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The Value of Microseismic Monitoring over a Thermally Assisted Gas Oil Gravity Drainage (TA-GOGD) Steam Trial in a Carbonate Field in Oman

Al-Kindy, Fahad H.*1; Schoofs, Stan 1; Al-Lawati, Mohammed 1; Saluja, Jasmeet 1; Al-Busaidi, Said S.1; Ita, Joel 2; Zwaan, Marcel 2; Oates, Steve 2; Berlang, Wilfred 2
(1) Petroleum Development Oman, Muscat, Oman. (2) Shell International Exploration and Production B.V, The Hague, Netherlands.

In a shallow carbonate field in Oman, a Thermally Assisted Gas Oil Gravity Drainage (TA-GOGD) steam injection trial is conducted as part of an EOR assessment over a pilot area. The trial location is covered with a surveillance program which includes well log, chemical, DTS, microseismic and InSAR data acquisition. Here we focus on the value of the microseismic data monitoring in understanding the reservoir and caprock.

Since the onset of steam injection, almost 900 microseismic events have been triggered, some in the reservoir but more importantly, others in the caprock as well as in underlying reservoir units. The latest observations combined with results from fluid salinity analysis reveal that condensed water from the target reservoir unit is leaking into an underlying unit, suggesting that a fluid pathway is present. The cloud of microseismic events between these layers may be highlighting one of the leak paths. Here, integrated data analysis helps steer management decisions such as the injection strategy and the frequency and location of monitoring or logging.

Complimentary to understanding the reservoir, the microseismic data is aiding in caprock integrity assessment in the form of a ‘traffic-light’ system developed. The system which bases its criteria on geomechanical models and experience from other fields can warn if there is a need to change the steam injection rates for example.

Finally, in addition to the microseismic event locations analysis, focal mechanism ‘beach-ball’ solutions are also calculated on a subset of the data to better understand the faulting and how it may differ in the reservoir and caprock. These results are currently being analysed.

In summary, by combining microseismic data with well log and fluid data as well as referring to geomechanical models, we have a much better understanding of the reservoir and caprock. This integrated approach may aid in future developments and management decisions for this or other similar fields in the area.

 

AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain