Sensitivity analysis fo treatment parameters on fracture geometry for acid fracturing in carbonates
Engineering Honours Degree 2008
University of Adelaide
Due to the high energy demand, the necessity for hydraulic fracturing to stimulate low-permeable reservoirs has increased. Acid fracturing is a reservoir stimulation technique used to increase the production rate and to improve ultimate recovery in carbonate reservoirs. There have been many successful cases, however acid fracture performance varies significantly with the acid fluid type, pumping schedule, formation composition, rock embedment strength and other downhole conditions. This has lead to the use of different fracture optimisation techniques to identify which treatment parameters have the most influence on the acid fracturing job. Inappropriate values of these parameters cause high treatment cost and poor stimulation success. Therefore, there is a need for treatment design engineers to understand which treatment parameters have the most effect on the success of the stimulation job. With this knowledge the engineer can optimise each acid fracturing job design and predict the acid treatment effect.
This work presents sensitivity analysis on two different fracture geometries and includes three models that account for the different fracture geometries, two being 2-dimensional and one being pseudo 3-dimensional. The models account for acid fluid type, pumping schedule, formation composition, rock embedment strength and other downhole conditions and provide a realistic description of the hydraulic fracture geometry. These models serve as tools to visualise hydraulic fracture propagation and help show the effect each treatment parameter has on the fracture geometry and fracture conductivity, thus the ultimate success of an acid fracturing stimulation job.
Through sensitivity analysis it has been determined that the power-law rheological properties are the most important parameters that affect the fracture geometry and conductivity. The power-law rheological properties have the added benefit of helping control leak off which is a key factor for optimal acid fracturing. Injection rate and injection time have also been found to be important parameters as they have a large influence on the fracture dimensions.