TITLE:
Hydraulic Testing of Compacted Bentonite Used for Plug and Abandonment Operations
AUTHORS:
Heinz-Gerd Holl
KEYWORDS:
Bentonite Plugs, Hydraulic Testing, Failure Pressure Prediction, Well Abandonment
JOURNAL NAME:
Journal of Minerals and Materials Characterization and Engineering,
Vol.7 No.5,
September
11,
2019
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.