Abstract
Enhanced Oil Recovery (EOR) processes are key to Petroleum Development Oman (PDO) longer term business performance. To date, PDO is operating four commercial scale EOR projects and a number of pilots that are either ongoing or recently concluded. The EOR projects and pilots cover chemical and thermal EOR as well as miscible gas injection.
Successful EOR projects require robust long term strategic plans with built-in flexibility and seamless execution, in order to continuously de-risk associated uncertainties through proper testing and piloting. One of the key contributors to PDO's successful EOR journey has been successful monitoring and surveillance through acquisition of high quality surveillance data.
An alkaline surfactant polymer (ASP) pilot, first of its kind in PDO was recently concluded with encouraging results. Key pilot successes parameters included achieving reduction of oil saturation to less than 10% in one layer at the observation well. The challenge of saturation monitoring through salinity independent and carbon insensitive technique in EOR fields was addressed by Nuclear Magnetic Resonance (NMR) time-lapse cased hole logging through fiber-reinforced plastic (FRP) casing. The other ongoing EOR pilot involves injecting polymer into a heavy oil bearing reservoir with a strong bottom aquifer drive. In this pilot, the key subsurface uncertainties are polymer injectivity, conformance and sweep efficiency. These uncertainties are being de-risked by deploying monitoring technologies such as distributed temperature sensing (DTS), distributed acoustic sensing (DAS), Pressure monitoring and time-lapse saturation logging based on both nuclear and electrical principals.
Some of the challenges in the miscible gas injection project include; gas breakthrough evaluation, reservoir connectivity, and gas sweep efficiency. These were assessed by implementing inter-well tracer test, production and time-lapse saturation loggings.
Surveillance in Thermal EOR project (cyclic steam soak, CSS) revolves around having dedicated temperature, pressure observation wells and systematic temperature surveillance across the field. Assessment of steam injection profile and steam quality has also been focus areas. The aim is not only to monitor areal and vertical sweep efficiency (of both steam and reservoir fluids) over time, but also to get leading signals for a proper reservoir management to maximize profitability. Further, pattern recognition from microseismic survey data helps monitoring the ‘cap-rock’ integrity and reservoir containment. Production logging in the ultra high viscosity oil zone still remains a challenge.
Detailed fiber optics reservoir monitoring was implemented in Thermal EOR in naturally fractured carbonate reservoir. The objectivities are the oil rim-management and safeguard the cap-rock integrity from fault re-activation
In this paper, PDO's experiences in handling EOR challenges and how different EOR monitoring and surveillance technologies were utilized will be presented. A recommended practice will be discussed based on PDO's experience.
