The Long-Term Performance of Sand-Control Completions in the Mokoko-Abana Field,Cameroon
Authors: Mason D. , Evans M. , Ekamba B. , Cameroon Pecten , Jones C. , Cameroon J. 
Published: October 2008

The proportion of new wells requiring sand control is increasing, and choosing the most economic sand control system from the available options is a central component in field development planning. The choice of sand control system depends on a number of factors such as production and sand control performance, reserves recovery, reliability, ease of installation and life cycle economics. Logistical and HSE issues are also becoming increasingly important, especially in areas with limited support infrastructure.

A key input to the process of sand control system selection is data on how the various systems compare in a given environment. Ideally, this comparison should be made over time in order to properly compare the long term performance and reliability. This data can only be obtained by analyzing existing installations equitably and objectively.

The Mokoko-Abana field is situated offshore Cameroon. It is a mature heavy oil field with unconsolidated formations that require sand control from the onset of production. A wide variety of sand control solutions have been used in this field, although with varying levels of success and performance. Cased hole internal gravel packs (IGP), milled casing openhole under-reamed gravel packs (MCGP) and cased hole frac-packs (CHFP) have been used in vertical wells. Prepacked stand-alone screens (PPSAS), openhole gravel packs (OHGP) and openhole expandable sand screens (OHESS) have been used in horizontal and highly deviated wells.

Each of the completion options now has several years of production history. This allows the initial performance and the performance over time to be modelled and compared. The wells chosen for study were in the same sand body with as near perfect installation as possible. The MCGP had relatively good performance as did the CHFP, unfortunately however the CHFP fractured into a water bearing leg and only added water cut. The PPSAS had initially low mechanical skins, but its performance declined quickly. The OHGP had higher initial skins but the rate of production decline is much slower. The OHESS had a very low initial skin with no impairment over the five year production period.

SPE 946511contains background information on the Mokoko-Abana field, and looks at the productivity performance of the PPSAS, OHGP and OHESS techniques on initial completion and after two years of production. This paper follows on from SPE 94651 and examines the operational, productivity, reliability and economical aspects of the completion techniques over five years or more of production.

Introduction

A comparison of the performance of sand control completions in the Mokoko-Abana Field was carried out in 2004 and 2005. This compared three wells completed on the same oil sand with essentially the same hole size, similar drilled trajectories, similar drilling mud, the same rig and with largely the same personnel. All were successfully executed and can be considered as fair and reasonable comparisons. Each well had(then) at least two years production history. Differences in reservoir properties, artificial lift method and minor differences in fluid characteristics were modelled and backed out.