Case Study of Proppant Fracturing Campaigns in a Mature Field, Onshore Gabon

Abstract Onshore Gabon, two proppant fracturing campaigns conducted between 2021 and 2023 resulted in the treatment of 25 wells. The mature asset, which has been in production since 2009, had experienced falling production and reduced reservoir pressure. To extend the life of the asset, a series of production and injection wells was selected for proppant fracturing. With a large number of total wells in field, a methodology was developed to screen, assess, and select final stimulation candidates. This was followed by the analysis of each well, type of intervention required, and pumping data for an optimum fracturing treatment. With 300 wells to consider for evaluation, the selection process started with simple elimination and progressed to more detailed analysis before the final 30 well candidates were selected. Many of the initial wells were eliminated based on well configuration and existing status. Then, a review of logs and the reservoir profile led to the final candidate list. This methodology for mature assets enabled design teams to focus on wells with the potential to give the most benefit from stimulation with the least amount of investment. Fracturing design was initially based on a single-well mechanical earth model using log assessment. This was further calibrated using pumping injection testing plus pre- and post-injection temperature logging. This enabled sufficient understanding of mechanical properties for proppant fracturing design. Post-treatment analysis of production data enabled assessment from fracture geometry and confirmation of the field mechanical model. Fracturing was carried out using a combination of conventional and channel fracturing techniques, plus the use of screens to prevent proppant flow back. Between 2021 and 2023, 25 wells were successfully stimulated, placing over a half a million pounds of proppant using conventional and channel fracturing methods. These wells were stimulated with either completion in place or utilizing a fracturing string with or without a packer for zonal isolation. The campaign demonstrated that workover operations can be achieved without a workover unit and can be supported with an external crane. Production results from each of the wells were analyzed, ranging from 50 to 300% increase in oil production, to give a better indication of fracture geometry and to help support field production. Contributions to hydraulic fracturing planning and operations from these campaigns include the assessment of fracturing design using multiple fracture simulation models including standalone simulators, integrated reservoir workflows, nodal analysis, the methodology of candidate selection, and a process for mature field intervention in remote locations.