Optimum Design for Proppant Fracturing to Unlock Oil Potential in a Marginal Low Quality Burgan Sands in the Greater Burgan Field

Abstract

In Greater Burgan Field, Burgan formation is the main oil producing reservoir since the start of oil production and with the reservoir mostly depleted, the focus in the asset team is now on the lower quality Upper Burgan (BGSU) sands with substantial remaining oil. In view of this, a multidisciplinary team is formed to evaluate opportunities to stimulate the BGSU reservoir, establish and sustain production from this reservoir to meet the production targets. The objective is to unlock potential in these tight sands especially targeting to revive old wells back which have drained the underlaying BGSM sands and have significant opportunities in the BGSU. The best way to exploit the resource potential of BGSU for its remaining oil is through hydraulic fracturing technology with an emphasis of its implementation via a thorough review of reservoir, well and completion data maximizing wellbore utilization and minimizing CAPEX investment. The review involves screening a batch of wells with low rock quality and low permeability, away from heavy oil zones and above bubble point pressure, with good shale barrier beneath to avoid fracture propagating into the underlying aquifer. In total, about 100 wells are reviewed from across the Greater Burgan Field for this exercise. Latest reservoir pressure and oil saturation maps for the target BGSU reservoir, built in-house by the asset technical team, are being used to identify wells for potential hydraulic fracturing implementation. Upon a review of historical Proppant fracturing jobs that were performed in five wells in 2015-16 in the BGSU sands, it was summarized that there was a substantial increment to the well productivity, in some cases up to four folds. After the review, detailed numerical well modeling of these five wells is performed with and without fracturing showed that well productivity increase by 2 to 3 times for most of the wells. Although the well productivity improved post stimulation, the wells had high drawdown pressures which resulted in early water breakthrough in few wells. An optimum well productivity can be achieved with large proppant volume placement in the reservoir to connect with the sands away from the wellbore. However, with large volumes there is significant risk of frac propagating "out of zone" increasing the risk of early water breakthrough. Presence of a shale barrier above and below the target zone is an important criterion in candidate selection and design the proppant volume to keep the fracture growth within the target zones and not reach to the zones, especially the underlying BGSM formation, having water. With the lessons-learnt from the past fracturing jobs, detailed modeling and simulation of well performance, a refined list of potential hydraulic fracturing candidates can be generated combined with advancements in the fracturing technology which will greatly enhance the success probability of the stimulation with maximizing well productivity. The successful implementation in the candidate wells will lead to unlocking oil reserve in low rock quality reservoir allowing the development of these low permeability sands for the BGSU upper which will help to achieve the aggressive production target of the South & East Kuwait (SEK) asset.