This paper describes the use of process simulation models to evaluate alternative drilling programs, and specifically to quantify the band of uncertainty in time and cost. The discussion also includes consideration of the interaction between the drilling program and the selection, design and installation of the process facilities. It is recognized that deepwater drilling operations are complex and risky endeavors. The cost of these drilling operations can represent a very significant proportion of the total field development, and so it is essential to understand the causes and magnitude of this risk. Modeling using Monte Carlo simulation is a natural tool to assess these risks and has been available for many years but, owing to the complexity of building and maintaining the models and evaluating the results, it has not often been applied to deepwater drilling. The authors have used the SLOOP simulation software to assist in planning and evaluating deepwater programs both West of Shetland and in the Gulf of Mexico. These were used to help plan an exploration program, and to evaluate alternative development drilling options. They were also used to help evaluate spar platform alternatives for a Gulf of Mexico field development. A key consideration in using simulation is the presentation and evaluation of the results. Presenting risk-based evaluations in a meaningful and concise format is difficult. With the use of SLOOP and interfaces to spreadsheets, ARCO and Vastar (now both merged into BP) and BMT have developed an approach which provides the results in a compelling and concise manner. The simulation results presentations were key ingredients in planning the West of Shetland Block 204 exploration program and in selecting the final development scenario for Horn Mountain. Introduction Deepwater operations are complex and risky endeavors. Specifically, it is very difficult to estimate the impact of the metocean environment (wind, wave and current) on drilling operations. This is particularly important in areas with harsh conditions, as it is essential to understand the magnitude and causes of the risk, in terms of both timing and cost. Modeling using Monte Carlo simulation is a natural tool to help quantify the impact of this type of risk. Though the method has been available for many years, it has not often been applied to operations such as deepwater drilling, but with the availability of fast and very economical computers and the development of convenient simulation software, simulation can now readily be applied to deepwater operations In this paper we discuss the use of this simulation model by ARCO and Vastar (now both merged into BP) to assist in planning and evaluating deepwater drilling programs both West of Shetland and in the Gulf of Mexico. For the West of Shetland operations, simulations were performed to plan the exploration program and to evaluate alternative development options. In the Gulf of Mexico, Vastar recently used the simulation to model alternatives for the Horn Mountain development options.
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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