Measurement-while-drilling devices with pad mounted sensors

Details Measurement-while-drilling devices with pad mounted sensors Measurement-while-drilling devices with pad mounted sensors

1998-12-18

2001-01-16

Pezzuto, Robert E. (Department: 3671)

Boring or penetrating the earth

With signaling, indicating, testing or measuring

Tool position direction or inclination measuring or...

C175S024000, C175S076000

Reexamination Certificate

active

06173793

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the acquisition and processing of data acquired by a measurement-while-drilling (MWD) tool during the drilling of a wellbore. More particularly, the invention relates to methods and devices for acquiring data downhole using sensors in contact with the borehole wall, processing the data and transmitting to the surface, in real-time, parameters of the formation penetrated by the borehole as the borehole is being drilled using MWD telemetry.
BACKGROUND OF THE INVENTION
Modern well drilling techniques, particularly those concerned with the drilling of oil and gas wells, involve the use of several different measurement and telemetry systems to provide petrophysical data and data regarding drilling mechanics during the drilling process. Data is acquired by sensors located in the drill string near the bit and either stored in downhole memory or transmitted to the surface using MWD telemetry devices. Prior art discloses the use of a downhole device incorporating resistivity, gravity and magnetic measurements on a rotating drillstring. A downhole processor uses the gravity and magnetic data to determine the orientation of the drill string and, using measurements from the resistivity device, makes measurements of formation resistivity at time intervals selected to give measurements spaced around the borehole. These data are compressed and transmitted uphole by a mud pulse telemetry system. The depth of the resistivity sensor is computed at the surface and the data are decompressed to give a resistivity image of the face of the borehole wall with an azimuthal resolution of 30°.
Prior art methods are limited to making resistivity measurements in the subsurface and fail to address the issue of other useful measurements that could be made using an MWD device. Prior art devices are also limited to measurement devices that rotate with the drill string and do not take advantage of current drilling methods wherein a mud motor is used and the drill bit could be rotating at a different speed from the drill string or wherein a non-rotating sleeve may be available on which substantially non-rotating measuring devices could be located. The rate at which measurements are made is selected to be constrained by the data transmission rate of the telemetry system. Prior art systems thus fail to take advantage of the inherently higher capability of measuring devices and the ability to use redundant data to improve the signal-to-noise (S/N) ratio. Prior art also relies on an uphole determination of the depth of the tool, whereas if the determination of the depth of the tool were made downhole intelligent decisions could be made about the amount of data to transmit uphole. The present invention overcomes these inadequacies.
SUMMARY OF THE INVENTION
The present invention is an apparatus and method of making measurements of a plurality of parameters of interest of the formation surrounding a borehole. In one aspect of the invention, the drill bit is mounted on a rotating drillstring and the downhole assembly is provided with sensors that rotate with the drillstring to make measurements of the parameters of interest. The assembly is provided with magnetic and inertial sensors to provide information on the orientation of the measurement sensors. A telemetry system sends information downhole about the depth of the drilling assembly. A processor downhole combines the depth and azimuth information with the measurements made by the rotating sensors, uses redundancy in the data to improve S/N ratio, compresses the data and sends it uphole by a telemetry system or stores it downhole for later retrieval.
In another aspect of the invention, the drill bit is driven by a downhole drilling motor. The motor may be on a rotating drillstring or on coiled tubing. The sensors for measuring the parameters of interest could be rotating with the drill bit. Alternatively, the sensors could have one of several configurations. In one configuration, the sensors are mounted on a substantially non-rotating sleeve; in another configuration, the sensors are mounted on pads that could be rotating or non-rotating, the pads being hydraulically or mechanically actuated to make contact with the borehole wall; in yet another configuration, the sensors are mounted on substantially non-rotating rib-steering devices used to control the direction of the downhole drilling tool. In any of these arrangements, the downhole assembly is provided with sensors that make measurements of the parameters of interest. The assembly is provided with magnetic and inertial sensors to provide information on the orientation of the measurement sensors. A telemetry system sends information downhole about the depth of the drilling assembly. A microprocessor downhole combines the depth and azimuth information with the measurements made by the rotating sensors, uses redundancy in the data to improve S/N ratio, compresses the data and sends it uphole by a telemetry system. The parameters of interest include resistivity, density, compressional and shear wave velocity and structure, dipmeter, acoustic porosity, NMR properties and seismic images of the formation.
As a backup to, or independently of, obtaining the depth information by downhole telemetry, the present invention also provides a capability in the downhole microprocessor to use measurements from sensors at more than one depth to provide a rate of penetration.


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