鄂尔多斯盆地双河地区延长组长6油层组地层水化学特征分布规律

Chemical Distribution of Formation Water in Yanchang 6 Oil Formation in Shuanghe Area,Ordos Basin

致密油藏油水关系复杂,地层水化学组分及其分布规律对指导致密油勘探具有重要意义。基于此,对双河地区长6油层组地层水化学组成、矿化度、水化学特征参数与沉积微相、有效厚度及产能之间的关系进行了深入研究。研究表明,双河地区地层水类型主要为CaCl_(2)型,地层水的矿化度主要分布在2201.2~153670.9 mg/L,平均为53947.2 mg/L。矿化度在50000 mg/L之前,含油饱和度随着矿化度的增加而降低的,而在50000 mg/L之后,含油饱和度随着地层水矿化度的增加而增加。这是由于,较高的矿化度代表好的保存条件,利于油气长期大规模聚集,因而含油饱和度较高;而当目的层矿化度处于10000~20000 mg/L相对低的范围时,主要对应3~5 m薄层单砂体组成的复合砂体,因而含油饱和度也相对较高。分析认为,目的层矿化度、钠氯系数、镁钙系数特征均表明目的层处于相对封闭的沉积环境,有利于油气的保存,这些水化学参数均与致密油藏聚集及产能有较为显著的相关性。

The relationship between oil and water in tight reservoirs is complicated,so the chemical composition and distribution of formation water are of great significance to guide tight oil exploration.Based on this,the relationship between formation water chemical composition,salinity,water chemical characteristic parameters,sedimentary microfacies,effective thickness and productivity of Chang 6 oil formation in Shuanghe area was deeply studied.The research shows that the type of formation water in Shuanghe area is mainly CaCl_(2) type,and the salinity of formation water is mainly distributed in 2201.2~153670.9 mg/L,with an average of 53947.2 mg/L.The oil saturation decreases with the increase of the salinity before the salinity value of 5000 mg/L,while the oil saturation increases with the increase of the formation water salinity after the salinity value of 50000 mg/L.This is because higher salinity represents good preservation conditions,conducive to long-term large-scale accumulation of oil and gas,so the oil saturation is high.However,when the salinity of the target layer is in the relatively low range of 10000~20000 mg/L,it mainly corresponds to the composite sand body composed of 3~5 m thin layer single sand body,so the oil saturation is relatively high.According to the analysis,the characteristics of salinity,sodium chloride coefficient and magnesium calcium coefficient of the target layer all indicate that the target layer is in a relatively closed sedimentary environment,which is conducive to the preservation of oil and gas.These hydrochemical parameters are significantly correlated with tight oil reservoir accumulation and productivity.