Abstract

Tight gas resources as exemplified by the dramatic increase in production in the USA and being aggressively developed worldwide, have analogues with Coal Bed Methane (CBM). CBM (sometimes known as Coal Seam Gas) is an unconventional resource where gas is adsorbed within the solid matrix of a coal seam. CBM projects are characterised by large, complex and repetitive gathering system infrastructure which are similar to the general traits of tight gas production systems, especially those associated with fracturing well stimulation techniques.

CBM has been utilised as a source of natural gas for decades, predominantly in the USA, Canada and Australia. However, the majority of the worlds’ 143 trillion cubic metres of Coal Bed Methane remain untapped. To date, the more favourable economics of conventional gas reserves extraction and the recent burgeoning shale gas resource in the USA has limited CBM exploitation. However, increasing demand for gas in eastern markets has led to renewed interest and investment in CBM development. This paper presents a "primer" for CBM covering the resources, extraction methods, gas characterisation and environmental considerations; including co-production of water and land management issues due to the thousands of wells required for a development. The collected gas is usually compressed, dehydrated and exported as sales gas, and provides an excellent feedstock for LNG production.

Unlike conventional gas production, the gas and water production rates from an individual CBM well cannot be known until the well is completed (and in the case of tight gas, fractured), so CBM/tight gas projects present design engineers with technical challenges in terms of optimisation, equipment sizing and modularisation. The geographically distributed, capital intensive nature of CBM projects also places great focus on cost and scope optimisation by operating companies and design contractors.

An introduction to CBM production and facilities design is presented in this paper, together with discussion of an innovative, patent pending method of modelling gas and water gathering system networks, using Monte Carlo analysis and a genetic algorithm for cost optimisation.

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