Integrated Production Optimization using Implicitly Coupled Multi–Reservoirs and Facility Modeling with Miscible Gas Injection EOR in South Oman

Abstract

An Integrated Production System Model (IPSM) is an essential tool to study the interactions between multiple reservoirs, wells and surface networks for any integrated optimal development. This paper describes a fully implicit IPSM for two interacting production system networks (critically sour facilities with >5% H2S) with multiple oil reservoirs and undergoing Miscible Gas Injection (MGI) for Enhanced Oil Recovery (EOR) using produced sour gas from oil and condensate fields in South Oman. A range of up to 17 reservoir models, with different complexities, were incorporated in this IPSM. Larger reservoirs were modeled using 3D, fully compositional, numerical discretized models, whilst smaller ones were based on decline curves. A new production system is connected to an existing system, within a closed loop, honoring all nodal constraints, e.g. multi-stage separators, gas compression, gas sweetening, and heat exchangers. Priorities were assigned such that sweet gas export commitment is achieved first, followed by miscible gas injection to oil reservoirs and gas recycling to a condensate reservoir for production optimization. An Equation of State (EOS) model is used to model the complex interactions of different fluids, at reservoir and facilities levels. This IPSM has been set-up to provide accurate and consistent short to long term forecasting, optimizing on oil/gas production and recycled gas injection. All surface network constraints are honored and cut-back logics based on different prioritizations are behaving reasonably. Current capabilities include determining the optimal strategy for development of these portfolio of reservoirs based on the different value drivers, tracking of composition for components like H2S that limits gas sweetening units and affects miscibility in reservoirs and longevity of the facilities. The IPSM is also intended for optimizing near-field potential in mature fields and developing new fields while operating under the facilities constraints. It can be used to analyse various business opportunities in the reservoirs and surface facilities (such as low-pressure operations) to the appropriate degrees of complexity. This work involved integration and collaboration across multiple disciplines, identifying complex interactions between facilities constraints and reservoir performance (associated with produced gas reinjection), through an implicitly coupled EOS IPSM. Fluid blending in the surface network, and recycling and apportioning of produced gas from the seventeen reservoirs for re-injection after meeting export requirements and honoring all system constraints and priorities makes this problem quite unique and challenging