Study On The Volumetric Acid Pressure Supporting Acid System Of High-calcium Fractured Tight Sandstone Reservoir

The target reservoir is the sandstone reservoir,which characterized by buried deep,ultra-high temperature,density,natural fractures filled or half-filled by calcareous,high tectonic stress,high reservoir pressure etc.The reservoir which has certain mechanical conditions and material conditions can choice volume acid fracturing technology as stimulation treatment,and field test has achieved good production effect.But for this kind of reservoir volume acid fracturing technology is still in the sporadic trial stage,relevant acid system is also in the exploratory stage,the current application of the acid system is mainly for the conventional mud acid system,but acid system must have some special performance because of the special conditions of the target reservoir,conventional acid systems often affect the stimulation effect of volume acid fracturing.Therefore according to reservoir conditions,we need to develop a set of suitable,feasible and efficient acid system.In the paper specific contents are as follows:(1)Fully considering the mineral composition and reservoir characteristics,this paper proposes multistage different acid systems which include "far well acid" "middle well acid""close well acid" injection mode,and puts forward the design principle of three kinds of acid.Finally the design principle provides the new ideas and guides the development of new acid system.(2)For the performance requirements of efficiently dissolving calcium fillings,inspiring and communicating natural fractures,reducing the damage of string,by the theoretical analysis and experiment research adsorption,chelation,corrosion and other features of acid system,creatively develops a set of non-fluorinated organic chelating low damage acid system "far well" acid system,which can form the pore structure in the tight because of the selective etching properties.The paper also proposes the law and affecting factors of the formation of acid etching channels in the tight sandstone/carbonate reservoir.(3)For the performance requirements of efficiently etching fracture surface,deeply extending fracture,removing drilling fluid damage,reducing the damage of reservoir and string,develops a set of composite "middle well" acid system which contains phosphoric acid chelating agents,chelating copolymer,organic fluoride etc.By experiments,theoretical analysis and simulation calculation researches the acid characteristics of retarded capacity,corrosion,low damage and others.The paper also considers the drilling fluid damage degrees of different widths of fracture and removing damage situation of acid,researches the acid etching forms of rock fracture surface,calculates the HF concentration distribution in fracture,reveals the retarding mechanism of retarded acid.(4)Based on the reservoir conditions of the target area,researches the reaction process and the damage of different acid,eventually forms a set of efficient acid system of volume acid fracturing,optimizes the acid fracturing technology and applies to the test wells,achieves the remarkable effect.In this paper,a new idea of acid system design of volume acid fracturing is formed,a set of matching acid system of volume acid fracturing for fractured tight sandstone reservoir is developed.The research results have some guiding significance of acid system research,the design and achievement of volume acid fracturing.