A Simplified Method To Predict Over-All Production Performance
Authors: Perez Godofredo , Kelkar Balmohan G. 
Published: March 2010

This paper presents a simple method to predict the over-all production performance of oil and gas systems. Conventional methods usually require time consuming graphical approaches. The proposed method is based on a simple mathematical algorithm that provides fast and accurate means to estimate the over-all performance of a production system. In addition, the proposed method has been designed EO search for unstable production conditions that might exist i11 the system.

The method has been used to develop a computer model representing a system consisting of several production components, The production components considered in the computer model are: reservoir, perforations, gravel pack, tubing, subsurface safety valve, wellhead choke, surface pipeline and separator. In addition, a gas lift system is also included.

Practical applications of the model are presented, and these include sensitivity analysis of the performance of an oil production system and evaluation of unstable conditions in a gas condensate system. Results from this model are compared and agree closely with several cases presented in the literature.

Introduction

Over-all production performance is the flow rate that a system is able to sustain under the restrictions imposed by the production components. Physical restrictions of production systems can be divided into several components such that the pressure losses across each component are evaluated independently. Correct determination of the performance of a production system depends ultimately on the accuracy of the pressure loss predictions across each component of the system. Research efforts in the last few years have resulted in several methods and correlations capable of accurately predicting pressure losses across different production components for a wide range of operating conditions. These include, correlations to estimate pressure losses in pipelines, vertical tubings, and other restrictions (chokes, safety valves) for multiphase flow conditions. Also, methods and correlations are available to estimate reservoir deliverability from stabilized well test data with good accuracy. On the other hand, additional investigation is required to improve methods for the prediction of pressure losses across well completions (gravel pack and perforations). Several of these methods and correlations used in this work are discussed in a later section.

Calculation of over-all production performance of a system in-volves a simple principle. This consists of dividing the production system into two parts at a fixed point (node), and for a given flow rate, starting for one pan at the reservoir and for the other pan at the separator, evaluating the required pressure at that point for each part by including the pressure drop across each component(1,2,3). The production performance is determined by the flow rate which provides the same pressure for each side of node al the selected node. It can be shown that production performance determined in this way is independent of the node used La divide the system(l).

Nodal Analysis(l) (trade mark of Flopetrol-Johnstone-Schlumberger) is a technique which provides guidelines to select the most convenient node to analyze a production system.