Logging-While-Coring Resistivity-at-the-Bit* System


lwc_rab_coringThe Logging-While-Coring (LWC-RAB) system, developed jointly by USIO/LDEO, Schlumberger Drilling and Measurements, and USIO/TAMU, took advantage of existing logging, drilling and coring technologies and synthesized them into a powerful new exploration system. Recent improvements in battery technology enabled the reformatting of the electronics in an 8-inch Schlumberger Resistivity-at-the-Bit (RAB) tool. By placing smaller batteries in the drill collar wall, an existing ODP core barrel can pass through the RAB to carry out coring operations while making simultaneous azimuthal geophysical measurements. The coring tool technology consists of the Motor Driven Core Barrel (MDCB) system developed by USIO/TAMU, which needed only minor modifications and the fabrication of crossovers and drilling subs. The assembled system was tested at the Genesis test facility in Sugarland, Texas, and successfully deployed for the first time during ODP Leg 204.


• Core-log data integration capability
• Assessment of borehole breakout for local and regional stress analyses
• Detection of formation heterogeneity using azimuthal resistivity images
• Lithology characterization

Log Presentation

Resistivity image and average resistivity data from the LWC-RAB plotted with physical properties data from cores.lwc_RAB

Tool Specifications

Temperature rating: 300° F (149° C)
Pressure rating: 18 kpsi (124 MPa)
Length: 13 ft (4 m)
Weight: 2,400 lbs (1,090 kg)
API nominal collar outside diameter: 8.25 in (21 cm)
Maximum outside diameter: 9 to 12.25 in (23 to 31 cm)
Minimum bit size: 9.75 in (25 cm)
Maximum bit size: 12.25 in (31 cm)
Flow range: 0-1,200 gpm
Maximum curvature – sliding: 13 deg/100 ft (13 deg/31 m)
Maximum rotary torque: 23,000 ft-lbf (7,010 m-lbf)
Minimum operating RPM: 30 rpm
Uphole connection: 6-5/8 Reg box
Downhole connection: 6-5/8 Reg box

Measurement Specifications 

Gamma Ray
    Range: 0-250 GAPI
    Accuracy: 7%
    Vertical resolution: 6 in (15.24 cm)
Azimuthal resistivity
    Range: 0.2-20,000 ohm-m
    Accuracy: 5% (0.2-200 ohm-m); 20% (200-2,000 ohm-m) n/a (>2,000 ohm-m)
    Vertical resolution: 2-3 in (5.08-7.62 cm)
Ring resistivity
    Range: 0.2-20,000 ohm-m
    Accuracy: 5% (0.2-2,000 ohm-m); 20% (>2,000 ohm-m)
    Vertical resolution: 2-3 in (5.08-7.62 cm)
Bit resistivity 
    Range: 0.2-20,000 ohm-m
    Accuracy: 5% (0.2-2,000 ohm-m); 20% (>2,000 ohm-m)
    Vertical resolution: 12-24 in (30.5-61 cm)

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