Abstract
This paper discusses the implementation of dynamic underbalance perforating in a subsea development, which helped address environmental concerns related to flaring during perforating. Use of a new perforating system implemented on recently completed wells has resulted in a significant reduction in flaring while maximizing underbalance during gun detonation. The elimination of flaring has also simplified perforating operations, resulting in significant time savings.
The Terra Nova offshore field is located 350 km off the East Coast of Canada. It is a subsea development producing from a multi layered, highly faulted oil reservoir to a Floating, Production, Storage and Offloading vessel (FPSO). The development plan utilizes high productivity producer-injector pairs in the individual fault blocks to optimize recovery. Initially, standard practice was to perforate wells using multiple runs of wireline conveyed guns, up to 6 runs per well. In order to maximize completion efficiency the wells were perforated in an underbalance condition. The underbalance was generated by flowing back and flaring the well at the Mobile Offshore Drilling Unit (MODU) during each wireline run. The net results were multiple flowbacks per well, with diminishing underbalance for each successive perforating run due to flare rate limitations. The multiple flowbacks increased the risk for environmental incidents due to unintentional releases while flaring. Alternative gun deployment methods had been considered but deemed undesirable due to sump limitations and potential for formation damage.
In order to minimize flaring an innovative perforating technique was implemented. This technique generates dynamic underbalance during gun detonation, mitigating the need to flare the well to create underbalance. Fast pressure gauges were run on wells perforated using this method and the data confirmed that dynamic underbalance was achieved. Successful implementation of the dynamic underbalance system has resulted in elimination of flaring related to perforating operations, and has significantly reduced the potential for unintentional environmental releases.
