Casing Collapse Study on Block VI Wells: Casabe Field

Abstract

Abstract This document presents the development and results of a study for determining the possible reasons of casing collapse in the Casabe Field, Colombia, specifically in block VI, where the phenomena occurred with more intensity. The study was requested as part of a revitalization strategy for this mature field, to maintain and improve the production performance of new and existing wells. The study consisted of different phases:Statistical and Probabilistic: firstly related to trend identification (i.e. well type, drilling date, well status and collapse localization), and secondly reliability and failure curves were created using the probabilistic Montecarlo analysis.Mechanical Integrity: casing integrity was analyzed using a software application called TDAS, by taking into account the corrosion effect and different operational and typical loads.Water flooding effects were also analyzed to take into account the stresses created by water injection on the casings at different formation levels (A or B). Figure 1 shows the four main phases that comprised the study. As a result of this study, a new well mechanical design was created and successfully applied on all new wells drilled in the Casabe field with zero collapse occurrences. Well longevity has been guaranteed, improving the economics of the field. The study gives a safety operational procedure considering a range in different parameters (tension, fluid level, corrosion, injection pressure and type of casing) that give support to critical well operations in order to mitigate casing collapse. Introduction Casabe is an old and mature field located in Yondó (Colombia), in the mid-Magdalena River Valley basin and has an extension of 25 Km2. Along the productive life of the field, well casing collapse was identified as a critical problem, as some 45% of producers exhibited collapse with different severity levels. This problem increased over time, but the causes had not been totally identified. Due to casing collapse, injection rates were reduced in an effort to reduce its occurrence rate. Consequently, the waterflooding process was underperforming. The field has eight blocks defined by normal faults. Block VI is the biggest of all in terms of reserves and presented in 2006 the highest proportion of collapsed wells, a total of 214. To produce those reserves, a re-development plan was implemented in 2006 with an intense drilling campaign. The study of the casing collapses became hence extremely necessary.