苏里格地区下古生界马家沟组地层水化学特征与天然气聚集关系

通过对苏里格地区44口井66个下古生界奥陶系马家沟组地层水样品测试结果的统计与分析,发现马家沟组地层水以偏酸性为主,具有矿化度高、Cl-和Ca2+占优势、以CaCl2水型为主等特征,反映出下古生界马家沟组地层水处于比较还原的阻滞—停滞水文地质状态,封闭条件较好,有利于天然气的聚集与保存.对苏里格地区马家沟组地层流体水化学组成变化与天然气藏关系的系统研究表明,地层水总矿化度高值区(>150 g/L)、CaCl2型水分布区、rNa+/rCl-低值区(≤0.3)、rCI-/rMg2+高值区(>15)、rMg2+/rCa2+低值区(≤0.2)等均与天然气富集区有较好的对应关系.从地层流体水化学特征平面变化来看,以乌审旗为中心的中部是最大的天然气富集区,中北部的苏11井区也是天然气较有利区,推测南部的陕185井区也将是天然气藏的分布区.

Relationship between hydrochemical characteristics of Majiagou formation water in Lower Paleozoic in Sulige region and natural gas accumulation

Through the comparison and analysis of 66 Ordovician Majiagou formation water samples from 44 wells in Sulige region,it is held that the formation water is characterized by acidity to weak alkalinity,high total mineralization,relative rich Cl-and Ca2+ ions and CaCl2 water type,which shows that lower Paleozoic Majiagou formation water is under the hydrologic exchanging-stagnant condition and is favorable for the accumulation and preservation of natural gas.It is suggested that there are close relations between chemical compositions of the formation water and natural gas reservoirs.While the formation water is of high total mineralization(>150 g/l),CaCl2 type water,low rNa+/rCl-(≤0.3),high rCl-/rMg2+(>15) and low rMg2+/rCa2+(≤0.2),there may be a beneficial gas enrichment area.Therefore,by the comprehensive studies of hydrochemistry and geochemistry,it is possible to predict natural gas enrichment areas(or gas prospect area).According to the plane distribution of formation fluid hydrochemical characteristics,it is predicted that the middle of the area as whose center is Wushenqi is the largest natural gas accumulation area,north-central Su11 well block is favorable gas accumulation area,and southern Shan185 well block also will be the gas distribution area.