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Simulation Of A Coal Seam Gas Reservoir (Case Study)

Dixon, David

Hart, Peter

Jachmann, Ashley

Engineering Honours Degree, 2010

University of Adelaide

Abstract

Economical recovery from coal seam gas (CSG) reservoirs is of great interest to the oil and gas industry. As the need for cleaner energy becomes more critical, coal seam gas is likely to become more profitable, yet at the present coal seam gas remains a marginal industry. Coal Seam Gas projects remain marginal due to the high cost associated with water treatment and disposal, during the dewatering and early stages of production. Often coal seam gas reservoirs must undertake a form of enhanced recovery to become profitable, such as the Tiffany field.

The Tiffany field is located in southern Colorado and is the focus of this study. The field is very tight (5md) and requires enhanced recovery to be profitable. This paper investigates some of the most significant parameters that effect production in coal seam gas reservoirs and tests them on a model created in Eclipse 100, based on data from the Tiffany coal.

The controlling parameters are varied and the results analyzed to understand how this affects production from the field. Also several methods of enhanced recovery are implemented on the field to test how they affect production and economics of the field.

Testing of the various enhanced recovery methods found very positive results for the Tiffany area field. The field can undergo enhanced recovery to improve its net present value significantly. For example testing of thermal recovery showed that an increase of 38K realizes a 16% increase in recovery of the total Original Gas In Place (OGIP). This was extremely significant considering the gas produced if the field remained without stimulation was 28.6%, which further increased to 44.8% using the thermal enhanced recovery. The increase in temperature also had a significant increase in the dewatering time and a minor effect on the total production of water. The 38K increase in temperature reduced the dewatering time from 180 days (322K) to only 8 days, for the reservoir at 360K. This is significant since the dewatering period is reduced significantly and could potentially be eliminated with further increases in temperature.

Thermal recovery has not been widely used in industry and as such there is little known field data of how it affects production. To test such thermal enhanced recovery methods the Langmuir isotherms is the main property that must be changed. In the field thermal recovery is done by coal gasification (UCG), geothermal methods or steam injection, unfortunately Eclipse simulates only isothermal cases and as such is limited. Also Eclipse cannot take into account the chemical effects of combustion that occur in the UCG process, for example the production of CO2. Hence thermal recovery is the main focus of the research component of this project.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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