Vertical Injection Wells For Sagd: A Practical Option Or Not?
Authors: Sawhney G.S. , Liebe H. , Butler R.M. 
Published: March 2010

The steam-assisted gravity drainage process (SAGD) is a promising method for the in situ recovery of bitumen and heavy oil. A horizontal well is employed as the producer because its extended contact with the reservoir makes it possible to achieve economic production rates. Either horizontal or vertical injection wells can be used.

It is possible to place the injection and the production wells wide apart vertically if the viscosity of the in situ oil is a few thousand cp, e.g., in Lloydminister type reservoirs, whereas in bitumen reservoirs, a much closer separation is usually employed.

A major incentive in the use of vertical injection wells is that they may already be available from previous production. The major disadvantage of using vertical wells is that the steam chamber has to grow in the direction of the axis of the horizontal well as well as transversely. Thus the effective length of the production well is less than its physical length at least until the operation becomes mature.

The present work focuses on the growth of the steam chamber along the production well under different operating conditions and with varying configurations of injection and production wells. Experiments were carried out using a three dimensional, scaled, cylindrical, physical model with central vertical injection wells. The effect of parameters such as the type of production surface, thermal conductivity of production well, point of injection along the vertical injection well, and the effect of the injection of non-condensible gas along with steam were studied. A theoretical model to predict the growth of the steam chamber around the vertical injection well is presented. Predictions from this model are compared to field and experimental data.

Introduction

Canada possesses about one sixth of the world's resources of Petroleum(1.2.8). However, 95% of this is in the form of bitumen which is at depths of from a few hundred metres to about one thousand metres and is practically immobile at reservoir temperature, The high viscosity of bitumen makes conventional methods of recovery impractical and other secondary and tertiary methods are required. Open pit mining is used successfully in the shallow Athabasca bitumen reservoirs of Fort McMurray in Northern Alberta, but for deeper reservoirs in situ methods are necessary. The efficient and economic recovery of heavy oil and bitumen is a major technical challenge.

Steam stimulation and steam drive(3.–1.5) have long been used for the production of heavy oil and bitumen, Steam stimulation is reasonably efficient for some cycles but becomes uneconomical after about 15% recovery. As the steam stimulation process matures it often is converted to steam drive in heavy oil reservoirs but this has had little success in bitumen reservoirs. Steamflooding faces the problem of gravity segregation, steam override and bypass of uncondensed steam. The steam-assisted gravity drainage process(6.7) (SAGO) is a promising method for (he in situ recovery of both bitumen and heavy oil. The process depends on the formation of a growing steam-saturated region or steam chamber, that is supplied continuously with steam from an injection well.