Research On Acid Fracturing Liquid System For Reef Limestone Reservoir In K Oilfield,Indonesia

K Oilfield of Indonesia was put into operation in July 1981,with an original oil geological reserve of 1.4×10~8 barrels.After 30 years of development,crude oil recovery rate of K oilfield is only 23.6%.Therefore,it is urgent to introduce new technologies to increase oil recovery.Based on the geological eservoir characteristic of this field,also with the formation stimulation history and literature search,found that acid fracturing technology may serve the problem of this low pressure reef limestone formation.In this paper,research of acid fracturing reservoir reconstruction technology was carried out combining with geological reservoir characteristics of K oilfield.A series of core analysis tests have been conducted on core(or simulated core)samples in order to master physical characteristics of reef limestone reservoir in K oilfield,Indonesia.The main contents include core X-ray diffraction,core scanning electron microscope,rock slice image analysis,and core stress sensitivity test and acid-rock reaction kinetics experiment.Composition,structure and characteristics of the core,stress sensitivity and kinetics of acid rock reaction were obtained.Found that high viscosity/concentration acid system could make very good reconstruction to the formation core,also should add formation protection addtives such as clay-trol agent/ferre-trol agent to control the stimulation effectiveness for the high content of chlorite and goeschwitzite-montmorillonite mixed layer.These parameters provide data support for optimization of the reservoir acid pressure liquid system.Combined with results of reservoir physical property analysis,the suitable main working fluids and additives were screened and evaluated.The performance of two kinds of acid fracturing fluid system was evaluated through acid rock reaction kinetics experiment and acid corrosion diversion ability experiment.Made some conclusions based on those tests:temperature controlled variable viscosity system and high temperature gelling acid system both can meet the requests based on single additive property,acid dissolve test,heat dilute test,compatibility test,increasing viscosity test,rheological property test,wettability test,resist shearing test,etc..But for the limitation of some additives,the application scope would be verified because the temperature request.Two kinds of acid fracturing liquid system for K oil field reef limestone reservoir were determined.The temperature controlled variable viscosity system formula is 20%HCl+1%corrosion Inhibitor+0.8%gelling agent+4%cross-linking agent+0.1%breaker+other additives,and the applicable temperature range of this system is 80~120°C.Gelled acid system formulation is 20%HCl+0.5~1.0%gelling agent and other additives,and the applicable temperature range of this system is 80~140°C.On-site jobs can choose the suitable acid fracturing system and performing technology by stimulation request and temperature.Field application results in K oilfield showed that the selected acid liquid systems had strong pertinence,and the stimulation effect was remarkable.Successful rate of the measure was 100%.This provides a good technical reference and basis for such reservoirs.