Research On Acidizing Plugging Removal Technique In Tanhai Sand Reservoir Of Dagang Oilfield

Tanhai area of Dagang Oilfield is rich of oil and gas resource,but it has poor reservoir physical characteristic,low permeability,high heterogeneity,and faces lots of difficulties in water injection.As a conventional method of increasing injection acidizing technology is widely used in the area.However,lots of problems have been found in the process of acidizing.For instance,generating kinds of sedimentary materials which plug channels,causing secondary damage of reservoirs,and affecting the acidizing effects seriously.In this paper,according to the problems encountered during acidizing plugging removal of Tanhai sand reservoir of Dagang Oilfield,we analyze the damage mechanism of the reservoir based on the reservoirs data and laboratory sensitive experiment.Tanhai area pores plugging is mainly caused by drilling mud particles,extraneous fluid and fine particle migration.As it's a reservoir with strong water sensitive,speed sensitivity and middle-strong acid sensitivity,drilling fluid,completion fluid and acidizing fluid can easily damage it.Through experiments the optimized acidizing fluid formulation for the reservoir is optimized,composite acidizing fluid system is 5%-8% HCl+0.5%-1.5% HF+5%-8% HBF4,multi-hydrogen acidizing fluid system is 5%-8% HCl+3% SA601+4% SA701.The acidizing fluid system has low surface tension,good demulsifying ability,great compatibility to formation water and iron ion stability.The plugging materials can be dissolved effectively by acidizing fluid,and the problem of plugging porous caused by clay swelling in sand reservoirs is solved.Field tests show that optimized acidizing fluid system can meet the need of Tanhai area of Dagang Oilfield.