An intensely fractured reservoir in central Oman is being developed by injecting steam into the crest of the field, heating the oil in the matrix and producing it via a Gas-Oil Gravity Drainage (GOGD) process. Both the static and the dynamic data support a strongly fractured (and leached) reservoir. Building 3D full field fracture models that capture the possible scenarios proved to be a challenge, largely because to date (i) most wells in the crest are vertical, (ii) a limited number of horizontal wells have been drilled on the flanks, (iii) seismic quality is relatively poor, and (iv) dynamic constraints on the permeability structure are limited, especially on the flanks. A new 3D fracture software tool (SVS) has been used to maximize the value of fracture-related reservoir data through improved integration, visualization, analysis and correlation. Rapid interactive analysis of the data set allows the user to efficiently characterize and understand the nature of the fracture system and its relationships to other reservoir parameters.
The data analysis indicates that two end member fracture system scenarios could be present in the reservoir i) a mechanical stratigraphy related and ii) fault/corridor related fracture system. This is particularly true of the flank wells, which despite being mostly located away from the main seismic scale faults on the crest, have evidence for fault related fracture clusters at intervals down the well bore. For these end member, and intermediate scenarios, "Low", "Medium" and "High" Case models were created using fracture trend maps/grids that combine the data and a range of geological constraints. More remote information was included from outcrop fault patterns in northern Oman. A combination of detailed process based discrete fracture generation and rapid fracture attribute generation was used to populate over 15 full field simulation grids capturing the range of remaining uncertainty of the fracture system across the field.
The field studied is an elongated dome structure that lies at relatively shallow depth. The field contains heavy oil within a relatively tight matrix in the Shuaiba, and the Kharaib reservoir units. To recover the heavy oil, steam is injected at the crest, passes into the extensive crestal fracture system, and starts to heat the matrix blocks.