Total Dissolved Solids Removal From Water Produced During The In Situ Recovery Of Heavy Oil And Bitumen
Authors: Kok S. , Zaidi A. , Solomon R. 
Published: March 2010

Based on a preliminary economic and technical comparison, evaporation, membrane processes and freeze desalination were identified as the most attractive technologies for removing total dissolved solids (TDS) from produced water. Vapour compression evaporation appeared to be the most cost-competitive. Subsequently, laboratory-scale experiments on the evaporation of produced waters were conducted on four produced water samples from various locations in Alberta and Saskatchewan he evaporator consisted of a 4.6 m long titanium tube; 50.8 mm o.d. by 6.3 mm wall thickness, heated by steam to effect evaporation. Feed flow rate was 19 L/h and each run lasted 1.5 days. Feed TDS levels ranged from 12 000 to 64 000 mg/L. Oil and grease concentrations ranged from 10 to 310 mg/L. Depending on the level of scaling components in the produced water, the evaporator was run in a seeded or unseeded mode of operation.

Produced water recoveries ranged from 67% to 93%. Heat transfer coefficients observed ranged from 3650 to 4050Im2.K. No operational problems with respect to foaming and fouling were observed.

A preliminary cost estimate, based on heat transfer design parameters obtained, indicated that the capital cost would be approximately $8.9 million (1986 Canadian dollars) for a plant treating 3800 m31d 0/ produced water. Estimated annual operating costs ranged from $1.2 to $1.9 million and were dependent on the produced water characteristics and the mode of operation of the evaporator.

Introduction

The production of heavy oil and bitumen by in situ methods using steam flooding Or steam stimulation generates large volumes of water called "produced water". The most attractive strategy from an environmental viewpoint to handle this water is to reuse it as feed water for steam generation. However, at some locations in Alberta and Saskatchewan, produced water contains very high levels of total dissolved solids (TDS), with concentrations &gt; &gt; 8000 mg/L(1). This water is unsuitable for reuse in oilfield steam generators unless it can be treated to reduce the TDS concentrations to approximately 8000 mg/L or less(2).

As part of an ongoing program dealing with the characterization and treatment of produced water, Environment Canada's Wastewater Technology Centre (WTC) is currently evaluating the technologies available for removing TDS from produced water. This paper presents the results of the first two phases of this evaluation:a literature review which identified the most promising processes, based on technical and economic factors, anda laboratory-scale experimental evaluation of vapour compression evaporation-one of the most promising processes.

Status of Produced Water Recycling

In situ recovery of heavy oil-bitumen by steam stimulation (or steam flooding) can generate 2 to 20 times as much water as oil, although in most cases, this ratio is approximately four(3, 4). Hence, the volume of produced water generated at some of these sites can be substantial. Water requirements for steam generation at these facilities can also be considerable. The water required for this purpose is approximately 5 to 6 times the volume of oil produced(5).