EFFECTS OF PARTIAL COMPLETION ON PRODUCTIVITY INDEX

EFFECTS OF PARTIAL COMPLETION ON PRODUCTIVITY INDEX

ABSTRACT

A new method for analysing productivity index (PI) on vertical wells is the main objective of this study. Well performance is often measured in terms of the well’s productivity which is dependent on a number of factors such as the reservoir’s configuration, the type of completion, petrophysical and fluid properties, formation damage, etc. The effect of partial completion is the main focus of making the productivity index analysis since almost all vertical wells are partially completed due to the reasons of water coning or gas cap issue, etc. It is also very expensive to fully complete a well especially when the formation thickness is so large.

Pressure behaviour solutions for both closed boundary and constant pressure boundary have been obtained, taking into consideration the effect of partial completion. Productivity of a well is usually evaluated on the long time performance behaviour, thus the pseudo-steady state (late time) approach has been employed for calculation of the productivity index.

Several key factors have been tested on productivity index such as pseudo skin, shape factors, penetration ratio, reservoir drainage area and etc. The effects of these factors have been analysed on PI. Theoretical data were used in carrying out the analysis with results indicating that, productivity index increases with increasing completion interval and vice versa, whiles pressure drop due to skin as a result of restricted entry to fluid flow increases tremendously with decreasing completion interval Shape factors of various well positions in bounded reservoirs were computed and compared with results obtained by Dietz, and Babu and Odeh.

CHAPTER ONE

INTRODUCTION

1.1         PROBLEM STATEMENT

Well productivity is one of the major concerns in oil field development, and provides the means for oil field development strategy. Sometimes, well performance is measured in terms of productivity index. In order to arrive at the economic feasibility of drilling a well, petroleum engineers require proven and reliable methods to estimate the expected productivity of that well. Well productivity is often evaluated using the productivity index, defined as the production rate per unit pressure drawdown. Petroleum engineers often relate the well productivity evaluation to the long-time performance behaviour of a well, that is, the behaviour during pseudo-steady-state or/and steady-state flow of a closed system or/and constant pressure system respectively.

The long-term productivity of oil wells is influenced by many factors. Among these factors are petrophysical properties, fluid properties, degree of formation damage and/or stimulation, well geometry, well completions, number of fluid phases, and flow-velocity type (Darcy, non-Darcy) (Yildiz, 2003).

EFFECTS OF PARTIAL COMPLETION ON PRODUCTIVITY INDEX