--> Abstract: Production-Induced Capillary Breakdown of Reservoir Barriers, by Brown, Alton A.; #90163 (2013)
[First Hit]

Datapages, Inc.Print this page

Production-Induced Capillary Breakdown of Reservoir Barriers

Brown, Alton A.

Slope changes on p/z vs. cumulative production plots and other production responses have been interpreted as breakdown of reservoir barriers. Petroleum flow through the Previous HitbarrierNext Hit can be caused by either percolation through a water-wet Previous HitbarrierNext Hit pore system (capillary breakdown) or fracturing the Previous HitbarrierNext Hit. This paper investigates the capillary Previous HitbarrierNext Hit breakdown mechanism by numerical modeling of flow across barriers isolating reservoir compartments.

Capillary Previous HitbarrierNext Hit breakdown results from increasing capillary pressure in the Previous HitbarrierNext Hit by decreasing water pressure. Water in the Previous HitbarrierNext Hit communicates with water in the producing compartment, so pressure drop by production reduces water pressure in the Previous HitbarrierNext Hit. Capillary pressure increases at the Previous HitbarrierNext Hit contact with the undrained (high petroleum pressure) compartment. When the capillary pressure reaches the Previous HitbarrierNext Hit threshold capillary pressure, petroleum from the undrained compartment invades the Previous HitbarrierNext Hit and quickly extends across the Previous HitbarrierNext Hit. This is Previous HitbarrierNext Hit breakthrough. Although the Previous HitbarrierNext Hit is "broken", flow across the Previous HitbarrierNext Hit is miniscule at breakthrough. Previous HitBarrierNext Hit breakthrough is not Previous HitbarrierNext Hit breakdown.

With further production, capillary pressure continues to drop. Petroleum relative permeability in the Previous HitbarrierNext Hit increases and cross-Previous HitbarrierNext Hit petroleum flow increases. Even where the Previous HitbarrierNext Hit petroleum relative permeability is high, petroleum flow may be negligible if the total flow resistance of the Previous HitbarrierNext Hit is high.

Capillary Previous HitbarrierNext Hit breakthrough is expected in any Previous HitbarrierNext Hit separating reservoirs with production pressure differences greater than the Previous HitbarrierNext Hit threshold pressure. In contrast, significant cross-Previous HitbarrierNext Hit petroleum flow (Previous HitbarrierNext Hit breakdown) requires low petroleum flow resistance combined with moderate capillary threshold pressure. This combination is rare unless the Previous HitbarrierNext Hit is exceptionally narrow. Previous HitBarrierNext Hit breakdown may be rare in real compartmentalized gas reservoirs and absent in reservoirs where petroleum can flow around the Previous HitbarrierTop.

Apparent changes in p/z slope, especially those early in the production, might alternately be explained by improper average reservoir pressure estimation and gas contribution from tight facies.

 

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013