Innovative Downhole Real Time PVT Sampling Solution Complementing a Comprehensive Well Integrity Strategy in a HPHT Sour Gas Environment

Abstract

Development of gas resources in the Middle East is taking an increasingly higher priority, driven by the growing demand for gas based power generation as well as the motivation for replacing oil as furnace fuel as is the case in several middle-eastern countries. Such fields are often characterized by corrosion formation fluids including CO2 and H2S, formation solids and other non-hydrocarbon components. These associated components have the capability to adversely affect on compatability with well completions, design of production facilities, maintenance costs, reservoir assets and product sales value among others. The failure to have such information could represent much more risk than taking the decision to perform downhole sampling and laboratory analysis. Corrosion induced by the presence of sweet or sour gas combined with water production has led to major well integrity issues in some of these fields. Continuous monitoring and remedial programs have been implemented to issues either before or when they occur. Sacrificial tubing completions are deployed periodically inspected using corrosion monitoring tools and replaced based on established criteria. However, this process is associated with high monitoring, completion hardware, work-over and intervention costs. Several corrosion studies in the past have been conducted to understand the properties of water and the effect on the precipitation and deposition of ferric salts in order to devise a predictive model for onset of corrosion which is related to tubular lifetime with a view of establishing a reliable corrosion preventive strategy which precludes expensive monitoring or remedial work-over operations. In the past, produced water collected at surface was analyzed for chemical composition and PVT analysis but such results are inherently inaccurate due to the change in the chemical/composition and physical state of the water from downhole up to the surface. Hence there has been more focus on collecting "representative bottom-hole water samples". Memory based PVT samplers do offer this opportunity but suffer from the disadvantage of having to collect the samples "blind", quite often obtaining samples from the sump or coming back empty. This paper presents a novel technique and engineering accomplishment which enhances the PVT and water sampling capabilities at in-situ conditions on gas producers in combination with full production logging stack deployed on electric line, offering real time control of the sampling operation. The volume captured is adequate for proper broad fluid analysis; lesser quantities generate uncertainties which ended incorporated into the results. Field case studies are presented based on the early stage successful deployment of this technology and its impact on facilitating the recovery of representative formation fluid samples. Results of the fluid analysis have demonstrably improved the understanding of true water chemistry, which is a significant departure from earlier theories and contaminated measurements. Wells were sampled in order to carry out the risk assessment for corrosion and scaling tendency. The impact of the study on developing more effective well integrity and well intervention programs are also presented.to maintain the continuity of operations.