Publications

Hydraulic fracturing is one of the well-known well stimulation techniques in coalbed methane (CBM) reservoir to enhance well productivity and improve gas recovery. In the early of Sanga Sanga CBM exploration phase, standard hydraulic fracturing was used and led to the uncontrolled fracture height growth into the adjacent water-filled sand layers due to unfavorable stress contrast. As the result, the well produces excessive water without able to create pressure drawdown to allow gas desorbed from the coal matrix and flow into the wellbore. To deal with these problems, limited height growth fracturing or small fracture treatment was selected as the result of systematic fine-tuning on fracture design validated by several field trials. The selection of small fracture treatment raises the question about the stimulation effectiveness given the wellbore stimulated area will be limited. To answer this concern, dual porosity numerical simulation model was developed to evaluate the effect of small fracture treatment on CBM well productivity. In this study, the fracture geometry around the wellbore is physically modelled, so that the effect of fracture conductivity & geometry can be evaluated easily. Due to similar stress profile with the adjacent layer, the penny shaped fracture geometry assumption was used in this study. The evaluation of fracture effectiveness was done by determining the skin factor from vertical well model which resemble the fractured well performance. Overall results show that the small fracture treatment is effective enough to stimulate the well regardless with limited fracture geometry as long as the dimensionless fracture conductivity (FCD) greater than four. The stimulation effect is more profound for the low permeability coal which the increase in gas recovery is more significant rather than the higher permeability. The knowledge gained from several successful field trials using this type of fracture treatment can be adopted for other CBM fields where similar challenges are encountered.