Flamborough Chalk Outcrops
October 2003
Steve Freeman and Noelle Odling
MSc Structure and geophysics
Overview
You are split into two groups, GetRichQuick Ltd and DrillItOrDie Plc.
Your two companies are competing to acquire the Spindrift prospect in this years
current license round. In order to be awarded the right to explore the block you have
to justify to the British Governments DTI that you have the most rigorous geological
understanding of the block so that you can produce the maximum tax return for the
country.
The chalk fields have little primary sedimentary porosity but are known to flow well
through fracture permeability where it is present. Seismic data over the prospect has
shown the presence of a series of faults, but widespread jointing is also known to
occur in the surrounding blocks.
You represent the geological portion of the evaluation team, you work in conjunction
with the reservoir engineers to define the most likely fluid flow model for the
prospect. The flamborough outcrops represent the best outcrop analogue to the field.
Your task is to provide detailed information to allow the distribution of permeability
to be evaluated for the field.
The structural entities fall in to two catagories, faults and associated fractures and
fracture-joints. You need to define the statistical distribution of these features so that
the reservoir can be stochastically populated from existing seismic and well data. The
seismic data provides information on large faults (~>20m throw) and the well data
provides lithology data (type and thickness) on the centimetre scale. You have 1 day
to acquire the data in the field. You must present your case to the DTI committee on
the following Tuesday (20 minute presentation).
Data to acquire
Sub-team 1 - Jointing
Fracture frequency (along bed) versus bed thickness
Fracture orientation distributions
Vertical connectivity of the fracture systems (vertical permeability);
1. Percentage of fractures that are bound by bedding versus those that
cross bed surfaces (relative to bed thickness, or type)
2. Total vertical extent of fractures that cross bed boundaries
Fracture connectivities;
3. In plan
4. In section
Sub-team 2 – Faulting and fracturing
Frequency of faults versus throw
Clustering of faults versus throw
Impact of faults – fault rock development (retard or enhancement of flow)
Width of the damage zones around the faults for varying throw
Fault timing relationship with joints
Morphology of the faults – stratigraphic controls
Outcrops – South Landing & the Headland
The majority of the day will be spent at South Landing that allows the most accessible
outcrop. We will remain at the outcrop for ~3-4 hours. We will then briefly visit the
headland outcrop that provides access to a seismic scale offset fault zone.
Digital data
Photos offer the possibility of very great resolution and accuracy and should be used
in conjunction to field data collection. When you have limited field time photos allow
data acquisition to occur back in the lab as long as you have references and scales to
work off. You will have access to a digital camera and a Laptop to stitch panoramas
back together if needed (can be time consuming). Make sure any photos you take
have a scale in them and a known orientation.
Timings
You have very little time to acquire all of this data. You will need to manage your
time carefully. We suggest that you split your group into two, one group focussing on
the jointing and the other on the faulting. It may be worth rotating members through
the groups through the day so that everyone has a chance to participate in all of the
field components.
Group Management
Successful data acquisition and project completion requires very good group
interaction. You will be evaluated on the whole geological evaluation not one single
component, as such it will be worth constantly evaluating whether the group is
achieving its global aims. Holding review meetings during the day should help keep
the focus for the data collection.
Safety
Both sites are tidal areas, as such care needs to be taken. The areas also contain steep
cliffs which can be unstable especially after its been raining. You will be provided
with hard hats that should be worn when near any cliffs. The hard hats though will not
stop 1 tonne blocks killing you if they fall on your head though, so please avoid any
dangerous overhangs or areas that look like they may slide. What ever happens do not
fool around on the outcrops.
Stephen@rdr.leeds.ac.uk