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Abstract: Capture of Bypassed Oil in a Steeply Dipping, Thick-Bedded Turbidite Reservoir Using Horizontal Wells: A Pilot Project from the Monarch Heavy Oil Reservoir, South Midway-Sunset Field, California


Steeply dipping, heterogeneous reservoirs provide unique geometric opportunities for horizontal well development. Realizing optimum drainage in such areas using conventional vertical technology is not always successful due to significant stream override and lack of downdip take-points. Specifically, multiple wedges of bypassed oil can occur updip (structurally higher than the uppermost injection well) and downdip (structurally below the lowest producing well). As such, horizontal wells drilled normal to strike and slightly above low S[o] zones or oil/water contacts can be used to capture the bypassed reserves.

The Monarch heavy-oil reservoir is an extremely heterogeneous, thick-bedded turbidite deposit, with gross reservoir thickness ranging from 500 feet to 1000 feet, and net pay ranging from approximately 200 feet to 450 feet. The SW portion of the field is characterized by steeply dipping beds (40 degrees to 60 degrees NE), which intersect a relatively flat transitional fluid zone (i.e., S[o] = 10% to 30%). In this steeply dipping area, multiple wedges of updip and downdip bypassed oil were identified and mapped. To capture the bypass, Mobil drilled 5 long radius horizontal wells normal to strike situated 10 feet to 50 feet above the transitional fluid zone. Lateral completion lengths for these wells ranged from 750 feet to 950 feet. This orientation allowed the wells to drain most parts of the reservoir irrespective of vertical stratigraphic barriers. In general, oil rates were a function of 1) placement of horizontal well relative to the transitional fluid zone; 2) reservoir temperature, and 3) volume of the bypassed oil wedge.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California