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A steam flood re-development of a mature field in the South of Oman is well underway with the first pattern of steam injection active since late 2008. The areal surveillance programme designed by a joint effort between Petroleum Development Oman (PDO) and Shell International Exploration and Production (SIEP) includes the simultaneous recording of a variety of seismic methods of different resolution. The main purpose of the time-lapse work is to monitor the steam conformance and sweep efficiency as the steam is injected in this heavy oil reservoir over 1,000 m below surface. Key aspects of the data acquisition campaigns, state-of-the-art processing and time-lapse interpretation will be discussed. The ultimate objective of the programme is to evaluate the effectiveness of the techniques used in order to select the most appropriate and economically viable reservoir surveillance tools for full field deployment.

After 26 years of cold production in a South of Oman heavy oil field, enhanced oil recovery through steam-flooding is currently planned. The first steam-injection pattern started in 2009 and the challenge is to monitor the rate of growth and shape of the steam chest at 1,000 m below surface. The Well and Reservoir Management (WRM) plan for this field includes a comprehensive set of areal surveillance activities including seismic and non-seismic methods that have been put together by a joint effort between Petroleum Development Oman (PDO) and Shell International EP (SIEP). The approach to monitoring the steam conformance and sweep efficiency as the steam is injected in the reservoir focuses on simultaneously deploying a wide range of proven technologies early on. The objective is to select the most appropriate tool for the later full field deployment. The first active pattern is currently being used to investigate the effectiveness of existing seismic techniques such as cross-well and 3D vertical seismic profiling (VSP) to detect early signs of steam front movement. Pre-steam baseline data has been acquired and forward modeling helped determine the best time for repeat surveys. The more traditional, though challenging in South Oman, surface seismic data is also being adapted to the crowded conditions of the field. Alternative plans also include state-of-the-art high resolution virtual source seismic as well as surface deformation and time-lapse geochemistry. Improved lateral and vertical resolution at depth are key factors for success in this and future similar developments. Details of the areal surveillance programme and initial results are summarized here.

A small area of carbonate field in North Oman was tested to monitor steam injection. The reservoir is a fractured carbonate and is overlain by a 250 m thick shale. Models are required to translate indirect observations or extrapolate point measurements of wells to give us a three dimensional view on field response. The microseismic monitoring system for the steam injection pilot consists of 6 dedicated observation wells. The objectives of the system are to detect any generation of new fractures or re-activation of existing fractures due to steam injection and monitor cap-rock integrity. 800 events were recorded by the micro-seismic system so far. The events occur mainly in a clustered fashion and are attributed to cooling- and heating, and potentially to re-activation of a fault zone close to updip injectors. Micro-seismic activity has expressed the extent of this fault zone. Finally, some of the events were attributed to well related noise. Microseismic events in the overburden could represent a continuum between two end members. One being that they represent failure of critically stressed asperities along pre-existing lineaments in which the faults and fractures are not critically stressed over a majority of surface area. The other end of the spectrum is that the minor events are indicative of incipient larger scale failure. To gauge where the subsurface is on this spectrum, 3D geomechanical simulations were performed to estimate the proximity to large scale failure in the reservoir and overburden. The base case model results suggest that the micro-seismic events are indicative of the first end member state, and represent asperities along pre-existing lineaments. Exploration of the full range of uncertainty in rock material showed that no large-scale fault re-activation is to be expected.