Summary
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 use the data collected to
identify and avail of optimization opportunities. The ensuing campaign resulted
in 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 initially carried out in two ways: 1)
with coiled tubing using only conventional coiled tubing and e-line coiled
tubing or 2) with the combination of coiled tubing and a hoist. Both methods
involved multiple well entries. Both of these methods were successful in that
they resulted in incremental net oil production but at relatively high
costs.
This paper presents an enhanced 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. These results are 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 by use of a state of the art self-diverting, non-damaging, acid
system. Technical and economic comparisons are made with conventional
practices. The new methodology is currently being used in this field and is
potentially applicable to other fields.
Introduction
The field under study is in north Oman and has been operating under
waterflood conditions since 1972. The reservoir is positioned within the Lower
Cretaceous Shuaiba formation, which is a chalky intrashelf basin floor
carbonate mudstone. Porosity ranges from 30 to 35%, while permeability ranges
from one md at the base of the Shuaiba to 200 md in thief zones at the top.
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 a
perforated 4 ½ in. cemented liner. The average water cut from this field is
currently 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 sound reservoir management practice
together with concerted coiled tubing (CT) and workover-rig (hoist)
intervention operations. A thorough evaluation of candidate selection is
conducted by use of appropriate reservoir evaluation techniques with strong
consideration to geology.
The development activities in this field traditionally had been targeted by
infill drilling with vertical wells until 1994, followed by horizontal wells.
The infill drilling targeting attic oil was suspended in early 2001. An
integrated field review was started to design the next stage of field
development to maximize the remaining value through effective well and
reservoir management. The reservoir management team identified the need for
data gathering including the monitoring of reservoir saturation by running
pulsed-neutron-capture tools (PNC) to identify additional perforation
opportunities. In gas-lifted wells, the PNC logging was run on coiled tubing
and in wells with Electrical Submersible Pumps (ESP) by pumping down the PNC
tool inside the work string during hoist operations. Based on the PNC logs,
additional perforation and selective stimulation were made in many wells which,
in most cases, improved their net oil production. Additionally, various cost
reduction measures were applied to reduce the operating cost per barrel. One of
them was a novel idea to use the coiled-tubing unit for cleanout, logging,
mechanical water shut-off, perforation, and stimulation in one intervention.
This paper describes this single rig-up coiled-tubing process that has
eliminated multiple entries and resulted in both cost reduction and improved
turn-around time.
© 2008. Society of Petroleum Engineers
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History
- Original manuscript received:
15 February 2005
- Meeting paper published:
12 April 2005
- Revised manuscript received:
13 June 2007
- Manuscript approved:
30 July 2007
- Version of record:
20 May 2008
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