Predicting Coalbed Gas Production On Semirara Island, Philippines, From Coalbed Methane Paradigms In The Powder River Basin, United States

Flores, Romeo M.¹, Stricker, Gary D.¹, Baquiran, George B.², Jimenez, Troadio M. Jr.², Ammugauan, Jaydee G.², Gayondato, Edna A.², Papasin, Ramon F.³, and Pendon, Ronaldo R.³

¹U.S. Geological Survey, MS 939, Box 25046, DFC,
Denver, Colorado 80225-0046, U.S.A.
²Semirara Coal Corporation, 2nd Floor, DMCI Plaza, 2281 Pasong Tamo
Extn, Makati City, Philippines
³Department of Energy, ERDB, Energy Center, Merritt Road, Fort Bonifacio, Taguig (1201),
Metro Manila, Philippines

Introduction

Coal gas-desorption measurements conducted during exploration and before coalbed methane development can predict first-year gas-production rates (Bodden and Ehrlich (1998). In the Powder River Basin, United States , gas desorption tests on core samples of subbituminous Fort Union Formation coals (Paleocene) were compared to subsequent production histories of cored and sampled coalbed methane wells. The monthly and annual gas production rates/volumes for coalbed methane wells in the Wyoming part of the Powder River Basin are available to the public from the database of Wyoming Oil and Gas Conservation Commission through their website address (wogcc.state.wy.us). The best predictors for first-year gas production in the Powder River Basin were measured gas after 40- and 120-day gas desorption tests divided by sample depths, which were analyzed using best-fit linear regression models. Both these desorption tests show linear regression coefficients of 0.74 (R²) using 14 coalbed methane wells, which the U.S. Geological Survey desorbed that have one year gas production. The 120-day gas desorption test (Stricker and Flores, 2005; Ellis, Stricker, and Flores, 2005) was used to predict the first-year gas production from gas desorption of the coal beds in the Semirara Formation (Miocene) in Semirara Island, Philippines . The number of days to desorb gas from initial recovery of the coal core to the final measured gas of the Semirara coals range from 145 to 184 days. This time of desorption suggests gas-diffusion rate for Semirara coals is slower than for Powder River Basin coals, as expected due to hydrostatic-pressure drop from mine dewatering. However, the gas diffusion or drainage for Semirara coals are not as affected by mine dewatering as for the Powder River Basin coals.