Fractured Reservoir Characterization Using Dynamic Data in a Carbonate Field, Oman

Abstract

Summary The main objective of this study was to extract fracture data from multiple sources and present it in a form suitable for reservoir simulation in a fractured carbonate field in Oman. Production is by water injection. A combination of borehole image (BHI) logs and openhole logs from horizontal wells revealed that water encroachment occurs mostly through fracture corridors and appears as sharp saturation spikes across fracture clusters. Dispersed background joints have little flow potential because of cementation, lack of connectivity, or small size. Image logs indicate that fracture corridors are oriented dominantly in the west/northwest direction. Most of the several injector/producer short cuts are also oriented in the west/northwest direction, supporting the view that fracture corridors are responsible for the short cuts. Flowmeter logs from vertical injector or producer wells intersecting a fracture corridor show a step profile. A comparison of the injection or production history of wells with or without a step profile provided a means to calculate permeability enhancement by fracture corridors. The field has more than 300 vertical wells and nearly 20 horizontal wells, which allowed us to generate detailed fracture-permeability enhancement and fracture-corridor density maps based on injector and producer data, short cuts, mud losses, openhole logs, and BHI logs. We also were able to build stochastic 3D fracture-corridor models using corridor density from dynamic data and orientation from BHI logs and seismic data. Fracture-corridor length and width were tied to fracture-permeability enhancement using wells with both image logs and production data. The fracture-permeability enhancement maps were verified independently by waterflood-front maps. Notwithstanding the uncertainties, the fracture data were sufficiently accurate and detailed to generate both single- and dual-porosity simulation results with good field-scale history match.