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 GOGDShuaiba matrix carbonates; with thin, transition-zone oil column and light oil, under waterfloodShuaiba 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.
PDO has a diverse portfolio of mature fields undergoing waterflood. These fields open-up an additional opportunity through infill drilling for enhancing the ultimate oil recovery. It has been established in the oil industry that increased well density does not only result in acceleration but will also lead to incremental recovery. This paper demonstrates the approach taken for identifying and maturing an infill development in a Shuaiba matrix carbonate reservoir within a thin oil column. The case study field has been developed predominantly with single long (~ 1.5 km) horizontal oil producers (lifted with ESPs) & water injectors in a Producer-Producer-Injector (PPI) pattern with a ~60 m spacing between Producer and Injector (P-I).The development team executed additional appraisal activities in parallel with implementing the field development plan. Seismic inversion was updated with the new well results which improved porosity prediction in un-drilled areas. Based on acoustic impedance guidance, appraisal wells have been drilled with encouraging indications in terms of producibility and opened new areas for further development. The history matched simulation model results showed that 120 m P-P-I spacing would recover 25% of in place volumes compared to 60 m P-P-I spacing with an ultimate recovery factor (URF) of 45%.The key success factors for the infill development are (1) well placement with geosteering, (2) balancing appraisal with development and (3) continually updating static and dynamic models. This is done to support development decisions such as well sequencing & placement, drilling activity and surface facilities expansion.The key learning from this case study is that developing fields initially with twice the proposed development spacing, nevertheless following the optimal water flood pattern, is the best way for appraising the whole field rapidly. This allows time to gather much needed information ahead of making tactical investment decisions on long lead-time surface facilities.
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