Most deepwater high rate wells are completed with sand control to avoid sanding issues, especially for a subsea development. However, sand control adds significant Capex to the development besides causing additional pressure drop across the completion. In addition, experiences to date have shown that sand control completions tend to increase in mechanical skin over time due to solids plugging or scaling leading to additional Opex required to stimulate these wells.
This paper describes the key steps taken for two major subsea deepwater developments in Ghana, in order for a paradigm shift towards Cased and Perforated (C&P) completions for full field implementation. Oil production and water injection in both fields are primarily from sand facies associated with Clustered Frontal Splays and Confined Channel Complex. All completions deployed initially were equipped with downhole sand control (mainly Frac and Packs), but driven by well impairment issues early in field life, a thorough review of completion type was initiated which lead to a staged implementation and move towards C&P design for all high rate oil producer and water injector wells.
Modified API RP 19-B Section IV tests were performed using core material from the fields for catastrophic sanding risk evaluation over well lifecycle, and examination of sanding under steady state flow conditions with varying fluid type. Laboratory test results and simulation data were then used to determine safe operating envelopes for the designs. A staged implementation commenced with C&P completions in two wells with the use of High Set Screens (HSS) with capability of bypassing the screens if required and ‘real-time’ downhole gauges to monitor pressure drop across the screens over time. Based on the confidence attained from the sand free production data from both these wells, HSS were removed altogether from subsequent completions.
Well performance data have demonstrated the successful application of C&P completions in typical deepwater turbidite setting. C&P completions have significantly lower skin than other completion types applied in the same fields and are capable of delivering more than 20,000 stb/d oil rates and more than 50,000 b/d water injection rates.