Publications

The first six Barito Basin Coal Bed Methane (CBM) wells were drilled between April 2011 and January 2012 to test coal distribution, gas content and in-situ permeability of the Miocene coal bearing Warukin Formation. A pre-drill basin-scale well planning study was performed, allowing for maximal flexibility during the early exploration phase. The basic well design was optimized to mitigate hole enlargement in swelling clays, sloughing coals and unconsolidated sands. Pushing the 9-5/8” surface casing below the base of the most reactive shales, switching to a ‘near-balanced’ mud system, and minimizing the open hole time proved to be most effective in reducing hole enlargement in coal seams. Hole enlargement in shales increased with decreasing mud weight, and is most likely controlled by a combination of an anisotropic stress field, clay mineralogy and mechanical vibrations induced while drilling. Both coring strategies used – twin well and coringon- the-fly – allowed for effective evaluation of the CBM play with depth, and allowed for meeting all geologic objectives. Improvements in work processes in the wireline-retrievable coring system and core canistering process resulted in reduced ‘lost gas time’ from 45 to 37 minutes. Core recovery remains relatively low (55 – 68%) due to * Esso Indonesia Inc., Jakarta, Indonesia ** Mobil Cepu Ltd., Jakarta, Indonesia *** ExxonMobil Exploration Company, Jakarta, Indonesia **** Indobarambai Gas Methan, Jakarta Indonesia jamming in rubbelized coal, bit balling and ineffective core catchers in sticky clays. The sampling program included evaluation of gas in place (GIP), gas composition and permeability in different CBM subplays across the basin, while testing lateral and vertical coal seam variability. Gas volumes were measured via gas desorption and adsorption on coal samples collected from 3” diameter cores in 2ft long canisters. Rigorous quality control and improvements in the sampling process resulted in reliable datasets being generated in all three core wells. Keywords: Coal Bed Methane, Well Planning, Hole Enlargement, Coring, Warukin Formation, Kalimantan