Drilling Fluid Reservoir Protection Technology In LG Area

Most of the reservoirs in Huabei Oilfield are medium and low permeability sandstone reservoirs,and the degree of reservoir damage is serious.The low and medium permeability reserves in LG area in this study account for 75%,the skin factor of the reservoirs in this area is-2.23-29.40,with an average of 5.20,the recovery value of permeability is 17%-65%,with an average of 46%,and the plugging ratio is 0.60-6.01,with an average of 2.23.The protection technology of medium and low permeability reservoirs needs to be solved urgently.In order to solve this problem,the reservoir lithology is analyzed by SEM,XRD and other technical means.The rock type is mainly lithic arkose,and the interstitial material contains argillaceous clay minerals.The reservoir characteristics and pore characteristics are analyzed by comprehensive application of core,logging interpretation results,mercury injection experiment,casting thin section analysis and other technologies,and the reservoir physical properties are widely distributed,There are three types of high,medium and low permeability,especially medium and low permeability,and most of them are large pores and throats,which contribute greatly to the seepage flow.At the same time,fracture development is conducive to oil and gas seepage and easy to cause damage.Through the evaluation of reservoir sensitivity experiment,it can be seen that the reservoirs in this area are mainly medium water sensitive to medium salt sensitive reservoirs.Further theoretical analysis of damage mechanism and simulation experiments show that the damage modes of reservoir are filtrate damage and solid phase damage.Therefore,the key work of reservoir protection in this area is to reduce the invasion of filtrate and solid phase.According to the D90 rule and ideal filling theory,combined with the radius of mainstream pore throat,the optimization scheme of particle size of temporary plugging agent is established,and the combination of temporary plugging particles with different permeability in the reservoir is determined.At the same time,the temporary plugging agent for fractures is optimized,and the combination ZD-1 of rigid temporary plugging particles and fracture temporary plugging agent based on the distribution of reservoir pore throat is further optimized In order to achieve high efficiency plugging,the water-based temporary plugging particle YD-1 and reservoir protection auxiliary agent yb J were introduced to form high-efficiency plugging reservoir protective agent combination.Through optimization,the drilling fluid system optimization formula for reservoir protection in the study area was determined as follows: non reservoir drilling fluid +3%-5%ZD-1 +1%-2%YBJ +0.5%YD-1.Laboratory experiments show that the reservoir protection combination has good adaptability for different drilling fluid systems,has no effect on rheological properties,and has a certain effect of reducing filtration.At the same time,the dynamic damage evaluation experiment shows that the core permeability can be reduced by more than 99%,and the recovery rate of core permeability natural reverse flow is 85.26%-95.48%,with an average of90.10% Compared with the previous non reservoir protection wells,the average skin factor is-2.92,and the average plugging ratio is 0.75,which shows that the drilling fluid formulation system has obvious effect and achieves the purpose of reservoir protection and wellbore stability.