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CBM, an Introduction September 10, 2010

Posted by ugmsc in Course and Workshop Summary.
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This Article Based on Regional Course “CBM”,
Joint organizer with SPE UGM SC

Introduction

CBM versus conventional Gas

Coal Bed Methane was a natural gas that extracted from coal that formed during coalification process. As a new energy, especially in indonesia, CBM have some advantage and disadvantage, and the main advantage is low price and potential for carbon sequestration

CBM was spread all over the world with different potential reserve, it associate with the deltaic system, transitional area, event back arc basin. In the future time, CBM will play a big role to fulfill the world energy demmand.

the location of Coal deposits in the world

Coal

Coal is a readily combustible rock containing more than 50% by weight and more than 70% by volume of carbonaceous material formed from compaction and induration of variously altered plant remains similar to those in peaty deposits  (Schopf, 1956).

The Atomic Structur of Coal

There are three maceral type that form a coal :

  • Vitrinite, is derived from woody plant tissue and includes the macerals collinite and telinite. Most coals have a high percentage of vitrinites.
  • Liptinite, macerals, characterized by a high hydrogen content, include alginite, cutinite, resinite,and sporinite [liptodetrinite, suberinite, exudatinite, bituminite, fluorinite
  • Inertinite, comprises fusinite, micrinite, sclerotinite, and semi-fusinite [and inertodetrinite,macrinite], which are all rich in carbon [due to primary oxidation from mouldering or charring].

Coal Rank

Coal Rank is a term to define how good the quality of coal and reflect the relative temperature, pressure that form a type of coal, there are two kind of ranks, the first is rank of proximate that use percentage of fixed carbon, volatile matter, and moisture as the parameter, the second is rank of ultimate which use the percentage of carbon, hydrogen, and oxyen as parameter.

Formation of Coal

schematic diagram of Coal formation

Coal can formed under broad different depostional environment, from the delta, fluvial, swamp, and many different continental and transitional environment. The formation of coal need temperature and pressure. To know more about the distribution of coal in subsurface, we must interprete the depositional environment clearly.

Under different condition and through time, coal formed as different type, from peat, lignite, bituminous and then antracite. The type and process that form a coal effected to the production of methane.

Coal Bed Methane (CBM)

In the CBM system, coal act as source, seal, and reservoir rock, it is mean that when we found a coal in subsurface, with some condition we must find the methane gas, this gas is the exploration target.

The methane gas from coal, is adsorbed on the coal surface, not act as a free gas. The gas itself delivered through the fracure network called cleat system. Cleat system has control the coal permeabilty to deliver gas and water.

Schematic of Cleats Terminology

the mechanism of methane extraction from coal

Cleats

Cleats are the fracture system in coals that allow gas molecules to flow towards the wellbore. Cleat develops in a coal from devolatilization occurring during coalification, as well as during regional and local structural events. Cleat as permeability on CBM.

Geological Control on CBM Resource

the geological control of CBM formation

There are some condition that control the CBM Resource, this condition, are mainly derived from the process of coalification.

CBM Exploration Method

CBM wellbore diagram

CBM exploration use the petroleum exploration method rather than coal mining method. The seismic survey, log, and coring are the key process to get into the coal bed. When at the exploitation phase, the extraction method has different way from the oil exploitation.

When the production bed determined, the production casing builded into the well, in order to get the methane, the coal bed perforated. When the dewatering process occur in the bed, the methane released from coal and maintain pressure to get into the surface, and automaticaly separate from water.

_________________

This article was from AAPG UGM SC – SPE UGM SC Yogyakarta Regional Course “Coal Bed Methane”, Yogyakarta June 26th 2010, Lectured by Mr. Teguh Setiawan (VICO)

More Detailed Article Please contact Didit Putra K (PR Div, look in “Contact Us”)

Cheerss.. 🙂

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