Page 214 - Hydrocarbon Exploration and Production Second Edition

CHA P T E R 9

Reservoir Dynamic Behaviour

Introduction and Commercial Application: The reservoir and well behaviour under
dynamic conditions are key parameters in determining what fraction of the HCIIP
will be produced to surface over the lifetime of the field, at what rates they will be
produced and which unwanted fluids such as water are also produced. This
behaviour will therefore dictate the revenue stream which the development will
generate through sales of the hydrocarbons. The reservoir and well performance are
linked to the surface development plan, and cannot be considered in isolation;
different subsurface development plans will demand different surface facilities. The
prediction of reservoir and well behaviour are therefore crucial components of field
development planning, as well as playing a major role in reservoir management
during production.
This section will consider the behaviour of the reservoir fluids in the bulk of the
reservoir, away from the wells, to describe what controls the displacement of fluids
towards the wells. Understanding this behaviour is important when estimating the
RF for hydrocarbons, and the production forecast for both hydrocarbons and water.
In, Chapter 10, the behaviour of fluid flow at the wellbore will be considered; this
will influence the number of wells required for development, and the positioning of
the wells.

9.1. The Driving Force for Production

Reservoir fluids (oil, water, gas) and the rock matrix are contained under high
temperatures and pressures; they are compressed relative to their densities at standard
temperature and pressure. Any reduction in pressure on the fluids or rock will
result in an increase in the volume, according to the definition of compressibility.
As discussed in Section 6.2, Chapter 6, isothermal conditions are assumed in the
reservoir. Isothermal compressibility (c) is defined as
1 dV
c ¼
V dP

Applying this directly to the reservoir, when a volume of fluid (dV )isremoved
from the system through production, the resulting drop in pressure (dP ) will be
determined by the compressibility and volume (V ) of the components of the
reservoir system (fluids plus rock matrix). Assuming that the compressibility of the
rock matrix is negligible (which is true for all but under-compacted, loosely

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