Borehole Seismic Introduction

Overview Introduction Seismic Signals in the borehole Borehole Environment Borehole survey types Borehole seismic deployment

What is a VSP? A VSP or Vertical Seismic Profile is the process of recording seismic data in a wellbore environment. The geophones are vertical in the earth versus horizontal along it as in surface seismic.

Borehole Seismic Surveys Checkshot Vertical Incidence Walkaway 3D-VSP DBSeis Offset VSP Salt Proximity Zero Offset LWD Tool SeismicMWD Integrated Seismic Surveys GECO LONGVA OSLO Pressure & Temperature Flow & Phase 4C Sensors Borehole seismic surveys : the past, the present and the future Checkshot surveys - The time taken for seismic energy generated from an explosive source to propagate downwards is measured at receivers positioned at key formation tops. From this information it is possible to calculate the formation interval velocities. Zero Offset VSPs - Geophones are evenly distribution along the well bore. As well as providing travel-time and velocity information from a single source positioned at the well-head, it is possible to measure the reflectivity of each horizon and build up a single trace seismic image at the wellbore. Moving Source VSPs or Walkaway VSPs - Here the geophone is stationary, with the sources moving, firing every 25 metres along a 6km line. As the boat traverses, a profile of reflected seismic energy for each horizon is built up, and is shown by the green and blue lines. This generates a 2D image of the sub surface underneath the path of the source line. This technique can be extended to 3D, by acquiring many 2D profiles at different offsets. Although acquiring 3D-VSP data-sets has been around since the late 1980s, until now positioning the data correctly both spatially and in depth (known as migration) has been done strictly using 2D techniques. Schlumberger over the past few years have improved their depth migration algorithm from 2D to 2.5D (used for the Brent survey acquired by Shell, and featured in a recent First Break) and now have a full 3D migration algorithm. Integrated Reservoir Technology The future challenge will be the application of integrated reservoir evaluation and monitoring technology in which 4D-4C borehole seismic surveys will be one of the key components for the complete reservoir monitoring NEXT SLIDE : Rationale for 3D VSP

Introduction Seismic Signals in the borehole Borehole Environment Borehole survey types Borehole seismic deployment

Seismic Signal in the Borehole Time Downgoing direct arrival Reflected upgoing primary Downgoing multiple Reflected upgoing multiple Depth

Vertical Seismic Profile Time-Depth Seismic Reflections Time Time-Depth Depth

One-Way Time vs. Two Way Time Surface Seismic VSP TWT = OWT + TT Time Reflection TWT Transit Time (TT) TT Reflection Time (OWT) OWT TT Depth

Borehole Multiples Upgoing Multiples

Borehole Multiples Downgoing Multiple

Borehole Multiples All Multiples

Tube Wave Energy Source Tube waves are generated when surface waves from the source come in contact with the borehole fluid and become a guided wave traveling up and down the borehole. As the tube wave travels vertically in the borehole it pushes the wall horizontally. When the geophones are properly clamped to the borehole wall most of the tube wave energy will be seen in the horizontal geophones. At changes in the borehole dimensions some of the tube wave energy will be reflected back to the surface. This will also occur when the energy reaches the bottom of the hole.

Tube Waves Raw Data One-Way Time Depth Vertical Channel Tube wave Horizontal Channel Vertical Channel Tube wave Y X HODOGM

Surface Seismic Comparison VSP Data Offset Depth One-Way Time Two-Way Time

Introduction Seismic Signals in the borehole Borehole Environment Borehole survey types Borehole seismic deployment

Resonance types & effects Resonance generates signal distortion Coupling resonance effect Modal resonance effect

Resonance Attenuation Reduce tool dimension & mass Increase tool application force Optimize contact geometry Combined tools Shaker Coupling contacts Geophones Isolating springs Versatile Seismic Imager - VSI Isolated geophone package: 3.5 lbs Positive mechanical anchoring Combinable Seismic Imager - CSI Isolated geophone package: 20 lbs Positive mechanical anchoring Array Seismic Imager - ASI Isolated geophone package: 9 lbs Magnetic clamping

Shaker Response

Introduction Seismic Signals in the borehole Borehole Environment Borehole survey types Borehole seismic deployment

Borehole Seismic History Checkshot Single Trace 2-D Lateral Coverage

Checkshot Surveys Formation Travel Times Formation Velocities Source Depth Model Surface Seismic Depth (m) Acoustic Impedance Formation Velocities Synthetic Seismogram Geophones Depth-Velocity Model Inputs Surface Seismic Correlation Time (s) Wavelet Processing

Zero Offset VSP Surface Seismic Correlation Source Depth Model Surface Seismic Depth (m) Over-pressure Zone Prediction Corridor Stack Geophones Multiple Pattern Identification Wavelet Processing Time (s) Formation Velocities

Vertical Incident VSP Surface Seismic Correlation WALKABOVE Vertical Incident VSP Surface Seismic Correlation Sources Depth Model Surface Seismic Depth (m) Lateral Coverage Beneath Well VSP Image Geophones Multiple Pattern Identification Fault and Dip Identification Time (s) Formation Velocities

Offset VSP Surface Seismic Correlation Fault and Dip Identification Source Depth Model Surface Seismic Depth (m) Fault and Dip Identification VSP Image Geophones Salt Proximity Identification Shear Wave Analysis Time (s) Surface Seismic Survey Design

Imaging Walkaway Surface Seismic Correlation Fault and Dip Source WALKAWAY Surface Seismic Depth (m) Geophones Fault and Dip Identification Shear Wave Analysis Depth Model VSP Image Surface Seismic Survey Design

True Seismic Amplitude AVO WALKAWAY AVO Walkaway Source Positions True Seismic Amplitude With Changing Offset P-Wave S-Wave P-P and P-SV Analysis Anisotropy velocity model Q factor analysis Reflector

Salt Proximity Survey Provides Accurate Salt Face Image 2D, 2.5D and 3D Imaging Solutions

3D VSP Very High Sub-Surface Imaging Resolution Well 1 Well 2 Exploration and Development Applications Surface seismic 3D PSDM Well 1 Well 2 Detailed Preplanning and 3D Modeling Required 3D-VSP Depth Migration

Introduction Seismic Signals in the borehole Borehole Environment Borehole survey types Borehole seismic deployment

Borehole seismic on Wireline Downhole Geophones Source Reference Sensors Recording Unit Downgoing Wavefront Pit Applications All seismic applications Operations - Max deviation dependant of well liquid type & well geometry (example: so far, ASI ran in 77 deg deviation, in Brine)

Pipe Conveyed Acquisition Applications All seismic applications Operations Max deviation: no limit (113o exp) Ex : 3 * CSI / MDT / Pex / DSI Extendable CSI sub isolates geophones from tool body & pipes Wet connect CSI Pressure sampling Sonic Neutron Gamma density Tension sub Resistivity Gamma spectroscopy Compression sub

Conventional VSP source Through Drill Seismic TDS Conventional VSP source GAC sensor Drill bit TDS Thru-Drill Seis Applications All seismic applications, & particularly... … Position of the drill bit: on the surface seismic from the target ... Imaging beside the well ... Prediction ahead of the bit Operations Data acquisition ... Tool Pumped down … Reciprocate between levels … No circulation … Acquisition 10 min max Min deviation so far = 7 deg Max deviation so far = 90 deg Saving rig time Taking effective and fast decisions

Logging While Drilling Drill Bit Seismics seismic reflector LWD Tool sea floor MWD telemetry SeismicMWD Sensor Surface System Source Applications Real Time checkshots... … Position of the drill bit: on the surface seismic from the target … Along with ISONIC: Calibration of ISONIC data & RT Synthetic seismogram Operations Saving rig time Taking effective and fast decisions Sensors Weights sea floor Drill Bit seismic reflector

Through Tubing Seismic VSP source Applications All seismic applications, & particularly... ... Imaging beside the well (coil tubing drilling, well redevelopment, etc) Operations Data acquisition - Stop production Geophones (GAC)

Simultaneous Acquisition Applications All seismic applications, & particularly... … Acquiring borehole seismic data before surface processing starts: Velocity anisotropy, Q attenuation, AVO, VSP-guided processing, shear model Operation Tool stays stationary in the well Platform Joint acquisitions with GP