Abstract
Post-stimulation proppant-flowback problems have been a major issue in both conventional and unconventional reservoirs. In coalbed methane-gas (CBM) wells that use pumps and plungers to dewater coal, proppant flowback with produced fluid could lead to well downtime because the pumps can get sanded off. This is costly and challenges well economics because losing production and replacing the pumps repeatedly can be expensive. A low-cost solution to this uncontrolled sand production is to clean the well with a workover rig or coiled tubing (CT), identify the zone (or zones) from which the proppant is being produced, isolate the zone (or zones), and pump a remedial proppant flowback-control treatment. Two types of proppant-consolidation remedial-treatment fluids have been successfully used—one is the low-viscosity, solvent-based curable resin, and the other is a new, water-based consolidation system.
A water-based consolidation system was successfully developed to overcome the operational, safety, and fluid-compatibility issues that most current solvent-based resins experience during field treatments. This paper presents the results of laboratory development and field testing of this consolidation system for proppant flowback. Extensive laboratory testing has indicated that an optimum concentration of coating is necessary to maximize the bonding between proppant grains. This allows the proppant pack to withstand high production flow rates and to overcome the effects of stress cycling while minimizing any reduction in its permeability. Field-study results in both sandstone and CBM reservoirs showed that the water-based consolidation system was successfully applied in treating proppant and formation solids in the near-wellbore region to lock them in place without damaging production flow paths. In these field tests, intervals in excess of 300 ft were treated effectively with the bullhead-squeeze method using consolidation treatment fluids that were foamed to a quality of 75% or higher to aid in diverting treatment fluids and extending treatment volumes.
The new system uses small treatment volumes to impart excellent consolidation properties, while at the same time retaining formation permeability. This makes the treatment system simple to deploy and economically viable. In addition to providing the results, this work discusses the criteria for identifying remedial candidates, optimal placement procedures, and the lessons learned from these treatments.
