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The Lakhra coal field is about 20 miles northwest of the ancient city of Hyderabad on the west side of the Indus River Valley in the southern part of Pakistan. The Lailian coal bed in the lower part of the Ranikot Formation underlies an area of at least 64 sq mi on the Lakhra anticline, averages 3.6 feet thick, but is locally as much as 8.2 feet thick. The estimated reserves in the bed total 239.7 million long tons, of which 21.9 million long tons is classified as measured reserves, 43.8 million long tons as indicated reserves, and 174 million long tons as inferred reserves. The coal is apparently subbituminous C and lignite A in rank. It lies at depths of 83 to 439 feet below the surface of the gently dipping rocks along the crest of the 43-mile-long Lakhra anticline. Though the coal is liable to burn spontaneously, the simplicity of the structure, the shallow depth of the coal bed, and the easy accessibility of the area should warrant large-scale utilization of the coal in the Lakhra field.

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Although SAGD is a very popular in-situ extraction method in Canada, this thermal process relies on huge energy and water consumption to generate the steam. Irregular growth of the steam-chamber due to heterogeneities further degrades its yield. Contact between the steam chamber and the overburden also leads to heat losses. The objective of this paper is to investigate how Foam Assisted-SAGD could mitigate these technical issues and improve the efficiency of the SAGD process. Compositional thermal reservoir simulations are used to simulate and analyze a Foam Assisted-SAGD pilot. The shear-thinning effect close to the wells is also accounted for. The simulations are run on a homogeneous model mimicking the Foster Creek project in Alberta, Canada. Several type of injection sequences have been analyzed in terms of foam formation, back-produced surfactants and cumulative Steam-Oil-Ratio. Results are compared with the original SAGD performance. In order to propagate the foaming surfactants throughout the steam chamber the injection sequence needs to be properly determined. A simple continuous Foam Assisted-SAGD injection would lead to an accumulation of surfactant between the wells due to gravity segregation, preventing the foam from acting on the upper part of the steam chamber. Furthermore surfactant production occurs after a few weeks due to the proximity of the producer and the injector. A proper injection strategy of the type SAGD/slug/SAGD/slug is found to delay the chemical breakthrough and increase the amount of surfactant retained in the reservoir while allowing the surfactant propagation throughout the steam chamber. After optimization the Foam Assisted-SAGD process appears to be technically promising.

No abstract