Abstract

Most SAGD projects currently operate at high enough pressure to utilize steam/gas lift. However, there are expected to be many applications where lower pressures are required because of thief zones or to improve the SOR. This will require new methods of artificial lift to meet difficult SAGD requirements. The fluids to be lifted from horizontal wells are hot, high volume, and prone to steam/gas flashing. Three-dimensional simulation studies for heterogeneous reservoirs and wells with pressure drawdown demonstrate a need for low steam-trap subcool values in the horizontal liner for optimum recovery performance. When the fluids reach the lift system, they are close to or at saturated steam temperature and will readily flash to steam. A new twostage lift system called ELift ™ has been specifically designed for low pressure SAGD applications. ELift incoporating gas lift was used at Gulf's Surmont SAGD pilot for 3 years. ELift incorporating a bottomhole pump has not yet been tested. The findings in this paper point to the need for field tests of potential lift systems at the earliest opportunity.

Introduction

Steam-assisted gravity drainage (SAGD) has provided promising recovery performance in several field pilots, and a number of commercial SAGD oil sand projects are planned in Alberta. SAGD has been the subject of numerous publications, and many features of SAGD are understood reasonably well. However, one of the issues that has not been resolved yet is the issue of artificial lift for SAGD production wells.

Except for a pilot on the Surmont lease operated by Gulf Canada Resources Limited., SAGD pilots have been operated at pressures high enough for natural steam lift or steam/gas lift to provide apparently adequate lift. However, in the near future numerous commercial projects may require low-pressure SAGD operations and artificial lift, and it is very important to develop the required artificial lift systems in advance.

The main focus of this paper is to document why lowpressure SAGD is important, define the lift requirements for low-pressure SAGD, determine what fluid conditions are expected at the intake to artificial lift systems (based on a simulation study of steam-trap control trends for optimum SAGD performance), and describe a lift system which, in principle, meets the requirements for SAGD lift at low pressures.

REASONS FOR LOW PRESSURE SAGD OPERATIONS

Low pressure SAGD may be required because of the presence of thief zones. Associated gas sands and/or water sands in the upper part of the McMurray formation in the Athabasca oil sands may constitute thief zones to SAGD operations. These potential thief zones for SAGD operations are common features of the Athabasca oil sand deposit. The upper gas and water sands are generally under-pressured at virgin conditions, and gas production operations are further lowering the pressure. When SAGD steam chambers achieve hydraulic communication with associated thief zones, the pressure in the steam chamber must be reduced to close to that in the overlying thief zone.

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