1.1 Background to 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.
a. 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).
b. To optimize the system to produce the objective flow rate most economically.
c. To check each component in the well system to determine whether it is restricting the flow rate unnecessarily.
d. 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:
a. Quick estimate of flow rate, and as such reduction in time taken to do this.
b. Alternative method for the prediction of flow rate.
c. 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
a. System Analysis Approach
b. Nodal Concept
c. Inflow Performance Relationships
d. Well Design
e. Theory of the Reservoir flow
f. Flow Restrictions
g. Completion Effects
h. Multiphase flow
i. Use of Computer software Program (PROSPER) for Complex Solution.
Some limitations encountered in the course of this study are:
a. Access to accurate data
b. Time constraint
c. Breech on internet access due to poor network
1.6 PROJECT MATERIALS
a. Production optimization text books, journals and papers
b. PROSPER software
c. Well/reservoir data Recent projects on nodal analysis ( for reference purposes)