TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractFollowing successful implementation of underbalanced drilling in Petroleum Development Oman (PDO) an evaluation of the value of underbalanced drilling (UBD) in a northern carbonate field was commissioned. The study showed that there was a production upside to developing the reservoir with UBD. A four-well trial campaign was conducted between June and October 2004 to assess the potential.The trial campaign was implemented following a structured program built from PDO's previous experience. During this campaign a Reservoir Characterization (RC) system allowing identification of multiple high permeability features was developed. Water shut-off devices were installed in two wells based upon the results of the Reservoir Characterisation system. Production in the four wells was equivalent to or greater than field average and the campaign scope has been increased. The campaign was also a stepping stone towards the goal of integrating UBD, Reservoir Characterization and water shut off techniques.

Following successful implementation of underbalanced drilling (UBD) in Petroleum Development Oman (PDO), an evaluation of the value of UBD in a carbonate field was commissioned. The study showed that there was a production upside to developing the reservoir with UBD. A four-well trial campaign was conducted between June and October 2004 to assess the potential.The trial campaign was implemented following a structured program built from PDO's previous experience. During this campaign, a reservoir-characterization (RC) system allowing identification of multiple high-permeability features was developed. Water-shutoff devices were installed in two wells on the basis of the results of the RC system. Production from the four wells was equivalent to or greater than the field average, and the campaign scope has been increased. The campaign was also a stepping stone toward the goal of integrating UBD, RC, and watershutoff techniques.

The Main Sultanat of Oman Gas Field is comprised of two deep tight gas clastic reservoirs, separated by thick shale layer, and has been on production since 1999. These reservoirs are encountered at depth ranges of 14,000 - 17,000 ft and the top reservoir is a rich gas condensate followed by a lean gas for the lower reservoir. Permeability is in the range of 0.01 to 10 mD, porosities of 1 % to 14% and this field being a swing producer, actual production is in the range of 700 - 1,000 MMsfcd. To ensure achieving a maximum value, from such complex reservoirs, the field has gone through several development stages. The first stage has focused mainly on appraisal and development wells to obtain better understanding of well and reservoir performance and further data acquisition for better reservoir characterisation. The second stage of the Field Development Plan (FDP), in 2005, was an update of the FDP reflecting all the information that have become available since the commission of the field as well as the production performance gained from the previous 5 years of production. Further optimization of total number of wells, better prediction of the field performance and firming up the first stage of depletion compression were the key elements of the FDP update. Hence, first stage depletion compression plant was pursued and commissioned in 2010. In addition, velocity strings from 51/2" to 27/8", for maximum utilisation of low producing wells, were evaluated and more appraisals activities, for further scope maturation, were assigned. The third stage of the FDP update has been completed. The key objectives were to validate the previous FDP, in particular, wells and reservoir performance as a result of stage-1 depletion compression. Besides, phase-2 depletion compression was proposed and the remaining development drilling were re-evaluated, optimised and confirmed. Furthermore, a plan to mature contingency reserves, from poor reservoir intervals, was initiated and associated studies, such as geomechanical models and fracturing optimisation were performed. In this paper, a case study of developing a complex and tight deep gas reservoir will be discussed. The experience of applying phase approach and associated value will be shared and how the multidisciplinary team came up with the best Field Development Plan taking into consideration the different challenges and options taken by every discipline to put the best development strategy to get the optimum ultimate recovery from the field.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractFollowing successful implementation of underbalanced drilling in Petroleum Development Oman (PDO) an evaluation of the value of underbalanced drilling (UBD) in a northern carbonate field was commissioned. The study showed that there was a production upside to developing the reservoir with UBD. A four-well trial campaign was conducted between June and October 2004 to assess the potential.The trial campaign was implemented following a structured program built from PDO's previous experience. During this campaign a Reservoir Characterization (RC) system allowing identification of multiple high permeability features was developed. Water shut-off devices were installed in two wells based upon the results of the Reservoir Characterisation system. Production in the four wells was equivalent to or greater than field average and the campaign scope has been increased. The campaign was also a stepping stone towards the goal of integrating UBD, Reservoir Characterization and water shut off techniques.