鄂尔多斯盆地苏里格气田西部盒8段地层水地球化学特征及成因

Geochemical behaviors and genesis of formation water in 8 Member of Xiashihezi Formation in western Sulige gas field,Ordos Basin

梁积伟 李荣西 陈玉良

Liang Jiwei Li Rongxi Chen Yuliang

通过对苏里格气田西部盒8段地层水性质及地球化学特征研究,推断地层水的成因,寻找天然气富集区,揭示气田油、气、水分布规律。苏里格气田西部39口井的地层水具有如下地球化学特征:①地层水阴、阳离子含量()高低差异悬殊,阴离子以Cl占绝对优势,HCO和SO含量很低,阳离子以Ca占优势,K+Na含量也较高,Mg含量低;②地层水呈弱酸性,具中-高矿化度;③水型以氯化钙Ⅴ型水为主,局部有氯化钙Ⅳ型和Ⅲ型水;④地层水化学特征参数具有钠氯系数(/)低、脱硫系数(2×100×/)高、变质系数[1/2(-)/]高和镁钙系数(/)低的特征。研究结果表明:苏里格气田西部盒8段地层水具有油气伴生水特点,属于天然气充注时留下的残余地层水,形成于封闭、还原的水文地球化学环境。地层水分布受砂体和成藏条件控制,可能有3种成因类型:孤立砂体封闭地层水、弱动力生烃气水驱替不完全的残留水及大砂体低部位滞水。

Genesis of formation water of 8 Member of Xiashihezi Formation (H8) and their relationships with gas accumulation in western Sulige gas field of Ordos Basin in central China was studied by means of analysis of the geochemical behaviors of formation water samples from 39 gas wells.The distribution regularity of oil,gas and water was investigated.There is an obvious difference in the concentration()of anion and cation of formation water.Content of Cl is very high and dominant among the anions of the water,while that of HCO and SO are very low.Content of Ca is the highest among the cations of formation water,followed by K+Na,while the content of Mg is low.The formation water show property of weak acidity with medium-high salinity.The calcium chloride Ⅴ-type water is predominant,with the calcium chloride Ⅲ-type and Ⅳ-type water occurring locally.The chemical characteristic parameters of the formation water are characterized by low sodium-chloride ratio (/),high coefficient of desulfurization (2×100×/),high metamorphic coefficient[1/2(-)/]and low magnesium-chloride ratio (/).The formation water of H8 in western Sulige gas field has the characteristics of gas-associated water.It could be residual formation water formed when gas was charged under a closed and reducing environment.The distribution of formation water is controlled by sand body and reservoir conditions.Three genetic types of formation water are identified,namely the closed formation water within isolated sand body,the residual water with weak dynamic and incomplete gas-water displacement,and the stagnant water at lower position of large sand body.

10.11743/ogg20130507