The Maastrichtian Reservoir, Kuwait - Saudi Arabia Partitioned Zone: Improved Reservoir Definition and Field Growth Through Integration and Teamwork
Turner, James W.¹; Al-Kandari, Abdullah²; Remila, Gamal³; Palar, Steve³; Iqbal, Afzal³; Reddie, David³
¹Chevron Energy Technology Company, Perth, WA, Australia.
²Kuwait Gulf Oil Company, Ahmadi, Kuwait.
³Saudi Arabian Chevron, Mina Al Zour, Kuwait.
The Maastrichtian Reservoir of Wafra Field is a giant resource. However, full field development has been problematic due to high variations in rate and reserves between wells. Oil quality was also known to be variable, ranging from 22° API in the southern part of the field to 13° API in the north. These complexities created a view that new wells were risky, even though dry holes were rare. Negative perceptions prevented expansion of the field, which was known to contain a substantially larger oil resource.
A campaign of barefoot, vertical wells allowed production logs to be run following initial completions. The production logs revealed that the flow of oil rarely came from the logged pay zones. Rather oil seemed to be produced from apparently tight rock. Ultimately, the production logs revealed the presence of "super k" zones (intervals that produce than 500 barrels of fluid per day per foot of vertical interval). The presence of karstic, super k zones helped explain the high variation in rate between wells and also appeared to explain the higher water cut seen in horizontal wells.
A subsequent program of step-out drilling encountered unexpectedly heavy and viscous oil, resulting in poor production performance. Discussions with Kuwait Oil Company (operator of the super giant Burgan Field) revealed that all oil produced from the Maastrichtian reservoir in Kuwait was biodegraded; however, oil found immediately adjacent to high angle faults in Burgan Field was producible and contained the gasoline group of molecules. Gas chromatographs from Wafra oils also reveal biodegraded oils that contain the gasoline group of molecules, but faulting is rare and the producible oil is more widespread. Isochore mapping of the top seal of the underlying Wara reservoir (the Ahmadi Shale) demonstrated a correlation between thin or missing shale and light oil in the Maastrichtian reservoir. Thus light hydrocarbons appear to seep from the Wara reservoir into the Maastrichtian reservoir, reducing the viscosity of the biodegraded oil. Knowledge of the geologic control of light oil distribution has high graded future development locations and provided a new exploration model.
The integration of production engineering methods, such as production logging and well testing, with reservoir geology and regional knowledge allowed the asset team to develop a new geologic model that provided the technical basis for adding significant reserves in 2010.
AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012