| Popis: |
The Sangomar Field (formerly known as the SNE Field), containing both oil and gas, is located 100 kilometres south of Dakar and is Senegal’s first offshore oil development. The deep-water field comprises a series of multi-stacked reservoir units. Treated and filtered seawater will be injected into the primary oil reservoirs to provide pressure maintenance and sweep to maximise production and recovery. The injection water treatment system is designed to safeguard well injectivity and support long term injection under matrix conditions. The window between initial reservoir pressure and fracture pressure is relatively narrow. On one hand, to eliminate any risk of out of zone losses, injection pressures should be capped at relatively low values. On the other hand, dynamic reservoir simulation results indicate a clear positive correlation between injection pressure and production and recovery, highlighting the benefits of higher injection pressures. To address these challenges, an integrated system for injection pressure management has been developed. Using clearly articulated fracturing concepts, such as slip re-activation of natural fractures, fracture re-opening of existing fractures and initiation of new fractures, all injector wells can be categorised according to their respective probability, reversibility and consequence of out of zone injection. This framework is then used to guide the process of managing respective injection pressure limits. To complement this process, a subsea control system has been designed in-house to safely maximise injection pressures for each well independently. While ‘steady-state’ injection pressure limits are set to avoid unintentional fracturing of the bounding shales between the reservoir units, the dynamic aspect of the control system enables the poro-elastic effects to be exploited to maximise injection pressures without initiating fracturing in the sandstone. This case study presents an original proactive approach to managing injection pressures that is significantly more nuanced than the bookends of matrix and fractured injection. The problems and solutions described in this paper required a truly multidisciplinary effort. The result is a comprehensive, and possibly unique, operational strategy combined with a novel pressure control system that is expected to maximise the value from waterflooding in Sangomar. |
