ABSTRACT
Solution gas drive reservoirs are characterized by rapid and
continuous decline of reservoir pressure. This rapid and continuous
decline of reservoir pressure causes direct decline of reservoir
performance at early stages of the life of the reservoir. The principal
source of energy which is gas liberation from the crude oil and the
subsequent expansion of the solution gas as the reservoir pressure is
reduced are inadequate to produce such reservoirs to their full
capacities. Ultimate oil recovery from natural flow of a solution - gas
drive reservoir makes it one of the least efficient primary recovery
mechanisms. This leaves a substantial amount of remaining oil residing
in the reservoir which must be produced.
Artificial lift technologies such as continuous gas lift, gas lift
with velocity strings and positive displacement pumping is therefore
employed at later phases of the reservoir’s life to increase the
ultimate recovery which is what this project sort to do. Synthetic data
based on material balance for a solution – gas drive reservoir is
analyzed to predict its primary oil recovery based on which gas lifting,
velocity strings technology and positive displacement pumping are
suggested to be employed with respect to time at different stages of
reservoir’s life.
Chapter 1
1.0 Introduction
1.1 Problem Statement
Solution gas drive also known as Dissolved gas drive or Internal gas
drive reservoirs are characterised by a rapid and continuous decline of
reservoir pressure. This reservoir pressure behaviour is attributed to
the fact that no extraneous fluids or gas caps are available to provide a
replacement of the gas and oil withdrawals (Tarek, 2001). This rapid
and continuous decline of reservoir pressure causes a direct decline of
reservoir performance at early stages of the life of the reservoir.
Moreover, the principal source of energy which is gas liberation from
the crude oil and the subsequent expansion of the solution gas as the
reservoir pressure is reduced are inadequate to produce such reservoirs
to their full capacities (Tarek, 2001). Ultimate oil recovery from
natural flow of a solution gas drive reservoir (less than 5% to about
30%) makes it one of the least efficient primary recovery mechanisms
(Tarek, 2001). The low recovery from this type of reservoir suggests
that large quantities of oil remain in the reservoir and, therefore,
solution gas drive reservoirs are considered the best candidates for
secondary recovery applications.
Artificial lift technologies such as continuous gas lift, gas lift
with velocity strings and positive displacement pumping method is
therefore employed at later phases of the reservoir in order to increase
the ultimate recovery. The main challenge is to know when to change
existing production mechanism to a new one for optimum recovery. A
production design has therefore been made in an attempt to solving this
problem with respect to constraints such as maximum production rate,
maximum drawdown, and available gas lift.
The flowing bottom-hole pressure required to lift the fluids up to
the surface may be influenced by size of the tubing string (Lyons, 1996)
and for that matter the time when tubing strings should be replaced as a
function of cumulative production is necessary.
1.2 Method of Conducting the Project
Designing the natural flow and artificial lift tubing strings for the
whole life of a well forms the tasks of this project. This is based on
certain constraints such as maximum production rate, maximum drawdown,
and available gas lift and horsepower requirement. Synthetic reservoir
performance based on a material balance is the main data source for this
project. A forecast of the production of oil as well as the time when
tubing strings should be replaced as a function of the cumulative
production is proposed.
1.3 Objectives
The objectives of this project are to:
· Design natural flow and artificial lift tubing strings for the whole life of a well.
· Forecast the production of oil as well as the time when
tubing strings should be replaced as a function of both cumulative
production and time.
1.4 Outline of this Project
The project consists of five (5) chapters. Chapter 1 defines the
problem at hand, the method which the project follows and objectives.
Chapter 2 presents a literature review of the topic as well as the
technical terms that make up the topic. Chapter 3 introduces a thorough
review of the material balance equation, methods of predicting primary
oil recovery with emphasis on Muskat’s method which has been employed in
this report. Application of the Muskat’s method is illustrated with a
synthetic reservoir data. Chapter 4 comes up with the natural flow
design as well as the artificial lift tubing strings with respect to the
set constraints.