Hydraulic Fracturing in the Congo Onshore: Continuous Optimization Improves Productivity

Abstract

This paper describes the successful ongoing process of optimizing hydraulic fracturing designs in a well campaign in Congo onshore to create best practices for continuing development. The fracture design program began by characterizing and evaluating the rock formation and its compatibility with stimulation fluids, including mineralogical and geomechanical properties, as well as regained permeability. For example, laboratory testing determined that the formation was soft and highly sensitive to water, indicating that a water-based fracturing fluid would require specialty additives to minimize formation damage. During the stimulation campaign, treatment designs were modified to optimize the final propped fracture geometry. For example, designs and operations were changed over time to relieve proppant embedment in the soft rock. In fact, post-frac evaluations demonstrate critical correlations between the final propped frac concentration and conductivity achieved versus production increase over time. The paper presents results to date and lessons learned while engineering the fracture stimulation design and execution to maximize oil production. Introduction Hydraulic fracturing, represents a great opportunity of business, it is the first time on eni's onshore field in which this technology has been applied in a massive campaign. Hydraulic fracturing operations in West Africa are not as common as in the US, Latin America and the Middle East. However, in Congo fracturing technology is spreading and has overcome more than few difficulties since the practice began: logistics and operational issues, related to the complexity of the field and even the complexity of the zones to be fractured. The most significant challenge has been the formation, which has shown through laboratory testing to be soft and strongly water-sensitive. For a recent campaign in Congo, a large number of hydraulic fracturing operations have been performed to stimulate productivity in the M'Boundi field. The success of this hydraulic fracturing campaign has been achieved by studying the reservoir to choose an initial fracturing fluid and develop some initial frac designs, and following each operation with thorough post-job analyses and carefully organizing the logistics. Currently, the contribution to the daily global production of the field, through fractured wells, represents more than 30 %, opening new horizons to the application of the technology in others eni's fields worldwide. In this paper, results of lab tests are described, allowing the identification of critical issues, such that of the formation heterogeneity, soft formation highly sensitive to water (particularly the risk of proppant embedment), the choice of fluid to be used, the equipment and the logistics and operational issues overcome in more than two years of operations and more than 60 jobs pumped. Analyses are presented to correlate some key parameters of frac jobs (conductivity of the fracture, proppant concentration) with the wells' production performance, confirming lab test results and allowing the definition of a strategy of improvement for the pumping in this type of formation, maximizing oil recovery.