Journal of Canadian Petroleum Technology
Volume 48,
Number 9,
September 2009,
33-40
Abstract
As SAGD is being increasingly used as a commercial technology to recover heavy
oil and bitumen, it is essential to determine the most economical operating
conditions for a SAGD operation by reservoir simulation. Furthermore, to
support the decision-making process of a SAGD project, it is also important to
quantitatively assess the uncertainty of its economicforecasts.
In this paper, the application of global optimization, experimental design,
response surface generation and Monte Carlo simulation techniques in the
workflow of SAGD simulation studies were demonstrated with a real field case
example. The field case is an infill SAGD project with two planned SAGD well
pairs and eight existing primary production wells which have 5 years of primary
production. A bottomwater zone is also present.
Three major steps of the workflow are: 1) history matching primary production
data; 2) optimizing SAGD performance; and 3) quantifying uncertainty of the
SAGD forecasts. Firstly, experimental design and DECE (Designed Exploration and
Controlled Evolution) optimization methods were used to achieve a faster and
better history match than the traditional manual history match. Secondly, SAGD
performance was optimized by adjusting the steam injection rate and producer
liquid withdrawal rate during different SAGD operation periods. Finally,
experimental design and response surface generation techniques were applied to
build a polynomial response surface through which the net present value (NPV)
of the SAGD project is correlated with uncertain parameters and a SAGD design
parameter. Monte Carlo simulation was then performed to quantify the
uncertainty of SAGD forecasts in terms of cumulative probability distribution
of the NPV at different values of the SAGD designparameter.
The results show that the economics of this project are improved considerably
through optimization. The optimum operating conditions obtained use a high
initial steam rate and high production rate to develop the steam chamber. After
the instantaneous steam-oil ratio reaches a certain value, both steam rate and
production rate are lowered to prevent steam breakthrough to the bottomwater.
The uncertainty of the project NPV was assessed, taking into consideration the
uncertainties in high temperature relative permeability endpoints and the
variation of the SAGD design parameter.
Introduction
Steam-assisted gravity drainage (SAGD) is a thermal oil recovery process which
consists of pairs of two parallel horizontal wells drilled near the bottom of
the pay(1). Typically, the length of the wells are between 500 and
1,000 m, the inter-well distance of the two parallel wells is between 5 and 10
m and inter-well pair spacing is between 90 and 120 m(2, 3). The top
horizontal well is used to inject steam, while the bottom horizontal well is
used to produce reservoir fluids. The steam injected from the top well rises
into the formation, forming an expanding steam chamber around and above the
injection well. The rising steam eventually loses its latent heat near the
boundary of the steam chamber, heats the oil and allows it to drain to the
bottom production well by gravity. Successful field tests have proven that SAGD
is a viable technology for in situ recovery of heavy oil and
bitumen(4-6).
© 2009. Petroleum Society of Canada (now Society of Petroleum Engineers)
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History
- Original manuscript received:
28 March 2007
- Meeting paper published:
12 June 2007
- Revised manuscript received:
11 June 2009
- Manuscript approved:
4 August 2009
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