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Mechanical Properties of the Middle Waseca Sand And Their influence on Heavy-Oil Recovery

Date

1986-08

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Degree Level

Masters

Abstract

The heavy -oil reservoirs in The Lower cretaceous Mannville Group in the Lloydminster area comprise mainly unconsolidated fine-sand-silts. Unlike the oil-sands of Alberta, the Lloydminster heavy-oils are mobile under reservoir conditions and more easily recoverable by conventional means. However, the oil and reservoir characteristics make economic, practical production difficult. Primary recoveries and secondary waterflooding recoveries are very low. The highly viscous oil, coupled with the fine-grained, unconsolidated nature of the reservoir leads to a high rate of sand production and consequential well stability problems. Development of enhanced oil recovery ( FOR ) methods to produce from heavy-oil reservoirs has not met with major success. Many problems, particularly those associated with particle migration and sand production remain unsolved with the application of FOR techniques. In-situ frozen oil-sand samples, from Middle Waseca sand in the Celtic pool, near Lloydminster area on the Alberta-Saskatchewan border, have been tested in the laboratory to determine their shear strength characteristics. The inherent shear strength ( or cohesion ) of the oil- sand material is than 100 KPa. The material displays a strongly non-linear failure envelope with apparent friction angle of 62 at low normal stresses and falling to as little as 25 at normal stress level of a few MPa. As the shear strength at low normal stress is a fundamental design parameter controlling the stability of underground openings, it is unlikely that a well drilled in the fine-sand-silts will either remain stable very low, perhaps less than 10 KPa, but certainly no more without casing or not be susceptible to breakdown when high fluid pressure gradients are imposed. During cyclic steam stimulation ( the most successful FOR technique for heavy-oil sand ), the control of sand production is a difficult task. Small changes in the fluid pressure gradient or viscosity may induce the migration of sand-silt particles along with the oil as it cools. The results of the laboratory tests can be used to explain the tendency for sanding of wells at the end of production cycle. The establishment of high permeability connections between wells during production-injection cycles may be explained, either by hydrofracture ( fracture propagation ), or by the linear developement of self-sustaining, backward-eroding flow tubes or pipes. The experimental data does little to distinguish between these alternative mechanisms although the susceptibility of fine-sand-silt to piping erosion and fluidization has been confirmed in the laboratory.

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Degree

Master of Science (M.Sc.)

Department

Geological Sciences

Program

Geological Sciences

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