Simulating Operating & Production Efficiencies for Deep Water Field Developments

Abstract

Computer simulations of oil & gas field operations are extremely helpful in planning field developments in deep water. They may be used to identify optimum or robust strategies, and to assess trade-offs among alternative scenarios. Through series of simulations, different development scenarios can be compared, and the sensitivity to diverse parameters investigated and quantified. The SLOOP simulator was developed in a Joint Industry Project to model the complete operation of offshore oil and gas facilities, including weather and other sources of downtime, well maintenance & subsea interventions, processing, storage and off-loading. SLOOP (Simulation of Long-Term Offshore Oil & Gas Production) has been applied to a range of deep water production scenarios to assess different concepts, and to quantify sensitivities to a wide range of influences. These include well performance and equipment reliability, weather severity and forecast accuracy, intervention resource availability, and thresholds for various operations. Example results are presented to compare simulated production performance for a number of scenarios, and illustrate the influence of reservoir performance and other uncertainties and options, on the production and operability. Introduction Designs of oil and gas production facilities are developed based on economic evaluations, which are in principle optimised on such measures as net present value and rate of return on investment. Three critical inputs to such evaluations are capex (installed cost of the facility), opex (cost to operate the facility through its life) and production efficiency (output of the facility compared to its target capacity). The three are obviously interrelated. Capex investment, such as in more reliable equipment or in higher storage capacities, lowers opex and increases efficiency. Opex investment, such as having dedicated repair and maintenance resources, increases efficiency, and may compensate for, or be necessitated by, lower capex. Even for simple facilities, quantifying the trade-offs among capex, opex and production efficiency is not easy. For deep water developments with extensive subsea systems, comparative assessments must at present be based on very limited experience and track record. For first time applications of system concepts or components, the exercise verges on the intuitive. The number and range of variables are daunting, and include times between failure for diverse hardware, consequences of failure and times to repair, mobilisation time and operating limits of repair resources, capacities of storage and transport, reservoir performance and types, frequencies and durations of well interventions. Virtually all offshore operations have limiting environmental conditions, and are thus subject to weather fluctuations, sometimes accurately forecast and sometimes not. The performance of such complicated systems can be realistically estimated via time-domain simulations, which model all the influences summarised above in as much detail as the data describing them allow. The SLOOP simulator (Figure 1) has been developed specifically for deep water oil and gas facilities in severe environments. In such applications, weather conditions significantly influence production efficiency, and therefore strategies affecting capex and opex investment. SLOOP's origins date from 1995 [1], when Conoco and BMT Fluid Mechanics developed quantitative predictions of the performance of different production systems on the Vøring Plateau, offshore Norway.

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