Summary
The Shallow Clastics field operated by
Sarawak Shell primarily targets two shallow gas-bearing reservoirs, H1 and H2,
at approximately 2,650 ft true vertical depth (TVD). An appraisal,
early-producer well was drilled with a deviated wellbore through the H1/H2
targets, and a completion design consisting of a cased, perforated, and
commingled completion inside 95/8-in. casing was implemented. The
sandface-completion design consisted of a large-outside-diameter (OD)
expandable sand screen with a 150-µ-weave opening across the two zones. Upon
completion, the reservoirs were cleaned up through a temporary well-cleanup and
test-facility to test productivity and evaluate the integrity of the downhole
sand-exclusion installation. Fines production, possibly caused by a failure of
the expandable screens, steadily increased to the extent that the well was
deemed unproducible to the facilities.
A re-evaluation of the sand-exclusion
method that included more extensive core analysis and the types of wells that
would be suitable for development of the H1/H2 reservoirs was initiated. From
this review, the operator and a service/engineering company were able to
develop an innovative sand-exclusion method that combined several new
technologies.
To date, four wells have been completed
with the new sand-exclusion method and well configuration chosen to address the
completion needs. These have been tested and, to date, have proved to be
operating satisfactorily. This paper will review the evaluation that led to the
revised sandface-completion design, the field implementation of the design, and
the key installation success factors that were required. Results and a summary
of best practices from the initial installations also will be
summarized.
Introduction
Sarawak Shell’s Shallow Clastics field
consists primarily of two shallow gas-bearing reservoirs, H1 and H2, at
approximately 2,650 ft TVD. These reservoirs are laterally extensive, covering
an area of 200 km2 with an estimated gas in place (GIP) in
excess of 2 Tcf. The reservoirs are made up of a sequence of highly laminated
sand and shale deposits with significant sand-size variability and high fines
content. Being highly unconsolidated, downhole sand exclusion is mandatory. The
primary drive mechanism is a depletion drive based on the weak aquifers seen in
existing fields in the area. The Shallow Clastics reservoirs overlay deeper
Central Luconia carbonate gas reservoirs, which are already on production with
further fields in development; therefore, a gas-processing and gathering system
was already in place. Gas from all of these fields is produced to the Malaysian
Liquified Natural Gas (MLNG) plants at Bintulu, East Malaysia. Production from
the Shallow Clastics field is intended to counteract decline from other fields
and is critical to maintaining the security of the supply to MLNG.
Significant log data (Fig. 1) on
the Shallow Clastics field were gathered from the appraisal and development
wells of the deeper carbonate gas reservoirs; however, core data were limited
to what could be generated from a single poor-quality core from E11-SC1. A
dedicated Shallow Clastics appraisal/ early-producer well (E11-SC2) had been
drilled with a deviated wellbore through the H1/H2 targets, and a completion
design consisting of a cased and perforated commingled completion inside
95/8-in. casing had been implemented. The sandface-completion design
consisted of a large-OD expandable sand screen with a 150-µ-weave opening
across the two zones. Upon completion, the reservoirs were cleaned up through a
temporary well-cleanup and -test facility to test productivity and evaluate
integrity of the downhole sand-exclusion installation. Fines production,
possibly caused by a failure of the expandable screen, commenced during the
cleanup and steadily increased to the extent that the well no longer could be
produced.
©
2007. Society of Petroleum Engineers
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History
- Original manuscript received:
15 February 2006
- Revised manuscript received:
08 February 2007
- Manuscript approved:
18 April 2007
- Version of record:
20 September 2007
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