Nimr Fields High Permeability Propped Fracturing Case Studies and Lessons Learnt

Abstract

AbstractHydraulic fracturing in oil wells within the Southern parts of the Sultanate of Oman has been considered a niche application until recently. This is due to high formation permeability which is a key differentiator of oil fields in the South compared to the North where hydraulic fracturing is more prevalent in tight gas fields. Yet recently, hydraulic fracturing has gained momentum in the South as it started becoming a major well completion technique to increase production while decreasing drawdown. In addition to growing interest in injector well fracturing to enhance overall injector well pattern performance.While hydraulic fracturing in high permeability formations has historically been attributed to damage bypass and creating a more conductive and a larger effective wellbore radius, it has been considered a risky endeavor in oil wells where post fracturing retained permeability may impair well potential especially in cases where oil is of moderate to high viscosity. Hence in Nimr fields, located Southern Oman, hydraulic fracturing of high permeability zones required a fit for purpose fracturing strategy that maintained good retained permeability at the targeted formation with minimal damage. This strategy included candidate selection using a pre-defined criterion derived from regression modelling, utilization of tip-screen-out designs, enhancing oxidizing breaker concentration for better cleanup and flowback, and optimal artificial lift pump designs to suit newly fracturing zones.In Nimr, several poorly performing producers and injectors were treated in 2021 using hydraulic fracturing after being assessed against a rigorous selection criterion. These included several water injectors. Production and injection results were compared to the initially estimated Folds of Increase (FOI) prior to interventions. All wells achieved the expected estimated gain using a pressure matched fracture geometry estimate. Hence this method has provided a basis for further design optimization to increase production yield. Results have also provided lessons learnt in artificial lift pump sizing and pump seating depth. Injector wells were also assessed in respect to their patterns where results have shown significant pressure support to nearby wells, which in some cases revived wells that were previously shut in due to poor pressure support.The success of hydraulic fracturing in high permeability wells in the South of Oman has driven the increase in frequency and magnitude of these otherwise niche interventions. Although further optimization in candidate selection and treatment designs are needed to ensure capital expenditure is justified by production gain.