Identifier

etd-07122007-092242

Degree

Doctor of Philosophy (PhD)

Department

Petroleum Engineering

Document Type

Dissertation

Abstract

This study addresses oil bypassing caused by water invasion to wells in edge and bottom water-drive oil reservoirs – a significant problem worldwide. It is shown that the amount of by-passed (not recovered) oil is significant and could be predicted analytically and reduced by modifying well’s completion. A large statistical sample from the population of possible reservoir-well systems with edge and bottom-water has been created theoretically using several databases of actual reservoirs properties worldwide. Dimensional analysis allowed converting reservoir properties distributions into dimensionless group distributions. Then, the amount of by-passed oil was correlated with the dimensionless groups using designed experiments conducted on a reservoir simulator. The resulting correlations determine the percent amount of movable oil that could be recovered by the end of well’s operation, when the water cut value reaches its maximum limit. They also show how operational parameters such as well spacing, penetration and production rate may affect oil recovery. From the sensitivity analysis, the end-point mobility ratio appears to control more than 55 percent of the oil bypassing process –far more than other groups. The statistical results also show that half of the typical edge and bottom-water well-reservoir systems would have at least 17% or 25% of their movable oil bypassed, respectively. The effect of reservoir heterogeneity defined by permeability stratification has been studied for edge-water systems having transgressive, regressive and serrated depositional sequences with a Dykstra-Parsons coefficient of 0.75. Oil bypassing showed to be qualitatively more significant in the transgressive sequences. It was also found that the effect of reservoir heterogeneity is more significant for reservoirs with high end-point mobility ratios. Numerical reservoir simulation is also used to investigate improved recovery of well’s completions of different penetration and dual-completed wells with segregated inflow from the top and bottom (water sink) completions. It appears that short completions perform best in reservoirs with large end-point mobility ratios produced at low rates by delaying water breakthrough and improving the amount of oil recovered per barrel of fluid produced. For most reservoirs with water drive, however, the results show that the best single completion strategy is the use of fully penetrating wells, since they improve the recovery rate. Dual well completions with “water sink” (DWS) enable independent (although synchronized) rate schedules at the two completions. This study offers a new method to operate DWS systems by using variable rates at the bottom completion for a constant production rate - with limited maximum water cut - at the top completion over the entire life of the well. The method provides better distribution of produced fluids, as it controls water saturation outside the well. When compared with conventional “short” completion, DWS well recovers oil faster and may also produce oil-free water for re-injection. However, a comparison with long single completion of similar length based on the same total fluid rate does not give different recovery rates but shows that DWS well operates at different pressure drawdowns and produces two streams of fluids having substantially different compositions. It is, then, concluded that the recovery performance of the two types of wells may be different if the basis for comparison is a maximum pressure drawdown rather than same total fluid rate.

Date

2007

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Andrew K. Wojtanowicz

DOI

10.31390/gradschool_dissertations.3886

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