Geosteering Resistivity Tool

Transcription

1 L o g g i n g t o o l s f o r o i l e x p l o r a t i o n Geosteering Resistivity Tool 4-3/4 inch 6-1/2 inch Page 1 of 6

2 Enhanced Resistivity Measurement Most MWD Resistivity tools are of the Wave Propagation type, and can accurately measure the average rock-formation resistivity. However, this type of tool may be difficult to use in horizontal drilling because it requires complex interpretation of phase and attenuation logs to see an adjacent bed-boundary. It is easy to mistake curve separations due to other effects such as anisotropy or invasion, resulting in drilling through a bedboundary, and then having to backtrack. CBG Corporation has invented and patented (US patent #6,064,210, Canada Patent #2,321,984, China Patent ZL , and UK patent 2,353,596), a method for measuring resistivity as a vector quantity. For example, up to one meter before mistakenly drilling out of a reservoir, advance indication of the distance and direction to a nearby shale bed is available so that corrective action can be taken. The addition of directional information to the resistivity reading provides a new enabling technology for geosteering, at a price that is affordable for directional-drilling companies. Modeled GRT current density The GRT is an advanced imaging laterolog device, incorporating four independent receiving electrodes to create an azimuthally-sensitive resistivity measurement. This capability allows the GRT to detect a nearby bed, determine whether it is conductive or resistive, and ascertain its direction and distance. In the diagram at top right (from a computer model), the electric current density is higher in the upper conductive rock region (e.g. a shale), so the upper electrode receives a bigger current. Unlike competing tools, it is not necessary to rotate the GRT to obtain directionally-sensitive resistivity measurements. Directional resistivity data from the GRT can be graphically presented on a surface display (US patent #7,657,377) in an enhanced version of the familiar compass rose drillers display typically employed in directional drilling. A continuously-updated borehole image showing the distance and direction to conductive/resistive anomalies enables the operator to intelligently direct the drilling process, without having to study resistivity logs. Sample resistivity display on compass rose Page 2 of 6

3 Advanced Cost-Effective Design State-of-the-art techniques were applied in creating the GRT. For example, FEMLAB 3D Finite-Element-Analysis modeling was used to optimize mechanical and electrical parameters. A graph (at right) from the model of the GRT illustrates how the ratio of current received by a pair of electrodes can be used to distinguish a parallel conductive bed from a resistive bed, and determine the distance to the boundary. Benefiting from its innovative electronic and mechanical design, the GRT provides accurate and reliable operation, combined with low cost and serviceability. Sophisticated self-calibrating measurement circuitry ensures that stability and precision are maintained across the full range of operating conditions. Should it be necessary to service or repair the GRT, its rugged, probe-based construction makes disassembly and reassembly quick and easy. The GRT does not employ any third-party proprietary technology so there are no licensing fees required. CBG also supplies a Windows TM based software package for downloading memory data, merging it with a depth log from the drilling rig EDR, and producing wireline-quality Resistivity/Gamma logs as shown in this example. GRT receiver electrodes Page 3 of 6

4 Logging While Drilling Of course, in addition to its application in directional drilling, the GRT performs exceptionally as a conventional LWD resistivity tool. In the graph at right, the 4.75 inch diameter tool is shown capable of very accurate measurements in a 6.5 inch diameter hole whatever the mud resistivity. Even in severe washouts up to 12 inches in diameter, the tool retains acceptable accuracy. A complete log is saved in the GRT internal memory and can be subsequently downloaded through a high-speed link to a PC when the GRT is retrieved from the well. It is not necessary to remove the tool from the BHA to download data. Furthermore, the GRT can include an internal Gamma-Ray tool (standard or directional), providing directional capability that is unique in the industry. The GRT can be provided as a stand-alone tool, or part of a complete LWD resistivity system, including a surface display, display software, and data communications/control electronics. A mud Pulser can be mounted above or below due to the Pulse, Flow, Power and Ground bus-wires passing through the tool. The GRT is available compatible with Tensor-type systems, and can be readily integrated into other industry-standard tool strings. A built-in Muleshoe helix at the top end of the tool ensures that the Directional Sensor package is always correctly oriented with the GRT sensors. Since the GRT is a laterolog-type tool, it will not give accurate results in oil-based muds if there is a significant amount of emulsion breakdown. However, in high resistivity formations operation at reduced accuracy is still possible. GRT Maximum Detection Distance measurement accuracy +/- 2.5% Laterolog tools excel in very high-resistivity formations, where it may be necessary to distinguish between oil and fresh water. An example is the heavy-oil Orinoco Basin of Venezuela, where the wave-propagation tools have been found unusable. Another example is in fresh-water injection well situations, such as in Saudi Arabia. Wave-propagation tools are not accurate in resistivities above about 200 ohm.meters. The GRT has another advantage over other directional types of resistivity tools. As the graph (at right) indicates, the detection distance for an adjacent contrasting rock formation is dependant only on resistivity contrast, and not on the actual resistivities. Detection distance is constant for a wide range of resistivities, particularly for the most important high values typical of oil reservoirs. Page 4 of 6

5 GRT Verifier Product Description The Verifier is a dual purpose accessory for CBG s Geosteering Resistivity Tool. It can be used to test the GRT over its full measurement range and confirm that it is operating properly. It is also capable of downloading the entire resistivity log from the internal memory of the GRT, and can subsequently transfer the log to a PC for analysis. Since the GRT electrodes are utilized for data communications, the log dump does not require timeconsuming disassembly of the tool. A 3-hour log can be transferred from the GRT to the Verifier in roughly one minute, and over 400 hours of log data can be stored. The Verifier is battery-operated and completely portable, and is housed in a rugged weather-resistant enclosure for use in the field. The Verifier has a simple menu-based user interface with an LCD display and 3-button keypad. It is quickly and easily attached to and removed from the GRT without the use of special tools or hardware. Verifier specifications: Battery Complement = six rechargeable cells Operating Time = 6 hours Recharge Time = 1 hour Comm. link to GRT = proprietary serial interface Comm. link to PC = RS232 serial link and USB link Typical Bottom-Hole-Assembly Page 5 of 6

6 GRT Specifications Operational Specifications Types of Measurement Average Resistivity Range/Accuracy Full-scale Resistivity Range Mud Resistivity Range Thin-Bed Resolution LWD Average Resistivity Log (ResB), and Real-time Resistivity Vector: Magnitude (ResV) + Angle relative to toolface (ResA) + Angle relative to gravity (ResC), and Gamma-ray or Focused Gamma ,000 Ω-m., ±10% (worst-case), ±1.5% (if borehole is on-gauge) ,000 Ω-m Ω-m., (not recommended for oil-based muds) 17 cm / 6.75 inches Maximum Operating Temperature 160 C / 320 F Maximum Pressure Detection Distance for Parallel Rock Formation Boundary Depth of Investigation (Invasion Tolerance) Internal Memory Mechanical Specifications for 4-3/4 inch version Tool Makeup Length Nominal Outside Diameter Wear-Band Diameter Tool Connections Recommended Maximum Makeup Torque Maximum Mud Flow Volume Maximum Dogleg Severity Electrical Connections Toolface / Directional Package Orientation Mechanical Specifications for 6-1/2 inch version Tool Makeup Length Nominal Outside Diameter Wear-Band Diameter Tool Connections Recommended Maximum Makeup Torque Maximum Mud Flow Volume Maximum Dogleg Severity Electrical Connections Toolface / Directional Package Orientation Measurement-Point position from Lower Shoulder Resistivity Gamma-ray Power Requirements Power Source Battery Life Read-time Output Data Serial ASCII format 1400 bar / 20,000 PSI > 1 meter (40 inches) with >10:1 resistivity contrast 0.64 meter (25 inches) 50% point on PGF curve 400 hour (16.7 day) log including all raw and processed resistivity, gamma, inclinometer, temperature, 3-axis shock level, internal and diagnostic data when data are recorded every 4 seconds. The acquisition rate is programmable from 1 60 seconds. Memory is downloaded through a high-speed port meters (11.34 feet) 121 mm. (4.75 inches) Standard Replaceable hard-faced size: 146 mm. (5.75 inches), or for holes drilled with 6 inch drill-bits: 133 mm. (5.25 inches) available or a slick version with hard-facing directly on the collar 133 mm. (5.25 inches) A.P.I. 3.5 inch IF, box upper/pin lower 13,560 N.m (10,000 lbf.ft.) 1.3 cu.meters/minute ( m./sec. (50 ft./sec.) velocity Rotating 15 /30 m. (100 ft.), Sliding 20 /30 m. (100 ft.) 6-pin CBG Radial male upper, Rotary female lower Muleshoe Helix built into upper box connection 3.52 meters (11.54 feet) 165 mm. (6.5 inches) Standard Replaceable hard-faced size: 190 mm. (7.5 inches), or for holes drilled with 7-7/8 inch drill-bits: 178 mm. (7.00 inches) available or a slick version with hard-facing directly on the collar 178 mm. (7.00 inches) A.P.I. 4.5 inch IF, box upper/pin lower 29,830 N.m (22,000 lbf.ft.) 3.3 cu.meters/minute ( m./sec. (50 ft./sec.) velocity Rotating 10 /30 m. (100 ft.), Sliding 15 /30 m. (100 ft.) 6-pin CBG Radial male upper, Rotary female lower Muleshoe Helix built into upper box connection meters (28.16 inches) 1.54 meters (60.62 inches) External Lithium Battery Pack (14.4V to 28.8V nominal) 200 hours with one 28.8 volt Battery Pack (50% duty cycle) +5V., 9600 Baud The specifications published on our website are the most complete due to our policy of continuous product improvement West Howard Lane Suite 900 Austin, Texas Tel: Fax: v w w w. c b g c o r p. c o m Page 6 of 6