塔里木盆地塔中地区地层水化学特征及其石油地质意义

Chemical characteristics of formation water in Tazhong area of the Tarim Basin and their petroleum geological significance

曾溅辉 吴琼 杨海军 钱诗友 孔旭 马中良

Zeng Jianhui Wu Qiong Yang Haijun Qian Shiyou Kong Xu Ma Zhongliang

塔中地区主要含油层系奥陶系、志留系和石炭系地层水化学研究结果表明,奥陶系、志留系和石炭系地层水矿化度很高,是阴、阳离子分别以Cl和K+Na为主的氯化钙型水,钠氯系数平均值在0.73～0.87,脱硫酸系数平均值在1.54～9.29,变质系数平均值在5.54～12.80.剖面上,奥陶系、志留系和石炭系地层水化学成分和离子比值随深度表现为反向型、正向型和稳定型3种变化类型;平面上,石炭系地层水化学相对变化不大,而奥陶系地层水化学变化比较复杂.奥陶系、志留系和石炭系现今地层水总体处于封闭的流体动力环境,但奥陶系、志留系和石炭系C油组内部的流体动力环境相差较大,油气的聚集和保存条件也相差较大;而石炭系C和C油组内部的流体动力环境相差较小,有利于油气的聚集与保存.平面上,在古隆起和沟通浅部地层的断层附近,地层水的矿化度比较低,封闭性相对较差.奥陶系和志留系地层水在地质历史时期曾经遭受过比较强烈的大气降水的入渗,为开放的流体动力环境.其中,志留系地层水曾经处于明显的开放流体动力环境,对油气的聚集和保存极为不利;而石炭系地层水一直处于相对封闭的流体动力环境,有利于油气的聚集和保存.

Study on the chemistry of the Ordovician,Silurian and Carboniferous formation waters in Tazhong area suggests that these waters are of CaCl type with high TDS and contains mainly cations K+Na and anion Cl.Their average sodium-chlorine coefficient is in the range of 0.73-0.87,the de-sulfuric acid coefficient averages at 1.54-9.29,and the metamorphic coefficient ranges from 5.54 to 12.80.The chemical composition and ionic ratio of these waters present positive,negative and steady variations along with depth.While horizontally,the chemical compositions of Carboniferous formation water remain relatively stable,but the Ordovician formation water is complicated in chemical changes.Generally speaking,the Ordovician,Silurian and Carboniferous formation waters are in a closed fluid dynamic environment now.However,the Ordovician,Silurian and Carboni-ferous unit C are quite different in their fluid dynamic environments and conditions of oil & gas accumulation and preservation.While the C and C units have similar fluid dynamic environments and are favorable for oil & gas accumulation and preservation.The of the formation waters is low and the fluid dynamic environment is less closed in the paleo-uplift and areas near faults that cut into the shallow formations.The Ordovician and Silurian formation waters suffered from strong leaching of meteoric water in the geologic history,thus their fluid dynamic systems were open.Especially,the Silurian formation water was exposed to significant open fluid dynamic environment,extremely unfavorable for hydrocarbon accumulations and preservation,while the Carboniferous formation water was,in the contrary,excellent for hydrocarbon accumulation and preservation due to its closed fluid dynamic environment.

10.11743/ogg20080211