潜江凹陷潜北断裂西南缘深层卤水化学和储层特征及成因分析——以潜江组四段为例

Hydrochemical and reservoir characteristics and genetic analysis of deep brinesin the southwest margin of Qianbei Fault,Qianjiang Depression:A case study ofthe 4 th Qianjiang Formation

潜江凹陷地下卤水资源富含K、Na等常量元素以及Li、Br、B等微量元素,具有广阔的开发利用前景。本次研究采集了潜江凹陷潜北断裂西南缘长湖地区ZK01钻井潜江组四段地下深层卤水样品35件,储层物性样品12件,通过测试分析结果,探讨卤水化学和储层特征及其成因。结果显示,研究区的卤水总矿化度在80.70~148.45 g/L,平均值为128.75 g/L,属于低矿化度,卤水总矿化度随卤水层深度的增加而变高;卤水类型主要为氯化物型,其次为硫酸镁亚型;卤水样品的Br-含量是综合评价指标的1.98~4.05倍,具有良好的开发利用前景。研究区共划分出5个砂岩储卤层,属于高—特高孔隙度、中渗透率储集层,厚度10~26 m不等;隔水层组以粉砂岩或者以泥岩、膏泥岩互层为主,属于低孔隙度、特低渗透率隔水层,厚度27~64 m不等。通过分析卤水化学特征系数可知,研究区卤水位于封闭性较差、低变质程度区域,推测卤水来自于早期石盐的溶解作用,各离子来源于岩盐、石膏和碎屑黏土矿物,为典型的大陆盐湖成因的溶滤型卤水。

The underground brine resources in Qianjiang Depression are rich in major elements,such as potassium,sodium as well as trace elements such as lithium,bromine,boron,iodine,rubidium,cesium and strontium,which have broad prospects for development and utilization.In this study,35 samples of underground deep brine and 12 samples of reservoir physical properties were collected from ZK01 well in Changhu area,southwest margin of Qianbei fault in Qianjiang sag.Through the test analysis results,the brine chemistry and reservoir characteristics and their causes are discussed.The results show that the total dissolved solids(TDS)in the study area ranges from 80.70 to 148.45 g/L,with an average value of 128.75 g/L,which belongs to low salinity.The TDS increases with the increase of brine depth.The main brine type is chloride type,followed by magnesium sulfate subtype.The Br-content of brine samples is 1.98-4.05 times of the comprehensive evaluation index,which has a good development and utilization prospect.The study area is divided into five sandstone brine reservoirs,which belong to highultra-high porosity and medium-permeability reservoirs,with thickness ranging from 10 meters to 26 meters.The water barrier group is mainly composed of siltstone or mudstone,paste mudstone interlayer,belonging to low porosity,extremely low permeability water barrier,thickness from 27 meters to 64 meters.By analyzing the hydrochemical characteristic coefficient of the brines,it can be seen that the brines in the study area is located in the area with poor sealing and low metamorphism,and it is speculated that the brines come from the dissolution of halite,and each ion comes from halite,gypsum and clastic clay minerals,which is a typical leaching brine of the origin of continental salt lakes.