Abstract
Western Canada's massive oil sands are being exploited at deeper levels by
steam-assisted gravity drainage (SAGD). Carefully geosteered parallel pairs of
large diameter horizontal wellbores are drilled for concurrent steam injection
into the upper well and oil production from the lower. The bitumen cemented
sands of the McMurray Formation have challenged both operational and
engineering personnel responsible for drilling these difficult wells.
Bits of all designs have required custom features to combat the highly abrasive
sands with sloughing and hole cleaning problems, while delivering an optimally
steered well path through tight reservoir tolerances. A cross-functional team
of operator engineers and drilling personnel, together with field engineers,
bit designers and office personnel from the bit manufacturer, joined together
to analyze the challenges and fast track fit-for-purpose solutions for all SAGD
projects in Alberta.
Steel tooth roller cone bits require extensive extra thick layers of hard
facing to resist tooth wear. Sand washing through the cones causes high levels
of erosion which is hindered by extensive hard facing. The gauge areas of the
bits are rotated and/or slid through a cuttings bed of coarse abrasive sand
particles, resulting in rounded gauge (RG) and shirttail damage (SD), which
again require tungsten carbide and hard facing wear pads and shirttail
protection. Elastomer or metal-faced seals have been enhanced to prevent sand
encroachment on the bearings during motor drilling.
Polycrystalline Diamond Compact (PDC) bits were also faced with significant
erosional problems drilling horizontally, which have required special wear pads
and updrill features to ensure hole gauge, steer ability and the ability to
back ream through the cuttings bed. Depth-of-cut (DOC) features for build rates
of 9 degrees per 30 m, ensure steer ability when linked to wear-resistant
cutters, especially when placed on the gauge. Spiral gauge features work like
an auger to clean sand away from the bit, while customized gauge lengths ensure
a match between bit and motor for optimized steerability. Collectively, these
PDC and steel tooth bits have become the enabling technology for drilling and
completing SAGD wells, especially now that bits can be re-run on future wells,
further reducing cost per metre.
Introduction
Steam-assisted gravity drainage (SAGD) is the most popular enhanced oil
recovery technology being adopted by Canadian heavy oil producers. It is very
effective in mobilizing bitumen and achieving high recovery from thick, high
permeability reservoirs (low gravity <10 °API). An estimated 174 billion
barrels of oil in the Athabasca, Cold Lake and Peace River deposits are
potentially recoverable with the present technology(1-3). However,
with technological improvements, Canada oil sands reserves could be close to
315 billion barrels. The biggest deposit is the Athabasca, which is thicker and
shallower; the Cold Lake deposit is thinner and deeper. Surface mining is only
feasible for recovering 10% of the oil sands deposits between 70 and 75 m of
surface. SAGD is the current method of choice to access resources too deep to
mine and will recover the potential 90% of the remaining oil sands deposits
with cyclic steam stimulation (CSS).
© 2009. Petroleum Society of Canada (now Society of Petroleum Engineers)
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History
- Original manuscript received:
30 March 2007
- Meeting paper published:
12 June 2007
- Revised manuscript received:
30 March 2009
- Manuscript approved:
4 May 2009
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