Schlumb_MWD LWD Basic

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(1)4/23/2004. Graham Raeper. Schlumberger Public. MWD and LWD Introduction LWD Interpretation & Development Schlumberger DCS Scandinavia. Schlumberger Public. 1.

(2) 4/23/2004. An asterisk is used throughout this presentation to denote a mark of Schlumberger. Other company, product, and service names may be trademarks, registered trademarks, or service marks of others.. Schlumberger Public. 2 GR 4/23/2004. Schlumberger Public. © Schlumberger 2004. 2.

(3) 4/23/2004. Measurement While Drilling Tools. Schlumberger Public. – Measure the Direction & Inclination of the wellbore – Allow drilling tools to be oriented (mud motors, Whipstocks) – Provide mechanism for transmitting downhole data to surface – May provide Gamma Ray & Drilling Mechanics measurements – May provide power for LWD tools. Logging While Drilling Tools – Measure petrophysical properties Schlumberger Public. 3 GR 4/23/2004. 3.

(4) 4/23/2004. MWD History • Early Patents. First WL log (resistivity) 1927 SP 1931. Schlumberger Public. 4 GR 4/23/2004. Schlumberger Public. •Jakosky patent, 1929 • Otis & Alder, 1955. Induction Resistivity & dipmeter 1947 Density – 1957 SNP (neutron) & compensated density - 1962. First DD in 30’s (1934 for first relief well). 4.

(5) 4/23/2004. MWD Evolution. Schlumberger Public. 5 GR 4/23/2004. Schlumberger Public. – 1960’s – Teledrift tool developed - mechanical inclinometer with positive mud pulse, still used today – 1969 – SNEA & Raymond Precision Industries start development work on mud pulse telemetry MWD system (these projects are combined to form Teleco in 1972) – 1978 – Teleco MWD tool commercialized – 1980 – Schlumberger complete first MWD job in the Gulf of Mexico -Multi-Sensor MWD tool (D&I/ GR/ RES/ DWOB/ DTOR) – 1984 – NL Baroid Introduce first 2MHz resistivity tool – 1986 – First Triple Combo (GR/ RES/ Density Neutron) LWD string – 1993 – Sonic compressional LWD tools introduced – 2001 – Seismic while drilling, Formation Pressure while drilling. 5.

(6) 4/23/2004. Telemetry Principles Mud. Pressure. Positive Pulse: 1 BPS Schlumberger Public. Time Mud. Pressure. Continuous wave: up to 12 Bits Per Second Time. Mud. Pressure. 6 GR 4/23/2004. Time. Starting with our telemetry, on this slide is represented the PowerPulse series of MWD tools.. Schlumberger Public. Negative Pulse: 2 BPS. All those tools specifications are listed in the drilling services catalogs that you were provided. Please refer to this documentation for specifications. All PowerPulse tools are identical except for the 6” holes where the standard PowerPulse is replaced by the Vision475 MWD, a combination of PowerPulse and Vision Resistivity. The PowerPulse comprises 5 elements, a collar, which only has one plugs on the outside (the read out port), extenders to allow communication with LWD tools, a turbine to power the tools, an electronic cartridge to control turbines and modulator as well as communication with LWD tools, and finally a unique telemetry system, the modulator. The way the modulator is working is simple as you can see on the right side of the slide, it is composed of a stator and a rotor, when the rotor turns it is closing and opening the gap on the stator thus creating a pressure wave. This pressure wave is captured on surface. The interesting thing is that we are actually not looking at the delta pressure seen on surface but rather at the frequency of this pressure wave. This gives us the fastest and the most reliable telemetry on the market today.. 6.

(7) 4/23/2004. MWD Inside.... Schlumberger Public. The MWD Sonde is centered in the collar (Mud flow in the center of the tool for some LWD tools) Schlumberger Public. 7 GR 4/23/2004. 7.

(8) 4/23/2004. Schlumberger Public. Schlumberger Public. 8 GR 4/23/2004. 8.

(9) 4/23/2004. MWD Systems available in different sizes PowerPulse* Schlumberger Public. Impulse*. SlimPulse*. Objective: MWD tools available today. Schlumberger Public. 9 GR 4/23/2004. 9.

(10) 4/23/2004. MWD Surveys Sensors. Extender. Extender. 3 Magnetometers. Schlumberger Public. 10 GR 4/23/2004. +. Schlumberger Public. 3 Accelerometers. 10.

(11) 4/23/2004. MWD Surveys Sensors. 11 GR 4/23/2004. Azimuth Error: - Magnetic parts - LWD Power - Collar Mass - Collar Hot Spots. Schlumberger Public. Inclination Error: - Movement - Misalignment of the MWD collar in the wellbore - Accelerometer misalignment - Temperature. Schlumberger Public. Sensor sets arranged orthogonally. 11.

(12) 4/23/2004. Uncertainties Well path is computed from surveys by minimum curvature method -1200. -1000. -800. -600. -400. -200. 400. SPIDER VIEW Scale (1 cm = 100 m). A-1 H Survey. 600. 800. 400. A-3 H Plan 1500. 1400. 1300. 12 00. 2100. 200. 1200. 1400. 1300. 1600. 1500. 1600. 1800. 1700. 1900. 2000. 77 21. 0 1700. 0. Azimuthal Accuracy: 1° (FMI GPIT Az. Acc. = 2°). -200. 00 19. Default Color Main Proposal Survey. A-2 H Pilot Survey. 20 00. 2325. 2300. 2200. 210 0. 2100. -400. -400. 1300. 00 20. 1400 19 190 000. 20 00. <<< SOUTH. 00 21. 1800. 1500. 1700. 00 16. -600. -600. A4H Plan. -1000. -800. -600 <<< WEST. -400. -200. 0. 200 EAST >>>. 400. 600. 800. Schlumberger Public. -1200. 12 GR 4/23/2004. Inclination accuracy: 0.1° (FMI GPIT Incl. Acc. = 0.5°). 1800. -200. 200. Schlumberger Public. NORTH >>>. 200. 1600. A-2 AH Survey. 400. 0. 12.

(13) 4/23/2004. Link from MWD tool to LWD tools. Extender. A BHA must be assembled from tools around 30 ft long . A link must be provided for electrical connection to other tools in the string – SLB use extenders to provide the link to between MWD and other tools – An alternative method is to use an electrode set into the thread face of the collar – Extenders provide both the communication and power link. Schlumberger Public. 13 GR 4/23/2004. Schlumberger Public. Extender. 13.

(14) 4/23/2004. Logging While Drilling. Schlumberger Public. 14 GR 4/23/2004. Schlumberger Public. The goal in developing LWD tools was to provide near wireline quality measurements while drilling Early MWD tools provided basic electrode (short normal) type resistivity & Gamma Ray measurements 2 MHz resistivity tools developed to obtain higher quality resistivity measurement in all mud types Density/ Neutron measurement developed to provide Triple Combo service – supports large percentage of wells. 14.

(15) 4/23/2004. Triple Combo Gamma Ray, Resistivity, Density, Pef, Neutron. Schlumberger Public. 15 GR 4/23/2004. Schlumberger Public. • Provides measurements of most commonly used wireline string • Majority of LWD logs are not duplicated by equivalent wireline service. 15.

(16) 4/23/2004. LWD FE Capability - Today… Measurements. Conveyance LWD. yes. yes. yes. yes. no. 16-bins. yes. yes. yes. no. 5 outputs. 20 outputs. 5 outputs. 5 outputs. 12-bins. 56-bins. yes. no. yes. yes. yes. yes. yes. yes. Yes. yes (memory only). yes. yes no. yes. yes. 16 GR 4/23/2004. Objective: High Service Quality. Schlumberger Public. yes. Schlumberger Public. Thermal Neutron Ø Bulk Density Azimuthal Density Photoelectric factor Spectroscopy / Sigma Multi-depth Propagation R Multi-depth Laterolog R Azimuthal Resistivity Micro-Resistivity Image Compressional Dt Shear Dt Seismic Check shot VSP Formation Pressure Fluid samples NMR. Conveyance WL. 16.

(17) 4/23/2004. LWD Acquisition Workflow - Differences between Wireline and LWD Wireline Data is directly associated to depth indexes as it is acquired- DLIS. . Depth is calculated from length of cable in hole - independant. LWD . Tools do not know the depth / only surface systems know the bit depth. . Tools record data in time (clock, resets, shifts). . 2 types of acquisition: Real-Time and Recorded Mode. . Real time data, transmitted by the MWD tool via pressure pulses in the mud column is associated with depth as it is acquired. Schlumberger Public. 17 GR 4/23/2004. Schlumberger Public. . 17.

(18) 4/23/2004. Surface Sensors. Schlumberger Public. 18 GR 4/23/2004. Schlumberger Public. Depth sensor SPT Weight/Torque Pump press. Pump stroke Surf. RPM Etc…. 18.

(19) 4/23/2004. The MWD unit. Schlumberger Public. Schlumberger Public. 19 GR 4/23/2004. 19.

(20) 4/23/2004. Signal Demodulation Principles Type of signals Downhole (MWD-Motor..). . Uphole (Pumps-Rig..). . Echoes & Reflections. Electrical Noise Characteristics . Frequencies. . Attenuation. . Direction Schlumberger Public. 20 GR 4/23/2004. . Schlumberger Public. . 20.

(21) 4/23/2004. DSPScope. Schlumberger Public. Schlumberger Public. 21 GR 4/23/2004. 21.

(22) 4/23/2004. DSPScope Spectrogram. Schlumberger Public. Schlumberger Public. 22 GR 4/23/2004. 22.

(23) 4/23/2004. Demodulation. Schlumberger Public. Objective: Understand Demodulation The Frame Display function is the parent application of SPM Demodulation. This application performs the following functions:. Schlumberger Public. 23 GR 4/23/2004. • Translates the raw bits demodulated by the receiver module into raw data point values (D-points). • Sends the D-points to the IDEAL backend. • Displays the decoded frame and decoding status. The Frame Display application also contains a toolbar to launch or open the associated window of many of the SPM Demodulation functions. Simply clicking on one of the toolbar buttons displays the appropriate control window. The Frame Display window displays any number of previous frames and is only limited by screen size. Simply resizing the window with the mouse covers or uncovers as much frame history as desired. The values are displayed in raw decimal format. The conversion to engineering units occurs after being sent to IDEAL. The Frame Display window displays the most important demodulation information on the screen. You can check the • Decoded raw D-points • Sync status (In Sync, Out Of Sync Pump Down, Signal Loss, Searching, or Precursor) • History decoded frame quality • Frame ID 23.

(24) 4/23/2004. Telemetry is Key Drilling Optimisation Data… 70. 50. 65. Increased rate of penetration. 40. 60. 55. 45. 40. AZI (deg). CD&I. INCL (deg). PWD. 20. Slip Stick. 10. 30. 25 1500. 2000. 2500. 3000. 3500. 4000. 4500. 0 5000. Schlumberger Public. 35. (/m). 30 50. MD(ft). Formation Evaluation Data… 1 bit per second 3 bits per second 6 bits per second QC Da. ta. Or 2.2 BPS log and a Real-time density image. Or 4.3 BPS log and a Real-time resistivity image. ced L Advan 0.8 BPS. WD 1.7 BPS. (m/hr). Schlumberger Public. 24 GR 4/23/2004. es High R. 24.

(25) 4/23/2004. Recording Mode Acquisition Rate. Schlumberger Public. 25 GR 4/23/2004. Schlumberger Public. To record 2 samples/ft with an acquisition rate programmed at 10 sec, your ROP have to be limited to180ft/hr (60m/hr). 25.

(26) 4/23/2004. Read-Out Port (ROP). Schlumberger Public. 26 GR 4/23/2004. Schlumberger Public. ROP Communication with tool to downlaod memory Battery switch (LWD). 26.

(27) 4/23/2004. Data vs Time -> Data vs Depth Depth vs Time. + Data vs Time. = Data vs Depth. Schlumberger Public. Schlumberger Public. 27 GR 4/23/2004. 27.

(28) 4/23/2004. Time to Depth Conversion Depth Based Data. Time Based Data. Schlumberger Public. HOUR. 28 GR 4/23/2004. 0.00. Gamma Ray. 150.00. Gamma Ray. 150.00. Schlumberger Public. 0.00. 28.

(29) 4/23/2004. Errors from Time/Depth merge To present recorded LWD logs, the data (recorded downhole against time) needs to be combined with a surface measurement of depth (also recorded against time).. . The clocks might be incorrectly synchronized.. . Clocks are not perfect, and will drift.. . Clocks can “reset”, causing jumps.. Schlumberger Public. This can lead to additional errors due to the incorrect alignment of the two independently recorded times:. Each of these effects cause unpredictable effects on the log.. 29 GR 4/23/2004. Schlumberger Public. However, the time/depth merge can easily be checked by comparing the RM data with the RT data.. 29.

(30) 4/23/2004. Depth Tracking. Schlumberger Public. Schlumberger Public. 30 GR 4/23/2004. 30.

(31) 4/23/2004. Depth Acquisition Any changes in depth entered by the engineer is reported Schlumberger Public. Depth encoders. Depth Log / Tracking Sheet. Schlumberger Public. 31 GR 4/23/2004. 31.

(32) 4/23/2004. Depth - What does the Client Want?. Schlumberger Public. 32 GR 4/23/2004. Schlumberger Public. True Depth Absolute Depth Relative Depth Reproducible Depth. 32.

(33) 4/23/2004. Which Depth is That? What is the depth of this formation top? Wireline depth, attempt 2. True depth. Schlumberger Public. Driller’s depth. Anadrill’s depth at time t2. 33 GR 4/23/2004. Wireline depth, attempt 1. Schlumberger Public. Anadrill’s depth at time t1. 33.

(34) 4/23/2004. LWD Depth vs Wireline Depth Wireline depth is the Geoscientist’s reference. Driller’s depth is the Driller’s reference.. those corrections are difficult to apply, and are often incomplete. The corrections are greater than the inaccuracy. Schlumberger Public. If Wireline depth is corrected properly, it is more accurate; but. of driller’s depth. The industry does not want two different measurements of the same thing. They want a repeatable measurement. Schlumberger Public. Depth is our most important measurement. 34 GR 4/23/2004. 34.

(35) 4/23/2004. Depth Measurement LWD’s depth is the driller's depth.. 1. Difference between driller’s depth and true depth. 2. Difference between LWD’s measurement of depth and driller’s depth. Schlumberger Public. There are 3 different areas that affect the accuracy of LWD depth (closeness to true value):. 3. Errors caused by the incorrect alignment in time of the depth file and the data file (time/depth merge problems) Schlumberger Public. 35 GR 4/23/2004. 35.

(36) 4/23/2004. Difference Between Driller’s Depth and True Depth Driller’s depth comes from measuring the length of pipe in the derrick. Effects it does not account for include:. Drillpipe stretch. . Thermal Expansion. . Ballooning effects. . Errors in the measurement. Schlumberger Public. . 36 GR 4/23/2004. •Additional errors are introduced when measuring the depth of deviated holes as the pipe does not lie in the center of the hole. •Errors are also introduced in the conversion from measured to true vertical depth.. Schlumberger Public. ItItisisaavalid validmeasurement, measurement,useful usefulfor for determining bed thicknesses and determining bed thicknesses and geosteering geosteeringapplications applications. 36.

(37) 4/23/2004. Summary of stretch calculations Horizontal Well.. The following results were obtained from the analysis for the amount of pipe stretch: Sliding into the hole 3.75 ft Reaming into the hole at 200 ft/hr 8.67 ft Rotating off bottom 8.75 ft Reaming out of the hole 9.08 ft Sliding out of the hole 13.52 ft. Schlumberger Public. 37 GR 4/23/2004. Schlumberger Public. A well was analyzed using drilling engineering software. The well was vertical to 3000 ft. Then, it built at 3 deg/100 ft to 38 degrees, which was held until 13000 ft. It built again at 3 deg/100 ft to 90 degrees This was achieved at 14679 ft. Total depth was 17960 ft.. 37.

(38) 4/23/2004. Difference between LWD’s measurement of depth and driller’s depth Draworks sensor, Geolograph and/or Rig Motion Sensor Clamp Line Tensiometer (CLT) used to determine when drillpipe goes into and out of slips.. Schlumberger Public. (RMS) used to determine block position. Combination of above used to determine length of pipe in the hole. Checked against driller’s pipe tally every connection. Schlumberger Public. 38 GR 4/23/2004. 38.

(39) 4/23/2004. MWD Depth Measurement. Schlumberger Public. Schlumberger Public. 39 GR 4/23/2004. 39.

(40) 4/23/2004. Schlumberger Public. LWD Measurements. Schlumberger Public. 40.

(41) 4/23/2004. Resistivity Frequency Range. Schlumberger Public. Schlumberger Public. 41 GR 4/23/2004. 41.

(42) 4/23/2004. Why 2MHz? Induction-type LF measurement relies on cancellation of the direct coupling (balanced arrays) very sensitive to geometry, not suited to LWD (shock). At 2MHz, phase-shift and attenuation can be measured between two coils Borehole compensation cancels differences between the two receivers. Schlumberger Public. 42 GR 4/23/2004. Schlumberger Public. . 42.

(43) 4/23/2004. 2 MHz Resistivity Theory Current from Top Transmitter induces an electromagnetic field within the formation. This propagates away from the transmitter. Schlumberger Public. The wave induces a current at the receivers. The phase and amplitude of the wave are measured and converted to resistivity.. Schlumberger Public. 43 GR. 43.

(44) 4/23/2004. Propagation Measurement. Transmitter. EM-wave is attenuated in conductive formations. Near receiver. Receiver. Far receiver. Schlumberger Public. Receiver. Finite propagation speed causes phase-differences Transmitter Schlumberger Public. 44 GR 4/23/2004. 44.



(47) 4/23/2004. Emag Wave Geometry. Schlumberger Public. 47 GR 4/23/2004. Equal amplitude lines. Schlumberger Public. Equal phase lines. 47.

(48) 4/23/2004. ARC475/Phasor induction DOI. Schlumberger Public. Schlumberger Public. 48 GR 4/23/2004. 48.

(49) 4/23/2004. ARC475/Phasor induction. Schlumberger Public. Schlumberger Public. 49 GR 4/23/2004. 49.

(50) 4/23/2004. DOI Considerations 2 Parameter Influencing DOI:. • The greater the distance T/R the deeper the DOI. Signal frequency. Schlumberger Public. Distance from Transmitter to Receiver. • The lower the frequency the deeper the DOI. Schlumberger Public. 50 GR 4/23/2004. 50.

(51) 4/23/2004. 400 KHz Measurement Depth of investigation: . Deeper in conductive formations. . Better signal in conductive formations (< 1 Ohm.m). Schlumberger Public. Similar in resistive formations Advantages: . Less sensitive to eccentering Limitation: . . Schlumberger Public. 51 GR 4/23/2004. Less accurate at higher resistivity (low PS & ATT sensitivity to Rt). 51.

(52) 4/23/2004. Depth Of Investigation Comparison. Schlumberger Public. Schlumberger Public. 52 GR 4/23/2004. 52.

(53) 4/23/2004. Blended (Best) Resistivity. Eccentering Effect. Schlumberger Public. 2MgHz Phase Shift 400KHz Phase Shift 2MgHz Attenuation 400KHz Attenuation. Sorry about the quality-This log shows a log that has been severely affected by eccentering. 2-MHz tools are severely affected by eccentering when there is a large Rt/Rm contrast or a large Rm/Rt contrast. In this case the blue curves in track two are the 2-MHz phase shift outputs and the black curves in track three are the attenuation curves. Both are affected by eccentering that has been exaggerated by a washout. In this case the environment had a large Rm/Rt contrast (OBM and a Rt of less than 1 ohmm.. Schlumberger Public. 53 GR 4/23/2004. One of the biggest advantages of the 400-kHz outputs is the immunity to eccentering. To take advantage of the deeper reading 400-kHz at low resistivity and the immunity to eccentering as well as take advantage of the higher signal to noise ratio and better vertical resolution of the 2-MHz a new output was created. It is called the blended or best resistivity (P16B--Phase shift 16 -in spacing /blended output). The 400kHz curve is presented below 1 ohmm, the 2MHz output is presented above 2 ohmm and the output is a weighted average between 1 & 2 ohmm. This will be the standard presentation for the commercial version of IDEAL 6.1 The blended outputs are the red and green curves. Note that they are very well behaved.. 53.

(54) 4/23/2004. Schlumberger Public. 54.

(55) 4/23/2004. Polarization Horn Effect. Schlumberger Public. Schlumberger Public. 55 GR 4/23/2004. 55.

(56) 4/23/2004. Polarization Horn Effect. Schlumberger Public. Schlumberger Public. 56 GR 4/23/2004. 56.


(58) 4/23/2004. VISION Resistivity vs. AIT Schlumberger Public. The VISION resistivity log is extensively used for formation evaluation. It has a similar response to the Array Induction Tool. Here five PS curves are plotted against the AIT. At low resistivities, PS curves have about a one foot vertical resolution. The resolution is not constant like the AIT, as the PS resolution degrades to 2 feet at 50 ohmms.. Schlumberger Public. 58 GR 4/23/2004. The attenuation curve resolution is severely affected by an increase in resistivity. The attenuation curve has a resolution of 2 feet at 1 ohmm but 8 feet at 50 ohmms. The curve mnemonics are also different from that of an AIT. For a VISION curve: •1st letter denotes the curve--either P for Phase Shift or A for attenuation •second two numbers represent the spacing (10,16,22,28,34, or 40 -inch) •. Unlike the AIT this is not the constant depth of Investigation!!!. •The last letter is either “H” for High frequency (2-MHz) or “L” for low frequency (400-kHz) Note that the IMPulse currently does not have the 400-kHz option but will be modified latter in 2000 that will provide it with increased memory to 50 MB, dual frequency, digital electronics and simultaneous acquisition.. 58.

(59) 4/23/2004. GeoVISION Resistivity Tool. Schlumberger Public. Schlumberger Public. 59 GR 4/23/2004. 59.

(60) 4/23/2004. GeoVISION Resistivity GVR Azimuthal Button Resistivity Measurements. Schlumberger Public. Schlumberger Public. 60.

(61) 4/23/2004. GeoVISION Current Focusing. Schlumberger Public. Schlumberger Public. 61 GR 4/23/2004. 61.

(62) 4/23/2004. Ring Resistivity Principle. Schlumberger Public. Schlumberger Public. 62 GR 4/23/2004. 62.


(64) 4/23/2004. WL dual laterolog Resistivity response. Schlumberger Public. Schlumberger Public. 64 GR 4/23/2004. 64.

(65) 4/23/2004. GVR focused Ring Resistivity response. Schlumberger Public. Schlumberger Public. 65 GR 4/23/2004. 65.

(66) 4/23/2004. GRV Imaging: Break-outs and Button Averaging. Schlumberger Public. Schlumberger Public. 66 GR 4/23/2004. 66.

(67) 4/23/2004. GVR Azimuthal Caliper. Schlumberger Public. Caliper data can be acquired from several sources using LWD data. • A real-time ultrasonic caliper is made with the Vision675 density tool. Schlumberger Public. 67 GR 4/23/2004. • resistivity caliper from the CDR, ARC and RAB in WBM Today the resistivity calipers are only available in memory but should be available in real-time by the end of the year (99). The caliper data provides a picture of the shape of the bore hole, indicating the severity of formation breakout and the primary directions of failure The diagram above shows caliper data from the Geovision resistivity tool at different depths, highlighting that breakout has occurred long the north-west / south-east plane. The resistivity image data from the same tool over the same interval clearly shows the areas of breakout along that plane The caliper data can also be used to potential hazardous areas while tripping, running tubulars or wireline. 67.

(68) 4/23/2004. GVR and FMI Comparison Azimuthal Resistivity for Geological and Fracture Analysis. Schlumberger Public. • Fracture presence and orientation are often key parameters to. Schlumberger Public. 68 GR 4/23/2004. drilling successful horizontal wells. • This examples compares a wireline FMI Formation MicroImager (left image) to a GeoVISION resistivity image (right image) acquired during the drilling process. • Note the fracture in the middle of each image. This sine wave has a different orientation to the bedding planes.. 68.

(69) 4/23/2004. GeoVISION Real Time Images Real Time Image. Recorded Mode Image. Schlumberger Public. 70 ft. Ref.: SPE - 71331 This is an example of a compressed and decompressed image compared to a recorded mode image straight from the tool memory (I.e. retrieved when the tool was on the surface. Although the resolution of the compressed and decompressed image is poorer the main feature of cutting up through a thin conductive bed can clearly be seen.. Schlumberger Public. 69 GR 4/23/2004. 69.

(70) 4/23/2004. Density Neutron Measurement. LWD tools use different methods to record density data with the lowest standoff as the tool rotates. Schlumberger Public. Wireline density tools typically use a skid mounted source & detector to obtain good contact with borehole. Neutron porosity measurements can be corrected for mud standoff Schlumberger Public. 70 GR 4/23/2004. 70.

(71) 4/23/2004. Vision Azimuthal Density Neutron (VADN). -C137 Gamma ray source Density Nal -Two gain-stabilized scintillationSection detectors. Schlumberger Public. 71 GR 4/23/2004. Schlumberger Public. -AmBe neutron source Neutron -He3 detectors Section -Thermal neutrons. 71.

(72) 4/23/2004. Density Borehole Compensation RHOmc < RHOb DRHO > 0. RHOmc > RHOb DRHO < 0. RHO ss. Schlumberger Public. RHO ls. RHOb = RHO ls + DRHO DRHO = f (RHO ls - RHO ss). RHOmc. Schlumberger Public. RHOb 72 GR 4/23/2004. “SPINE & RIBS” algorithm compensates up to 1” stand-off. 72.


(74) 4/23/2004. ADN Dual Source Assembly. Schlumberger Public. Assembly. Density Source Neutron Source. Schlumberger Public. 74 GR. 74.


(76) 4/23/2004. CLAMP-ON STABILISER. Schlumberger Public. BUILT-IN STABILISER. Schlumberger Public. 76 GR 4/23/2004. 76.

(77) 4/23/2004. ADN Images Theory Azimuthal Azimuthal source source and and detectors detectors Schlumberger Public. ADN ADN Density Density Image Image. Color Color scale scale Quadrant Quadrant arrays arrays. Schlumberger Public. 77 GR 4/23/2004. 77.

(78) 4/23/2004. Image Resolution (Relative pixel sizes). Schlumberger Public. One inch scale. Pef. GVR. UBI. FMI. Despite this coarseness of image, density images can prove invaluable. They can be acquired in oil and water based muds. Using LWD allows measurements in complex shaped wells that would require risky TLC runs if they are possible at all.. Schlumberger Public. Density 78 GR 4/23/2004. Furthermore many of these wells are logged at high angles, where even thin bed are seen over many feet within the borehole. As with any imaging tool a contrast in the medium being measured is required to identify beds.. 78.

(79) 4/23/2004. Image resolution Limitation. 35°. Schlumberger Public. The sinusoids are not resolved for apparent dips of less than 35 Degrees. Schlumberger Public. 6 in. 8.5 in. 79.

(80) 4/23/2004. VADN Images PowerDrive - 2D Images. Schlumberger Public. 80 GR 4/23/2004. Schlumberger Public. Ultrasonic Pef RHOS RHOB (quad.) ROSI RHOB (sect.) ROIM RHOL. 80.

(81) 4/23/2004. Comparison Real Time vs. Memory Image RTI. RMI. Schlumberger Public. Schlumberger Public. 81 GR 4/23/2004. 81.

(82) 4/23/2004. LWD Calipers Ultrasonic Caliper. direct. Density Caliper Caliper from multiple DOI Resistivity Neutron Caliper. Derived. Schlumberger Public. 82 GR 4/23/2004. Schlumberger Public. Phase Caliper from Propagation Tool. 82.

(83) 4/23/2004. Ultrasonic Caliper Measurement. Schlumberger Public. 83 GR 4/23/2004. Schlumberger Public. Borehole spiraling. 83.

(84) 4/23/2004. Advantages of the Ultrasonic Caliper • Direct and Azimuthal Measurement • Works in OBM and WBM • Good Precision (0.1 –0.2 in.). Factors that Affects Accuracy. 84 GR 4/23/2004. Schlumberger Public. Acoustic Impedance Contrast between Mud and Formation Signal Attenuation in Heavy Mud Standoff Range up to 2.5 in. Hole Rugosity / Target Alignment. Schlumberger Public. • Available in Real Time. 84.

(85) 4/23/2004. VADN/FMS Image Comparison Drilling down sequence. Schlumberger Public. parallel to bedding. 85 GR 4/23/2004. Schlumberger Public. Drilling down sequence. 85.

(86) 4/23/2004. Schlumberger Public. VADN. Density Dynamic Image. Pef Dynamic Image. Schlumberger Public. VADN. 86.

(87) 4/23/2004. Azimuthal Density Reveals Filtrate Drape Azimuthal Formation Evaluation - Gravity Segregation of Fluids. Schlumberger Public. Gas. filtrate. • This is a quadrant density presentation from a horizontal well in a high. Schlumberger Public. 87 GR 4/23/2004. permeability gas zone. • All quadrant densities (top, bottom, left and right) are “crossed-over” the neutron in the characteristic gas signature. • The quadrant densities themselves do not agree in the homogeneous formation. The bottom density has the highest reading. The top density is the lightest. • This is due to filtrate drape - gravity segregation to the bottom of the wellbore. This generally occurs in high permeability gas zones due to the buoyancy force. •Note the difference that this may make on resistivity measurements - GVR would be useful in this case to compute quadrant water saturations.. 87.

(88) 4/23/2004. Azimuthal Porosity GeoSteering. Schlumberger Public. Schlumberger Public. 88 GR 4/23/2004. This example illustrates the benefit of azimuthal density geosteering. A gas zone is overlain by a shale. In zone A, all four quadrants measure low densities and crossover the neutron, indicating a gas zone. The top quadrant has a lower density than the bottom quadrant. This may be a result of “filtrate drape”, which is gravity segregation of filtrate invasion toward the low side of this horizontal well. The drillpipe is sliding for a short section, until zone B. The density measurement for the top of the wellbore has increased as it is now measuring the shale bed above the wellbore. The other three quadrants (bottom, left and right) still indicate gas. With the azimuthal measurement, you would now make a decision to turn down, away from the shale boundary. However, with an average density, it may not even be recognized that the wellbore was approaching a shale boundary. The tool and drill pipe slides again to zone C. Now the wellbore is further into the shale section. Only the bottom density indicates gas. Only now, would an average density reading indicate that a steering decision would need to be made, but it still would not provide a direction.. 88.

(89) 4/23/2004. Sonic while drilling transmitter. Receivers. Schlumberger Public. Receivers. Attenuator. Transmitter. Bottom Hole Assembly - ISONIC. Schlumberger Public. 89 GR 4/23/2004. The ISONIC8 is combinable with any 8-in. LWD measuring device and is traditionally run with LWD triple combo tools (e.g. CDR/RAB and CDN). Similarly, the ISONIC6 can be run with all 6 3/4-in. collar LWD/MWD tools. Both tools can be run with all bit types. Pictured is a typical quad-combo bottom hole assembly. In such a configuration, the ADN/CDN will always be at the top of the BHA to allow for source retrieval. The ISONIC would be typically next, but it can be placed anywhere in the string, above or below the MWD tool, even just above the bit in “low noise” environments (e.g. rotary drilling - not hard rocks). The ISONIC can be run with or without a downhole motor or geosteering assembly.. 89.

(90) 4/23/2004. ISONIC-Array Sonic While Drilling. Schlumberger Public. Schlumberger Public. 90 GR 4/23/2004. 90.

(91) 4/23/2004. Recorded Mode Data. Schlumberger Public. Schlumberger Public. 91 GR 4/23/2004. 91.

(92) 4/23/2004. ISONIC Vs. Wireline Sonic. Schlumberger Public. Schlumberger Public. 92 GR 4/23/2004. 92.

(93) 4/23/2004. Delta-T in Overpressure Zone. Schlumberger Public. Schlumberger Public. 93 GR 4/23/2004. 93.

(94) 4/23/2004. ISONIC Applications Real-time. Recorded mode. Schlumberger Public. Porosity measurement Lithology identification Seismic correlation real-time input for synthetic seismograms Pore pressure trends while drilling Real-time decision making. Porosity measurement Lithology identification Mechanical properties (hard rocks) Improved quality sonic measurements . Formation alteration (shales) & invasion Hole enlargement. 94 GR 4/23/2004. ISONIC Applications. Schlumberger Public. . ISONIC applications can be divided into two groups - real time and recorded mode applications . Real time measurements provide the client with unique opportunities for better drilling decisions. The two main applications are real time seismic correlation and pore pressure indication. Real Time Seismic Correlation From real time ISONIC compressional slowness measurements, real time synthetic seismograms can be computed. These seismograms can be used to correlate the client’s surface seismic data to driller’s depth. The client will learn where the bit is located on his seismic section. This gives the client the opportunity to re-evaluate his drilling operation before he reaches total depth. Pore Pressure Indication In most sand/shale sequences, compaction increases with depth due to increasing overburden with depth. Sound travels faster through sand/shale sequences the more compacting occurs. Therefore, compressional delta-t lessens with depth at relatively constant rate. When overpressured formations occur, pore space is greater than normal and the delta-t value increases above the expected trend. Therefore, slow delta-t values above the compacting trend indicate overpressured formations. Recorded Mode The major recorded mode application is wireline sonic replacement. Seismic tie and sonic porosity (computed from delta-t and used as an input to the petrophysical evaluation (i.e. lithology, porosity, etc.) are the primary customer objectives for sonic data. When running ISONIC in fast rocks, shear slowness can be acquired from the recorded data. Combining shear with compressional slowness allows for mechanical property computations such as IMPact*, MechPro* and Frachite*. ISONIC compressional data is gathered well before wireline data can be acquired. This means that the measurements are made before formation alteration, stress relief, invasion and increasing hole enlargement can occur. The result is that ISONIC slowness measurements may be a truer representation of the formation properties than subsequent wireline sonic measurements.. 94.

(95) 4/23/2004. LWD Shear Measurement in Slow Formations. Schlumberger Public. 95 GR 4/23/2004. Schlumberger Public. The presence of drill collar requires an alternative to standard wireline-like technology. A Dipole measurement requires a very large dispersion correction R&D programs led to the starting of development work in quadrupole technology for LWD. 95.

(96) 4/23/2004. Why Quadrupole? Empty borehole. Borehole with collar. Dipole. Formation Shear. Strong collar interference Collar mode. More sensitive to shear. Less sensitive to shear. Schlumberger Public. Borehole mode. Borehole mode Formation Shear. Quadrupole. Small collar interference. 96 GR 4/23/2004. Shear slowness in slow formations is derived from the measurement of dipole or quadrupole modes. Both of these modes are dispersive. They propagate at the shear slowness at low frequencies. As the frequency gets higher sensitivity to the shear slowness decrease and sensitivity to mud slowness and other environmental parameters increase. Therefore, one would like to make the measurement at as low frequency as possible. However, for the dipole mode the presence of the drilling collar in the borehole interferes with the formation dipole wave at the low frequencies making it very difficult to extract formation shear information if at all possible. The quadrupole collar mode on the other hand is cut-off at low frequencies and interferes very little with the formation quadrupole wave. In summary quadrupole measurement is much better suited to shear logging in slow formations in LWD environment.. Schlumberger Public. Collar mode. 96.

(97) 4/23/2004. Seismic While Drilling Principle Surface System. sea floor. LWD Tool. 97 GR 4/23/2004. Schlumberger Public. seismic reflector. Surface source Downhole receivers Waveforms recorded in downhole memory Downhole processing Real-time check-shot via MWD telemetry Look-ahead imaging. Schlumberger Public. MWD telemetry. Source. 97.

(98) 4/23/2004. SeismicVision System Downhole Tool. Surface System. Schlumberger Public. Rugged LWD technology Multiple sensors (3 Geophones, 1 Hydrophone) Processor, memory, telemetry. Triangular cluster (450 in3) Bottled air supply Special control system. SPE71365. The SeismicMWD system has two main components, a downhole tool and a surface system.. Schlumberger Public. 98 GR 4/23/2004. The downhole tool was constructed of typical rugged LWD technology. It was configured with multiple sensors including geophones, hydrophones and accelerometers. In addition, it has a processor for downhole computations, memory for storing data and a telemetry system for transmitting data to the surface. The surface system for these tests included a triangular airgun cluster with a total volume of 450 cu in. A bottled air supply was used to reduce maintenance for the long “while-drilling” operation. A specially developed control system was used to activate the source in a manner that would be synchronized with the downhole recordings.. 98.

(99) 4/23/2004. Check shot data from Seismic While Drilling. Schlumberger Public. Wireline. First field test in Wyoming.. Schlumberger Public. 99 GR 4/23/2004. Traces in top section acquired while tripping down. Bottom trace acquired while drilling at connection time. Wireline VSP was run after the test. Very good match in che-ckshot times.. 99.

(100) 4/23/2004. Applications Real-time check-shot Put the bit on seismic map. . Update seismic velocities for PPP. . Optimize ECD boundaries and drilling parameters. . Update velocities for seismic reprocessing. Real-time salt proximity Seismic look-ahead, 500+ ft (2003) Replace intermediate wireline check-shot, save rigtime. Schlumberger Public. 100 GR 4/23/2004. Schlumberger Public. . 100.

(101) 4/23/2004. Example Exploration Well Plan 20”. Schlumberger Public. 16”. Normally pressured clastics. 13 3/8” 11 3/4”. Pressure ramp. 9 5/8”. 101 GR 4/23/2004. Now let’s imagine drilling an exploration well in a highly challenging environment with the SeismicMWD tool.. Schlumberger Public. Reservoir. The exploration basin is characterized by normally pressured clastics in the shallow section, then a section with a severe pressure ramp and highly over-pressured reservoirs. To reach a deeper reservoir, the well must be geosteered accurately through a step out section with an uncertain velocity profile. To meet all of the objectives, wells in this region normally require flawless planning, many casing strings and careful execution. The well plan calls for a 20-, 13 3/8- and 9 5/8-in casing sequence and contingent liners of 16 and 11 3/4-in. If needed, the contingent liners would require underreaming and add considerable extra cost. The key to success is to push the 20-in casing as deep as possible and to set the 13 3/8-in casing exactly at the top of the pressure ramp that is an obvious reflector on the surface seismic map but not easily recognizable as a lithology change.. 101.

(102) 4/23/2004. Drilling Office - Bit on Seismic. Surface Seismic in Depth. Schlumberger Public. Time-Depth Curve and Depth Prediction. Distance to Target. Schlumberger Public. 102 GR 4/23/2004. 102.

(103) 4/23/2004. Bit On Seismic. Schlumberger Public. Schlumberger Public. 103 GR 4/23/2004. 103.

(104) 4/23/2004. LWD-NMR. Schlumberger Public. This is a picture of the tool taken while testing at RMOTC (Rocky Mountain Oilfield Test Center) in June 1999 this is actually a picture of the first generation tool, but the second generation is essentially identical in the antenna region shown here. The only difference is in the new tool has a longer section of slick drill collar than the original tool. The tools currently being deployed are second generation tools.. Schlumberger Public. 104 GR 4/23/2004. Describe picture The spiral piece at the bottom is the field replaceable screw on stabilizer that is changed in the same way as a drilling motor stabilizer. Above this are antenna and wear bands. The rest of the tool is slick. Outline Presentation. Questions rules (encourage interruption?). 104.

(105) 4/23/2004. NMR While Drilling Tools available to measure T2 (or T1) in real time. . Measurement complicated compared to wireline by tool motion. Schlumberger Public. 105 GR 4/23/2004. Schlumberger Public. . 105.

(106) 4/23/2004. LWD-NMR Outputs. Schlumberger Public. Real Time Outputs – Lithology Independent Porosity – Bound Fluid Volume (BFV) / Free Fluid Volume (FFV) – T2LM (Log mean of T2) – Permeability – Hydrocarbon from Multi-Wait Time Porosities Additional Outputs from Recorded Mode – Raw Echoes – Full Data Re-Processing – Full T2 Spectra – Motion Data. LWD-NMR Outputs. Schlumberger Public. 106 GR 4/23/2004. The tool performs downhole a T2 inversion and computes outputs for transmission in real time. These real-time outputs could be used for GeoSteering, well placement, sidetrack decisions, etc…. Direct hydrocarbon identification using porosities from multiple polarization times (examples shown later) (see FAQ’s for description of hydrocarbon identification/characterization methods) Permeability is calculated uphole from the bound fluid free-fluid ratio using Coates-Timur equation or from the SDR equation if T2LM is transmitted, coefficients and exponents for these equations can be set by the user at the wellsite based on client desires. The tool records the raw echoes and this data can be used to reprocess the data in the IDEAL wellsite software. A more detailed (more components in T2 spectrum) can be computed from the raw data. In addition, the tool records full accelerometer and magnetometer data whose primary purpose is for QC of NMR data, but some interesting drilling engineering applications will also be shown. ------------------------------Note that the downhole memory of the tool is obviously not unlimited. No “maximum footage loggable” specification can be given as the tool records verses time. Currently the tool can record around 104 megabytes of memory. Note that the tool only records while circulating. Prior to the job during the planning stage the memory can be set up to record for longer periods of time by stackking the raw echoes. As NMR data is inherently statistical and when reprocessed the echoes are stacked anyway, there is no significant loss of information. In this way, the memory can be programmed to last as long as required. 106.

(107) 4/23/2004. Schlumberger Public. Resonant region. Measurement & Motion. Borehole Wall. Resonant Region. Experiment Region. The slide above shows the tool at first centered in the borehole at the beginning of the measurement cycle. An experiment region is established with the 90degree pulse, the 180 pulse should then be performed with a coincident resonant zone, i.e. the tool should not move. The diagram on the right shows how the resonant region stays at a fixed radius around the tool but the experiment zone is fixed in the formation. In other words the experiment is now in error due to movement.. Schlumberger Public. 107 GR 4/23/2004. This is clearly a very great challenge with the drilling environment, either the experiment has to be fast compared to the motion and or the tool should be stabilized to reduce motion. Also the slide demonstrates where the measurement is made. In a cylinder of a particular thickness around the tool. It is where the magnetic field and the frequency of the radio signal combine to produce a resonant effect in the hydrogen nuclei, this is how only hydrogen is measured in the experiment. And also that no signal is received from in front of or behind the resonant zone. In other words there is a well defined and constant measurement region from this tool unlike other nuclear or resistivity tools.. 107.

(108) 4/23/2004. Drilling Dynamics From Accelerometry 0.1 cm. Schlumberger Public. Bit Whirling & Hole Enlargement. 1.0 cm. The above are examples of the kinds of whirling motion it is possible to resolve using the tools capabilities.. Schlumberger Public. 108 GR 4/23/2004. Each graph shows the locus of lateral movement of the center of the tool, as it moves in the bore hole. The scale is in meters, top left shows millimeter size whirl, top right sub millimeter and bottom left shows centimeter range movement of about an inch that was constrained by the tool hitting the borehole wall. These motions are more or less damaging according to their shape and frequency of oscillation. The lower left hand one may be particularly damaging as the oscillations are much larger amplitude (6-7 cm) and the BHA is whirling around the outside of the borehole contributing to borehole enlargement and possibly damaging formation by compressing mud cake into the formation. ------------------------------------------------------------------------These were all recorded in one bit run in a shallow vertical hole with a rock bit at 500 ft/hr and 80-150 rpm parameters.. 108.

(109) 4/23/2004. Quality Control of Motion Effects. Schlumberger Public. Lateral motion leads to shortening of T2’s Effects Understood Accelerometers Æ lateral motion velocity QC from Accelerometry data. QC from NMR data. Accelerometry Data Æ Maximum Measurable T2. Accelerometer Package is for QC Purposes. Schlumberger Public. 109 GR 4/23/2004. The motion data can be used for quality control of the log in recorded mode or real-time by utilizing the lateral velocity of the tool, to compute the maximum T2 that can be resolved. This is an example drilling through a gas sand. From the accelerometry package we can calculate an average lateral velocity shown in track 1. This leads to the red line in the T2 track that shows the limit of the T2 that could be resolved under the motion conditions experienced by the tool while the measurements are made. You can see that the transition from shale to the shaley gas sand sees the appearance of a second T2 peak that is to the left of the T2 maximum line. A separation from the line of about a decade indicates that there is probably little or no motion shortening of the T2. Further down in the slightly better pay the T2 peak increases in time to the right but is still to the left of the line so is certainly not noise, but because it is a little closer to the line it will be somewhat shortened due to tool motion. NMR standalone QC is also being investigated by looking only at the NMR data and determining motion effects by looking at the NMR data itself.. 109.

(110) 4/23/2004. Formation Pressure While Drilling . . Draw Down Pump Pressure Gauge. Sealing Element System Volume. Schlumberger Public. . Measurement principle identical to wireline formation pressure measurements Rely on direct contact with the formation Drill string movement must be stopped A small area of the formation is sealed off, and the pressure & mobility is tested Dual packer type tools also exist Tool shown is not a Schlumberger tool. Schlumberger Public. 110 GR 4/23/2004. 110.

(111) 4/23/2004. GeoSteering -The full picture…. UDR Distance to boundary Schlumberger Public. Vision Res. Medium DOI. T. T. R. Base Balder. GVR or VDN Real-Time Image. Gas injectors shall be drilled near top reservoir. Top Heimdal. 111 GR 4/23/2004. Top Chalk. Schlumberger Public. Base Heimdal. Producers shall be drilled 9 m above OWC or near base reservoir. 111.

(112) 4/23/2004. Drilling Performance Sensors. Schlumberger Public. VISION has a variety of Drilling performance sensors. Schlumberger Public. 112 GR 4/23/2004. Downhole weight, torque and multi-axis vibrations are not available on VISION475. PERFORM is a service which provides a Specialist Engineer who uses the drilling performance sensors, surface indicators, offset well data, knowledge database and local knowledge to improve the drilling process to identify and reduce risk as well as improve overall ROP.. 112.

(113) 4/23/2004. Increase Drillstring and Bit Life BHA whirling in vertical hole. Multi axis shocks • Reduce drillstring fatigue • Reduce borehole enlargement • Increases ROP/bit life Schlumberger Public. Larger shocks result in more shock counts. All of Anadrill’s MWD and LWD tools are designed with downhole shock measurements.. Schlumberger Public. 113 GR 4/23/2004. In the MWD tools shock data is transmitted in real-time such that in the event of high shocks drilling parameters can be adjusted and the effects monitored. Real-time shocks can reduce non productive time, as trips can be saved by: • reducing pipe fatigue • failure of downhole components • increasing bit life. Multi axis shock measurements are also available (ie. Axial, lateral and torsional) With this information it is possible to determine the type of vibrations experienced (e.g. bit bounce, stick slip, resonance etc.) and thus take appropriate action The shock measurements are alsoused to track wear and tear on the tools and the level of maintenance required on a tool is based upon the severity of shocks experienced. It should be noted that although the MWD/LWD electronics are the most susceptible damage from shocks, failure of these components is not catastrophic. Where as the effect of high shocks on BHA connections can lead to catastrophic failures.. 113.

(114) 4/23/2004. Early Washout Detection BHA whirling in vertical hole. Schlumberger Public. Output Voltage vs. Flow Rate for 8-in. Turbine. The PowerPulse/Impulse MWD system uses a downhole turbine to generate power. The output voltage from this turbine is directly proportional to the flow rate passing through the tool and is thus a valuable downhole flow meter which is sensitive to very small changes in flow.. Schlumberger Public. 114 GR 4/23/2004. As the example shows, any washout above the MWD tool is easily seen from the turbine voltage, a lot earlier than it is seen at surface. Early identification can help reduce non productive time for expensive fishing trips. This can be set up as a smart alarm on the IDEAL system, thus requiring no continuous interpretation of the data by the engineer.. 114.

(115) 4/23/2004. Stuck Pipe Avoidance. Schlumberger Public. Weight on Bit. Torque. The PowerPulse tool can be configured to provide real-time measurements of downhole weight on bit and torque. These measurements are made based on strain gauges mounted in the MWD tool.. Schlumberger Public. 115 GR 4/23/2004. The gauges for the weight on bit are aligned so that they are only sensitive to the axial load (tension and compression on the drillstring). The torque gauges are aligned so that they are only sensitive to the torsional effects on the drillstring (I..e. not the axial forces) These measurements are particularly valuable in deviated wells where surface parameters of weight and torque can be unrepresentative of the true downhole conditions. By using the downhole measurements the performance of the bit can be optimized and premature damage of PDC bits avoided. By comparing both surface and downhole parameters a calculation of the friction in the wellbore can be made and the onset of pipe.sticking detected and action taken The example shows how the sliding friction (drag) is increasing, indicating the onset of a potential sticking problem. A wiper trip was made and the log shows the impact of the corrective action. In this case it was successful and drilling was resumed. Thus using these measurements NPT an be reduced by optimizing bit performance and avoiding stuck pipe. The calculated friction factors are also a valuable input into the planning of the next well.. 115.

(116) 4/23/2004. Accurate control of ECD Modeled vs. Actual ECD. Schlumberger Public. • Key for Deepwater drilling. Anadrill can provide real-time annular pressure measurements in each hole size. This measurement is used to calculate the true ECD (effective circulating density) while drilling to ensure that the ECD remains higher than the formation pore pressure, yet lower than the fracture gradient of the formation.. Schlumberger Public. • Detect shallow water flows • Detect cuttings loading and swab/surge effects • Manage the pore pressure fracture grad window 116 GR • Minimize mud weight for optimum ROP 4/23/2004. Right hand diagram: shows the theoretical ECD (black). Without downhole measurements this is the value used to define the mud weight required to drill the well. The red curve shows the actual ECD as measured by the downhole sensor and shows that there are major fluctuations, compared to the modeled value, as a result of changing flow rate and RPM. Other key factors that can effect the ECD are cuttings loading pipe eccentricity, swab surge effects and temp/pressure effects. It is clear therefore that in a well where there is a tight window between the formation pore pressure and the fracture gradient to rely on a modeled ECD value is dangerous and that real-time monitoring is crucial. This is particularly true in the case of deepwater drilling where there can be a very narrow window. The ECD can also be calculated there is no circulation for accurate leak off/formation integrity test measurements and to monitor swab/surge effects The APWD measurement has also proven to be a valuable tool for the early detection of shallow water flows (a sharp increase is seen) All annular pressure measurement can also be stored in the tools downhole memory. 116.

(117) 4/23/2004. Staying within the Pressure Window Staying within the pressure window. ISONIC example. Schlumberger Public. Left hand diagram: shows a real-time plot of the real-time ECD measurement plotted against the theoretical fracture gradient and a realtime calculation of pore pressure based on LWD resistivity. The pore pressure calculation is compared to the seismic pore pressure calculation that was made prior to drilling the well.. Schlumberger Public. 117 GR 4/23/2004. Accurate monitoring of both the pore pressure and ECD are key. This is particularly the case in deepwater wells were the window between fracture gradient and pore pressure can be very narrow. Right hand diagram:shows an example of how LWD sonic data can also be used for real-time pore pressure evaluation. The normal compaction trend of the formation would result in a gradual decrease in sonic transit time. However, in overpressured formations we see that the formation becomes less compacted and the sonic transit time diverges from its normal trend and increases as a function of over pressure.. 117.

(118) 4/23/2004. Identification of Failure Modes Shear Failure Mud Weight too Low Schlumberger Public. Tensile Failure Mud Weight too High. Stress Direction. LWD images can be acquired from both the GVR (GeoVISION Resistivity) and ADN (vision density).. Schlumberger Public. 118 GR 4/23/2004. As well as clearly showing the interbedding of the formations and the dip of the beds, these images can be used to define fractures. Both the direction of the fractures and the failure mode can be determined. When combined with Real time images, this will be very valuable in refining or confirming wellbore stability models and drilling practices. But in the above example, the explanation shows that the mud weight is too high AND too low. How can this be--which is it?. 118.

(119) 4/23/2004. Conclusion. – is there a need for RT data?. Schlumberger Public. MWD/ LWD has developed quickly compared to wireline technology The technique is widely used in deviated wells and where rig rates are high In vertical wells and low rig day rates wireline is more economical Almost all OH wireline measurements can be performed with LWD – fluid sampling and high definition images are the significant measurements not yet available. 119 GR 4/23/2004. Schlumberger Public. DEPTH control is the biggest single quality factor that affects LWD measurements. 119.

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