Summary
In this study, we present a new analytical model to predict water influx
from finite bottomwaterdrive aquifers (BWDAs). The new model can be used for
aquifer representation in reservoir simulators and material-balance analysis.
The new model is computationally fast. The model has been verified against the
results from the Coats (1962) and Allard and Chen (1988) models. Using the new
model, we compare the cumulative water influx from bottomwaterdrive (BWD) and
edgewaterdrive (EWD) aquifers.
In the second part, we couple the new aquifer model with the
material-balance equation (MBE) and demonstrate its use in reserves estimate.
Production data from a BWD oil reservoir simulated by Allard and Chen (1988) is
analyzed. We conducted a McEwen analysis (1962) to predict the reserves.
Introduction
Hydrocarbon reservoirs may be classified on the basis of their drive
mechanisms. In the reservoirs adjoined by water aquifers, waterdrive may be the
primary production mechanism. In these reservoirs, production of hydrocarbons
causes a pressure drop in the hydrocarbon/water interface. Because of this
pressure drop, the aquifer reacts by encroaching into the reservoir and filling
its pore spaces. The invasion of reservoir rock by aquifer water may have a
significant impact on reservoir performance. Therefore, water influx into
hydrocarbon reservoirs must be predicted accurately as a function of time,
pressure history at the reservoir/aquifer interface, reservoir/aquifer size
ratio, and aquifer characteristics.
To forecast the performance in a waterdrive reservoir, an aquifer model
simulating the fluid flow in the aquifer and flow from the aquifer into the
reservoir is needed. Aquifer models may be classified on the basis of flow
regimes and flow geometries. In terms of flow regimes, aquifers may be grouped
as pot model, steady-state models, pseudosteady-state models, and
unsteady-state models. On the basis of flow geometry, the aquifer/reservoir
systems may be categorized as zero-dimensional, linear, and radial. The aquifer
models considering radial-flow geometry may additionally be sorted as EWD or
BWD.
Aquifer models are commonly used in two different reservoir-engineering
applications, reserves estimation and reservoir simulation. The main
functionality of aquifer models is to predict cumulative water influx in
material-balance computations. Along these lines, the Allard and Chen (1988)
model, among others, has been incorporated into commercial software. In the
large-scale simulation studies, the number of gridblocks may be reduced to have
reasonable computation time and expense. Typically, in such large-scale
simulation cases, the aquifer is represented implicitly by use of an analytical
model. In commercial reservoir simulators, several analytical models are
available for implicit representation of aquifers.
© 2007. Society of Petroleum Engineers
View full textPDF
(
1,938 KB
)
History
- Original manuscript received:
28 June 2006
- Meeting paper published:
24 September 2006
- Revised manuscript received:
3 March 2007
- Manuscript approved:
11 March 2007
- Version of record:
20 December 2007
View Cart
