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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Surveillance Well Utility in 4-D Modeling of Oil Saturation Changes at Kern River Field, California, USA
(1) Chevron, Bakersfield, CA.
Primary “gravity assisted” production of a dominantly heavy oil at Kern River Field extends back to initial field discovery in 1899. Since the late 1960’s, production has been dominated by steam assisted gravity drainage. Initial surveillance of temperature and oil saturation in the reservoir using carbon/oxygen (C/O) logs began in 1996. Schlumberger Reservoir Saturation Tool (RST) collection of C/O logs has varied in frequency across the field, but a 3 year interval in time is the most common measurement timing. The current active cased borehole surveillance well count exceeds 650.
3D reservoir modeling has been routinely used at Kern River since the late 1990’s to estimate remaining oil and identify both cold and heated oil opportunities. Since 2007, the Kern River asset development team has incorporated modeling processes into a 155 million cell full field 3D model developed using over 12,000 normalized resistivity logs. Temperature, steam and oil saturation data from the surveillance wells are periodically incorporated into this static framework. Our challenge has been to properly characterize time-stepped oil saturation changes observed in surveillance well logs in the 3D reservoir model.
Identifying active flow pathways and quantifying volumes of oil in motion is of value to optimizing reservoir management. Down-dip gravity drainage of oil appears to follow higher permeability pathways as identified with our resistivity log data. These densely distributed resistivity logs provide us with an improved means to conditionally distribute observed fluid changes at less dense surveillance wells into the 3D model.
Collocated cokriging of time stepped oil saturation log data with resistivity log data within the full field 3D model illustrates significant movement of oil volumes both within the reservoir as well as to the surface via production. Early indications suggest that there is as much un-captured oil moving down-dip across the field as there is being produced at the surface. This is very significant given that Kern River Field produced about 29 million barrels of oil in 2009. Oil saturation change modeling represents an important tool for managing the reservoir for the remaining life of Kern River Field. This new 4D reservoir management tool is currently helping us identify and drill new opportunities and will help us to better quantify the timing, volume, and location of "gravity assisted" oil migration field wide.