Journal of Canadian Petroleum Technology
Volume 48,
Number 6,
June 2009,
71-77
Abstract
This paper investigates the feasibility of bitumen production using SAGD
technology with a longer wellbore. A longer wellbore can be used to exploit a
greater volume of the reservoir with a single wellpair as opposed to multiple
wells; thus, decreasing pad and drilling costs.
The major concern in using a longer wellbore from a reservoir engineering point
of view is the potentially non-uniform steam chamber growth over the whole well
length due to pressure drop in the horizontal well. Reservoir simulation was
performed using Computer Modelling Group's STARS ™?simulator and the QFlow
thermal wellbore simulator to address the issue. The pressure drop inside the
wellbore was calculated using QFlow. Reservoir simulations were performed using
STARS. A sectioned model was constructed, dividing the whole length of the
horizontal wellbore into multiple sections, each with its own pressure
restriction to match the pressure drop obtained from QFlow. The results showed
that with a sufficiently large wellbore size that resulted in a sufficiently
low pressure drop, one longer well performed as well as two shorter wells. When
a smaller wellbore size was used, production from a longer well was
significantly impeded due to the large pressure drop.
Introduction
Since the discovery of oil sands, many techniques have been tried - and
improved upon - to recover the highly viscous bitumen for energy consumption.
One of the methods of bitumen recovery that is becoming increasingly prevalent
is a thermal in situ method called Steam-Assisted Gravity Drainage (SAGD).
Butler(1) first proposed this method in the late 1970s and it was
field tested in AOSTRA's Underground Test Facility (UTF) in the 1980s. The
initial phase of UTF testing produced successful field results(2,
3). Following Phase A, Phase B was started, implementing the use of
longer horizontal wells(4, 5). Surface-operated SAGD was studied in
Phase D(6). Following these successful pilot tests, a number of
commercial projects have been developed, including Petro-Canada's MacKay River
project.
One of the factors that needs to be considered in commercial projects is the
optimization of the horizontal well length. Typically, the horizontal sections
of the SAGD wells are 500 to 700 m long. This paper will examine the
effectiveness of using a longer horizontal wellbore in SAGD. There is
tremendous potential for economic savings in implementing longer wellbores in a
SAGD project.
A longer wellbore has the ability to reach greater lengths within a reservoir
with one single wellbore as opposed to multiple wells. When multiple wells are
drilled, multiple pads must also be built - one for each group of wells. Thus,
to cover a given reservoir, the average pad cost will be lower for longer
wellbores.
Another significant cost advantage of the longer wellbore is the fact that
fewer riser sections (also known as build sections) need to be drilled and
completed. The riser section has a significantly higher cost than the
horizontal section because it is generally much larger in diameter. By
decreasing the number of wells in a pattern with the use of longer wells, the
cost of all the riser sections is decreased significantly.
© 2009. Petroleum Society of Canada (now Society of Petroleum Engineers)
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History
- Original manuscript received:
22 February 2007
- Meeting paper published:
12 June 2007
- Revised manuscript received:
29 January 2009
- Manuscript approved:
29 April 2009
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