Model Study On Acid-etched Fracture Conductivity Of Yijianfang Formation Of Tahe Field

There are many factors affecting the reservoir stimulation effects during acid fracturing of low permeable fields, and the influence of conductivity is most directly. What impact immediately on well capacity is fracture conductivity, and the key to success of acidizing is to form a fracture with high flow conductivity.Acid-etched conductivity experiments of cores from Yijianfang Formation of Tahe field were conducted based on a large number of domestic and foreign literature research, and acid-etched conductivity apparatus under condition of high temperature and high pressure designed by the team of state key laboratory of Chengdu University of Technology. Predictive model is set up of acid-etched conductivity of different acid systems, concentration distribution of acid on acid-etched effective distance is studied, and the relation model of well capacity and conductivity is deviated; finally the feasibility of the model is validated which has certain guiding role to acid fracturing.Main understandings and achievements are:(1)Make a survey of reservoir’s general situation, and describe the restrictions of acid fracturing in detail.(2)Research the definition of the acid-etched fracture conductivity, and analyze effects of closure stress, closure time, acid concentration and acid type on conductivity.(3) Using artificial spilt cores instead of cores with natural fracture, conductivity experiments were conducted and its feasibility is verified. Make detail introduction of experimental method and steps.(4)Analyze the acidizing effects after reactions between cores and gelled acids, variable viscosity acids and cross-linked acids with HCl concentrations of 20%, 15%, 10%, 5%. Results show corrosion quantity of acids and fracture conductivity with high acid strength is higher than that with low acid strength. Conductivity decreases fast with increasing of closure stress, and the value of fracture conductivity is relatively equal before and after acid-etching under closure stress of 50 MPa.(5)Previous prediction model of conductivity did not consider the effect of acid concentration on conductivity. Based on the summary of experimental data, using the relation of closure stress and conductivity under average acid concentration, obtain prediction models of conductivity of different acid systems, prediction model of gelled acids is WKf=33.317Ctexp(-0.10375σ), prediction model of variable viscosity acids is WKf=36.743Ctexp(-0.0792σ), prediction model of cross-linked acids isWKf=5.463Ctexp(-0.104σ).(6)Using the known acid-rock reaction kinetics and effective distances of three kinds of acids, acid concentration distribution on the effective length of fracture was obtained.(7)Based on flow model in formation, productivity model under different conductivities is built:This model is brought into prediction model of acid-etched conductivities under different acid concentrations, and the model is verified, it is provided some guidance to operation.