Patent Application
20100154531
The present invention relates generally to a downhole tool for making standoff and caliper measurements. More particularly, exemplary embodiments of the invention relate to a downhole tool having at least one angled ultrasonic transducer. Another exemplary embodiment of the invention relates to a standoff sensor including at least first, second, and third transducer elements.
Logging while drilling (LWD) techniques are well-known in the downhole drilling industry and are commonly used to measure various formation properties during drilling. Such LWD techniques include, for example, natural gamma ray, spectral density, neutron density, inductive and galvanic resistivity, acoustic velocity, and the like. Many such LWD techniques require that the standoff distance between the various logging sensors in the drill string and the borehole wall be known with a reasonable degree of accuracy. For example, LWD nuclear/neutron measurements utilize the standoff distance in the count rate weighting to correct formation density and porosity data. Moreover, the shape of the borehole (in addition to the standoff distances) is known to influence logging measurements.
Ultrasonic standoff measurements and/or ultrasonic caliper logging measurements are commonly utilized during drilling to determine standoff distance and therefore constitute an important downhole measurement. Ultrasonic caliper logging measurements are also commonly used to measure borehole size, shape, and the position of the drill string within the borehole. Conventionally, ultrasonic standoff and/or caliper measurements typically include transmitting an ultrasonic pulse into the drilling fluid and receiving the portion of the ultrasonic energy that is reflected back to the receiver from the drilling fluid borehole wall interface. The standoff distance is then typically determined from the ultrasonic velocity of the drilling fluid and the time delay between transmission and reception of the ultrasonic energy.
Caliper logging measurements are typically made with a plurality of ultrasonic sensors (typically two or three). Various sensor arrangements are known in the art. For example, caliper LWD tools employing three sensors spaced equi-angularly about a circumference of the drill collar are commonly utilized. Caliper LWD tools employing only two sensors are also known. For example, in one two-sensor caliper logging tool, the sensors are deployed on opposite sides of the drill collar (i.e., they are diametrically opposed). In another two-sensor caliper logging tool, the sensors are axially spaced, but deployed at the same tool face.
The above described prior art caliper LWD tools commonly employ either pulse echo ultrasonic sensors or pitch-catch ultrasonic sensors. A pulse echo ultrasonic sensor emits (transmits) ultrasonic waves and receives the reflected signal using the same transducer element. Pulse echo sensors are typically less complex and therefore less expensive to utilize. Pitch catch sensors typically include two transducer elements; the first of which is used as a transmitter (i.e., to transmit ultrasonic waves) and the other of which is utilized as a receiver (i.e., to receive the reflected ultrasonic signal). Pitch catch ultrasonic sensors are known to advantageously reduce, or even eliminate, transducer ringing effects, by substantially electromechanically isolating the transmitter and receiver transducer elements. They therefore tend to exhibit an improved signal to noise ratio (as compared to pulse echo sensors).
The above described caliper logging tools generally work well (providing both accurate and reliable standoff determination) when the drill string is centered (or nearly centered) in a circular borehole. In such instances the transmitted wave is essentially normal to the borehole wall, which tends to maximize the reflection efficiency at the receiver. In many drilling operations (e.g., in horizontal or highly inclined wells) the drill string can be eccentered in the borehole. Moreover, in certain formation types the borehole may have an irregular (e.g., elliptical or oval) shape. In these operations the transmitted ultrasonic waves are sometimes incident on the borehole wall at a non-normal (oblique) angle, which can result in reduced ultrasonic energy at the receiver. In some cases there may be blind spots at which the reflected waves are undetected by the sensor. In such cases, a portion of the borehole wall is invisible to the standoff sensor. Since standoff measurements are essential to interpreting certain other LWD data, these blind spots can have significant negative consequences (e.g., especially in pay zone steering operations).
Therefore, there exists a need for an improved caliper LWD tool and/or a caliper tool utilizing improved standoff sensors, particularly for use in deviated (e.g., horizontal) well bores in which the drill string is commonly eccentered (e.g., on bottom). Such a tool and/or sensors may advantageously improve the reliability of caliper LWD measurements.
The present invention addresses one or more of the above-described drawbacks of prior art standoff measurement techniques and prior art drilling fluid ultrasonic velocity estimation techniques. One aspect of this invention includes a downhole measurement tool having at least one angled ultrasonic standoff sensors. Another aspect of the present invention includes a downhole standoff sensor having at least three circumferentially spaced piezoelectric transducer elements. At least a first element is configured for use in pulse echo mode and therefore both transmits and receives ultrasonic energy. At least second and third elements are configured to receive ultrasonic energy transmitted by the first element in pitch catch mode. An electronic controller is configured to determine a standoff distance from the ultrasonic waveforms received at the at least first, second, and third piezoelectric transducer elements. The controller may further be configured to estimate the eccentricity of a measurement tool in the borehole, for example, from a difference or ratio between the ultrasonic energy received at the second and third transducer elements.
Exemplary embodiments of the present invention advantageously provide several technical advantages. For example, exemplary embodiments of the invention may improve borehole coverage and data quality and reliability in LWD caliper logging. In particular, the invention may advantageously reduce or even eliminate the blind spots when logging eccentric bore holes. Since standoff measurements are critical to certain LWD data interpretation, the invention may further improve the quality and reliability of such LWD data.
In one aspect the present invention includes a downhole logging while drilling tool. The logging while drilling tool includes a substantially cylindrical tool body having a longitudinal axis and is configured to be connected with a drill string. At least one standoff sensor is deployed in the tool body. The standoff sensor is configured to both transmit ultrasonic energy into a borehole and receive reflected ultrasonic energy. The standoff sensor has a sensor axis which defines a direction of optimum signal transmission and reception. The sensor axis is orthogonal to the longitudinal axis of the tool body and is further oriented at a non-zero angle relative to a radial direction in the tool body. The logging while drilling tool further includes a controller including instructions for determining a standoff distance from the reflected ultrasonic energy received at the at least one standoff sensor.
In another aspect, this invention includes a downhole logging while drilling tool. The logging while drilling tool includes a substantially cylindrical tool body having a longitudinal axis and is configured to be connected with a drill string. The tool further includes at least first, second, and third circumferentially spaced piezoelectric transducer elements. At least a first of the transducer elements is configured to both transmit ultrasonic energy into a borehole and receive reflected ultrasonic energy. At least a second and a third of the transducer elements are configured to receive the reflected ultrasonic energy transmitted by the first transducer element. The logging while drilling tool further includes a controller having instructions for determining a single standoff distance from the reflected ultrasonic energy received at the first, second, and third transducer elements.
In still another aspect, this invention includes a method for estimating downhole an eccentricity of a logging drilling tool. The method includes deploying a downhole tool in a subterranean borehole, the tool including an ultrasonic standoff sensor having at least three circumferentially spaced piezoelectric transducer elements, at least a first of the transducer elements being configured to both transmit ultrasonic energy into a borehole and receive reflected ultrasonic energy, at least a second and a third of the transducer elements being configured to receive the reflected ultrasonic energy originally transmitted by the first transducer element. The method further includes causing the first transducer element to transmit ultrasonic energy into the borehole, causing at least the second and the third transducer elements to receive the ultrasonic energy transmitted by the first transducer element, and processing the received ultrasonic energy to estimate a degree of eccentricity of the downhole tool in the borehole.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Referring first to
It will be understood by those of ordinary skill in the art that the measurement tool 100 of the present invention is not limited to use with a semisubmersible platform 12 as illustrated in
Referring now to
With continued reference to
Although not shown on
A suitable controller typically further includes a digital programmable processor such as a microprocessor or a microcontroller and processor-readable or computer-readable programming code embodying logic, including instructions for controlling the function of the tool. Substantially any suitable digital processor (or processors) may be utilized, for example, including an ADSP-2191M microprocessor, available from Analog Devices, Inc. The controller may be disposed, for example, to calculate a standoff distance between the sensor and a borehole wall based on the ultrasonic sensor measurements. A suitable controller may therefore include instructions for determining arrival times and amplitudes of various received waveform components and for solving various algorithms known to those of ordinary skill in the art.
A suitable controller may also optionally include other controllable components, such as sensors, data storage devices, power supplies, timers, and the like. The controller may also be disposed to be in electronic communication with various sensors and/or probes for monitoring physical parameters of the borehole, such as a gamma ray sensor, a depth detection sensor, or an accelerometer, gyro or magnetometer to detect azimuth and inclination. The controller may also optionally communicate with other instruments in the drill string, such as telemetry systems that communicate with the surface. The controller may further optionally include volatile or non-volatile memory or a data storage device. The artisan of ordinary skill will readily recognize that the controller may be disposed elsewhere in the drill string (e.g., in another LWD tool or sub).
As also shown on
With reference now to
With reference now to
In the exemplary embodiment 200 shown on
In the exemplary embodiment 200′ shown on
It will be appreciated that downhole tools 200 and 200′ are not limited to embodiments including three transmitter and receiver elements. Alternative embodiments may include, for example, four, five, six, or even seven transmitter and/or receiver elements.
With reference now to
Piezoelectric transducer elements 322, 324, and 326 are mounted in a sensor housing 330, which is further mounted in the tool body 310. Piezoelectric transducer element 322 is preferably normally mounted (as described above with respect to sensor 52 in
It will be appreciated that the invention is not limited to sensor embodiments having three transducer (transmitter and receiver) elements. Additional transducer elements may be utilized. For example, alternative sensor embodiments may include four, five, six, and even seven transducer elements. The invention is not limited in this regard, so long as the sensor includes at least three transducer elements. The invention is also not limited to embodiments having a central transducer element (e.g., element 322) and outer receiver elements (e.g., elements 324 and 326). Nor is the invention limited to embodiments in which only a single element transmits ultrasonic energy.
With continued reference to
Measurement tool 300 further includes a controller configured to calculate a standoff distance from the reflected waveforms received at transducer elements 322, 324, and 326. The controller may be further configured to estimate tool eccentricity in the borehole from the reflected waveforms received at transducer elements 322, 324, and 326. When the tool is centered in the borehole, the reflected ultrasonic energy tends to be approximately symmetric about the transducer element 322 such that elements 324 and 326 received approximately the same ultrasonic energy. When the tool is eccentered in the borehole, the reflected ultrasonic energy is asymmetric about transducer element 322 such that one of the elements 324 and 326 receives more energy than the other. In such a scenario, the degree of eccentricity may be estimated based on the difference (or the normalized difference or the ratio) of the ultrasonic energy received at elements 324 and 326. In general, an increasing difference or ratio (indicating a more asymmetric reflected signal) indicates a greater eccentricity. By combining such measurements with a conventional tool face measurement, the direction of the eccentricity may also be estimated.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alternations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
