Some of the large carbonate fields in North Oman have been on production for some 40 years. However, substantial contingent volumes exist in these mature fields, highlighting the need to understand the characteristics of the remaining resources and their potential to generate oil and value.
The Petroleum Development Oman (PDO) carbonate oil portfolio can be subdivided into a number of area-themes based on (similar) reservoir types, oil type and reservoir development methods (current and future). In this paper, we illustrate how modeling methodologies can be adjusted for three of these area-themes by focusing on the key subsurface parameters most relevant to the recovery mechanism:
Shuaiba fractured carbonates, with heavy oil, under appraisal for steam-assisted GOGD
Shuaiba matrix carbonates; with thin, transition-zone oil column and light oil, under waterflood
Shuaiba matrix carbonates; with reasonable oil column and light oil, under waterflood
Any reservoir modeling methodology is also influenced by the purpose of the models (what decisions it enables), as well as the resources (computation, manpower and time) and data available. The examples described above also differ in these respects: The modeling of a fractured carbonate, heavy-oil reservoir (example A) focused on testing the feasibility of steam-assisted GOGD and required intensive analogue use due to limited data availability. In example B, a transition-zone field where oil saturation, matrix features and relative permeability are key parameters, the modeling supported a waterflood development implementation, consisting of ongoing drilling of 150+ geosteered, horizontal producers & injectors (2 new wells per month). In example C, for a light-oil, reasonable-thick oil column field, waterflood development decision-making on redevelopment options was enabled by multiple-deterministic scenario modeling.