INTRODUCTION
1.1 Background of study
Nodal analysis also known as “system analysis” is a systematic
procedure/approach applied to the enhancement or optimization of
production of oil and gas wells by analyzing and evaluating the
complete production system. Every component that constitutes the
production system can be optimized to achieve the objective production
(flow) rate most economically. The production system comprises of flow
of hydrocarbon fluids from the reservoir to the surface production
facilities, and including inflow performance, as well as flow across
the completion, up the tubing string (including any down hole
restrictions and safety valves) across the surface choke (if
applicable), through horizontal flow-lines.
The production system can be relatively simple or can include many
components in which energy or pressure losses occur (fig, 1-1).
Any production well is drilled and completed to move the oil or
gas from its original location in the reservoir to the stock tank or
sales line (for gas). Movement or transport of these fluids requires
energy to overcome friction losses in the system and to lift the
products to the surface. The fluids must travel through the reservoir
and the piping system and ultimately flow into a separator for gas
liquid separation. The pressure drop in the total system at any time
will be the static initial fluid pressure minus the final fluid
pressure, PR-Psep. This pressure drop is the
sum of the pressure drops occurring in all of the components of the
system (fig 1.2). Since the pressure drop through any component varies
with producing rate, the producing rate will be controlled by the
components selected. The selection and sizing of the individual
components is very important, but because of the interaction among the
components, a change in the pressure drop in one may change the
pressure drop behavior in all the others. This occurs because the
flowing fluid is compressible, and, therefore, the pressure drop in a
particular component depends not only on the flow rate through the
component, but also on the average pressure that exists in the
component.
The final design of a production system cannot be
separated into reservoir performance and piping system performance and
handled independently. The amount of oil and gas flowing into the well
from the reservoir depends on the pressure drop in the piping system,
and the pressure drop in the piping system depends on the amount of
fluid flowing through it. Therefore, the entire production system must
be analyzed as a unit.
The production rate or deliverability of a well
can often be severely restricted by the performance of only one
component in the system. If the effect of each component on the total
system performance can be isolated, the system performance can be
optimized in the most economical way.
1.2 STATEMENT OF RESEARCH PROBLEM
There are numerous oil and gas wells around the world that
have not been optimized to achieve an objective rate efficiently. Past
experience has shown that large amounts of money have been wasted on
stimulating the formation when the well's producing capacity was
actually being restricted because the tubing or flow line size was too
small. Another example of errors in completion design is to install
tubing that is too large. This often happens on wells that are expected
to produce at high rates. It has been shown that this practice not
only wastes money on oversized equipment, but tubing that is too large
can actually reduce the rate at which a well will flow. Thus can cause
the well to load up with liquids and die, which necessitate; the early
installation of artificial lift equipment. In fact, many wells may have
been completed in such a manner that their maximum potential rate
cannot be achieved.
1.3 OBJECTIVE OF STUDY
The objectives of nodal analysis are as follows.
- To determine the flow rate at which the existing
oil or gas well will produce considering well bore geometry and
completion limitations (by natural flow).
- To optimize the system to produce the objective flow rate most economically.
- To check each component in the well system to determine whether it is restricting the flow rate unnecessarily.
- To permit quick recognition by the operator's management and engineering staff of ways to increase production rates.
1.4 SIGNIFICANCE OF STUDY
Nodal analysis is a great tool for production
optimization; its effects to the oil and gas industry are vast and
include the following:
- Quick estimate of flow rate, and as such reduction in time taken to do this.
- Alternative method for the prediction of flow rate.
- Identify the reservoir and well parameter that
affect the flow rate the most and as such will aid engineers to
concentrate on these factors when sourcing for data and when performing
PROSPER run.
One of the most important aspects of
nodal analysis is to recognize wells that should be producing at rates
higher than their current rate. Therefore, it can serve as an excellent
tool to verify that a problem exists and that additional testing is
necessary.
Nodal analysis can determine which component is
restricting the rate or can determine that incorrect data are the cause
of the higher predicted rate.
1.5 SCOPE AND LIMITATION OF STUDY
This study is intended to cover the following areas
- System Analysis Approach
- Nodal Concept
- Inflow Performance Relationships
- Well Design
- Theory of the Reservoir flow
- Flow Restrictions
- Completion Effects
- Multiphase flow
- Use of Computer software Program (PROSPER) for Complex Solution.
Some limitations encountered in the course of this study are:
- Access to accurate data
- Time constraint
- Breech on internet access due to poor network
- Power
- PROJECT MATERIALS
- Production optimization text books, journals and papers
- PROSPER software
- Well/reservoir data
- Recent projects on nodal analysis ( for reference purposes)