黏土矿物组合类型对泥岩盖层排替压力的影响——以三水盆地布三段为例

Influence of clay mineral assemblage types on displacement pressure of mudstone caprock:Taking the third member of Buxin Formation of Sanshui Basin as an example

为研究黏土矿物组合类型对泥岩盖层排替压力的影响,以三水盆地布心组三段(简称布三段)泥岩为研究对象,开展了岩石矿物分析,并针对不同黏土矿物组合的泥岩开展排替压力测试,进而分析排替压力特征及其影响因素。研究结果表明,布三段泥岩有2种不同的黏土矿物组合类型:类型1为伊利石+高岭石+伊蒙混层组合,主要分布于盆地西北部宝月背斜;类型2为伊利石+高岭石+绿泥石组合,主要分布于盆地东南部东部斜坡华涌凹陷;布三段1150m左右的泥岩全部样品排替压力介于7.43~13.76MPa,平均值10.25MPa;其中类型1的泥岩样品排替压力介于9.51~13.76MPa,平均值11.40MPa,为一类盖层指征;类型2的泥岩样品排替压力介于7.43~9.68MPa,平均值8.87MPa,为二类盖层指征;当黏土矿物中伊蒙混层含量升高时,泥岩盖层排替压力较高,封闭能力较强;当泥岩黏土矿物中绿泥石、高岭石含量升高时,泥岩盖层排替压力降低,封闭能力相应降低;这3种黏土矿物的膨胀性、可塑性的排序为伊蒙混层>高岭石>绿泥石,因此其含量对于泥岩盖层封闭性产生直接影响。该研究可为该区有利盖层条件预测和类似岩性盖层研究提供参考。

In order to study the influence of clay mineral assemblage types on the displacement pressure of mudstone caprock,the mudstone of the third member of Buxin Formation(Bu3 member for short)of Sanshui Basin was taken as the research object to carry out rock mineral analysis.Then,the displacement pressure of mudstone with different clay mineral assemblages was tested,and the displacement pressure characteristics and its influencing factors were analyzed.The results show that there are two different types of clay mineral assemblages in the mudstone of Bu3 member.Type 1 is illite+kaolinite+illite-smectite mixed bed assemblage,mainly distributed in Baoyue anticline area in the northwest of the basin;Type 2 is illite+kaolinite+chlorite assemblage,mainly distributed in Huayong area of eastern slope in the southeast of the basin.The displacement pressure of all mudstone samples at about 1150m in the third member of Buxin Formation is between 7.43 and 13.76MPa,with an average value of 10.25MPa.Among them,the displacement pressure of mudstone samples of type 1 ranges from 9.51 to 13.76MPa,with an average value of 11.40MPa,which is the indication of typeⅠcaprock.The displacement pressure of mudstone samples of type 2 ranges from 7.43 to 9.68MPa,with an average value of 8.87MPa,which is the indication of typeⅡcaprock.When thecontent of Yimeng mixed bed in mudstone clay minerals increases,the displacement pressure of mudstone caprock is higher and the sealing capacity is stronger.When the content of chlorite and kaolinite in mudstone clay mineralsincreases,the displacement pressure of mudstone caprock decreases and the sealing capacity decreases correspondingly.The order of the swelling and plasticity of these three clay minerals is Yimeng mixed bed>kaolinite>chlorite,so their contents have a direct effect on the sealing capacity of mudstone caprock.This study can provide a reference for the prediction of favorable caprock conditions and the study of similar lithologic caprocks in this area.