Cawley, Stephen1, Tim Watts1
(1) BP-Amoco, Aberdeen, United Kingdom
ABSTRACT: Integrated Pore Pressure Prediction for the HPHT Rhum Gas-Condensate Field, Block 3/29, UKCS
Optimising well design for HPHT field development is a zero-tolerance HSE issue. We
describe an integrated project using offset well drilling data, petrophysical log
interpretation/modelling, seismic velocity analysis and semi-regional scale 3D fluid flow
basin modelling to provide pore pressure assurance for well planning on the Rhum Field in
the North Sea, UKCS.
Sonic and velocity log-derived porosity trends suggest overpressures within Tertiary shale
sequences. Hence recent wells have tended to be drilled with heavier mudweights than
earlier discovery wells. A zone of apparent low density/high sonic travel times commonly
occurs in the early Tertiary in this area of the North Sea leading to over estimation of
pore pressure despite adjacent normally pressured sands. Conversely calculated
velocity/porosity-derived pressure estimates at depth within the HPHT zones in the Lower
Cretaceous and upper Jurassic often fall well below the actual measured values from test
data.
Analysis of seismic velocities in the Rhum area suggest normal shale compaction for most
of the Tertiary overburden and significant overcompaction in certain lithologies. To help
resolve this, a 3D dynamic fluid flow basin model was built to provide extra pore pressure
assurance for development well locations.
The results from the offset drilling data, new seismic velocity analysis and 3D fluid flow
modelling were similar to each other, yielding a pressure envelope within which casing and
mudweight programmes consistent with the discovery well could be planne
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.