砂岩微观孔隙模型两相驱替实验

EXPERIMENTS OF TWO FLUID PHASE DISPLACEMENT IN SANDSTONE MICROMODELS

目前在水驱油实验中使用的光刻孔隙模型虽较以往有很大改进,但模型的孔隙结构及表面物理性质仍与实际储集岩有较大差距。最近我们研制成功的砂岩微观模型克服了这一缺陷。本文概要地介绍了新研制的砂岩模型及其初步实验结果,并讨论了排驱和吸入过程的驱替方式、自吸现象及残余油、水的形成机制。

Although the photoetched pore micromodel used in experiments of two fluid phase displacement has been greatly improved in recent years,its pore structure and physical surface properties are still far different from reservoir rocks.A new type micromodel presented in this paper which is made dire- ctly from natural sandstone can eliminate those depects.Preliminary results studied are presented;forms of drainage and imbibition processes,the imbi- bition phenomena occured during drainage process,and the mechanisms of formations of residual oil and residual water,i,e.,connate water are discu- ssed in this paper.The major conclusions are as follows. 1.The new sandstone micromodel is more practical in comparison with photoetchcd micromodel,and it is usefull in the studies of enhanced oil recovery,evaluation of formation damage,formation acidization,and secondary migration of hydrocarbon etc. 2.There are two type of displacements both in processes of displacing of water by oil and oil by water(the water is a wetting phase and the oil is a nonwetting phase).They are pistonlike and unpistonlike displacements. 3.The experimental results obtained with sandstone micromodels show that the residual water distributes mainly in corners of pores,micropores and microfractures,and large pores surrounded by them,and some regions of rock caused due to by-passing.The preservation of residual water caused by by-passing during the geological history is still a controversial question. 4.The amount of residual water saturation caused by displacing of water by air is much larger than that caused by displacing of water by kerosene. It is clear that,this is related to the difference between wettability and surface tension of two fluid systems.Consequently the surface physical pro- perties must be considered in determination of initial water saturation of an oil and gas reservoir. 5.The imbibition phenomena have been observed in all experiments for systems of air-water,kerosene-water and n-octyl alcohol-water,in which are mainly imbibitions of cements,cleavage of minerals,microfractures,and wedge crack on the edge of the pores.The difference in velocity of imbibi- tion for various compositions of rocks has further verified the heterogeneity of wettability for reservoir rocks. 6.The principal reasons causing residual oil traping are unpistonlike displacement of oil by water and by-passing.