DSI* Dipole Shear Sonic Imager Introduction The AIT is the newest generation of induction tool built at Schlumberger. The design is a fundamental departure from previous induction tools. The AIT-B is the first induction that is through wired. (Dual ended) The tool uses CTS telemetry, but can easily be upgraded to DTS telemetry. The AIT is combinable with most existing tools, new combinations should always be tested in the shop. The tool uses the principle of simple coil array instead of the traditional fixed focus. The AIT service provides better vertical resolution than ever before. Five depths of investigation for more precise descriptions of invasion. The tool uses 8 arrays, real and quadrature signals from each, and 3 frequencies resulting in 28 conductivities. The 28 conductivities are processed through a borehole correction scheme, and then into the 5 log curves at a choice of 3 different vertical resolutions.

Lecture Plan Wave Propagation - Monopole & Dipole Hardware Waveform Processing Operations Applications Lecture Plan This lecture is normally expected to take around 7 hours to give. Typically it should be given in 2 sessions. The first session should end on completing BHC theory. The second session is improved by including an AIT set up demonstration on the Maxis classroom display monitors.

DSI* Dipole Shear Sonic Imager Wave Propagation Introduction The AIT is the newest generation of induction tool built at Schlumberger. The design is a fundamental departure from previous induction tools. The AIT-B is the first induction that is through wired. (Dual ended) The tool uses CTS telemetry, but can easily be upgraded to DTS telemetry. The AIT is combinable with most existing tools, new combinations should always be tested in the shop. The tool uses the principle of simple coil array instead of the traditional fixed focus. The AIT service provides better vertical resolution than ever before. Five depths of investigation for more precise descriptions of invasion. The tool uses 8 arrays, real and quadrature signals from each, and 3 frequencies resulting in 28 conductivities. The 28 conductivities are processed through a borehole correction scheme, and then into the 5 log curves at a choice of 3 different vertical resolutions.

Wave Propagation Modes Compressional: Particle vibration parallel to direction of wave propagation Shear: Particle vibration perpendicular to direction of wave propagation

Wave Propagation Modes Slowness depends on rock mechanical properties: rock density elastic dynamic constants Shear slowness: stiffness of the rock Compressional slowness: compressibility

Wave Propagation Modes Fluid-saturated rocks, slowness depends on: amount and type of fluid the makeup of the rock grains degree of intergrain cementation Soft, loosely consolidated rocks: generally less stiff and more compressible than hard rocks sound waves travel slower in soft rocks than in hard ones Fluids (completely unconsolidated rocks): have no stiffness at all will not support shear wave propagation

Wave Propagation Modes  Stoneley: Surface wave guided by the borehole Travels slower than mud Does not penetrate the formation It’s energy concentrates on the bore-hole surface It’s amplitude exceeds that of other waveforms At low frequency there is little energy decay by comparison to high frequency

Monopole Source Non-directional pressure source Pulse created in bore-hole & propagates into the formation Excites both P & S waveforms in the formation Head-waves are created in the mud & detected by the receivers Operates in the 10 Khz to 20 Khz range (Not suitable for Stoneley)

Hard (Fast) Formation — Monopole Compressional wave Wellbore Compressional wave Head waves Formation Formation shear slowness less than mud compressional slowness Vmud < Vshear Both the compressional and shear formation waves propagate along the borehole Energy leaks back into the borehole as headwaves, which are detected Shear wave Fluid wave Omnidirectional source Compressional wave Shear wave Stoneley wave

Soft (Slow) Formation — Monopole Formation shear slowness greater than mud compressive slowness Vmud > Vshear Snell’s Law predicts in slow formations the shear wave transmitted into the formation travels away from the borehole The shear headwave in the borehole is only marginally detectable or absent Shear curve is discontinuous when ‘slow’ zones are present, log is of limited value Wellbore Formation Compressional wave Head wave Fluid wave Omnidirectional source Shear wave Compressional wave Stoneley wave

Dipole Source Directional pressure source Pulse created on one side of the bore-hole causing a small amount of flexing. (Flexural Wave) Excites both P & S waveforms in the formation Flexural waves travel up the bore-hole & are detected by the directional receivers. Operates at low frequencies (~2.2 Khz)

DSI Transducer - Dipole A dipole tool utilises a directional source and receivers The dipole source creates a pressure increase on one side of the hole and a decrease on the other This causes a small flexing of the borehole wall which directly excites compressional and shear waves in the formation

DSI Transducer - Dipole Propagation of this flexural wave is coaxial with the borehole Displacement is at right angles to the borehole axis and in line with the transducer Dipole has low operating frequencies, below 4 kHz where excitation of these waves is optimum

Soft (Slow) Formation - Dipole Compressional and shear waves radiate straight out into the formation An additional shear/flexural wave propagating up the borehole. It creates a "dipole-type” pressure disturbance in the borehole fluid It is this pressure disturbance that the directional receivers detect Wellbore Formation Compressional wave Shear wave Flexural wave Directional source Compressional wave Shear wave Flexural wave

Soft (Slow) Formation - Dipole The shear/flexural wave, initiated by the flexing action of the borehole, is dispersive At low frequencies it travels at the same speed as the shear wave; at higher frequencies it travels at a slower speed Unlike monopole-only tools, the dipole tool can record a shear/flexural wave even in slow formations Wellbore Formation Compressional wave Shear wave Flexural wave Directional source Compressional wave Shear wave Flexural wave

Dipole Waveforms - Slow Formation Shear/flexural wave is: short in duration concentrated at lower frequencies Additional higher-frequency compressional arrival In this typical slow formation example, there is a clear flexural wave from which the shear slowness is inferred Compressional wave Shear wave Flexural wave

Dipole Waveforms - Fast Formation Shear/flexural wave is: long in duration very dispersive Low frequency components, traveling near the shear slowness, become fairly well separated from the slower, higher frequency components Shear can often be detected and the formation shear slowness estimated directly from the waveforms Shear Flexural Mode

DSI* Dipole Shear Sonic Imager Hardware Introduction The AIT is the newest generation of induction tool built at Schlumberger. The design is a fundamental departure from previous induction tools. The AIT-B is the first induction that is through wired. (Dual ended) The tool uses CTS telemetry, but can easily be upgraded to DTS telemetry. The AIT is combinable with most existing tools, new combinations should always be tested in the shop. The tool uses the principle of simple coil array instead of the traditional fixed focus. The AIT service provides better vertical resolution than ever before. Five depths of investigation for more precise descriptions of invasion. The tool uses 8 arrays, real and quadrature signals from each, and 3 frequencies resulting in 28 conductivities. The 28 conductivities are processed through a borehole correction scheme, and then into the 5 log curves at a choice of 3 different vertical resolutions.

DSI-Dipole Shear Sonic Imager Monopole Compressional and Dipole Shear measurements provide Sonic data in hard and soft formations

DSI vs DSLT The borehole physics limitation of a Monopole Sonic to acquire DT shear in formations where DT shear > DT mud. Dipole Sonic acquisition overcomes this limitation & DT formation >> DT mud are acquired.

DSI Hardware SPAC (Sonic Parallel Acquisition Cartridge) Microprocessor controls: Digitizing Stacking Transmitting signals up-hole Sending commands to the other tool components via a dedicated serial link

DSI Hardware SMDR 8x receiver stations Each station has 2x hydrophone pairs: 1x oriented in line with the upper dipole transmitter (odd pair) 1x oriented in line with the lower dipole transmitter (even pair) The outputs from each pair are: Differenced for dipole reception Summed for monopole reception Receivers are carefully matched during manufacture . Selectable filters and programmable amplifiers are also in the SMDR sonde.

DSI Hardware SSIJ (Sonic Sonde Isolation Joint) Mechanical shock absorber to prevent: Direct acoustical tool arrivals from the transmitters Reduces noises coming from below the receiver section Do not log with more than 900-lbs.of weight below the SSIJ Do not log without the SSIJ

DSI Hardware SMDX 3x transmitter elements: 1x omni-directional monopole, ceramic transducer 2x unidirectional dipole transducers oriented perpendicular to each other Monopole transducer: Low frequency pulse for Stoneley High or low frequency pulse for compressional and shear Dipole transducers: Standard frequency Low frequency (for large borehole and very slow formations) All transducers can be fired at a rate of up to 15 Hz.

DSI Specifications Temperature rating 350°F [175°C] Pressure rating 20,000 psi [138 MPa] Tool diameter 35/8 in. [92 cm] Minimum hole size 51/2 in. [13.9 cm] Maximum hole size 21 in. [53.3 cm] Tool length 51 ft [15.5 m] Maximum logging speed One eight-waveform set 3600 ft/hr (single mode) All six modes simultaneously 900 ft/hr (without BCR) Digitizer precision 12 bits Digitizer sampling interval limits Variable from 10 to 32,700 µsec per sample Digitized waveform duration limits Up to 15,000 samples/ all waveforms Acoustic bandwidth Dipole and Stonely 80 Hz to 5 kHz High-frequency monopole 8 to 30 kHz Combinability All MAXIS tools, any resistivity tool

Depth of Investigation Depths of investigation for sonic devices is a function of: formation type shear and compressional slowness transmitter-to-receiver source frequency (wavelength) etc

DSI Hardware Versions: DSI-A CTS telemetry , TCC ( DTC/DTA ) +SPAC-A+SMDR-A+SSIJ-B+SMDX-A DSST-A is obsolete; its production started in August 1990 and stopped in July 1995. There will be no support for DSST-A in OP 9.2 and later OP versions. SKK recommends that you upgrade all your current SPAC-A tools to the SPAC-B version

DSI Hardware Versions: DSI-B DTS telemetry , DTC-A/H +SPAC-B+SMDR-A+SSIJ-B+SMDX-A DSST-B production started in July 1995. The SMDR-AA receiver sonde is also going to become obsolete soon. SKK recommends that you upgrade all your current SMDR-A sondes to the SMDR-BD/BE version.

DSI Hardware Versions: DSI-II (DSI-Plus) Enhances the measurement quality & improves tool reliability. Enhances shear slowness measurement by improving waveform amplitude The SMDR receiver array has been redesigned to achieve these improvements To implement the upgrade of DSI to DSI-II, SMDR-AA MR-2 & SSIJ-BA MR-2 is needed. These are mandatory modifications that must be implemented only by trained and qualified personnel The SMDR-AA becomes SMDR-BD

DSI Hardware Versions: S-DSI DSI logs run in slow formations with the standard DSI sleeve result in a strong sleeve arrival in the data. Do not run the standard SMDR slotted sleeve in formations slower than 500 us/ft. When in doubt about DTs & when logging surface formations, use S-DSI and not DSI-II (DSI Plus). S-DSI uses a slow-formation sleeve that replaces the standard SMDR sleeve to extend the range of DSI-II dipole slowness measurement from 500 usec/ft to 1200 usec/ft. To implement the upgrade of DSI-II to S-DSI a Slotted Sleeve is required, which is SMDR-BD MR-3 (optional). The slotted sleeve is intended for use only with DSI-II tools.

DSI Operating Limits

DSI Hardware Versions: BARS DSST-C ( BARS ) DTS telemetry , DTC-A/H +SPAC-B+SMDR-C+SSIJ-B+SMDX-A DSST-C is available in OP 9.1 and later version as an experimental tool for BARS (Borehole Acoustic Reflection Survey) operations. SMDR-C is identical in every aspect to the SMDR-B with the exception of its PGA board;

DSI* Dipole Shear Sonic Imager Waveform Processing Introduction The AIT is the newest generation of induction tool built at Schlumberger. The design is a fundamental departure from previous induction tools. The AIT-B is the first induction that is through wired. (Dual ended) The tool uses CTS telemetry, but can easily be upgraded to DTS telemetry. The AIT is combinable with most existing tools, new combinations should always be tested in the shop. The tool uses the principle of simple coil array instead of the traditional fixed focus. The AIT service provides better vertical resolution than ever before. Five depths of investigation for more precise descriptions of invasion. The tool uses 8 arrays, real and quadrature signals from each, and 3 frequencies resulting in 28 conductivities. The 28 conductivities are processed through a borehole correction scheme, and then into the 5 log curves at a choice of 3 different vertical resolutions.

DSI Acquisition & Processing Acquisition: Waveforms of the acquired modes, one for the Rx & one (optionally) for the Tx are built into sets. STC (Slowness Time Coherence): Rx & Tx waveform sets are processed to identify coherent arrivals. Labelling: Detects the desired arrival from among the peaks identified by STC.

STC Computation - 1 Array Waveforms STC - Slowness-time-coherence processing

STC Computation - 2 Contour Plot

Slowness Time Plane Projection Labeling Poisson's Ratio Delta-T Comp. .25 .50 100 200 Gamma Ray Delta-T Shear 0 100 100 500 Caliper Dtc Coherence Dts Slowness Time Plane Projection 6 16 0 1. 1. 0 10200 10250 10300 10350

Dipole Waveforms - Bias Correction Shear Flexural Mode Shear slowness Flexure slowness Bias Correction Bias correction is small for fast formations and averages about 5 percent in slow formations Shear Flexural Mode

Dipole Waveforms - Bias Correction One of the coherence peaks will correspond to the dispersive flexural mode The slowness of this peak is always greater (slower) than the true shear slowness In fast formations a low-frequency band pass filter usually produces a coherence peak very close to the true shear slowness In slow formations the formation shear must be estimated from the flexural data 10250

Dipole Waveforms - Bias Correction Low-frequency source tends to minimize the dispersion Some correction is still needed to obtain the true formation shear A precomputed correction, derived using data generated from numerical modeling, is included in the processing to correct for the bias caused by flexural wave dispersion Amount of correction depends on: the acoustic response signature of the source the STC filter characteristics the borehole size shear slowness 10250

Dipole Waveforms - Bias Correction Bias correction is small for fast formations and averages about 5 percent in slow formations 10250

DFMD - Digital First Motion Detection Amplitude threshold-crossing times derived in the cartridge for each receiver waveform Input into Identification and tracking algorithm Algorithm selects crossing time the one on each waveform that corresponds to first motion, and tracks it over depth

DFMD - Digital First Motion Detection First-motion travel times are then input into an algorithm to compute the first-arrival slowness averaged over the array

DSI* Dipole Shear Sonic Imager Environment Introduction The AIT is the newest generation of induction tool built at Schlumberger. The design is a fundamental departure from previous induction tools. The AIT-B is the first induction that is through wired. (Dual ended) The tool uses CTS telemetry, but can easily be upgraded to DTS telemetry. The AIT is combinable with most existing tools, new combinations should always be tested in the shop. The tool uses the principle of simple coil array instead of the traditional fixed focus. The AIT service provides better vertical resolution than ever before. Five depths of investigation for more precise descriptions of invasion. The tool uses 8 arrays, real and quadrature signals from each, and 3 frequencies resulting in 28 conductivities. The 28 conductivities are processed through a borehole correction scheme, and then into the 5 log curves at a choice of 3 different vertical resolutions.

DSI Borehole Compensation DDBHC = average (RA & TA) RA - Receiver array derived from one tool position TA - pseudo-transmitter array derived from several tool positions

DSI Borehole Compensation SAM 1 & 2 (Dipole) - RA only SAM 3 (Stoneley) - RA only SAM 4 (P&S) - DDBHC SAM 5 (DFMD) - N/A SAM X (Expert) - N/A Note: There is no theoretical basis for borehole compensation for the Stoneley mode or for the dipole modes

Road Noise MST - Monopole Stoneley LDP - Lower Dipole CME-Y new centralizer LCME-A Cause: contact between centralisers / standoffs and borehole wall Use correct method and placement of centralisation Reduce OD of CME-Z close to BS to reduce road noise New LCME-A (CME-Y) shows similar order of noise as CME-Z’s

DSI* Dipole Shear Sonic Imager Tool Maintenance Introduction The AIT is the newest generation of induction tool built at Schlumberger. The design is a fundamental departure from previous induction tools. The AIT-B is the first induction that is through wired. (Dual ended) The tool uses CTS telemetry, but can easily be upgraded to DTS telemetry. The AIT is combinable with most existing tools, new combinations should always be tested in the shop. The tool uses the principle of simple coil array instead of the traditional fixed focus. The AIT service provides better vertical resolution than ever before. Five depths of investigation for more precise descriptions of invasion. The tool uses 8 arrays, real and quadrature signals from each, and 3 frequencies resulting in 28 conductivities. The 28 conductivities are processed through a borehole correction scheme, and then into the 5 log curves at a choice of 3 different vertical resolutions.

Air Volume Check Procedure

DSI* Dipole Shear Sonic Imager Applications Introduction The AIT is the newest generation of induction tool built at Schlumberger. The design is a fundamental departure from previous induction tools. The AIT-B is the first induction that is through wired. (Dual ended) The tool uses CTS telemetry, but can easily be upgraded to DTS telemetry. The AIT is combinable with most existing tools, new combinations should always be tested in the shop. The tool uses the principle of simple coil array instead of the traditional fixed focus. The AIT service provides better vertical resolution than ever before. Five depths of investigation for more precise descriptions of invasion. The tool uses 8 arrays, real and quadrature signals from each, and 3 frequencies resulting in 28 conductivities. The 28 conductivities are processed through a borehole correction scheme, and then into the 5 log curves at a choice of 3 different vertical resolutions.

Applications Mechanical property analysis — sanding analysis — fracture height — wellbore stability Formation evaluation — gas detection — fractures — permeability Geophysical interpretation — synthetic seismograms — VSP — AVO Introduction The AIT is the newest generation of induction tool built at Schlumberger. The design is a fundamental departure from previous induction tools. The AIT-B is the first induction that is through wired. (Dual ended) The tool uses CTS telemetry, but can easily be upgraded to DTS telemetry. The AIT is combinable with most existing tools, new combinations should always be tested in the shop. The tool uses the principle of simple coil array instead of the traditional fixed focus. The AIT service provides better vertical resolution than ever before. Five depths of investigation for more precise descriptions of invasion. The tool uses 8 arrays, real and quadrature signals from each, and 3 frequencies resulting in 28 conductivities. The 28 conductivities are processed through a borehole correction scheme, and then into the 5 log curves at a choice of 3 different vertical resolutions. Formation Shear Anisotropy

[ ] Dynamic Elastic Properties Lateral strain 1/2 (DTS / DTC) 2 – 1 Longitudinal strain (DTS / DTC) 2 – 1 v Poisson’s Ratio G Shear Modulus E Young’s Modulus Kb Bulk Modulus Cb Bulk Compressibility (with porosity) Applied stress pb Shear strain DTS 2 Applied uniaxial stress Normal strain 2G (1 + v) [ ] Hydrostatic pressure Volumetric strain 1 4 DTC2 3DTS2 pb x a Volumetric deformation Hydrostatic pressure 1 Kb Note: coefficient a = 1.34 x 1010 if pb in g/cm3 and DT in µs/ft.

IMPACT Log

Sanding Model Diagram Pe, Far Field Pressure Pw Pp, Pore Pressure  x r y  Far Field Stresses Flow  r = Pw (1—)

vp/vs versus Dtc

vp/vs versus Dtc

Fracture Evaluation - Stoneley

Permeability indications - Stoneley Energy 6300 6400 7100 Gamma Ray Density-Neutron Resistivity Stoneley Energy Differential Energy

Permeability indications - Stoneley Energy

Poisson’s Ratio— It is increases in width of a rock along one axis when compressed a certain amount along the other. Ratios for normal well-consolidated rocks range from 0.2 to 0.4, while unconsolidated rocks can have ratios as high as 0.5. Poison’s Ratio is a good indicator of formation consolidation.

Poisson’s Ratio— Vp / Vs 2 - 2 = 2 Vp / Vs 2 - 2 0 0.1 0.2 0.3 0.4 0.5 Poisson’s Ratio Vp / Vs 2 - 2 = Relates rock compressibility with stiffness 2 Vp / Vs 2 - 2

Poisson’s Ratios Poisson’s Ratios Reference Sediment Podio et al. (1968) Green River Shale 0.22–0.30 Hamilton (1975) Shallow Marine Sediments 0.45–0.50 Gregory (1976) Consolidated Sediments Brine Saturated 0.20–0.30 Gas Saturated 0.20–0.14 Domenico (1976) Synthetic Sandstone Brine Saturated 0.41 Gas Saturated 0.10 Domenico (1977) Ottawa Sandstone Brine Saturated 0.40

AVO Response

Synthetic Seismograms Compressional Shear 1.600 1.700 1.800 1.900 2.000 2.100 2.200 2.300 2.400 2.500 2.600 2.700 2.800 2.900 8000 9000 10000

Shear anisotropy measurements

Shear anisotropy measurements

Summary The DSST tool has advantages over the previous sonic tools like SDT It utilises both Dipole and Monopole transducers The dipole capability allows the tool to measure the shear slowness in typical slow or unconsolidated formations to overcome the limitation of monopole Remember: Always use DSI job planner and understand why the job is being run Always run the tool well-centred and under the recommended logging speed limit Never run the tool without SSIJ Run DSST with GPIT for BCR mode