Shale Gas Play Definition using Controlled Source Electro-Magnetic Geophysics

介绍。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，可以在钻探前检测到地下碳氢化合物，特别是页岩气的存在。CSEM在页岩气探测中的应用尚属首次。我们计划在苏格兰现有的地震线上进行测试。碳氢化合物具有电阻性。因此，目标是利用地面CSEM调查数据绘制地下电阻率变化图。有两个目标：(1)获得高质量的瞬态CSEM数据；(2)从数据中恢复电阻率。采用瞬变电磁法采集Csem数据。该方法采用与地震反射类似的场布局，有一个电流源，通过一对源电极向地球注入电流（~40A），还有一排电场接收器，每个接收器测量一对接收电极之间地球的电压响应。对记录的数据进行处理，以恢复每对源-接收机的地球脉冲响应。我们将使用的设备最初是由爱丁堡大学开发的，后来由MTEM有限公司和石油地质服务公司（PGS）开发。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。测量所需的组件更多，提供冗余，并将设备故障导致的停机风险降至最低。tem实地调查。MTEM调查将在苏格兰坎伯诺德附近米德兰山谷的Deerdykes地区进行页岩气勘探，该地区的页岩气/油区被怀疑存在于地表以下3000米的深度。以前的陆地MTEM调查已经获得了2000米以下目标的数据。该地区的石油勘探和开发许可证（PEDL）由ReachCSG（项目合作伙伴）持有，他们已经掌握了与该地区相关的重要地质和地球物理信息，包括将为该项目提供的历史二维地震反射数据。测量线将穿过一个地方，在那里，Reach已经获得了钻探页岩气勘探井的现有规划许可。数据。数据将获得与最新的商业级设备，预计将是优秀的质量。这将是有史以来第一次记录页岩气远景的CSEM数据集。从数据中恢复电阻率。我们将使用正演建模例程从MTEM数据中恢复电阻率，以计算综合脉冲响应数据，这些数据将在调查中使用的所有源接收器配置的模型上获得。电阻率模型将被调整，以尽量减少合成数据和实际数据之间的误差，这是一个被称为反演的过程。数据将以两种方式反转：第一，没有任何优先级信息或约束；其次，利用从现有地震反射数据中获得的亚地表岩层界面，项目合作伙伴ReachCSG将对这些数据进行重新处理。

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.