Shale Gas Play Definition using Controlled Source Electro-Magnetic Geophysics

导论.该项目旨在表明，通过在目标上方的地球表面进行可控源电磁（CSEM）调查，可以在钻井前检测地下碳氢化合物，特别是页岩气的存在。CSEM在页岩气检测中的应用是前所未有的。We plan计划to do this over an existing现有seismic地震line线in Scotland苏格兰.碳氢化合物是电阻性的。因此，目的是利用地面CSEM测量数据映射地下电阻率变化。有两个目标：（1）获得高质量的瞬态CSEM数据;（2）从数据中恢复出折射率。该方法采用与地震反射法类似的场布局，有一个电流源，通过一对源电极向大地注入电流（~ 40 A），以及一排电场接收器，每个电场接收器测量一对接收器电极之间大地的电压响应。对记录的数据进行处理，以恢复每个源-接收器对大地的脉冲响应。我们将使用的设备最初是在爱丁堡大学开发的，后来在MTEM有限公司和石油地质服务公司（PGS）开发的。2009年，PGS停止进行土地调查。2014年4月，PGS将MTEMland系统捐赠给爱丁堡大学用于研究目的。该系统价值50万英镑，是该项目的关键部分。有比调查所需的更多的组件，提供冗余，并最大限度地减少因设备故障停机的风险。MTEM现场调查。MTEM调查将在康伯诺尔德附近苏格兰米德兰山谷Deerdykes现场的页岩气前景上进行，怀疑页岩气/石油区存在于地表以下3000 m的深度。以前的陆地MTEM调查已经获得了2000米以下目标的数据。该场地的石油勘探和开发许可证（PEDL）由ReachCSG（项目合作伙伴）持有，他们已经拥有与该场地相关的重要地质和地球物理信息，包括将提供给该项目的历史二维地震反射数据。勘探线将通过一个位置，其中达到现有的规划许可钻探页岩气勘探钻孔。这些数据将使用最新的商业级设备获得，预计将具有优异的质量。这将是有史以来记录的第一个页岩气前景的CSEM数据集。从数据中恢复电阻率。我们将使用forwardmodeling例程从MTEM数据中恢复双折射率，以计算将在调查中使用的所有sourcereceiver配置的模型上获得的合成脉冲响应数据。电阻率模型将被调整以最小化合成数据和真实的数据之间的误差，这是一个被称为反演的过程。数据将以两种方式进行反演：第一，没有任何优先信息或限制;第二，使用从现有地震反射数据中获得的地下岩石层界面，该数据将由项目合作伙伴ReachCSG重新处理。

INTRODUCTION. This project aims to show that the presence of subsurface hydrocarbons, especially shale gas, may bedetected before drilling by performing a controlled-source electromagnetic (CSEM) survey on the earth's surface above thetarget. The application of CSEM for shale gas detection has never been done before. We plan to do this over an existingseismic line in Scotland. Hydrocarbons are electrically resistive. So the objective is to map subsurface resistivity variationsusing the surface CSEM survey data. There are two goals: (1) to acquire good quality transient CSEM data; and (2) torecover 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 ofelectric 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 Limitedand Petroleum Geo-Services (PGS). In 2009 PGS ceased to perform land surveys. In April 2014 PGS donated the MTEMland system to the University of Edinburgh for research purposes. This system, valued at £500k, forms a key part of thisproject. There are more components than are required for the survey, providing redundancy, and minimising the risk ofdowntime due to equipment failure.MTEM FIELD SURVEY. The MTEM survey will be conducted over a shale gas prospect at the Deerdykes site in theMidland Valley of Scotland near Cumbernauld, where shale gas/oil plays are suspected to be present at depths ranging to3000 m below the ground surface. Previous land MTEM surveys have acquired data for targets down to 2000 m. ThePetroleum Exploration and Development License (PEDL) for the site is held by ReachCSG (project Partner), who alreadyhave significant geological and geophysical information relating to the site, including historic 2-D seismic reflection data thatwill be made available to the project. The survey line will pass through a location where Reach have extant planningpermission 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 ofexcellent 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 forwardmodelling routines to compute synthetic impulse response data that would be obtained over the model for all the sourcereceiverconfigurations used in the survey. The resistivity model will be adjusted to minimise the error between thesynthetic and real data, this is a process known as inversion. The data will be inverted in two ways: first, without any a prioriinformation or constraints; second, using sub-surface rock layer interfaces obtained from the existing seismic reflectiondata, which will be re-processed by project partner ReachCSG.