Abstract

This paper describes new methods to economically improve production levels in one of the mature fields of Petroleum Development Oman. This field had been developed by infill drilling programs, which were suspended in early 2001 to review the development strategy.A reservoir management team set a challenge to effectively conduct logging operations and quickly utilize the data collected to identify and avail of optimization opportunities, thus maximizing the production of the wells whilst lowering overall costs.The optimization activity consisted of clean-out, saturation logging, perforation and stimulation. These activities were carried out either with coiled tubing only utilizing conventional practises and e-line coiled tubing, or with the combination of coiled tubing and hoist through multiple well entries. Both of these methods were successfull in that they resulted in incremental net oil production but at relatively high costs.

This paper presents a methodology which enables clean-out, logging, stimulation and perforation with one coiled tubing intervention, which includes a plastic coated "e-line" coiled tubing, coiled tubing perforating head and new perforation technology.All systems are in complete compliance with the most stringent safety criteria.The new method has a considerable time and cost savings impact, and this is fully illustrated in this paper with field trial case histories, in which a multi-disciplinary team effectively targeted the most suitable zones for perforation and stimulation using a state of the art self diverting, non damaging, acid system.Technical and economic comparisons are made with conventional practices.The methodology is currently being employed in this field and is potentially applicable to other fields.

Introduction

One of the matured fields of Petroleum Development Oman, situated in North Oman and is mainly producing from the Lower Cretaceous Shuaiba formation which is heavily faulted and consists of intrashelf basin floor carbonate muds. Porosity ranges from 30 to 35% while permeability ranges from 1 md at the base of the Shuaiba to 200 md in thief zones. Average matrix permeability is approximately 10 md. Permeabilities in fault and fracture zones are believed to be orders of magnitude higher than the average matrix permeability. Most of the production comes from horizontal wells with 4½" cemented liner and perforated. The average current water cut from this field is 93%. The high water cut presents longer term concerns and Petroleum Development Oman has implemented a multi-disciplinary effort with the ultimate goal of improving production through a concerted CT and Hoist operations.A very thorough evaluation of candidate selection is conducted utilizing appropriate reservoir evaluation techniques, with strong consideration to geology.

The development activities in this field traditionally have been targeted by infill drilling with vertical wells until 1994 followed by horizontal wells. The infill well drilling was suspended in early 2001. An integrated field review was initiated to design the next era of this field development to maximize the remaining value through effective well and reservoir management.The well and reservoir management team identified the need for data gathering through recording reservoir saturations by running pulse neutron capture tools (PNC) for identifying additional perforation opportunities. In gas lifted wells the PNC logging was run on a coiled tubing and in ESP (Electrical Submersible Pump) wells by pumping the PNC tool inside the work string during hoist operations. Based on the PNC logs, additional perforations were made in many wells and the additional perforations improved the net oil production from them. Hence, through PNC logging, additional perforation and stimulation were given prime importance in this field during the year 2004 in order to maintain production levels. Various cost reduction measures were applied to reduce the operating cost per barrel. One of them is the novel idea of utilising coiled tubing for cleanout, logging, mechanical water shut-off, perforation and stimulation in one go. This paper describes the single rig-up coiled tubing process that has eliminated multiple entries and resulted in both cost reduction and less turn around time.

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