Hydraulic Testing of Compacted Bentonite Used for Plug and Abandonment Operations

Abstract

The University of Queensland Centre for Coal Seam Gas (UQ CCSG) has investigated plugging wells with bentonite through laboratory experiments and with field trials. This paper presents the laboratory tests, which were used to investigate the stability range of plugged sections for later well plug and abandonment operation designs. The plugs were tested on a specially built well simulator facility at The University of Queensland (UQ), School of Chemical Engineering. The bentonite material used for the plug production was treated with water and 1 weight% polyvinylpyrrolidone (PVP) which acted as a binder to allow the bentonite to be pressed into a cylindrical shape suitable for dropping into vertical wells. The experiments have shown that the best performing plug/casing size combination is able to hold pressure gradients of up to 5.9 bar/m (25.9 psi/ft) after 296 days of hydration before failing. Open hole simulations on the testing facility showed surprisingly high failure pressure gradients of 21.1 bar/m (93.3 psi/ft) after 146 days of hydration. The findings of this research indicate that the use of compressed bentonite is a viable method for sealing wells , whether they can be coal seam gas wells, conventional oil and gas wells, water wells, or coal exploration wells.