Reservoir Saturation Monitoring in Saudi-Aramco; Benefits, Challenges and Opportunities

Abstract

Oil production from the giant oil fields of Saudi Arabia is said to be one of the big levers that drive the world economy. Saudi Aramco has been providing the support of this lever with over 70 years of oil production. To maintain its level of production, Saudi Aramco has had to place some of its fields on a water injection scheme, for pressure support and to enhance reservoir recovery. Hydrocarbon sweep and water contact movement through these reservoirs is then monitored through saturation logs. In Saudi Aramco, hydrocarbon saturation within the reservoir after water has swept through is typically measured with two types of tools:A Gamma ray (GR) detection tool. This tool acquires GR in two modes, namely the sigma/capture mode and the Carbon-Oxygen/inelastic mode.A resistivity tool. This can be logged in cased hole with a cased hole formation resistivity, and in barefoot completions using the slim induction tools. Both types of monitoring devices, when logged under the right environmental conditions have been found to add significant value to the way we manage our reservoirs. Some of the Saudi Aramco business drivers for logging these tools are:Reservoir management and optimizations.Optimal well placement.Location of the pool of attic or bypassed oil.Calibration of reservoir simulation models.Identification of cost saving workover opportunities. The existing reservoir monitoring tools in the market are dogged with some challenges. The measurement envelope of the GR tools are very shallow, therefore they suffer from washouts and near wellbore fluid effects, while the resistivity tools require a good knowledge of the flood water salinity for accurate saturation computation. Thus, it is critical that these tools are logged under the right conditions. In spite of the above challenges, Saudi Aramco continues to look ahead for cost-effective solutions through collaboration with service companies. This paper will review some of the benefits that Saudi Aramco has derived from over 200 Reservoir Saturation Monitoring (RSM) logs acquired annually, while also highlighting some challenges and opportunities for the future development of these tools.

Optimizing Reservoir Monitoring: Improving PNL Logs in Changing Borehole Environments

“…PNC tools are best utilized in formations with high and known water salinities, while the Pulsed Neutron Spectroscopy (PNS) or Carbon-Oxygen (C/O) logging are best employed in reservoirs with low or fresh water salinities, or with mixed injection and connate water salinities (Ariwodo, et al, 2009). …”

Combining Resistivity and Capture Sigma Logs for Formation Evaluation in Unknown Water Salinity--A Case Study in a Mature Carbonate Field

“…At present, most of the saturation monitoring in the field under study in this paper is performed using C/O logs, in both openhole and cased-hole-completed wells (Eyvazzadeh et al 2004;Ariwodo et al 2009). From C/O logs, it is possible to compute the oil volume directly from the ratio of carbon to oxygen yields, and, therefore, provide oil saturation independent of formation-water salinity.…”

“…The depth of investigation (DOI) of C/O logs is limited to a few inches, typically between 6 and 8 in. To overcome this limitation, passes with the well flowing are recorded when possible, to bring the formation fluids in the virgin zone closer to the borehole, flushing as much as possible the near-wellbore invasion (Ariwodo et al 2009). Basic production-logging-tool (PLT) data (such as spinner, gradio-manometer, and temperature) are recorded simultaneously to assist the interpretation.…”