Aqueous Phase Trap Damage Law Of Drilling Fluid Cross Flow Filtration In Tight Gas Reservoir

Tight gas reservoirs are often characterized by complex petrophysical property.The damage of drilling fluid to reservoir during drilling is greater than that of conventional oil and gas reservoirs.Especially in the process of exploratory well drilling and horizontal well drilling,formation damage will reduce the discovery efficiency of tight gas reservoirs and affect the correct evaluation of gas reservoirs.Therefore,reducing the damage of drilling fluid to reservoir and accurately evaluating its damage degree are of great significance for the accurate evaluation of tight gas reservoir.Previous studies on the damage mechanism of tight gas reservoirs were mostly based on the results of core-scale laboratory experiments.In the field evaluation methods of formation damage,the evaluation results obtained by methods such as well testing and logging have many influencing factors,which cannot reflect the results of the drilling process.Formation damage degree and mechanism,it is necessary to establish the relationship between the core-scale damage evaluation results obtained from the experiment and the wellscale damage degree.According to the damage mechanism of tight gas reservoir,the drilling fluid damage model is established and its damage law is revealed,so as to provide a theoretical basis for the accurate evaluation of drilling fluid damage in tight gas reservoir and improve the effectiveness of tight gas reservoir evaluation.In this thesis,the invade damage of tight gas reservoirs and drilling fluid to tight gas wells is the research object,considering the influence of reservoir conditions and engineering conditions on the invasion process of drilling fluid in tight gas reservoirs.The damage law of cross flow filtration aqueous phase trap of drilling fluid in tight gas reservoir is studied in detail through the combination of indoor experiment,mathematical model establishment and numerical simulation analysis,The main research contents and results are as follows:Carry out reservoir lithology analysis and sensitivity damage evaluation experiment,study the damage mechanism of tight gas reservoir,and make it clear that the solid-phase damage depth of tight gas reservoir in Dehui area is small,and the aqueous-phase trap damage is the main cause of reservoir damage.Through theoretical analysis,combined with indoor filtration experiment,electron microscope scanning analysis and particle size distribution test,the cross flow filtration mechanism of drilling fluid is put forward,the criterion for evaluating the proportion of deposited particles is established,and the dynamic law of selective deposition of solid particles in drilling fluid under the condition of cross flow filtration is clarified.According to the variation law of mud cake thickness,permeability and filtration rate measured in drilling fluid filtration experiment,the generation model of dynamic mud cake under different well deviation angles based on the analysis of solid particle attachment possibility is established,and the generation law of dynamic mud cake under different influencing factors of tight reservoir under cross flow filtration is explored according to the calculation results of the model.The model can calculate the mud cake thickness under different conditions.The comparative analysis of numerical simulation results shows that the greater the pressure difference,permeability of percolation medium,well inclination angle and particle density,the greater the mud cake thickness,while the greater the flow rate,solid content of mud cake are conducive to the formation of thin mud cake.Based on the above research and comprehensively considering the temporal and spatial variation law of mud cake performance under the conditions of seepage,capillary force self absorption and cross flow filtration,the mathematical calculation model of local water saturation and skin coefficient are established,and the evaluation method of aqueous phase closure damage of drilling fluid filtration in tight gas reservoir is proposed,The variation of aqueous phase trap damage with time in the near well area of single well scale is obtained,and the quantitative evaluation of drilling fluid filtrate distribution and damage degree evolution under the condition of wellbore mud cake formation coupling is realized.Finally,the method is applied to the damage evaluation of Dehui tight gas reservoir,and the influencing factors and laws of aqueous phase trap damage are discussed.Reservoir porosity,over equilibrium differential pressure,well deviation angle,drilling fluid circulation velocity and average particle size of drilling fluid solid particles are the main factors that significantly affect the damage of aqueous phase traps;The increase of reservoir porosity,overbalance differential pressure,drilling fluid circulation velocity,average particle size of solid particles of drilling fluid and the decrease of well deviation angle will increase the filtrate filtration volume,filtrate invasion radius and skin coefficient,and aggravate the damage of aqueous phase trap.