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Abstract

The production of heavy oil under primary or secondary recovery, like that of conventional petroleum fluids, is accompanied by a large volume of produced water. The disposal of that water can be expensive as the produced water contains contaminants including total dissolved solids (TDS), total suspended solids (TSS), oil, and grease. In addition, most heavy oil reserves occur in shallow and unconsolidated sandstone formations, which produce a considerable amount of sand. The disposal of the produced sand can also be expensive. The major contaminants in that sand stream are hydrocarbon and chloride.

In this paper, the results of a systematic characterization of the produced water and sand, along with the evaluation of available options for treatment and ultimate disposal, are presented. In addition, a membrane process for water treatment and a flotation process for sand treatment are presented. The results indicate that the membrane process was successfully used to reduce the contaminants in the produced water and, hence, reduce the volume of water to be disposed of. In this process, 90% of the TDS was rejected. The flotation treatment was also successfully used to reduce the contaminants in the produced sands. In this process, more than 99% of the unbound hydrocarbons and chlorides were removed.

Introduction

The volume of heavy oil and bitumen in the world is considerably larger than that of conventional crude oil. Alberta and Saskatchewan are the two richest heavy oil and bitumen provinces in Canada, where the so-called "oil sands" consist largely of unconsolidated or sometimes weakly consolidated sand. These sands contain mainly hydrocarbon and water. In addition to the sand grains, other finer solids are often present in the form of silts and clays.

Tar sands are characterized as "oil sand containing bitumen, asphalt, or oil that is too viscous to flow in commercial quantities at reservoir conditions". The oil sand deposits from the Fort McMurray area in Alberta are produced using surface mining technology. In this process, sand containing variable amounts of oil is produced as solid waste.

Heavy oil is characterized as "petroleum heavier than 250 API, but sufficiently fluid at reservoir conditions to be produced commercially by natural flow". In Canada, heavy oil, usually produced from shallow and unconsolidated formations under primary or enhanced recovery processes, is accompanied by sand and water. During the production phase, the formation fluid is brought to the surface and stored in a field tank, where it is allowed to settle by gravity into three layers: oil, water, and sand. The oil is then pumped into a truck to be transported to a cleaning plant. The remaining two streams (i.e., produced water and sands) are removed from the field tank for disposal. The primary contaminants in the produced water from heavy-oil, conventional-oil, and gas reservoirs include total dissolved solids (TDS), total suspended solids (TSS), oil, and grease.

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