杭锦旗地区地层水特征研究及其油气地质意义

Chemical characteristics of the formation water in Hangjinqi area and their petroleum and gas geological significance

通过对鄂尔多斯北部杭锦旗地区地层水化学组分分析,结合水化学特征参数纵向和平面分布特征变化规律,探讨地层水化学特征与油气保存条件的关系.研究表明:地层水是低p H值、高矿化度的Ⅳ型和Ⅴ型Ca Cl2型水.平面上,地层水化学特征具有东西分区、南北分带的特征,西部大部分地区及泊尔江海子断裂带两侧的局部地区表现出高矿化度(TDS)、高(rCl--rNa+)/rMg2+、低rNa+/rCl-、低(100×rSO42-/rCl-)和(rHCO3-+rCO32-)/rCa2+的特征,表明其封闭性条件较好.纵向上,泊尔江海子断裂带两侧矿化度和离子浓度随深度变化表现为正向型,表明现今地层水处于封闭的流体动力环境,有利于天然气的保存.地层水所表明的封闭环境均有良好的油气藏发现,可利用地层水离子特征寻找天然气气藏勘探区.

The relationship between chemical characteristic of formation water and preservation of gas reservoir has been discussed based on analysis of the chemical composition in Hangjinqi area.The vertical and plane variations in chemical characteristic parameters in Hangjinqi area in the north of Ordos basin. The results show that most of these formation waters with low p H value and high total dissolved solid（ TDS） are calcium chloride Ⅳ-type and Ⅴ-type waters. The plane distribution features show west-east differentiation and north-south dissimilitude. The high TDS and（ rCl^--rNa^＋） /rMg^2 ＋values and the low rNa^＋/ rCl^-,（ 100 × rSO4^2-/ rCl^-）,and（ rHCO3^-＋ rCO3^2-） /rCa^2 ＋values in the west and local area of Boerjianghaizi fault indicate better sealing condition. The relatively positive correlation of the TDS and ion concentration with depth in the north and south of theBoerjianghaizi faulted zone indicates that the formation water exists in a closed fluid dynamic environment,which is beneficial to preservation of the natural gas. All the formation water-indicative sealed environments have natural gas discoveries,which indicates a good correlation between them.The water chemical characteristics provide clues to the natural gas prospects.