Techniques to Identify Pay and Optimize Completions in Heavy Oil Sands, Tulare Formation, Hill Property South Belridge Field, California
In the heavy oil Tulare Formation reservoir at South Belridge field, San Joaquin Basin, it is difficult to distinguish fresh water from oil using standard resistivity logs. In fact, no relationship between oil saturation from core samples and resistivity is found in some Tulare intervals. This ambiguity can lead to expensive coring operations to identify the top of pay or to a conservative completion strategy to avoid excessive water in open-hole gravel pack completions. Additionally, the Tulare reservoir has been extensively steam flooded. Thus, the current reservoir salinity is unknown. This complicates the differentiation of producible oil from residual oil in swept intervals. To improve completion design and better estimate remaining pay, the Advanced Dielectric Tool (ADT) was incorporated in a recent drilling program.
The ADT estimates water-filled porosity by measuring dielectric permittivity. It is very insensitive to formation water salinity. While the measurement is taken in the flushed zone, this has little consequence in heavy oil zones where invasion is limited. In a 2011 Tulare drilling program, ADT logging was performed on 21 wells with sidewall core acquisition in four wells to validate tool results. Oil saturation curves calculated from the Archie-based resistivity method and the ADT method were compared, and sidewall core values were plotted where applicable. The ADT method returned better correlation to core-based oil saturations and enhanced our understanding of discrete Tulare reservoir intervals. ADT results improved completion decisions by revealing high water saturations in some reservoir intervals previously interpreted as pay and identifying additional hydrocarbons in the main pay interval. The tool also validated the Archie-based saturation model in the thick high-quality pay sands. Correlation with whole core demonstrates that the upper high resistivity sands are not hydrocarbon-bearing and that additional hydrocarbons, not well expressed in the resistivity log, occur in thinly interbedded sands and shales and in very fine-grained sands.
As a result of ADT logging, producer completion
techniques have been optimized to maximize oil production and minimize water
production. Injector completion techniques have also been enhanced by
identifying pay intervals that would benefit from steaming. The addition of ADT
logging has provided new insight for this mature asset and will assist in
improving continued development.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California