Well Reservoir Management and Surveillance Enabling Alternate Field Development Leading to Significant Cost Savings

Abstract

South Oman's critically sour oil fields are producing for last more than 2 decades from over-pressured carbonate-stringers that are encapsulated in salt. There is no aquifer support in most of the discovered stringers and existing facilities are designed with close to zero water handling. However, unlike other adjacent fields, another sour field Field-A had a strong aquifer; hence required a CAPEX intensive surface facility for water handling or a strategy for field development with dry oil only. Field-A is prolific undersaturated oil reservoir with light oil (45-API), excellent productivity (well-test KH:~20000md-m) and very strong aquifer (R-ratio:9-10). The field was initially developed with 5 oil producers. Due to near zero water tolerance at the facilities, the regular surface sample collection and analysis were conducted to monitor any water production. For proactive Well Reservoir Management (WRM), the time-lapse PNX logging (Pulse-Neutron-Extreme) was deployed in 2017 to regularly monitor the behind-casing contact movement and hydrocarbon saturation changes. Field development scenarios of high-offtake with water or controlled-offtake of dry oil and arresting the OWC movement (as seen in PNX) were evaluated. During the initial development, higher per well offtake led to faster OWC movement and generation of large water cones. First PNX logging survey acquired in 2017 revealed that the current OWC has moved up approx. 60-70 m with strong oil desaturation in all the wells. As an immediate response to it, the offtake per well was halved with introduction of regular annual monitoring of oil water contact movement by the PNX logging. The time lapse PNX surveys acquired in 2017-20 revealed the contact movement pace has been arrested after implementing the lower per well offtake since 2017. The previous further development plan of the field was to build a large CAPEX intensive water handling facility to handle water during oil production. However, the well surveillance information confirmed the benefits of gravity stable displacement process and the better displacement efficiency by reduced well offtakes with favorable mobility ratio present in the field with excellent reservoir properties. This led to a significantly cost-effective field development plan which was based on reducing per well offtake, increasing the infill count and producing dry oil only. This work reinforces the value of WRM stream and operational excellence into the field development plans for capital efficiency. Implementation of the well reservoir surveillance and management-based development plan yielded RF ~50% with dry oil production and eliminated the need of large water handling facility in sour environment, paving the way for a competitive further development plan of the field which was 75% cost effective than previous development plan. This work can be beneficial to similar developments to emphasize embedding WRM streams for cost reduction staircase of field development.