Development and testing of an advanced acid fracture conductivity apparatus

摘要

Since the oil price has been stable at a high level, operators are trying tomaximize their production to get maximum return of investment. To achieve thisobjective, all kinds of well stimulation technologies are applied to the proper candidatewells. Acid fracturing is a standard practice to increase the production rate and toimprove ultimate recovery in carbonate reservoirs. There have been successful cases inmost carbonate reservoirs around the world. However acid fracture performance variedsignificantly with the acid fluid type, pumping schedule, formation composition, rockembedment strength, reservoir pressure, and other downhole conditions. Engineers havetried to understand the acid transportation and dissolution mechanism and, wanted tooptimize each acid job design and to predict the acid treatment effect.We made an acid fracture conductivity apparatus capable of conducting acidfracturing experiments at conditions as close to the field treatment conditions as possible.With reliable laboratory experimental results, engineers will understand the acidfracturing mechanism and build a realistic model to improve the treatment design.Our lab facility is customized for its tasks. The setup and experimentalprocedures are optimized to make the operations feasible and the results accurate. Thefracture conductivity cell is per API standard and is modified to accommodate thick rocksamples. The thick rock will create a similar downhole leakoff condition when acidflows across the fracture surface. The Chem/Meter pump is able to provide a pump ratethat matches field operational conditions. All necessary measurements are recorded.The experimental data are processed and interpreted with statistics methodology.Some preliminary acid fracture conductivity experiments were carried out. A fewdifferent types of fluids are used to investigate the effects of acid concentration, fluid viscosity, and emulsification. All acid fluids had 15, 30 or 60 minutes contact time withcarbonate rocks. The acid leakoff velocity is controlled at velocity 0.003~0.01 ft/min tosimulate the downhole condition. Most of the experiments are successful. They can beused to validate an acid fracture conductivity model.