Casing Failure Analysis for API N-80 Grade in Sudanese Thermal Oil Recovery Production Wells: Case Study

Abstract

Implementation of the Cyclic Steam Stimulation (CSS) and Steam Flooding as thermally Enhanced Oil Recovery (EOR) methods increase the commercial value of the existence Field through increasing oil recovery and field extension. When the steam is generated, processed and injected with high peak temperature into shallow wells (total depth of 700m) for oil recovery, it may result in high thermally induced stresses, which might exceed its design limit of the material and lead directly to the plastic deformation in the casing and thread connection. The objective of this paper is to premineraly investigate and analyze the reasons behind the casing failure in some well candidates at Fula North East (FNE) thermal oilfield based on the analytical analysis targeting the related structural and operational aspects of these applications. There are several casing failures have been reported; but so far no enough evident to correlate these failures to the mentioned stresses. Therefore, Ensuring adequate structural integrity and seal ability of the connections over the full service life of a thermal recovery well is a significant challenge. In this work, the Root Cause Analysis (RCA) on premineraly manner has been used through correlation of the problem to casing’s grade and materials, cement formulation, sand production and steam injection parameters and thermal insulation process, by using step by step methodology. The results show that some supporting measures are recommended in order to minimize the casing damage and extend the life time of the thermal wells in FNE oil field. The above mentioned methodology has been used as the first time in Sudan to analyze casing failure in thermal oilfield