鄂尔多斯盆地陇东地区长8致密砂岩油藏地层水化学特征成因及其油气指示意义  

Hydrochemical Feature Genesis and Hydrocarbon Exploration Significance of Chang 8 Tight Sandstone Reservoir in Longdong Area,Ordos Basin

作　　者：斯扬[1,2] 张文选[3] 罗安湘[3] 孙勃[3] 朱玉双[1,2] SI Yang;ZHANG Wenxuan;LUO Anxiang;SUN Bo;ZHU Yushuang(State Key Laboratory for Continental Dynamics,Northwest University,Xi'an,Shaanxi 710069,China;Department of Geology,Northwest University,Xi'an,Shaanxi 710069,China;Exploration and Development Research Institute of Changqing Oilfield Company,Petro China,Xi'an,Shaanxi 710018,China)

机构地区：[1]西北大学大陆动力学国家重点实验室,陕西西安710069 [2]西北大学地质学系,陕西西安710069 [3]中国石油长庆油田分公司勘探开发研究院,陕西西安710018

出　　处：《现代地质》2019年第5期1106-1117,共12页Geoscience

基　　金：“十三五”国家科技重大专项(2016ZX05046)

摘　　要：国内对地层水与油藏的关系研究多集中在断块坳陷内,在岩性油藏中此类研究相对较少。基于鄂尔多斯盆地陇东地区长8致密砂岩油藏大量的地层水化学分析及薄片和扫描电镜资料,对长8地层水化学特征及其成因进行了分析,并结合油藏地质条件,探讨其油气指示意义。长8致密砂岩岩性油藏地层水矿化度平均为33.6 g/L,地层水类型以Ca Cl2型为主,整体为封闭的水文地质环境,有利于油气保存。长8地层水中的离子特征与砂岩成岩具有良好的对应关系。Mg2+亏损、Na+轻微亏损及富集主要与绿泥石化、斜长石的钠长石化及溶解作用有关;Ca2+富集不仅与斜长石的钠长石化及溶解作用有关,还与泥岩中火山灰大量释放的Ca2+有关;SO42-与HCO3-含量则主要受脱硫酸作用和碳酸盐胶结作用控制。此外,由于长8砂岩成岩作用受烃类充注影响较大,研究区西部与中部及东部地层水化学特征存在差异,西部地层水中的钠氯系数整体小于中部及东部,SO42-平均含量及脱硫系数平均值大于中部和东部等特征都与长8油藏在平面上充注条件差异有着很大联系。Domestic studies on the relationship between formation water and reservoirs are mostly concentrated in fault block depressions,and such studies are relatively rare in lithologic reservoirs.Based on a large data set of the formation water chemical compositions,thin-section petrography and scanning electron microscopy of the Chang 8 tight sandstone reservoir in Longdong area of Ordos Basin,the chemical characteristics and genesis of the Chang 8 formation water were analyzed and their hydrocarbon exploration implications were discussed.The study shows that the average salinity of formation water in the reservoir is 33.6 g/L.The formation water is mainly of CaCl2 type,and the hydrogeological system is closed,conducive to oil preservation.Ionic characteristics of the formation water are closely linked with the Chang 8 sandstone diagenesis.The Mg2+depletion and slight Na+enrichment/depletion may have mainly related to chloritization,albitization and dissolution of plagioclase.The Ca2+excess is unlikely only related to albitization and plagioclase dissolution,but also related to the Ca2+release by volcanic ash in mudstone.The SO42-and HCO3-contents may have been controlled mainly by desulfurization and carbonate cementation.Since the diagenesis of the Chang 8 sandstone was much affected by hydrocarbon charging,the water chemistry characteristics of the western/central/eastern sequences of the study area are different.The Na/Cl coefficient of the formation water in the western part is lower than that of the central and eastern parts,whereas the SO42-content and desulfurization coefficient of the formation water are higher.We suggested that this is closely related to the different filling conditions of the reservoir.

关 键 词：鄂尔多斯盆地 致密砂岩油藏 地层水 水岩相互作用 油气指示意义 

分 类 号：P641[天文地球—地质矿产勘探] TE133[天文地球—地质学]