带压渗吸核磁共振实验研究——以江汉盆地潜江凹陷潜江组泥质白云岩为例

Experimental study on forced imbibition by NMR:A case of argillaceous dolomite of Qianjiang Formation in Jianghan Basin

渗吸油水置换作用可提高非常规储层原油产量,目前渗吸实验研究以自发渗吸为主,即在常压条件下模拟岩心在毛细管力作用下的渗吸过程,而在实际施工过程中,压裂液在地层中滞留往往存在压力,传统的实验方法无法体现带压条件下的渗吸特征。为此,以江汉盆地潜江凹陷潜江组泥质白云岩为研究对象,开展基于低场核磁共振技术的带压渗吸实验,研究在流体压力作用下的渗吸规律。结果表明:根据T2谱孔隙分类,页岩油储层岩样中98.14%~99.49%的孔隙为小孔和中孔,中孔是其主要储集空间;相较于常压渗吸,附加流体压力使较小孔隙得到更多动用,5和10 MPa带压渗吸采收率分别提高24.32%和62.59%;渗吸使高黏土矿物含量岩样表面产生裂缝,增大接触面积,提高油水置换效率,同时渗吸作用存在改善物性及伤害储层的两面性。

The imbibition can improve the crude oil production of unconventional reservoirs by the oil-water displacement.Currently,the spontaneous imbibition predominates in the experimental research,which simulates the imbibition process in cores under the capillary force at atmospheric pressure. However,there are fluid pressures during the actual fracturing in the reservoirs,and the traditional experimental methods cannot reflect the forced imbibition characteristics. Taking the argillaceous dolomite of Qianjiang Formation of Qianjiang Sag in Jianghan Basin as an example,this paper designed an forced imbibition experiment based on low field NMR(LF-NMR)technology and studied the imbibition laws at fluid pressures.The results show that according to the T2pore classification,98.14%-99.49% of the pores in the shale oil core samples are the small holes and medium holes,and the medium holes are the main reservoir spaces. Compared with spontaneous imbibition,the additional fluid pressure makes more use of smaller pores,and the recovery of 5 MPa and 10 MPa forced imbibition is increased by 24.32% and 62.59% respectively. The imbibition causes fractures on the surface of cores with high clay content,increases the contact area,and improves the oil-water displacement efficiency. At the same time,the imbibition can not only improve physical properties but also damage reservoirs.