The Bearberry ultra-sour resource is estimated to be 61-75 Bern (2-3 Tcf) of natural gas with an H2S content In excess of 90%. Hence Bearberry is a potential in place source of approximately 100 million tonnes of sulphur. In 1991/92 this source of sulphur was brought into production (two wells into a nearby processing plant) to assess the viability of long term production of this resource.

At reservoir conditions (37 Mpa, 118 C) the 90%+ H2S gas contains significant dissolved elemental sulphur which precipitates as liquid sulphur (analagous to retrograde condensation) in the formation and the wellbore during production. During the production test, approximately 6 tonnes/day of elemental sulphur were precipitated. Unique equipment and production techniques were required in order to produce the Bearberry gas stream. For example, continuous circulation of sulphur solvent was required to prevent plugging of tubing and flowlines.

From a reservoir engineering perspective, the concern was long term well productivity impairment due to precipitation of elemental liquid sulphur in the reservoir as the reservoir pressure declined. In order to quantify the productivity decline a one meter interval was completed in the 11-35 well. This technique enabled a region of low pressure to be created in the near wellbore area of the reservoir which simulated the long term performance of future commercial wells. Permanent gauges with continuous surface readout were used to measure downhole temperatures/pressures and track performance with time.

This paper describes how the reservoir data was evaluated and the basis for the conclusion that it is technically viable to produce the Bearberry resource.

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