鄂尔多斯盆地南部地区上三叠统延长组6段地层水成因及其油气意义  

Genesis of formation water in the 6^(th) member of the Upper Triassic Yanchang Formation in southern Ordos Basin and its petroleum significance

作　　者：刘福田[1] 李荣西[1] 左智峰[2] 刘雪峰[3] 赵帮胜 吴小力[1] 李得路[1] Liu Futian;Li Rongxi;Zuo Zhifeng;Zuo Zhifeng;Zhao Bangsheng;Wu Xiaoli;Li Delu(School of Earth Science and Land Resources,Chang’an University,Xi’an,Shaanxi 710054,China;Division and Exploration,Changqing Oilfield Co.Ltd.,PetroChina,Xi’an,Shaanxi 710021,China;Xingzichuan Oil Production Plant, Yanchang Oil Field Co.,Ltd.,Yan’an,Shaanxi 717400,China)

机构地区：[1]长安大学地球科学与资源学院,陕西西安710054 [2]中国石油长庆油田分公司勘探部,陕西西安710021 [3]延长油田股份有限公司杏子川采油厂,陕西延安717400

出　　处：《石油与天然气地质》2018年第6期1179-1189,共11页Oil & Gas Geology

基　　金：国家自然科学基金项目(41772118);国家重点研发计划项目(2016YFC0601002);国家青年科学基金项目(41602128);中央高校基本科研业务费专项资金项目(310827172101)

摘　　要：鄂尔多斯盆地南部地区延长组6段(长6段)地层水化学分析结果表明,地层水总矿化度较高,离子以Cl-、(Na++K+)和Ca2+占绝对优势,水型主要为Ca Cl2型。总矿化度主要受Cl-和(Na++K+)控制,纵向上,其随深度的增加具有递增趋势,反映深部地层水逐渐浓缩,环境封闭性增强。平面上总矿化度与砂体厚度具有较好的一致性,沉积相控制了总矿化度的分布。南部地区长6段地层水具有较小的钠氯系数、镁钙系数、脱硫系数和阳离子交换系数,较大的变质系数,表明长6段地层水整体位于交替停滞带,为封闭缺氧的还原环境,有利于油气聚集和保存。分析表明,南部地区长6段地层水为与地表水隔绝的深层封闭水,总矿化度及Ca2+浓度均与孔隙度具有一定正相关关系,结合区域热演化史,综合表明长6段地层水成因与成岩作用和有机质的热演化等有密切联系,其是经过较强浓缩变质作用并受油气等有机流体影响的原始沉积成因水。综上所述,长6段油气伴生地层水反映的盆地南部油气藏处于稳定封闭的环境下,油气勘探前景良好。Chemical analysis of formation water in the 6 th member of Yanchang Formation(Chang 6 member)in the sou-thern Ordos Basin reveals that the formation water is high in total salinity;Cl-,(Na++K+)and Ca 2+are dominant,and thus the water is of CaCl 2 type.Vertically,the total salinity,mainly controlled by ions of Cl-and(Na++K+),tends to increase with increasing depth,demonstrating the ever-condensing feature of formation water with depth and the ever-growing sealing conditions subsurface.Laterally,the distribution of the total salinity is relatively consistent with the sand body thickness,and is controlled by sedimentary facies.Given that the formation water in Chang 6 member is characte-rized by low sodium-chloride ratio,magnesium-calcium ratio,coefficient of desulfurization and exchange coefficient of cations,and high metamorphism coefficient in chemistry,we are sure that the formation water therein is located in alternating stagnant zones,a closed anoxic and reducing environment,which is conducive for hydrocarbon accumulation and preservation.Besides,the formation water therein belongs to the enclosed deep water isolated from the surface water,and both its total salinity and Ca 2+concentration have a certain positive correlation with porosity of Chang 6 member.Accor-dingly we may conclude that the origin of formation water in the area is closely related with the diagenesis and thermal evolution of organic matters,based on the regional thermal evolution history.What’s more,it is original sedimentary water,having undergone strong condensation and metamorphism and been affected by organic fluids such as oil and gas.All in all,the formation water associated with oil and gas in the 6 th member of Yanchang Formation in the southern Ordos Basin manifests that the hydrocarbon reservoirs in the southern part of the basin is in a stable and closed environment,and the prospects for its oil-gas exploration are brighter.

关 键 词：地球化学 地层水成因 延长组 上三叠统 鄂尔多斯盆地 

分 类 号：TE133[石油与天然气工程—油气勘探]