A Feasibility Study of Hybrid Thermal and Chemical EOR Methods in a Low-Permeability Carbonate Heavy Oil Reservoir with Strong Aquifer Drive

Abstract

Abstract KOC's Umm Gudair/Abduliyah Tayarat reservoir has large oil reserves but is a challenging target due to low formation permeability and high oil viscosity. This study is focused on feasibility assessment of hybrid thermal and chemical methods incorporating both laboratory and simulation results. A recent updated static geological model for West Kuwait fields was used as the basis to generate a full-field dynamic reservoir model with representative reservoir geometry, heterogeneity, and complexity. Carter-Tracy aquifers were added to model lateral and bottom aquifers. Laboratory data were incorporated to model physiochemical properties. Gridblocks were globally refined to gain better resolution for heavy oil and EOR simulations. The full-field reservoir model was used to systematically study the potentials of hybrid thermal and chemical EOR methods in comparison with conventional waterflood and chemical EOR methods. Our studies show that in order to produce oil at an economic rate, long horizontal wells on the order of kilometers or horizontal wells stimulated by acidizing, multistage fracturing, or multiple laterals should be deployed. Vertical wells yield low oil production rates due to limited contact areas and severe water coning. Aquifer water intrusion from the west side of reservoir overshadows the bottom aquifer and the edge east side aquifer due to the heterogeneity of reservoir permeability. A sector model was extracted from the full-field Eclipse model and further refined to avoid grid effects in simulation of EOR processes. Simulation results show that hybrid thermal and chemical methods (hot polymer/Surfactant-Polymer/Alkaline-Surfactant-Polymer flood) can effectively increase oil recovery from high-permeability, high-saturation sweet spots of the Tayarat reservoir. With the help of horizontal wells, hot polymer flood shows the best performance after 20 years of oil production and yields more than 30% of incremental oil recovery. Hot Surfactant-Polymer flood shows slightly lower cumulative oil recovery but sustained oil production rates and less production decline in the late stage of the flood. Phase 2 coreflood experiments confirmed that hot polymer flood can effectively enhance oil recovery. In summary, this research study identified sweet spots for oil recovery and EOR applications in the challenging Tayarat reservoir and demonstrated the potential of producing significant amount of oil with appropriate IOR (e.g., extended reach horizontal wells, multistage fractures, stimulation, etc.) and EOR (e.g., hybrid thermal and chemical methods) techniques.