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Applying Root-Cause Failure Analysis Enhances Artificial-Lift Performance

Topics: Artificial lift

This paper describes the use of a root-cause-failure-analysis (RCFA) process to improve artificial-lift-system performance in a project in Chad. The process was established with the objective of evaluating every failed pump system to determine the reason for failure, identify contributing factors, and monitor trends. The process has helped to reduce the failure frequency by more than 70% on electrical submersible pumps (ESPs) and by more than 50% on progressing-cavity pumps (PCPs), despite the fact that the ESP population has more than tripled and PCP installations have more than doubled.

Introduction

The Chad Project is in the central African country of Chad, approximately 430 km south of N’Djamena, the capital city. The vast majority of the wells are completed with 9⅝-in. production casing and perforated with 7-in. conveyed perforating guns at 12 shots/ft. The wells are surged to remove perforating debris and are gravel packed for sand control before the artificial-lift system is installed. Typically, ESPs are run with 4½-in. production tubing and PCP systems are conveyed with 5½-in. tubing (Fig. 1).

Formation properties are quite favorable, with permeability ranging from 0.5 to 10 darcies and porosity ranging from 24 to 28%. The hydrocarbon-bearing deposits are found at depths as shallow as 3,000 ft and as deep as 6,000 ft. The crude produced from these reservoirs has a gravity of 17 to 24°API, in addition to being heavily biodegraded and undersaturated, with viscosities ranging between 40 and 800 cp. Production is sweet, with no hydrogen sulfide or carbon dioxide, and reservoir temperature is low at 140°F.

High viscosities are encountered when water-in-oil emulsions are formed in the pump when the produced oil and produced water are mixed. At high water cuts, the mixture becomes an oil-in-water emulsion and ESP performance is not degraded. The inversion point varies because of stabilizing conditions but may be in excess of 80% water cut. The PCPs are not affected directly by the presence of severe emulsions; however, the emulsion typically creates higher flowline pressures, causing the pump to work harder because of higher backpressure and higher differential pressure across the pump.

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper IPTC 17230, “Artificial-Lift-Performance Enhancements by Applying Root-Cause Failure Analysis,” by S.G. Lapi, SPE, and M.E. Johnson, SPE, ExxonMobil Production Company, and B. Arisman, SPE, GE Oil & Gas, prepared for the 2014 International Petroleum Technology Conference, Doha, Qatar, 20–22 January. The paper has not been peer reviewed. Copyright 2014 International Petroleum Technology Conference. Reproduced by permission.
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Applying Root-Cause Failure Analysis Enhances Artificial-Lift Performance

01 July 2014

Volume: 66 | Issue: 7

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