Development Of Self-diverting Acid System For Sandstone Reservoir

Acidizing technology is an effective way to remove practical plug and increase production.It is being widely used.For the multi-layer,long and strong heterogeneous sandstone reservoirs,the effective placement of acid in the treatment layer plays a key role in the relief of damage.Conventional acid system often suffers from uneven distribution of acid and poor effect of removing plugging.Therefore,it is an effective way to solve the above problems by selecting effective chemical cloth acid process and high efficient new acid system.In view of the problems existing in the multi-layer/long well acidification process in L19-3 oilfield,combining with the characteristics of the reservoir and requirements for the acid system,the paper tries to develop a self-diverting acid system suitable for the sandstone reservoir of Bohai Bay oilfield and explore the influence of the permeability difference on the diverting effect.In this way,the efficiency of acid liquid placement in oil well and water injection well is increased.What’s more,the effect of uniform acidizing for oil well and uniform plugging removel for injection well are achieved.(1)Through a series of evaluation experiments,we re recognize and analyze the reservoir characteristics and provide basic information for future research.Combined with reservoir geology and reservoir characteristics,requirements for acid system for acidification of oil well and injection well are put forward.(2)Oleic acid,N,N-two methylamino propylamine and sodium chloroacetate are used as raw materials to synthesize oleic amides propyl betaine through amidation and quaternylation reaction.The surfactant depends on the concentration of hydrogen ion to control the viscosity of acid solution,and meets the requirement of sandstone reservoir for diverting agent.In addition,the reaction conditions such as reactant mass ratio,reaction time and reaction temperature are optimized.(3)Factors affecting the rheological properties of oleic acid amide propyl betaine are tested and analyzed,such as surfactant concentration,temperature,acid concentration and metal cation.The rheology of fresh acid is tested and evaluated.The influence factors of the rheological properties of the residual acid,such as the acid concentration,temperature,shear rate and related additives,are tested and analyzed.(4)The optimization experiments and performance evaluation of key additives are carried out.A series of compatibility experiments are carried out.In order to study the diverting performance,a static test,a single core plugging experiment and a double core shunt experiment have been carried out.A double core parallel experiment is also carried out to investigate the diverting effect of diverting acid by the injection of sandstone acidification treatment solution.Artificial small core and long square core are also used to explore the influence of permeability gradation on the diverting effect.