Propped Fracturing in Tight Carbonates Reservoir – A Case Study

Abstract

Abstract Reservoir properties in the Lekhwair satellite fields targeting carbonate formation (Natih C1) oil reservoir were found to be lesser quality in mobility than prognosed. Post-drilling stimulation was performed using 20% HCl with limited success. A frac stimulation opportunity was considered to unlock the Natih C1 reserves as the permeability is low. An integrated multidiscipline approach was developed to design the frac treatment in carbonates setting. As a result, a significant production improvement was observed in Natih C1 carbonate formation. Conventionally, carbonates are stimulated using acid, however, in Lekhwair satellite fields, the acid stimulation was performed and showed limited success. Extensive reviews were done using multi-disciplinary approach to assess the feasibility of proppant frac treatment in tight carbonate reservoirs. Integration of FMI data, geo-mechanical analysis, petrophysical logs, etc. were used to an optimal proppant frac trial. During the candidate selection, the main challenge in carbonates was to ensure it is designed to contain the fracture height and fracture half-length to an optimum. This was done to avoid lateral uncontrolled fracture propagation towards nearby water injector wells and producers. In addition, mitigate vertical propagation that would potentially comprise the integrity of the cap rock (natural barrier) in a carbonate setting. Initial results from two trials in the first campaign enhanced the inflow and improved production by high magnitude in a sustainable manner. Prior to the frac treatment, and due to poor inflow, the candidate wells were barely producing with very low gross and net oil production. These wells were operated under ON/OFF schedule/regime for reservoir pressure management and in turn mitigate issues with ESP reliability caused by very low rates. Post-frac well treatment results indicated huge improvement in gross and net oil production in Natih C1 carbonates. For example, in one of the wells, oil production increased by 20x and productivity was sustained much longer compared to pre-frac. These wells were able to produce continuously within ESP optimal operating envelope and were removed from ON/OFF schedule. The uptime on these wells improved from 25% to 100%. After the initial campaign, three additional wells were executed and showed continued gains in production compared to the first two trials. Through an integrated discipline approach, the concept of proppant fracture in tight oil carbonate formations were implemented successfully through two campaigns. Specifically, the proppant frac treatments were executed to yield controlled fracture height and half-length. This mitigated the risk of fracture propagation to other wells while ensuring production enhancement. In addition, the proppant fracture concept in tight oil carbonate was assessed to be technically and economically feasible. Overall, the concept can be extended to future field development plans through drilling less wells with proper optimum spacing.