Studyon Change Regularity Of Acid-Etched Fracture Conductivity Of Carbonate Reservoir

Fracture conductivity is an important evaluation criterion, which is used for the evaluation of acid fracturing effect in reservoirs. Therefore,the study on fracture conductivity influence factors and variation of fracture conductivity provides the foundation ofimproving fracture conductivity, and it plays an important role in acid fracturing construction.In this paper, carbonate reservoir is chosen as the study objective, in the condition of different acid types, acid concentrations, temperatures and flow rates, acid etched fracture conductivity shows the declining trend under the closure pressure. Acid-rock reaction rates can reflect different reaction conditions and the interaction between different factors. Based on the relationship between acid-rock reaction rate and fracture conductivity, prediction model of fracture conductivity is built.Main results are shown:(1)The formation mechanism of the acid-etched fracture surface andthe fracture conductivitiescaused by different surface morphologytypes were analyzed. The influence of closure pressure, acid-rock reaction rate and other factors on the fracture conductivity was studied.(2)Acid etched fracture conductivity experiments were designed and completed at the conditions ofdifferent acid types, concentrations,temperatures and flow rates. Fracture conductivities at the closure pressures of 10-50 MPa were obtained. Results shows that with the increasing of temperature and acid concentration and acid flow rate, fracture conductivity shows a rising tendency, but with the increasing of closure stress, the tendency is not always like that because ofthe difference of the fracture surface morphology.(3)Through the acid etching fracture experiment, the quality of corrosion, time and area of fracture surface can be obtained which can be used to study the relationship between acid-rock reaction rate and fracture conductivity. Average acid-rock reaction rate shows a rising tendency with the increasing of temperature, acid concentration and acid flow rate. Combing the change law of fracture conductivity under single condition of acid etching fracture, facture conductivity.(4)Base on the previous study result of the team of reservoir stimulation, fracture conductivity data were analyzed after data drawn to be curves. Differential coefficients of the curves are used to analyze the decreasing amounts of fracture conductivity. Semi-logarithm relationship of the curve is used to get the relevant parameters(a, b).(5)The minimum radius of curvature of the particular points of the curve is analyzed. With the increasing of closure pressure, the retention rate of the conductivity increases. The model related to therelationship between pressure and conductivity is built.(6)The relationship between the acid-rock reaction rate and conductivity is analyzed. Combing the relational expression of the pressure at the minimum radius of curvature and fracture conductivity, the relation model of the acid-rock reaction rate and fracture conductivity is built. The final models are different at the condition of different acid types.