塔里木盆地沙井子断裂带油气地质条件及勘探潜力

Oil and gas geological conditions and exploration potential of Shajingzi fault belt in Tarim Basin

通过钻井、地震和野外露头等资料的综合分析,根据构造特征及派生断层的差异性,将塔里木盆地沙井子断裂带划分为东段、西段、中段及阿恰段等4段。沙井子断裂带具有加里东晚期开始发育、海西期—印支期—燕山期多期活动、喜马拉雅期定型的演化特征,发育构造、地层、潜山等多种类型的圈闭,是油气运聚的有利区。研究表明:①下寒武统玉尔吐斯组和中奥陶统萨尔干组2套优质烃源岩为研究区油气的主要来源;②寒武系盐下丘滩相白云岩、志留系柯坪塔格组潮坪-滨岸复合沉积相的潮汐水道砂岩及滨岸砂坝、三叠系俄霍布拉克组扇三角洲及克拉玛依组辫状河三角洲砂岩为研究区的3套主要储层;③中寒武统厚层膏盐岩、志留系塔塔埃尔塔组泥岩夹层及依木干他乌组厚层泥岩、三叠系俄霍布拉克组及克拉玛依组泥岩夹层为研究区的3套主要盖层;④油气充注呈现多期性、以晚期为主的特点。建立了志留系、三叠系“构造主控、多期充注、晚期成藏”和寒武系盐下“构造主控、连续充注”2种油气成藏模式,指出沙井子断裂带下盘的志留系和三叠系、上盘阿恰段的寒武系盐下为有利勘探区。

Shajingzi fault belt in the northwest of Tarim Basin has achieved exploration breakthrough,showing a good exploration prospect,but the study of oil and gas geological conditions in this area is relatively weak.Based on the comprehensive use of the latest drilling,seismic and field outcrop data of Shajingzi fault belt,the segmented structural characteristics and evolution process of Shajingzi fault belt are described in detail.Combined with the evaluation of oil and gas geological conditions,oil and gas accumulation models of multiple sets of strata are proposed,and favorable exploration directions are pointed out.It is shown that Shajingzi fault belt can be divided into east section,west section,middle section and Aqia section according to the difference of structural features and derived faults.The Shajingzi fault belt has the characteristics of multi-stage activity and late finalization.It has been in the position of structural slope for a long time and has developed many types of traps.It is a favorable area for oil and gas migration and accumulation.At the same time,the source-reservoir-cap is well configured in time and space,and the conditions for oil and gas accumulation are available:(1)Two sets of high-quality source rocks,the Lower Cambrian Yuertus Formation and the Lower Ordovician Sargan Formation,are developed,which have been proven to be the main source of oil and gas in this area.(2)Three sets of reservoirs are developed:dolomite reservoir of the Cambrian subsalt mound-shoal facies,tidal channel sandstone reservoir and shore bar reservoir of tidal flat-shore composite sedimentary facies of the Silurian Kepingtage Formation,fan delta sandstone reservoir of the Triassic Ohoborak Formation and braided river delta sandstone reservoir of the Triassic Karamay Formation.(3)Three sets of caprocks are developed,including the Middle Cambrian thick layer gypsum salt rock,the Silurian Tataelta Formation’s mudstone interlayer and Yimugantawu Formation’s thick layer mudstone,and the mudstone interlayer of the Triassic Ohoborak Formation and Karamay Formation.(4)The oil and gas filling shows the characteristics of multi-stage filling and late stage dominated.Two oil and gas reservoir models of"structure dominated,multi-stage filling and late stage reservoir formation"in Silurian and Triassic and"structure dominated,continuous filling"under the Cambrian salt are established.It is considered that the Silurian system,Triassic system in the footwall of Shajingzi fault belt and the Cambrian subsalt of Aqia section in the upper wall are favorable exploration areas.