The Management and Optimization of a Major Wellwork Program at Prudhoe Bay

Abstract

J. P. Martins, SPE, J. M. MacDonald, C. G. Stewart, SPE, and C. J. Phillips, SPE, BP Exploration (Alaska) Inc. Abstract Over 800 remedial wellwork operations are performed each year at Prudhoe Bay. A hierarchy of performance measures and targets has been developed to facilitate the management and optimization of such a large and costly program of work. The paper discusses the Wellwork Evaluation Tracking System (WETS) which has been used over the past 7 years to assess the benefits achieved by a given wellwork operation, taking into account the appropriate facility constraints. The paper describes the process employed for using the performance measures to ensure the timely identification of both problems and opportunities across the field and it provides numerous examples of how the success of the wellwork program has been improved, despite more complex candidates, with the use of the performance measures. Introduction The Prudhoe Bay field currently produces almost 1 million barrels of oil per day (bopd), from some 1200 wells. A major program of remedial wellwork has been conducted for the last several years since the field went on decline, with the purpose of maximizing oil production and reserves recovery while controlling excessive gas and water production. The wellwork program involves some 800 operations per year (excluding surveillance), and currently contributes approximately 170,000 bopd (or 17%) of the field rate, when the residual benefits from previous years' programs are taken into account (Fig. 1). In 1991, two years after the field came off plateau, well work accounted for some 400,000 bopd (or 30%) of the production. The wellwork techniques employed include hydraulic fracturing, matrix acidizing, rig workovers, coiled tubing gas and water shut-off operations (involving 34 cements, polymers and new mechanical options) plus a wide range of other routine coiled tubing operations. As the field matures, the technical challenges become more complex and there is a continual need for new technology. In order to manage and optimize such an extensive program of work, it is essential to have a comprehensive and consistent method for analyzing the results on a regular basis. This has been achieved through the development of a hierarchy of performance measures (Fig. 2). These range from the high level measures required from a management perspective to assess the commercial value of the program, down to more detailed technical measures required by the specialist engineers to optimize wellwork techniques and control the level of technical risk. Each wellwork category is regularly analyzed in order to evaluate the performance of both existing and evolving technologies; to update guidelines for job designs and candidate selection; and to identify the need for new technologies to tackle emerging problems. In addition, some performance measures are used to incentivize BP's Well Service Alliance contractors, by linking their total remuneration to measured performance against agreed targets. This paper starts by describing the Wellwork Evaluation Tracking System (WETS), which has been used and developed over the past 7 years, to assess the incremental benefits achieved by each individual wellwork operation over time, taking into account the gas handling constraints of the surface facilities. The combined WETS data from all wellwork operations are used to track the success of the whole program and form the basis of a hierarchy of commercial and technical performance measures which are used to optimize the wellwork program. P. 193