Conventional hydraulic fracture stimulation techniques have been widely used to enhance production from tight gas reservoirs. Since the initial use of this method to increase production rates, the industry has witnessed continued advancement in terms of fracturing theory, fluids, and techniques. The use of carbon dioxide (CO2) since the early 1960s has continued to be a significant part of these advances. CO2 has been used for many years as an energy source to aid fluid recovery of well stimulation fluids. This technology predominantly has been used to stimulate tight sandstone reservoirs. There are very limited applications for low permeable tight carbonate reservoirs because of complexities associated with the physical and mechanical properties of carbonate rocks and its interaction with fracturing fluid. Nevertheless, the advantages of using assisted CO2 stimulation fluids as the elimination of potential formation damage normally associated with fracturing fluids and very rapid cleanup are still present.
This paper outlines one of the first acid fracturing jobs assisted with CO2 conducted on a tight gas well reservoir in Saudi Arabia. It describes in a simple manner the screening methodology and key parameters considered during selection of a well candidate and the design process, which was based on petrophysical, mechanical, and chemistry properties of the formation and the respective interaction with treatment fluids. Moreover, primary operational procedures and guidelines are discussed, highlighting a safety risk assessment point of view.
Implementing this technique in a more generalized manner in the field can help save considerable operational time and costs. CO2 used to energized fracturing fluids can increase the productivity of the well while using less water and less acid than conventional acid fracturing, which is of primary importance in such a harsh environment, requiring less water consumption.