Experimental Evaluation Of Acid Sensitivity And Acidification On Deep Marine Sandstone Reservoir

Deep reservoirs as the most important development field of the petroleum industry in the future,it is the most important strategic and practical field in which China petroleum industry leads the future of oil and gas exploration and development.Its importance is increasingly evident.In the deep marine sandstone reservoir of the Y area of Tarim Basin,the reservoir seriously damaged after drilling and completion,and used acidification to increase production and transformation.After acidification,the production improved,but carried ourt some water production problems,also the sand production condition of reservoir is very serious.Therefore,clarified the mechanism of acidification-induced water outflow and sand production,which provides suggestions for optimizing the acid of acidification operations is of great significance for ensuring the economical and efficient development of oil reservoir.Taking the deep marine sandstone reservoir in Y area in the Tarim Basin as the research object,aiming at the phenomenon of water production and sand production after the acidification of oil wells in the development process,based on using modern analytical methods to define the reservoir characteristics.Designed and carried out a series of evaluation experiments of acid-sensitivity and acidizing capacity.Combined with the geological characteristics and engineering background of the reservoir,clarified the effects of acidification on the water production and sand production,revealed the damage mechanism,formed the method of selecting the acid in the deep marine sandstone reservoir,and finally providing relevant guidance suggestions for on-site acidizing operation.Designed and carried the acid sensitivity evaluation experiment of reservoir.The experimental results show that the basic rock sample decreases with the pH value of the acid solution,the permeability gradually decreased,and the acid sensitivity degree is finally moderately strong;the fractured rock sample decreases with the pH value of the acid solution,the permeability gradually increased.After soaking in soil acid,the Young's modulus of the rock sample decreased,the hydrophilicity decreased,and the relative permeability of the aqueous phase increased.It indicates that the acidizing will reduce the rock strength and increase the water permeability.Evaluated the acidizing capacity of deep marine sandstone reservoirs.The solid particle size D50 of the drilling fluids is 4.339?m,which is less than the main pore throat radius of the Y area.The drilling fluid is easy to invade pores and block the pore throat.The corrosion rate of the filter cake by soil acid was 40.12%.After damaged by the drilling fluid,samples was acid-washed by the soil acid,the permeability recovery rate could reach more than 80%,the acidizing effect was good.Also the permeability recovery rate can be used as an indicator to evaluate the acidizing capacity.Revealed the mechanism of oil well producing water induced by acidification.The Y area is a deep edge-bottom water reservoir with the same oil-water interface.Its natural energy is sufficient,the oil-water viscosity ratio and Kv/Kh is large,natural fractures developed,and the mudstone interlayer above the bottom water destroyed by acid cracking,so the mudstone interlayer cannot formed the bottom water effectively.Then changed the wettability of the crack surface,increased the permeability of the water phase,also the production pressure was large in the early stage of oil well production,the oil production rate was too fast,the water cone formation time was shortened,and accelerated water production of the oil well.Revealed the link between acidification and reservoir sand production.The location of sand production of Y area is near the well,which closely related to acidification.When the acid entered the reservoir and stayed for a long time,the strength of the rock weakened;and the mylonite formed by the extrusiong dissolved by the acid,which gradually transported along the cracks to the wellbore under the effect of pressure.After the acidification operation,the water content of the oil well rise rapidly,and the high water content will lead to the high risk of reservoir sand production.Formed a preferred method for selecting acid of deep marine sandstone reservoirs.It mainly includes the acid liquid type preferred method and the acid liquid concentration preferred method.According to the acid concentration preferred method evaluation index that acid concentration can be reduced by 0.62 to 0,87 times,and the negative effect of the acid liquid on the reservoir can be reduced by surfactant addition to ensure the economic exploitation of the well.