The Production Of Conventional Heavy Oil Reservoirs With Bottom Water Using Steam-Assisted Gravity Drainage
Authors: Saskoil S. Sugianto , Butler R.M. 
Published: March 2010

Developing and producing conventional oil economically from reservoirs containing bottom water is' one of the most challenging technical problems in Canadian petroleum engineering This paper investigates a new, innovative thermal oil recovery process that shows potential for the economic of production heavy oil from reservoir when recovery is limited by water coning.

The process as envisaged at present, would use parallel horizontal wells placed near the bottom of the reservoir with horizontal steam injection wells located vertically above the producers near to the top of the reservoir.

Experiments were performed using a scaled, two-dimensional reservoir model containing an active aquifer system. The model was designed to provide dimensional similarity with specific "Lloydminister-type heavy oil" field conditions. The study investigated the mechanism, the process and the effects of steam injection Pressure, bottom water thickness, and the location of the production well; the laboratory results were extrapolated to the field conditions.

It is shown that the process may produce heavy oils economically. The severity of steam coning is because the high productivity index of a horizontal well, allows practical production alrates which are below the critical steam coning rates. Water production from the aquifer is greatly reduced by operating the production wells at pressures close to that of the aquifer.

The cumulative oil recovery varied from 48% (bottom water case with 41% water in the model) to 87% (no bottom water with 0% water in the model) of original oil-m-place above the production well (OOIP*). The thickness of the bottom water zone and The well configurations employed had a significant effect on the cumulative oil recovery.

Introduction

In Canada, there i, a vast amount of heavy oil reserves (3.5 million M3) underlying the Lloydminster area of Alberta and Saskatchewan(1). These heavy oils are usually mobile al reservoir conditions and most can be produced at a low ultimate recovery by primary production. Waterflooding is not effective because the mobility ratio of heavy oil to Water is not favourable.

Most heavy oil reservoirs in Saskatchewan have thin pay zone, which have been judged unsuitable for thermal recovery. Many of the thicker reservoirs have underlying water, Attempts to produce such reservoirs by conventional means result, quickly, in the production of excessive water. The mechanism for this is well understood and is a result of the much lower viscosity or water compared to that of the oil; the Water "cones" upward into tlte well. The conventional steamflood or in situ combustion processes are usually unsuccessful due to prohibitive heat loss or air channelling through the underlying water and also excessive water will be produced(2). Therefore, the chance of recovering this type of petroleum reserves is further limited.

An advantage of the technique Studied here is that the process can be operable, even though there is a significant underlying water layer. The reason that the water can be tolerated is that the pressures involved in the SAGD process, can be adjusted so that there is no tendency for water to now from the aquifer to the production well(s).