川中北部磨溪—高石梯地区地层水特征及其油气地质意义

Characteristics of formation water and its geological significance in Moxi-Gaoshiti area,north-central Sichuan Basin

川中北部磨溪—高石梯地区是四川盆地天然气的主要产区,但该区地层水特征及其油气地质意义方面的研究比较薄弱。基于油气运移聚集理论,在分析地层水的离子组成、化学参数、氢氧同位素等特征的基础上,揭示了地层水特征与油气聚集的关系。结果表明:龙王庙组、长兴组、雷一1亚段和须家河组的地层水均以CaCl_(2)型为主,嘉二段以CaCl_(2),MgCl_(2),Na_(2)SO_(4)等3种水型为主。雷一1亚段和须家河组地层水的矿化度高,龙王庙组次之,嘉二段和长兴组的矿化度低。5个产层地层水的钠氯系数为0.3~0.8,镁钙系数为0.1~0.5,其中嘉二段脱硫系数最大(大于2),龙王庙组脱硫系数为0.2~0.5,长兴组和雷一^(1)亚段脱硫系数相当,为0.1~0.8,须家河组脱硫系数为0。川中北部地区天然气保存条件较好,须家河组封闭性最好,岩-水作用强,嘉二段封闭性最差,岩-水作用弱。

The Moxi-Gaoshiti area is the main natural gas producing area in Sichuan Basin,but the study on the formation water characteristics and its geological significance with oil and gas is still weak.Based on the theory of hydrocarbon migration and accumulation,combined with the analysis of ion composition,chemical parameters,hydrogen-oxygen isotopes of formation water,the relationship between formation water characteristics and hydrocarbon accumulation was revealed.The results show that the formation water is mainly of CaCl_(2) type in Longwangmiao Formation,Changxing Formation,submember of Leikoupo Formation(Lei-11 submember)and Xujiahe Formation,while mainly of CaCl_(2),MgCl_(2) and Na_(2)SO_(4) type in the second member of Jialingjiang Formation(Jia-2 member).The salinity of formation water in Lei-11 submember and Xujiahe Formation is high,followed by Longwangmiao Formation,and low in Jia-2 member and Changxing Formation.The sodium chlorine coefficient of formation water in the five production layers ranges from 0.3 to 0.8,and the magnesium calcium coefficient ranges from 0.1 to 0.5.The desulfurization coefficient of Jia-2 member is the largest(greater than 2),the desulfurization coefficient of Longwangmiao Formation ranges from 0.2 to 0.5,and the desulfurization coefficient of Changxing Formation and Lei-1^(1) submember is equivalent,ranging from 0.1 to 0.8,while the desulfurization coefficient of Xujiahe Formation is 0.The natural gas has good preservation conditions in the north-central Sichuan Basin.The formation sealing of Xujiahe Formation is the best,the rock-water interaction is strong,while the formation sealing of Jia-2 member is the worst,and the rock-water interaction is weak.