Print this pageRevisiting the ‘Conventional’ Log Analysis Equations for Estimating Coal Bed Methane Data: A South Sumatera Case, Indonesia
Determination of gas contents for coal bed methane (CBM) reservoirs is of utmost importance upon which feasibility of exploitation is placed. Parameters such as ash contents, moisture contents, volatile matters, and fixed carbon - commonly obtained from log analysis - are direct input to calculation of gas contents. However, recent studies on some coal samples taken from a South Sumatera CBM pilot project have shown that the commonly used log analysis equations are simply inapplicable for the field’s coal samples. Calculation results tend to give far different magnitudes when compared to laboratory results. After a series of re-evaluations and re-measurements on the laboratory results it was convinced that the problem does not lie with the laboratory results but with these ‘conventional’ equations. Therefore modification efforts are spent to find better equations.
Comparisons between measured data (coal samples taken from two coal seams in the field) and calculated data show that only equation for ash contents gives accurate results. Other proximate analysis output data - i.e. moisture contents, volatile matter, and fixed carbon - is at considerable odd with their corresponding calculated data. Calculated gas contents data provided through the use of Kim, Langmuir, Mavor, and Mullen equations also show significant difference compared to measured data. The following modifications on the equations have produced analogous but different empirical equations to the original equations. These equations certainly work more reliably for the field’s coals underlining that future log analyses in the field have to use the modified equations. Other very important conclusions are that individual field has to be treated individually and sufficient reservoir rock sample acquisition is suggested to support that, and that the nature of the field’s coal may serve as the main cause of error in using the conventional equations.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil