Study On Mechanical Mechanism Of Carbonate Acid Fracture Conductivity In Tahe Oilfield

Increasing the conductivity of acid corrosion fractures is the main goal of acid fracturing in carbonate reservoirs.The conductivity of acid-etched fractures is jointly determined by fracture width and permeability.In the process of exploitation,the reservoir pressure will change.When the pressure acting on the fracture surface exceeds the ability of asperity to resist breaking,the asperity will be broken.The height of broken asperity decreases,resulting in the decrease of fracture width;At the same time,the broken fragments of the asperity will block the fracture,reduce the permeability,and aggravate the decline of fracture conductivity.Therefore,the property that the asperity can resist the change of reservoir pressure without breaking is called the mechanical stability of fracture surface.This paper first reveals that the ability of fracture surface asperity to resist breaking after acid etching is the key to maintain the fracture conductivity.Based on this theory,a mathematical model of fracture conductivity considering the influence of mechanical strength is established.The model integrates the influence of mechanical properties distribution of acid etched fracture surface,effective support area and support height on the stability of asperity.The mechanical criterion for maintaining the stability of the acid etching fracture surface is clarified.The relationship among etching shape,mechanical properties and conductivity was established.According to the experimental data,combined with the conductivity calculation model,the influencing factors of the mechanical properties of the surface asperity of the acid etching fracture are studied.It is clear that too short or too long acid etching time makes the support area and height of the support insufficient,and it is difficult to resist the change of reservoir pressure,which easily leads to the asperity break and makes the rapid decline of the conductivity unable to maintain stability.Therefore,it is necessary to clarify an optimal acid etching time in acid fracturing to maximize the ability of the asperity to propped fracture.According to the reservoir of Yingshan Formation in Tahe Oilfield,the optimal acid etching time of gelled acid and cross-linked acid in acid fracturing is comprehensively designed by mathematical model,which ensures that the asperity of reservoir fracture surface can obtain the maximum resistance to fracture after acid fracturing,and finally realizes stable fracture conductivity and achieves the effect of increasing production and stabilizing production.Based on the study of the mechanical properties of the asperity on the fracture surface,this paper reveals the mechanical mechanism of maintaining the stability of the conductivity of the acid etched fracture.The mathematical model of conductivity is established,which provides theoretical support and technical means for acid fracturing design and optimization of carbonate reservoir.