Experimental Study On Optimization Of Drying Parameters Of Low Permeability Sandstone Reservoirs

Hydraulic fracturing technology has been widely used in the exploitation of low permeability sandstone gas reservoirs.Water-based fracturing fluid is widely used in fracturing process.Research shows that only 5%?50%of fracturing fluid can be successfully discharged after fracturing.Residual water-based working fluid can cause water lock damage to low permeability sandstone gas reservoirs.Permeability damage rate can reach more than 70%,and gas well production will decrease to less than 1/3 of the original,which seriously restricts and affects the development effect of low permeability gas reservoirs.On the basis of in-depth investigation on the characteristics of low permeability sandstone reservoirs at home and abroad,the formation mechanism of water lock damage,the evaluation model of water lock damage and the method of water lock damage relief,this paper proposes that the water phase in the formation should be consumed by the way of"reaction+evaporation",which is called "drying",in order to achieve the drag reduction of matrix and micro-fracture channel near the fracture surface and increase the control criterion of single well.For the purpose of improving reserves utilization and recovery,based on the drying mechanism of desiccant in low permeability reservoirs,the optimization experiment of drying parameters,long core seepage experiment and visualization model seepage experiment are carried out.Qualitative or quantitative conclusions of evaluation of desiccant effect are obtained by means of orthogonal experiment analysis,data processing and chart analysis.The main research contents are as follows:(1)The influencing factors of water lock damage are analyzed from two aspects of Geology and engineering.Geological factors mainly include pore structure and fracture development degree,water saturation of original formation,clay mineral types,rock surface wettability,etc.Engineering factors mainly include physical properties of injection fluid,formation temperature and operating pressure difference.(2)Based on the indoor orthogonal experiment,the parameters of injecting desiccant into core are optimized.When the concentration of injected desiccant is 1-5g/L,the amount of injected desiccant is 1-2PV,the injection rate is 0.5-1mL/min,the reaction temperature is 70-90?,and the reaction time is 90-120min,the recovery degree of core desiccation permeability is the greatest,that is,the optimum injection parameters.At the same time,the influence of each factor on the recovery degree of desiccation permeability is determined by the analysis of the range value.Response time,injection rate,injection drying agent concentration and injection volume.(3)Evaluating the influence of reservoir permeability heterogeneity on the drying effect of desiccant based on long core experiments.The drying effect of drying agent decreases with the increase of injection distance of drying agent,and the displacement pressure decreases with the increase of injection distance,and the later displacement time prolongs.For the standard short core of low permeability gas reservoir,under the condition of injection pressure of 2.5MPa and medium permeability heterogeneity,the formation water drying amount of desiccant decreases with the increase of injection distance of desiccant.If the injection pressure is increased and the concentration of desiccant is increased accordingly,the formation water desiccation amount per unit mass of desiccant can be effectively increased.(4)Based on the pore structure characteristics of low permeability reservoirs,a visual model of micro-glass etching is established.On this basis,the dried seepage displacement process of drier and formation water is observed,and the phenomena in the process of drier-water contact,reaction and miscibility are qualitatively analyzed.Based on laboratory experiments,this paper reveals the mechanism of desiccant reducing water saturation of low permeability sandstone reservoirs,and optimizes and evaluates the injection parameters of desiccant and its desiccation effect.The conclusions and understandings obtained have important theoretical significance and practical application value for unlocking water lock damage and improving gas seepage capacity of low permeability sandstone gas reservoirs.