Research And Application Of Well Fluids For Removing Plugging And Reforming Of Low-permeability Reservoirs In K Area

At present,the development potential of low permeability oilfields in China is enormous.However,reservoir damage directly leads to the difficulty of development of such oilfields.Therefore,reducing reservoir damage and effectively removing and reforming reservoirs are the key to enhance the development level of low permeability oilfields.In this study,taking the low permeability reservoirs in K area of Bohai Bay Basin as an example,under the guidance of reservoir protection theory,based on the indoor micro-analysis,the geological characteristics,reservoir physical properties,fluid properties and potential reservoir damage factors of the low permeability reservoirs are analyzed and evaluated.Furthermore,the optimum and experimental evaluation of removal acidizing fluid and reformed f'racturing fluid are carried out,and further optimization of corresponding engineering technology is carried out.By means of field tests,the engineering application effect of the formula has been examined,which provides an important theoretical and experimental support for improving the removal and reformed effects of low permeability reservoirs in K area and for removing reservoir damage.Finally,the formula and technology of the injection fluid for plug removal and reconstruction of low permeability reservoirs in K area have been formed.The main achievements and understandings of this study are as follows:The fluid sensitivity of low permeability reservoirs in K area is revealed,which lays a foundation for the optimization of plugging removal of injection fluids.The speed sensitivity of group z4 is moderately weak,the water sensitivity is moderately weak,the acid sensitivity to hydrochloric acid is moderately strong,and the soil acid is moderately weak;the speed sensitivity of group z5 is moderately weak,the water sensitivity is moderately strong,the critical salinity is 25 000 mg/L,the acid sensitivity to hydrochloric acid is moderately,weak,and the acid sensitivity to soil is moderately strong;the velocity sensitivity of group Ek2 is weak,and the water sensitivity is moderately weak.The sensitivity was moderate to weak,the acid sensitivity to hydrochloric acid is moderately weak,and earth acid had no acidity.The f'ormula of acid shutof-f fluid is optimized and evaluated,and the corresponding technology for optimizing acidification is applied in field.On the basis of theoretical research,through screening different acid additives and comparing experiments,the formula of acid fluid is optimized to be 15%HCl+3%HF+2%effective chemical additive DX-3+l%mutual solvent+2%temporary plugging agent.The performance of acid fluid system is evaluated,and the result shows that it meets the given requirements.It is acid fluid system adapting acidizing plugging removal of low permeability reservoirs in K area.A method of temporary plugging acidification by throwing balls for multi-layer acidification is applied and the corresponding technology and parameters are optimized.Based on this method,acidification tests have been carried out in Exploration Well D15 of K Reservoir.The result shows that the residual liquid backflow rate has been improved obviously,the success rate of operation is 100%,the liquid production has been increased obviously,and the et'tect of acidizing measures is obvious.The formulation of low damage fracturing fluid is optimized and applied in the field.Aiming at the problem that the residue of early fracturing fluid after hydration seriously affects the permeability of formation and sand filling fracture,high qualitied additive is optimized and a new type of GHPG low damage fracturing fluid is developed.The formula of this new fracturing fluid is as follows:0.5%GHPG thickening agent?0.2%FSJ-2 dispersant+0.1%CYY-02 assistant drainage agent+2%KCI+ 2%A-28 clay swelling inhibitor.The result shows that GHPG thickener has the low gel breaking residue and little damage to reservoirs,which could reducing reservoir damage sharply.It is a high-quality fracturing fluid with good temperature resistance and low damage.Large displacement construction technology is adopted in the field,the scale of modification is increased.Multi-particle combination sand adding technology ensures the success rate of construction,realizes high conductivity,applies multi-element strong drainage technology,guarantees the smooth development of blowout operation after fracturing,and has been applied in W98-4 well,the residual liquid backflow rate is high and the production-increasing effect is obvious.