Shale Gas Play Definition using Controlled Source Electro-Magnetic Geophysics

Lead Research Organisation: University of Edinburgh
Department Name: Sch of Geosciences


INTRODUCTION. This project aims to show that the presence of subsurface hydrocarbons, especially shale gas, may be
detected before drilling by performing a controlled-source electromagnetic (CSEM) survey on the earth's surface above the
target. The application of CSEM for shale gas detection has never been done before. We plan to do this over an existing
seismic line in Scotland. Hydrocarbons are electrically resistive. So the objective is to map subsurface resistivity variations
using the surface CSEM survey data. There are two goals: (1) to acquire good quality transient CSEM data; and (2) to
recover the resistivities from the data.
CSEM DATA ACQUISITION USING THE MTEM METHOD. Using a field layout similar to that used in seismic reflection,
the method has a current source that injects current (~40A) into the Earth via a pair of source electrodes, and a line of
electric field receivers, each of which measures the voltage response of the earth between a pair of receiver electrodes.
The recorded data are processed to recover the impulse response of the earth for each source-receiver pair.
EQUIPMENT. The equipment we will use was developed initially in the University of Edinburgh and later in MTEM Limited
and Petroleum Geo-Services (PGS). In 2009 PGS ceased to perform land surveys. In April 2014 PGS donated the MTEM
land system to the University of Edinburgh for research purposes. This system, valued at £500k, forms a key part of this
project. There are more components than are required for the survey, providing redundancy, and minimising the risk of
downtime due to equipment failure.
MTEM FIELD SURVEY. The MTEM survey will be conducted over a shale gas prospect at the Deerdykes site in the
Midland Valley of Scotland near Cumbernauld, where shale gas/oil plays are suspected to be present at depths ranging to
3000 m below the ground surface. Previous land MTEM surveys have acquired data for targets down to 2000 m. The
Petroleum Exploration and Development License (PEDL) for the site is held by ReachCSG (project Partner), who already
have significant geological and geophysical information relating to the site, including historic 2-D seismic reflection data that
will be made available to the project. The survey line will pass through a location where Reach have extant planning
permission to drill a shale gas exploration borehole.
THE DATA. The data will be obtained with the most up-to-date commercial grade equipment and are expected to be of
excellent quality. This will be the first CSEM data set ever recorded over a shale gas prospect.
RECOVERING THE RESISTIVITIES FROM THE DATA. We will recover resistivities from the MTEM data using forward
modelling routines to compute synthetic impulse response data that would be obtained over the model for all the sourcereceiver
configurations used in the survey. The resistivity model will be adjusted to minimise the error between the
synthetic and real data, this is a process known as inversion. The data will be inverted in two ways: first, without any a priori
information or constraints; second, using sub-surface rock layer interfaces obtained from the existing seismic reflection
data, which will be re-processed by project partner ReachCSG.

Planned Impact

The primary beneficiaries of this research are expected to be oil companies, and geophysical service companies who
acquire and process geophysical data for oil companies. . The application of transient EM to the mapping of shale gas is
novel and there are currently no companies provide such surveys onshore commercially. The end users of this specific
application are companies within the UK involved with shale gas exploration such as IGas, Caudrilla and Total. There are
potential end users of the technology in Europe and North America , such as Chevron, Shell and Talisman Energy. In
addition, the successful exploitation of the UK's shale gas reserves will help to secure UK energy supplies and reduce the
reliance on imports. The resultant industry will also generate significant revenues for the UK government.
There is the potential for intellectual property to be developed as part of this project and any such IP will be owned by the
University of Edinburgh. The University stands to benefit from royalties as a result of licensing and patents which result
from the research. The PI and Co-I have delivered impact through this route in the past. The University of Edinburgh
received £8.6m for its share in MTEM Ltd. which resulted from its stake in the initial IP of the method.
There are several ways in which the end users identified above will benefit. The primary use of EM data in exploration for
gas and oil is to reduce the risk associated with drilling exploration wells. The identification of resistive anomalies when
used in conjunction with other geophysical data such as seismic reflection data can reduce the number of potential targets
identified through seismic data alone. This results in fewer 'dry' wells being drilled. As well as saving the exploration.
companies money on drilling unproductive wells, there is also the benefit of less environmental impact as a result of drilling
fewer wells. Geophysical service companies benefit by acquiring data such as CSEM data. PGS currently carries out
transient EM surveys offshore and has offices in the UK. There are currently no companies acquiring CSEM data for
exploration onshore commercially. The results of the project may create an opportunity to commercialise the method
onshore in association with PGS in the first instance.


10 25 50