Nitrified Acid Fracturing Treatments in HPHT Carbonate Formations: Results of the Large Campaign in the Middle East

Abstract Hydraulic fracturing for tight and depleted high-pressure high-temperature (HPHT) gas carbonate reservoirs poses a particular challenge as reservoir pressure is often not sufficient to support post-fracturing flowback. This paper will describe the utilization of nitrogen in the fracturing treatment to guarantee successful flowback of the fracturing fluids. When depleted wells are stimulated with traditional acid fracturing fluids, nitrogen lifting is required to allow for flowback. Incorporating nitrogen into the treatment itself eliminates the need for this resulting in time and cost reductions as well as more efficient utilization of resources. Since nitrogen is pumped as a gas, specialized high-pressure pumps are required for the operation. In terms of treatment design, one of the benefits of using nitrogen to energize the treatment fluids is its ability to be used in most conventional pumping schedules due to being chemically inert and therefore compatible with a wide range of fluid systems. Because this type of treatment involves pumping energized fluids, it is important to discuss the additional safety concerns inherent in the operation. Equipment requirements, typical treatment design and fluids, and job execution are also presented. With extensive utilization over the past several years, the benefits and effectiveness of this technique have been clearly proven to outweigh the minor changes in equipment and operational requirements over conventional acid fracturing stimulations. Candidate selection is of particular importance to the success of the treatment, and consideration must be given to the reservoir conditions when evaluating a potential application. Improvements in operational efficiencies compared with traditional completions utilizing nitrogen lifting are also highlighted. Additionally, improved flowback results from the energized fluids have been observed and given per categories of wells reaching up to 48% productivity gains when compared to conventional fracturing technique, mainly in the depleted areas of the formation. The study also provides comprehensive candidate selection guidelines to choose either regular or nitrified acid fracturing techniques based on productivity index analyses. Although the study focuses on nitrified fracturing treatments in the Middle East, the technique can be widely applied to many tight and depleted carbonate formations worldwide. Therefore, the operational overview, treatment design, and overall field development results presented in the paper will be of significant interest to stimulation professionals throughout the industry.