Overcoming Formation Evaluation Challenges in Short Radius Re-entry Wells in Aging Reservoirs

Abstract

Innovations in drilling and completion technology has opened a new era in the oil and gas sector revitalizing old fields either to tap bypassed pockets of hydrocarbons or enhance the recovery factor with re-entry wells. Now enhancing production from aging fields has become a major activity for oil and gas companies. However, this is not a straight-forward decision and often the oil companies are challenged with the casing integrity, inadequate or missing log data and being able to complete the well economically. The history of re-entry wells goes back to 1950's but it is only recently that the industry is seeing more medium and short radius wells to improve operational efficiency and to make the projects more economical. Slim borehole, complex geometry and high dogleg severity are the common attributes of such re-entry wells. Unequivocally, these complex wellbore geometries will improve recovery of reserves and maximise the net present value (NPV); however the real challenge lies with the acquisition of formation evaluation data. In these challenging conditions conventional Wireline or LWD techniques cannot provide adequate solutions to obtain much needed formation evaluation data. It was one of the reasons why most of the challenging re-entry wells in the past were not logged. Saudi Aramco faced similar challenges in one of their re-entry aging wells. The well was drilled in 1968 as a vertical open-hole producer. A series of work-overs were performed over the life of the well and in 2002, the well was side-tracked and a short radius trajectory was chosen to drill a horizontal section. During drilling the operator encountered a total loss circulation zone and was forced to plug the zone blindly without being able to log and investigate the cause. Memory logging and slim tools have been introduced in the last decade. The operator planned to carry out another work-over in 2014.