溶孔、粒内溶孔和晶间微溶孔;(3)颗粒滩发育于潮坪背景下海进过程中的潮间高能带,叠加准同生期大气淡水溶蚀,形成粒间溶孔;(4)粉晶藻白云岩主要发育于云坪和膏云坪,微生物诱导的白云石调整和膏盐等易溶物质的溶蚀是晶间孔和晶间微溶孔形成的关键。综合柯坪地区吾松格尔组的构造高部位特征、膏盐潮坪背景、岩性组合及其成因等,指出环塔南隆起和牙哈-轮南凸起等周缘发育6个吾松格尔组有利勘探区。

The Wusonggeer Formation is a set of dolostone adjoining the gypsum pool of the Middle Cambrian.Its lithological combinations and genesis are therefore of great significance to the exploration strategy transition from "approaching source rocks" of the Lower Cambrian to "gypsum or gypsum-related strata" of the Middle Cambrian in the Tarim Basin.The study investigates the lithology and reservoir space types and discusses the sedimentary facies evolution and reservoir forming mechanisms in the Wusonggeer Formation of the Keping area through observation of outcrops and analyses of representative wells.The result shows that the Wusonggeer Formation in the Keping area is dominated by tidal flat facies of the mixed flat with terrigenous clastics and carbonates,dolomitic flat,gypseous-dolomitic flat and grain shoal flat,lithologically corresponding to the terrigenous clastic dolomite,argillaceous dolomite,granular dolomite,muddy-silty algal dolomite,stromatolite dolomite and etc.The algae-related dolomites including the grain dolostone,silty alga dolostone,and stromatolite dolostone,provide most reservoiring space with their intergranular and intragranular dissolved pores.The grain shoal was developed in the intertidal high-energy zone during a transgression against a tidal flat environment and contains intergranular pores dissolved by atmospheric fresh water during a penecontemporaneous stage.The silty algae dolostone was mainly developed in the dolomitic tidal-flat and gypsum dolomitic tidal-fat environment and contains intercrystalline pores and intercrystalline dissolved micro-pores due to microbial-induced dolomitization and dissolution of soluble substances like gypsolyte.Based on an integration of the tectonic high characterization,tidal flat settings of gypsolyte,lithological combinations and genesis of the Wusonggeer Formation in the Keping area,we identified six potential exploration targets in the periphery of several paleo-uplifts in the south of Tarim Basin and the south of Luntai and Yaha areas.