Page 236 - Hydrocarbon Exploration and Production Second Edition

Reservoir Dynamic Behaviour 223

At the field development planning stage, reservoir simulation may be used to
look at questions such as

most suitable drive mechanism (gas injection, water injection)
number and location of producers and injectors
rate dependency of displacement and RF
estimating RF and predicting production forecast for a particular development proposal
reservoir management policy (offtake rates, perforation intervals).
Once production commences, data such as reservoir pressure, cumulative
production, GOR, water cut and fluid contact movement are collected, and may be
used to ‘history match’ the simulation model. This entails adjusting the reservoir
model to fit the observed data. The updated model may then be used for a more
accurate prediction of future performance. This procedure is cyclic, and a full field
reservoir simulation model will be updated whenever a significant amount of new
data becomes available (say, every 2–5 years).

9.6. Estimating the Recovery Factor

Recall that the RF defines the relationship between the HCIIP and the UR
for the field

Ultimate recovery ¼ HCIIP recovery factor ðstbÞ or ðscfÞ
Reserves ¼ UR cumulative production ðstbÞ or ðscfÞ

Section 9.2 indicated the ranges of RFs which can be anticipated for different
drive mechanisms, but these were too broad to use when trying to establish a range
of RFs for a specific field. The main techniques for estimating the RF are
field analogues
analytical models (displacement calculations, material balance)
reservoir simulation.

These are listed in order of increasing complexity, reliability, data input
requirements and effort required.
Field analogues should be based on reservoir rock type (e.g. tight sandstone,
fractured carbonate), fluid type and environment of deposition. This technique
should not be overlooked, especially where little information is available, such as at
the exploration stage. Summary charts such as the one shown in Figure 9.19 may be
used in conjunction with estimates of macroscopic sweep efficiency (which will
depend on well density and positioning, reservoir homogeneity, offtake rate and
fluid type) and microscopic displacement efficiency (which may be estimated if core
measurements of residual oil saturation are available).
Analytical models using classical reservoir engineering techniques such as material
balance, aquifer modelling and displacement calculations can be used in
combination with field and laboratory data to estimate RFs for specific situations.
These methods are most applicable when there is limited data, time and resources,