Development and Evaluation of a Hyperbranched Polymer for Temporary Plugging Coalbed Methane

To solve the problem of reservoir damage in coalbed methane development, a hyperbranched polymer temporary plugging agent MTA was developed based on the theory of reservoir protection by temporary plugging. The synthesis of MTA involves the use of raw materials such as methyl methacrylate, methyl acrylic anhydride and tert-carboxyl betaine etc. The performance of MTA was evaluated in laboratory experiment. IR spectroscopy shows that the three monomers have successfully copolymerized to form a new polymer. The thermal decomposition temperature of MTA is 252 ℃. Physical-chemical performance analysis results show that MTA has a molecular weight of 6 × 10⁴, an amine number of 17.52, a pH of greater than 7.0 and an average particle size of 0.69-3.32 μm. Compared with the commonly used plugging agents, MTA has better ability in reducing pressure transmission. The capacity of MTA in inhibiting the swelling of clays is equivalent to the inhibitive capacity of polyamines; it reduces the interlayer space of a clay from 1.92 nm to 1.58 nm. Under the action of a differential pressure, MTA can plug the micropores in formation rocks to stop the invasion of water into the formation. Furthermore, MTA can be adsorbed onto the surfaces of a rock by the action of electric charges, thereby forming a layered structure to hinder the filtration of water molecules into the rock. Evaluation of MTA reveals that MTA has good compatibility with other additives in a working fluid, and reduces the amount of filtrate of the work fluid by 41.2%. At 150 ℃, MTA working fluid has excellent performance sustainability and contamination resistance; it is resistant to contamination by 10% NaCl, or 5% CaCl₂, or 10% clays of poor quality. Rock samples treated with the MTA fluid have their permeability recovered by 87.3%. In field operations, MTA showed excellent performance in maintaining borehole stability; the rate of hole washout was less than 5%.