3 research outputs found
Deformation of chalk through compaction and flow.
Hydrocarbon bearing chalks are of significant economic importance within the Central
Graben of the North Sea. The reservoirs have formed within predominantly allochthonous
deposits which exhibit a range of sedimentary and diagenetic features not
necessarily found in their onshore equivalents. Reservoir quality is closely related to
the preservation of high porosity and is associated with high pore pressures. Today,
during hydrocarbon production, change in pore fluid pressure has led to both compactional
deformation of the reservoir and localised flow of chalk through perforations into
production wells.
This project has been undertaken to investigate, in the laboratory, the compaction and
flow characteristics of chalks of medium and high porosity. The data obtained are used
to evaluate the present day compaction and flow characteristics of chalk from the
standpoint of reservoir engineering, and also to interpret the mechanical conditions
that prevailed during allochthonous chalk deposition. This experimental investigation
has show that the mechanical behaviour of all porous chalks is similar. Quantitatively,
this behaviour is dependent on a number of parameters, the most important of which
is the pre-deformational porosity.
The experimental study, utilised high pressure triaxial equipment to determine the
mechanical characteristics of a number of different chalks with pre-deformational
porosities in the range 19-49%. Behaviour during loading under undrained triaxial and
uniaxial strain conditions has been investigated. The former experiments provide data
of importance to evaluating flow, both today, due to pore pressure drawdown in
hydrocarbon production wells, and in the past during mobilisation and redeposition of
the Central Graben chalks in Cretaceous and Palaeocene times. The experiments using
the uniaxial strain path were conducted, primarily, to determine the compactional
characteristics of the chalk for computer modelling of reservoir compaction and associated
sea-floor subsidence using the finite element method. Compaction associated factors such as permeability change, and possible instability of chalk during sea water
injection have also been investigated. A number of experiments were conducted at slow
strain rates in an attempt to determine the influence of strain rate on the magnitude of
the deformation
Reservoir compaction and surface subsidence due to hydrocarbon extraction
36.50Available from British Library Document Supply Centre- DSC:6244.38(OTH--87-276) / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo