Pre-fracture Treatment of Coal Seams for Fracture Conductivity Enhancement in Hydro Fracturing of CBM Wells and Coal Fines Mitigation in Multilateral CBM Wells through Wettability Alteration of Coal Fines - A Laboratory Study

Abstract

Abstract India has sixth largest coal reserves in the world and estimated to be at 206 billion tons and it ranks 10th in CBM resources having 4.6 TCM methane gas covers 20,000 km2 of area. The CBM reservoirs is multilayered, heterogamous, naturally fractured (cleats) and having fine micro pores. Bulk porosity of the coal is very small (<5%), the initial gas saturation is very low (<10%) and most of the gas in coal (>90%) is adsorbed in the micro pores of coal matrix and under saturated condition. Rapid dewatering is needed for reduction the reservoir pressures below critical pressure for desorption of gas from coal bed. Therefore, conventional / horizontal well with fracturing, multilateral well to cover many zones in CBM is being opted for economic exploitation. More than 60 no of conventional and horizontal/multilateral wells are drilled so far and many of them are completed with hydro-fracturing. As coal is a weak substance and small pressure can cause the coal to fail and generate fines, hence enormous coal fines are normally produced during production (in case of high draw-down) and during hydro fracturing of coal seams. In some fracturing job, fines generation & migration reduces the fracture length and conductivity lead to reduced dewatering. Similarly, in multilateral well of CBM, coal fines are accumulated at the heel of the well in case of high draw drawdown and creating the restriction in dewatering and gas production. In view of the above, innovative pre-fracture treatment technique with innovative formulation (Mixture Nonylphenoxy polythyleneoxide and Nonylphenoxy polythyleneoxide in the ratio of 1:2 with 0.5 % biopolymer) is developed & successfully tested in laboratory to change the wettability of the coal fine by making it hydrophobic to hydrophilic. Coal fines can easily come out with water based fluid during pre-treatment, hydro-fracturing and multilateral wellbore cleaning.