Interpretation of ESP reliability using weibull analysis and dynamic run life analysis

Abstract

Electrical Submersible Pumps (ESPs) are the most common used artificial lift method in Kuwait. The life data analysis of an ESP is important in design, operation, and to meet the deliverability of the reservoir. Weibull Reliability combined with the Dynamic Average Equipment Run-Life (DAERL) allows to construct confidence intervals for the survival of ESP system based on equipment, design information, reservoir data, and operating performance. Statistical methodology using a combination of Weibull and DAERL is developed and applied to a data set which covers all ESP systems installed in Kuwait with over 8 years of data covering 5,000 ESP installations. Through the addition of operating history data (including the number of trips and the specific reasons of trips) into the analysis provides a more accurate reliability measure of running wells today. The primary advantage of Weibull analysis is the ability to provide reasonably accurate failure analysis and failure forecasts with small samples. By performing linear regression, parameter estimates can be obtained that will enable to interpret the survival of an ESP system based on equipment, reservoir, and operating information. Weibull Analysis shows better and more accurate results than an average method of reliability in evaluating ESP system performance. The DAERL analysis looks at the overall run life of a group of wells (operating and non-operating) and the change in performance over time. Cross comparisons of equipment types (such as round cable instead of flat cable) yield results of a longer expected run life and higher reliability. The paper shows that in most cases both Weibull and DAERL show similar performance trends, but the value of the results presented for each has different applications. The effect of survivability in this study is applied on different types of ESP surface and downhole equipment, reservoir data, failure reasons, and the operating history. The results of the analysis generate recommendations that are used to improve performance of both current running ESP wells and future ESPs to be installed. One of the major priorities of the authors in this study was to use the results to better operate running wells today, by measuring the average days between shutdowns combined with Weibull reliability, an analysis tool is built to higlight specific wells that are at risk of failure.