碳酸盐岩储层水敏性实验评价及机理探讨

通常认为，碳酸盐岩储层少含或不含黏土矿物，水敏性很弱，甚至可以忽略。然而越来越多的研究显示，碳酸盐岩储层也可表现出较强水敏性。为此，选取川东北地区三叠系嘉陵江组、飞仙关组、长兴组储层碳酸盐岩岩心，进行了水敏性实验评价。结果表明，储层存在较强水敏性；随着用于实验的流体矿化度的逐渐降低，岩心渗透率持续下降，且当流体矿化度急剧降低时，岩样水敏性损害加剧。进而从化学平衡，电化学角度分析了储层的水敏机理，认为伊利石微结构是储层水敏性的潜在因素，其分散/运移及石膏水化膨胀，溶解-再沉淀、碳酸盐矿物的析出，是储层水敏性的主要原因；水敏实验中的离子强度效应大于同离子效应对石膏溶解度的影响。

LABORATORY INVESTIGATION OF WATER SENSITIVITY OF CARBONATE RESERVOIRS AND DISCUSSION OF ITS MECHANISM

It is generally accepted that water sensitivity is very weak or negligible in carbonate reservoirs as no or few clay minerals exist.However,more and more examples show that carbonate reservoirs can also have relatively strong water sensitivity.Water sensitivity experiments are performed on cores collected from the Triassic Jialingjiang,Feixianguan and Changxing formations in Northeast Sichuan Basin.The experimental results show that these reservoirs have relatively strong water sensitivity.Core permeability lowers along with the decreasing salinity of fluid used in the experiment,and water sensitivity damage intensifies when fluid salinity decrease sharply.The mechanism of water sensitivity in carbonate reservoirs is analyzed from the perspective of chemical balance and electrochemistry.It is believed that microstructure of illite is a possible factor causing water sensitivity of carbonate reservoirs,while dispersion/migration of illite,hydration-dilatation and dissolution-reprecipitation of gypsum,and separation of carbonate minerals are the main causes of water sensitivity of carbonate reservoirs.In water sensitivity experiments,the impacts of the ionic strength effect on solubility of gypsum are higher than that of the common ion effect.