Fully Compositional Integrated Subsurface-Surface Modeling:Carito Production Unit Case

摘要

A fully compositional integrated subsurface-surface model for the Production Unit Carito was develop to support a future exploitation plan that considers the maintaining of the oil production plateau and an aggressive infill drilling for the next 3 years.These issues make imperative an integrated asset modeling that conduct and help the reservoir management,decision making and accurate estimation of additional facilities capabilities. The Production Unit Carito comprises two of the most important fields located to the east of Venezuela: El Carito and Mulata.These fields present deep and complex reservoirs with an unconventional column of fluids,showing a marked compositional gradient which cover from an initially undersaturated gas condensate at the top of the structure to an undersaturated black oil zone toward the base.The OOIP is about 7,000 MMSTB and the current oil production rate reaches 230 MSTB/D.A secondary recovery process was implemented over 12 years ago,based on the injection of approximately 1,000 MMSCF/D of natural gas. Because of prevailing reservoir pressure conditions,the increasing volumes of produced gas has led that some points of the surface facilities reach their operational limits.Furthermore,the first of all,187 well models in compositional format were built,performing sensitivities to define the multiphase flow correlations for vertical pipe and for critical/subcritical flow in chokes,considering dynamic gradients and production tests.A network model,which comprises more than 800 Km of lines,was also built in compositional mode honoring line sizes,lengths,elevation changes and connection points,reducing the number of nodes to decrease computing time.The robust numerical simulation model comprises more than 300,000 active cells,and represents the most reliable characterization of the reservoirs.Each model was firstly initialized and isolated run to discard internal inconsistency.Finally,the full integration was done considering the sand face on the wells as the coupling point. The integrated subsurface-surface simulation allowed predicting the behavior of reservoir production taking into account the constraints of the surface facilities.In this way,it was reduced the uncertainty of forecasts,and were identified limitations at surface facilities.It was also possible to determine accurately the details of the hydrocarbons streams at different pressure stages of the network,with an excellent matching with the oilfield production data.