Successful Revival of Long Time Closed-In Gas Wells by Right Matrix Stimulation Treatments
Authors: Al-araimi N. , Mahajan M. 
Published: January 2008

Gas wells have traditionally been seen as problem areas with regard to wellstimulation or remedial treatments. This due to the fact that success ratio forthese remedial treatments has been poor compared to the similar treatments inoil reservoirs. There are quite a few specific issues involved with treatmentsin gas reservoirs owing to their comparatively low permeabilities, sensitivityto aqueous fluid systems etc. which calls for more considerations on treatmentdesigns. Over last few decades there has been lot of work in industry torightly address these specific issues and to develop techniques to enhance thechance of success of these treatments.

Another general area of concern in the industry has traditionally been themanagement of idle wells. In spite several innovations in terms of technologyin this area, it is very common to see huge hydrocarbon production potentialstill remains locked-up in to idle/closed-in wells. Usually these wells reallystruggle to compete with their active counterparts in terms of resourceallocations and thus remain poorly attended to. In general, with the vastexpansion of activity level in industry mostly driven by high market pricescoupled with chronological aging of major oil fields, the population of idlewells is on steep rise and as a result locked-in potentials into these wellshave increased by several folds.

This paper is intended to describe a case history on joint efforts betweenOperator and Service companies on 10 such long term closed-in gas producerreservoirs in Brunei offshore field which have been successfully revived withcoiled tubing conveyed acidizing remedial treatments and put back on productionwith impressive gains.All these well strings have been closed in sincelast 6 years and most were also the single drainage points for the reservoirs, so any data on performance from any offset wells was not known. The suggestionsfor the need of some remedial treatments on these well strings was raised atthat time but were not supported by line Management in view of the historicallyvery poor, and at times adverse performance of gas reservoir remedialtreatments during earlier Service Campaigns.

Introduction

The process kicked off with the initiative of a Production technologistresponsible for one specific offshore field in Brunei. Instead of reacting tousual situation of not enough barrels in the bag situation in conventional wayby picking up candidate wells on either highest expected returns and/or lowestanticipated risk basis, a different approach was followed in this case ofscanning through each and every idle well in this field. A team was constitutedby picking representatives from several work groups from the operating companyalong with several operations and design engineers from the Service Company tocarefully look into and identify every opportunity that existed in these idlewells. Consultative opinions were also considered from professionals withinother regions of the operating company's business units, Service Company andthird party sources as required during the process.

During this exercise, over and above all usual technical criterion forworking out a description of suspected damage, the major emphasis was alsogiven to the figures of remaining reserves, which were on the operatingcompany's books against each of these reservoirs. After the primary work on thereview of data on these wells, a proposed action plan was discussed with theoperating company's management for seeking a go head on the Project. The riskfactor in terms of these treatments was bare minimum, may be limited only tothe additional cost of servicing, as all of the wells under consideration werelong time closed-in. The operating company's management was also aware of thefact that if planned remedial treatments are not supported, or fail, then allreserves must be written off. To nobody's surprise the response came positivefor the work to go ahead. Total 10 reservoirs were selected as candidates fortaking up further works on.