新场气田地层水地球化学特征及成因初判

Geochemical Characteristics and Preliminary Genesis Judgment of Formation Water in Xinchang Gasfield

新场气田包括上三叠统须家河组,下侏罗统白田坝组、中侏罗统千佛崖组、下沙溪庙组和上沙溪庙组,以及上侏罗统遂宁组和蓬莱镇组,各气藏均产水,但各气藏地层水性质缺乏系统性分析。从地层水矿化度、p H值、离子组成、微量元素等出发,对陆相各气藏纵向上产出地层水性质进行了分析,结果表明,各气藏地层水由浅至深总矿化度增加,以CaCl_2型为主,显示地层水封闭条件相对较好;各气藏钡、锰、锶、溴、碘等5种微量元素均存在,其中钡、锰、锶三种元素由浅至深有增加趋势;陆相各气藏地层水的各项指标纵向趋势明显,但界限不明确。钠氯系数、脱硫系数、变质系数、阳离子交换指数分析证实,陆相地层水主要属于原始沉积水;海相地层水微量元素中,具有含锰和碘、不含钡的特征。对锶、钡、锰、碘和溴等5种微量元素分析,初步判断陆相各气藏地层水可能来源于深层海陆过渡相。

Xujiahe Formation of Upper Triassic, Baitianba Formation of Lower Jurassic, Qianfoya Formation,lower Shaximiao Formation and upper Shaximiao Formation of Middle Jurassic,and Suining Formation and Penglaizhe Formation of Upper Jurassic were all found in Xichang gasfield.Formation water was produced in all gas reservoirs,but there was no systematic analysis on their properties.The formation water produced in the continental gas reservoirs on the vertical was analyzed from the aspects of salinity,p H value,ion composition,trace element and so on.The results show that the salinity in each gas reservoir increases with depth;the main type of the formation water is CaCl_2 that shows relatively good sealing condition of the formation water;trace element Ba,Mn,Sr,Br and I exists in each gas reservoir and the content of Ba,Mn and Sr has a trend that increases with depth.The parameters of the formation water in the continental gas reservoirs have an obvious trend on the vertical,but boundaries are not clear.The analysis of ratio of natrium and chlorine,desulfurization coefficient,metamorphic coefficient and IBE indicates that the continental formation water be-longs to original sedimentary water.The trace elements in the marine formation water have the characteristics of Mn and I containing and without Ba.The analysis of Sr,Ba,Mn,I and Br indicates that the formation water produced by each continental gas reservoir comes from deep marine-continental transitional facies.