Many of the once prolific North Sea reservoirs have been reduced to mature assets, with a majority having reserves down to a fraction of their initial value. A significant number of isolated pockets of hydrocarbon bearing sands, however, remain available for production. The advantage of pursuing such bypassed assets is the availability of an existing infrastructure to support any incremental production. The biggest challenge when considering production enhancement initiatives is the marginal nature of the associated economics combined with project risk. In addition, marginal and mature assets seldom generate required engineering firepower to solve complex problems. Lack of investment results in decreased production and downward spiral that only can result in often-premature field abandonment. This paper describes how Marathon identified a requirement for an alternative commercial arrangement and together with a selected service company, built an effective team that rejuvenated a dwindling gas asset. An inter-disciplinary study was initially undertaken to quantify and manage economical risk associated with this project. Previous attempts at rejuvenating production were revisited to assess reasons for their ineffectiveness, or success. An alternative commercial model was then applied to help overcome the marginal nature of the economics. A data acquisition campaign was subsequently undertaken to determine the optimum intervention alternatives. Successful execution of the intervention activities has delivered a two-fold increase to total field production. Several recently introduced technologies were employed during the course of the project. The project also spawned multiple field practices. Their conceptualization, field implementation and long-term effects on production are also described. Contributions. This paper will present the application and results from several initiatives, including:Descriptions of an alternative commercial model, where the operator and service company mutually participate in the project risk, and its rewards.Implementation of the lift-log procedure, a single trip, combined, coiled tubing N2-lift and production logging operation.Utilization of scale-inhibitor impregnated proppant. This specialized proppant prevents loss of conductivity due to scale deposition within a fracture.Technical, commercial and operational best practices for use with mature field rehabilitation projects. Introduction The Beinn field was the first high pressure gas condensate development in the North Sea. The field is located in North Sea Block 16/7a and lies structurally below the North Brae field at depths of 13,700 to 14,700 ft TVDss (Figure 1). The reservoir is composed of shallow marine sandstones of the Middle Jurassic Hugin Formation with four distinct hydrocarbon bearing reservoir intervals. Reservoir quality is moderate with porosity averaging 12% and permeability ranges of between 2 and 100 millidarcies (average field perm is 74 md). Due to the low permeability in some of the reservoir layers, hydraulic fracture stimulation was attempted on three of the four completions. The first treatment (B20) was considered to be very successful and the others showed marginal improvements. The Hugin Formation fluid is a gas condensate with initial yield of 137 bbls/MMscf. Due to the high initial pressure (11,347 psi at datum) and the low dew point (6,938 psi), the reservoir was produced under depletion rather than gas cycling. First production from the field was achieved in 1992 and drilling of the four well development was completed in 1995.

A new application of electric wireline tractors in combination with the well milling technology has been successfully proven in an offshore Equatorial Guinea well. In July 2011 on a small, unmanned offshore platform in Equatorial Guinea, a downhole tractor and a milling tool were conveyed on electric line to remove an obstruction created by Lost in Hole (LIH) electric line cable and production logging tools (PLT). By using customized core milling bits, 13 successful milling runs were made. During this unique operation, most of the milled wireline material was recovered, and the challenges of controlling torque and milling penetration were achieved. In between milling runs, slickline fishing attempts were made in order to recover the remaining LIH wireline. After the last milling run, a major breakthrough was made when the PLT string moved downhole to a position that uncovered the proposed new completion interval. Ultimately the well was perforated and returned to production at projected gas and condensate rates. Milling of wireline and other well bore obstructions on electric line offers a cost efficient alternative technology to existing methods. Furthermore, it offers reduced Health, Environment and Safety (HES) risk benefits and logistical advantages. This paper will describe the actual process from preparation to completion of this first-of-its-kind fishing operation.

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