Concentric Workover Operations in Deep Sour Wells

This paper describes an effort to reduce workover cost by applying concentric workover operations to deep sour wells. A medium-duty workover rig performed a variety of remedial procedures through the production tubing. Successful use of the concentric technique at great depths and in a hostile sour environment provides a valuable tool for recovery of additional oil and gas at lower cost. Introduction Exxon Co. U.S.A. operates more than 130 deep [15,500-ft (4724-m)] sour Smackover and Norphlet oil and gas wells in five fields in northwest Florida and south Alabama. Concentric workovers were performed in four of the fields (Jay/Little Escambia Creek, Big Escambia Creek, Blackjack Creek, and Flomaton); however, the program at Jay/Little Escambia Creek (LEC) field has been the largest and is the one discussed here. Conditions applying at Jay/LEC also apply in the other fields.Conventional workovers to recondition a well require a rig to remove the Christmas tree and pull the production tubing. At Jay/LEC this involves using drillpipe to mill out a permanent-type packer to perform the required remedial work. These conventional workovers cost between $700,000 and $1,000,000. In contrast, concentric workovers perform the required work by use of small work pipe run through the production tubing using a small rig or other hoisting unit. The cost of a concentric workover at Jay/LEC averages about $175,000 or approximately one-fourth the cost of a conventional workover.Concentric methods are not new. The techniques have been in use for about 25 years. Concentric workovers have been used at lesser depths to wash out obstructions, fish, acidize, squeeze cement, drill cement, consolidate sand, etc. The uniqueness of the work described in this paper is that the work was performed at greater-than-usual depths and in wells which produce with 10% hydrogen sulfide in the well fluids. Objectives of Workover Program Work is performed on producing wells and water-injection wells with the following objectives:to increase well producing capacity, capture additional reserves, and improve waterflood conformance by opening zones not perforated or stimulating zones perforated but not producing,to restore dead wells to production and capture additional reserves by sealing off zones of floodwater invasion and recompleteing in water-free zones,to prevent interzonal crossflow to water-free zones by plugging zones of water breakthrough,to improve waterflood conformance by opening selected new zones for water injection, andto restore to production wells off due to mechanical blockage in the tubing. JPT P. 1674＾