In the process of illustrating the primary functions of a reservoir engineer, namely, the estimation of hydrocarbons in place, the calculation of a recovery factor and the attachment of a time scale to the recovery; this page introduces many of the fundamental concepts in reservoir engineering.
ü The description of the calculation of oil in place concentrates largely on the determination of fluid pressure regimes and the problem of locating fluid contacts in the reservoir.
ü Primary recovery is described in general terms by considering the significance of the isothermal compressibility of the reservoir fluids; while the
determination of the recovery factor and attachment of a time scale are illustrated by
describing volumetric gas reservoir engineering.
ü The chapter finishes with a brief quantitative account of the phase behavior of multi-component hydrocarbon systems.
Operation of system of reservoirs
ü It is not very uncommonystem‟toffindreservoirsagroup river or in a river and its tributaries. An example of the former are the dams
proposed on the river Narmada (Figure 7) and an example of the latter are the dams of the Dam odor Valley project (Figure 8).
ü In case of system of reservoirs, it is necessary to adopt a strategy for integrated operated of reservoirs to achieve optimum utilization of the water resources available and to benefit the best out of the reservoir system.
ü In the preparation of regulation plans for an integrated operation of system of reservoirs, principles applicable to separate units are first applied to the individual reservoirs.
of schedule so developed should then be considered by working out several
alternative plans. In these studies optimization and simulation techniques may be extensively used with the application
of computers in water resources development
VOLUMETRIC GAS RESERVOIR ENGINEERING
ü Volumetric gas reservoir engineering is introduced at this early stage in the book because of the relative simplicity of the subject.
ü lt will therefore be used to illustrate how a recovery factor can be determined and a time scale attached to the recovery.
ü The reason for the simplicity is because gas is one of the few substances whose state,
as defined by pressure, volume and temperature (PVT), can be described by a
relation involving all three parameters.
One other such substance is saturated steam, but for oil containing dissolved gas, for instance, no such relation exists and, as shown in Chapter 2, PVT parameters must be empirically derived which serve the purpose of defining the state of the mixture.
RESERVOIR DRIVE MECHANISMS
ü If none of the terms in the material balance equation can be neglected, then the reservoir can be described as having a combination drive in which all possible
of energy contribute a significant part in producing the reservoir fluids and determining
the primary recovery factor.
ü In many cases, however, reservoirs can be singled out as having predominantly one main type of drive mechanism in comparison to which all other mechanisms have a negligible effect.
ü In the following sections, such reservoirs will be described in order to isolate and study the contribution of the individual components in the material balance in influencing the recovery factor and determining the production policy of the field.
ü The mechanisms which will be studied are:
- solution gas drive
- gas cap drive
- natural water drive
- compaction drive
ü And these individual reservoir drive mechanisms will be investigated in terms of: reducing the material balance to a compact form, in many cases using the technique of Helena and Odeh, in order to quantify reservoir performance
MATERIAL BALANCE APPLIED TO OIL RESERVOIRS
- determining the main producing characteristics, the producing gas oil ratio and water cut
- determining the pressure decline in the reservoir
- estimating the primary recovery factor
- investigating the possibilities of increasing the primary recovery.