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There IS ROTATION in the S wave

Rotational Seismic: SEG Standards Proposal – Sept., 2013. What is it - - - & why consider standards at this early stage?. There IS ROTATION in the S wave. There is NO ROTATION in the P Wave. The Rotation Signal is purely from the S wave. 3-Theta Data – What is it?.

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There IS ROTATION in the S wave

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  1. Rotational Seismic: SEG Standards Proposal – Sept., 2013 What is it - - - & why consider standards at this early stage? There IS ROTATION in the S wave There is NO ROTATION in the P Wave The Rotation Signal is purely from the S wave

  2. 3-Theta Data – What is it? • Measure Rotation • around 3 axes - 3θ • θ-x • θ-y • θ-z • Vector Curl • of displacement • Record 3-θ Rotation in • addition to 3-C or 4-C “Theta Data” is comprised of “Curl Traces”

  3. Origins – Where Did Rotational Seismic ‘Come From’? • Earthquake Seismology: • William H. K. Lee (USGS) & others • Int’l Working Group on Rotational Seismology (IWGRS) • BSSA (May, 2009) • Sensor technology development - decades: • Defense(US and USSR) • inertial guidance, etc.

  4. Rotational Sensors Typically flat spectral response for angular velocity. MET Tech, ATA Eentec, Rotaphone, FOG, SAGNAC, Sercel, etc.

  5. Electrokinetic Rotational Sensor Rotational Fluid flow through screen electrodes

  6. Transverse Rotational – TR Mode 6 Components: 3 Linear, 3 Theta

  7. Transverse Linear – TL Mode 6 Components: 3 Linear, 3 Theta

  8. PSV- 3C-Vert., 3C-Radial, 3θ-Trans.

  9. SH- 3C-Trans., 3θ-Vert., 3θ-Radial

  10. Proposed Rotational Standards • Proposing standards before commercialization due to risk of confusion. (analogous to some other industries, such as computer networking) • ‘Default’ (Right-Handed coordinates & rotations, positivevoltages / numbers) • Consider 6-C, or more: 7-C (including Pressure), • or 10-C (vector Pressure Gradient) • Consider particular relationships with vector linear seismic - - -

  11. Example of Relationship between Theta and Linear Ordinate and Slope Sampling to double the Effective Spatial Nyquist

  12. Example of Relationship between Theta and Linear Pressure (P wave only) + TR-Theta (S wave only) AVO for gas sandstone David Aldridge, et. al., Sandia National Lab, 2007-2009 PP SP PS SS (No Free surface; buried phones)

  13. Example of Relationship between Theta and Linear Igel / Aldridge Point Array At a single 3-C / 3-Ɵ sensor: transverse linear acceleration S VELOCITY = ----------------------------------------------------------- orthogonal transverse rotational velocity Potential use for shear statics: get shear velocity around each 6-C phone. From 3-C and 3-Ɵ data can determine direction AND velocity of shear wave propagation.

  14. Example of Relationship between Theta and Linear Tilt Correction of Linear using Rotation If a Horizontal Linear Phone tilts by angle α, then it picks up error: Gravity * sin(α) Micro- or milli-radians of tilt give a potentially significant error compared to weak seismic reflections (C-waves). Consider a worse case: weak C-wave data on horizontal phone at same time as strong ground roll in uncorrelatedvibroseis data

  15. Some Suggested Specifics: • Right Handed coordinate system • Z-axis point down (note ‘Parity’ issues, e.g. Z-up) • Right-Handed rotation (‘Chirality’) • Theta-Phones typically angular velocity • Positive voltages for RH rotation (‘Polarity’) & Positive numbers forRH rotation • Nominal scaling: number “1” =1.0 μ-radian/sec • Consider(?) recommended nomenclature • Carefully consider relationships of • rotational and linear, • … and also future processing

  16. Thank you for your interest! • Some level of interest in Rotational Standards: • 3+ major E&P cos. • 2 Geophysical service cos. • 2 Rotational sensor manufacturer’s • Most companies unaware • Small but increasing interest and activity in rotational testing, patent activity, and presentations. • Next step - ? • Draft Rotational Standards • to be developed by 3 to 6+ companies • with technical interest / knowledge

  17. Rotational Summary Presentation @ 2012 SEG ALSO Various Presentations, particularly Schlumberger , Cambridge at EAGE 2012, 2013 and Stanford SEP THETA-DATA: Introduction to rotational seismology and its potential uses David Aldridge Sandia National Lab Mirko van der Baan U. of Alberta, Edmonton Robert Brune Consultant/Geokinetics Jim Gaiser Geokinetics, now CGG Everhard Muyzert Schlumberger, Cambridge Rotational Seismic: • measure & analyze • rotational motion at geophones, in addition to linear motion. Potential applications: • spatial sampling, micro-seismic, elastic wave, . . . Background Refs

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