Well Integrity Analysis Applied to Workover Prediction
Authors: Mendes Jose Ricardo Pelaquim , da Fonseca Tiago Cardoso , Miura Kazuo 
Published: June 2014

Abstract
Well integrity may be defined as the well's capability to prevent leaks to the environment and is therefore a very important feature for oil and gas wells. Its importance has grown in past years, especially after recent events have shown the impact of oil spills on the operators' financial wellness. One way to avoid leaks during well operation is performing maintenance interventions, or workovers, seeking to keep redundancy in the well's safety barriers throughout the well production life. Cost assessment regarding the wells maintenance interventions shall be done during the well design phase of the Production Development project, when the wells construction campaign is both technically and economically evaluated. This work presents a methodology for well integrity analysis based on the concept of Barrier Integrated Sets (BIS) and on Reliability Engineering techniques. Through the computation of the mean time to failure of each BIS identified in the completion configuration it is possible to estimate when the well hits a degraded status, in which it relies on a single BIS and when the well is expected to leak, i.e. there are no BIS in place. These estimations may be used for a well workover interventions resource assessment, in a well construction and operation campaign.

Introduction
Mankind has used Petroleum as fuel for more than two thousand years, and the current importance of oil products in the societies explains the growth of extraction activities throughout the world. The increasing demand for oil and gas has lead the industry to explore and produce hydrocarbons in scenarios more and more challenging. Deserts, polar regions, lakes, river mouths and maritime environments, continental shelves and slopes, have been common scenarios for Exploration and Production (E&P).
The evolution of E&P scenarios has led to a consequent increase in the complexity of both well design and maritime units (drilling rigs) used in well construction and workover interventions. As expected, overall costs and risks have also followed this increase tendency.
Cost associated to the Well Engineering discipline in the development of the Brazilian Campos Basin (begun in the late 1970s) represented about 1/3 of the total investments (Miura, 2004). In the pre-salt projects, the new Brazilian oil play, costs associated to well drilling, completion and workover represent about 50% of total budgets (Formigli Filho, 2008). Resource forecasting, such as drilling rigs and equipment, has been elevated to a new level of importance in the economical assessment of Production Development projects.
Risks associated to E&P have also increased as the complexity of scenarios evolved, making more critical the issues related to well integrity - i.e. the containment and the prevention of the escape of fluids to subterranean formations or surface. Total budget spent by BP after the Macondo oil spill and subsequent market value loss characterize the negative extension that an accident during well engineering activities may impose to an organization.