Experimental Study And Numerical Simulation On Static Imbibition In Tight Gas Reservoirs During Shut-in Stage After Fracturing

With the increase of energy demand and the adjustment of energy structure in China,more and more attention has been paid to tight gas as an unconventional gas reservoir.In order to efficiently develop tight gas reservoirs and provide a basis for optimizing the time of well shut-in and well opening system after fracturing for tight gas reservoirs.Combined with mercury test,electron microscopy and X-ray diffraction experiments,natural core of tight sandstone in Daqing Oilfield were selected to conduct an indoor static imbibition experiment to study the effects of different factors on the static imbibition of tight gas reservoirs.At the same time,combined with nuclear magnetic resonance imaging and CT scanning technology,numerical simulation techniques were used to simulate the production of gas wells under different well opening regimes.The research results are as follows:(1)The average porosity of the tight reservoirs in the study area is 2.99%and the average permeability is 0.06m D.The reservoir properties of the Shahezi Formation are better than those of the Base Formation.Linked with the original intergranular pores which are the main spaces for gas storage,the secondary generated dissolution pores,intergranular and marginal dissolution cracks provide smooth channels for imbibition.(2)Static imbibition of liquid and gas-liquid exchange in tight sandstone cores mainly play a role in the early stage of static imbibition process;The degree of static imbibition increases with increasing the permeability within the range of tight gas reservoirs;The stronger the core’s wettability is,the higher the imbibition rate and recovery factor is;The fracturing fluid used in fracturing has an impact on the reservoir infiltration effect.(3)The retention of fracturing fluid in the reservoir is not good to productivity,because it will lead to serious water locks and reservoir pollution;but on the other hand,it can increase productivity,because the“gas-water replacement”between pores is beneficial to the flow of gas.And it can not only increase the conductivity of cracks by cleaning with water-based fracturing fluid,but also increase permeability of the reservoir by inducing new fractures with fracturing fluid.(4)A plate with stable production days and corresponding cumulative production is obtained according to the time of‘shut-in’and daily water prodution.The plate shows that for the testing well,keep producing for 480 days at daily water production of 60 m~3is the best solution that takes recovery and daily production into account.