Assessing Technical and Economic Recovery of Oil Resources
Assessing Technical and Economic Recovery of Oil Resources
Assessing Technical and Economic Recovery of Oil Resources
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B. Examining the Effects <strong>of</strong> Hydrodynamics <strong>and</strong> Reservoir Propertieson Creating a Tilted OWC. Some in the industry have questioned whether (<strong>and</strong>how) hydrodynamic flow is truly able to reshape the oil column in a reservoir, resulting ina substantial ROZ. One answer to this question is set forth in the theoretical equationabove. This equation states that the tilt <strong>of</strong> the OWC <strong>and</strong> the subsequent development<strong>of</strong> the ROZ are influenced by aquifer flow rates <strong>and</strong> reservoir properties. To explore thisissue in more depth, we first constructed a hypothetical 2-D cross section <strong>of</strong> a typicalPermian Basin oil reservoir <strong>and</strong> its underlying aquifer. Next, we subjected this reservoirto varying horizontal aquifer flow rates <strong>and</strong> permeability values to examine the effect <strong>of</strong>these variables on the OWC tilt <strong>and</strong> the creation <strong>of</strong> a ROZ.Figure 6, Initial <strong>Oil</strong> Reservoir/Aquifer Conditions, shows the initial geometry <strong>of</strong>the reservoir/aquifer cross section before a change in aquifer flow is induced. TheWasson Denver Unit San Andres reservoir was used for input data for the simulation.The key reservoir data include: porosity (12%), horizontal permeability (5 md), verticalpermeability (0.5 md), oil gravity (33°API), <strong>and</strong> residual oil saturation (35%), amongothers. This 2-D system is 5,000 ft long horizontally <strong>and</strong> 600 ft tall vertically, with a 400ft thick original oil column. Next, published Permian Basin San Andres formationcapillary forces were imposed on the reservoir/aquifer, resulting in a 50 ft thick transitionzone (TZ) <strong>and</strong> a 350 ft thick main pay zone. A 200 ft thick aquifer lies below the oilcolumn. The water source is on the left side <strong>of</strong> the cross section <strong>and</strong> the spill point is onthe right side, so flow is from left to right.Figure 7, Effects <strong>of</strong> Low Hydrodynamic Flow on OWC Tilt, depicts the results <strong>of</strong>2,000 years <strong>of</strong> water movement in this 2-D system. A steady-state aquifer flow system,with a low constant flows velocity <strong>of</strong> 0.1 feet per year was first introduced. Shown inFigure 7 are the resulting changes in the oil-water contact (OWC), transition zone (TZ),<strong>and</strong> residual oil zone (ROZ). Only modest OWC tilting <strong>and</strong> ROZ development occursfollowing the initiation <strong>of</strong> this low rate <strong>of</strong> water flow.2-7 February 2006
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