Showing papers by "Thomas E. Rufford published in 2018"

A phase inversion polymer coating to prevent swelling and spalling of clay fines in coal seam gas wells

Abstract: We report a phase inversion polymer coating as a novel concept with potential to prevent clay swelling and fines generation in coal seam gas, or other petroleum, wellbores. Our approach uses polyethersulfone (PES) with N-methyl-2-pyrrolidone (NMP) as a water-soluble solvent to form a dense, low-porosity film across the clay-rich interburden layers, but a porous and permeable membrane on coal seams. This contrasting behaviour occurs because the coal contains much more free water than the clay-rich interburden layers. We demonstrate the efficacy of the method to prevent clay spalling in immersion tests and under a flow of fresh water in a visual swell test apparatus. The clay-rich rocks studied were mudstone and siltstone, and these were dip coated in the PES/NMP solution. The uncoated mudstone swelled and broke apart quickly in the immersion test and visual flow test, but the PES coated rock samples were stable for 30 days. The coated rock and coal samples were characterised by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. The morphology of coated mudstone and coated coal samples showed that the polymer formed a dense layer across the low-permeability mudstone, but an open porous structure on the coal surface. The effect of the coating on the permeability of KCl brine through coal was measured in a core-flood apparatus. Although the permeability of the coal showed some deterioration after coating, from (0.58 ± 0.12) mD to (0.3 ± 0.03) mD, these results demonstrate the potential of a smart polymer coating to prevent clay swelling while remaining permeable to gas and water on coal layers.

Techno-economic evaluation of multistage membrane combinations using three different materials to recover helium from natural gas

Abstract: Our study evaluates membrane processes to recover helium from natural gas as an alternative to the current cryogenic distillation technologies used in liquefied natural gas (LNG) plants. The process simulations were implemented in Aspen HYSYS v.10 to separate helium > 90% purity at a recovery 99% of helium from a feed gas containing 1% He + 98.3% N2 + 0.7% CH4, which is a typical gas coming from a N2 rejection unit (NRU) in an LNG plant. In this study, we designed six four-stage cascade membrane process configurations (cross-flow and counter-current flow pattern used) based on the glassy membranes such as Hyflon AD60X, Polyimide and Polysulfone: Concept-A-1, A-2, B, C-1, C-2 and D. A techno-economic analysis for the process configuration of > 90% He purity was conducted using a net present value (NPV) method and internal rate of return (IRR). Advanced cascade membrane configuration concepts-C-2, C-1 and A-1 show the best performance in terms of upgraded-He production price respectively.

Mitigating the Failure of Downhole Pumps Due to Gas Interference in Coal Seam Gas Wells

Abstract: Coal seam gas (CSG) well operators typically follow an industry rule of thumb 0.5 ft/s liquid velocity to prevent the onset of gas carryover during CSG dewatering operations. However, there is very little experimental data to validate this rule of thumb with only a publication by Sutton, Christiansen, Skinner and Wilson [1] available in the open literature. A review of more general studies on two-phase gas-water flows in vertical pipes and annuli revealed that experimental conditions, especially pipe and annuli diameters, can have a significant impact on development of two-phase flow phenomena. As such, the limited available data may not be applicable due to differences in experimental conditions. This study experimentally investigates the onset of gas carryover using an experimental setup intended specifically for the study of CSG wells. The University of Queensland Well Simulation Flow Facilities were designed to replicate as closely as possible the production zone of a typical vertical CSG well in Queensland, Australia in transparent acrylic pipes to observe two-phase flow behavior in simulated downhole conditions. The annular test section in the rig was constructed of a 7-in casing and 2¾-in tubing. Modification of the experimental setup to include a vertical separator allowed for the detection of gas carryover. Conceptual demonstrations of gas carryover were captured and have been illustrated. The experiments in this study validate the industry rule of thumb of 0.5 ft/s liquid velocity as an appropriate guideline for onset of gas carryover in a casing-tubing annulus dimension similar to a typical CSG well in Queensland.