Optimisation of Well Scheduling with Loading and Minimum Turn-Down Constraints

Abstract

Abstract Breagh, a moderately tight gas field in the Southern North Sea started production in 2013. Until compression is available, Breagh has been constrained by minimum turn-down constraints and the need to keep wells flowing above their loading rates leading to complicated well scheduling optimisation. This paper describes a tool that makes hourly forecasts for cycling and non-cycling wells used to rapidly assess a proposed well scheduling for loading and minimum turn-down compliance. The Breagh short term forecasting tool uses empirical equations to match historical pressures and production rates. Parameter values have been found for each of the existing nine flowing wells which match build-up pressures, predict the initial gas rate via a pseudo-PI approach and decline the gas rate over its flowing period. By matching the wells’ hourly rates over multiple months, these same parameters are then used to predict future well flows and display the results in a number of graphics for easy history matching and well scheduling assessments. Due to the steep decline of the cycling wells, an hourly forecast was required. Excellent matches were obtained over multiple month periods. A single framework was found to be sufficient for both cycling and non-cycling wells, but with different sets of parameters: the Breagh short term forecasting tool was born and has proved to be very useful for: short term forecasting over a few months; rapid assessment of well schedules, including cases where a well issue has required a well to be closed in at short notice and alternative well schedules devised to enable uninterrupted production; and to assess the need for additional production tests to further lower minimum turn-down. A new framework is provided for the performance forecasting of cycling gas wells, some with significant declines on an hourly basis, thus enabling rapid response times to well schedule optimisation issues. The following are the key findings:Hourly data rather than daily were required to make quality forecasts for cycling wells with extending a few months ahead.New potential well cycling schedules could be rapidly assessed, and more optimal schedules selected.The Breagh Short Term Forecasting Tool was one of three key contributors to returning Breagh from weekly cyclic to continuous production.