Optical fluidic methods for a rheometer

Systems and methods of the disclosed embodiments include a rheometer having a housing with a fluid inlet and a fluid outlet, a cylinder with a cavity located to receive fluid that passes into the fluid inlet, a motor configured to rotate the cylinder, a torsion bob within the cavity, and a controller located remotely from the rheometer. The controller includes a pressure regulator configured to pressurize fluid to power the motor, a rotation sensor configured to receive an optical rotation signal indicating a rotation speed of the cylinder, and a torque sensor configured to receive an optical signal indicating a torque on the torsion bob. The controller may be configured to receive a rotation speed signal from the rotation sensor, a torque signal from the torque sensor, and to calculate a shear stress for the fluid based on the rotation speed signal and the torque signal.

BACKGROUND

Rheometers typically require electrical connections to send and receive signals. For example, a rheometer may make a rheological measurement which is then sent to a database or processor for further interpretation of the data points. Furthermore, rheometers typically require electrical connections to drive mechanical components such as a fluid pump or valve to keep a testing fluid flowing, or to perform the tests on the fluid. Such electrical connections, however, can cause problems in certain locations.

For example, certain atmospheres may develop concentrations of dusts or vapors that can be volatile or detrimental to operation of devices. Governmental bodies have criteria for classifying such locations as “hazardous locations.” The criteria may include locations where: ignitable concentrations of flammable gases or vapors may exist under normal operating conditions; ignitable concentrations of such gases or vapors may exist frequently because of repair or maintenance operations or because of leakage; or breakdown or faulty operation of equipment or processes might release ignitable concentrations of flammable gases or vapors, and might also cause simultaneous failure of electric equipment. Hazardous locations such as these might exist in oil and gas production, aircraft hangars, gasoline stations, paint-finishing locations, or grain bins.

Equipment used in hazardous locations is subject to enhanced requirements such as special wiring and protective electrical components. These restrictions can make it difficult to obtain rheological information from fluids in particular locations.

DETAILED DESCRIPTION

Due to the restrictions placed on electrical connections and devices operating in controlled locations (e.g., governmentally classified hazardous locations), rheological information can be difficult to obtain from fluids located in controlled locations. The embodiments described below include rheometers that do not use electrical connections. Rather, the rheometers use optical signals and air pressure originating from a safe location to communicate with and drive mechanical components in the controlled location. The optical signals may communicate through fiber optics, and the air pressure may drive rotating motors for testing a fluid within the rheometer.

FIG.1is a schematic view of an embodiment of a system100for monitoring rheological properties of a fluid102. The fluid102flows through a flow control104(e.g., pipeline, hose, pipe, etc.), at least part of which is located in a controlled location106(e.g., a rig site, mud pit, mud pit room). The controlled location106may be governmentally classified as a hazardous location, and thus subject to enhanced restrictions for devices used inside. In certain embodiments, any accessible portion of the flow control104is located entirely in the controlled location106. For example, the fluid102may include drilling mud being used in an oil production wellbore (during or after drilling) such that the flow control104is located inaccessibly downhole, or near production fluid in a controlled location106. Real time measurements of the rheological properties of the fluid102are nevertheless very useful, and thus it is beneficial to have rheological measurement within the controlled location106.

To perform the rheological measurements, the controlled location106includes a rheometer110that tests the fluid102. The rheometer110may be installed in-line with the flow control104, and additionally or alternatively may be located in a diverted portion of the flow control104. The rheometer110does not include electrical connections, but rather includes power and communication from lines112. The rheometer110may receive any number of lines112, and the system100ofFIG.1includes three lines112. A fluid line114; a rotation monitoring fiber116; a torque monitoring fiber118.

The lines112extend a distance120away from the controlled location106. The distance120may be several hundred feet (100 meters) to a safe area130that has a controller132. In alternative or additional embodiments, the safe area130is located within an insulated or explosion-proof box proximate the controlled location106. In these embodiments the distance120is short, for example a few feet (1-2 meters). The rheometer110is typically not included in the explosion-proof box that has a flash arrester because governmental regulations often will not permit drilling fluids with suspended weighting material to move into and out of an explosion proof box.

The safe area130does not have restrictions and thus any device with an electrical connection is located within the safe area130. A controller132, for example, is located within the safe area130and includes any processors, memory, computer storage, or other components with electrical processing capabilities for recording and controlling the mechanical components within the controlled location106.

FIG.2is a cross-sectional schematic view of an embodiment of a rheology measurement system200having a rheometer210for use within a hazardous location (e.g., controlled location106). The rheometer210tests a fluid202that may be flowing, for example during a drilling operation. The fluid202may include drilling mud, water, oil or other hydrocarbon production fluids, or other liquids or gases. The fluid202enters a housing240having a fluid inlet242and a fluid outlet244. In various circumstances of the operation of the rheometer210, the fluid202may continuously flow through the housing240, or may intermittently stop flowing while the rheological tests are conducted.

To conduct the rheological tests, the system200rotates a cylinder246that has an opening248at the top of a cavity250. One of ordinary skill in the art will know that the cylinder246may include other geometries such as cone and plate, parallel plate, and vane without leaving the spirit of the embodiments disclosed herein. As the fluid202flows into the housing240from the fluid inlet242, it fills the cavity250. The cavity250also contains a torsion bob252that is surrounded by the fluid202when the cavity250is filled. The rotation of the cylinder246imparts a force into the fluid202that is between the cylinder246and the torsion bob252. The fluid202in turn imparts a force onto the torsion bob252. Furthermore, in certain embodiments the cylinder246remains stationary while the torsion bob252is rotated. The rheological properties of the fluid determine the amount of the force that is imparted on the torsion bob252. This force is measured as a torque on a detecting element260that is attached to the housing240and the torsion bob252. The detecting element260communicates any detected torque to a controller232through a monitoring fiber218. Additionally or alternatively, the detecting element260includes an optical temperature sensor that communicates a temperature of the fluid202within the housing240optically through the monitoring fiber218. The monitoring fiber218utilizes, for example, a fiber optic cable, an optical encoder, a fiber grating (e.g., Bragg grating), or multiple fiber optic cables, optical encoders, and fiber gratings containing optical fibers within a protective coating.

A controller232controls the operation of the rheometer210by sending and receiving non-electrical signals to and from the rheometer210. The controller232is connected to the rheometer210through a fluid line214, a rotation monitoring fiber216, and the monitoring fiber218. The fluid line214conveys pressurized fluid from a pressure regulator262within the controller232to a fluid motor264located proximate the rheometer210. The fluid may include any fluid (e.g., water, hydraulic oil, air, etc.) that may be pressurized. The fluid motor264is powered by the pressurized fluid to rotate the cylinder246. Certain embodiments may have a belt265or other speed reduction system, or a monitoring wheel266, while other embodiments may have the fluid motor264directly coupled to the cylinder246.

In the illustrated embodiment, the monitoring wheel266includes reflectors268that reflect a light signal from the rotation monitoring fiber216. The light signal is generated at a rotation monitor270. The rotation monitor270generates the light signal as a constant beam of light or intermittent pulses of light that travel through the rotation monitoring fiber216to the monitoring wheel266. As the monitoring wheel266rotates, the reflectors268reflect the light signal back through the rotation monitoring fiber216to the rotation monitor270. The rotation speed of the monitoring wheel266affects the speed, intensity, or pattern at which the light signal is reflected. The rotation monitor270detects the speed, intensity, and pattern of the reflected light signal and determines a speed of rotation for the monitoring wheel266, and therefore the cylinder246within the rheometer210.

Based on the determined speed of rotation, the controller232increases or decreases the pressure provided by the pressure regulator until the fluid motor264rotates the cylinder246at a desired rotation speed (e.g., shear rate of the fluid202). The desired rotation speed may include, for example, 3, 6, 100, 200, 300, and 600 revolutions per minute. Once the correct rotation speed is achieved, a torque sensor272monitors the monitoring fiber218, which reads the torque imparted on the torsion bob252by the fluid202. The torque sensor272sends and receives light signals or other non-electrical signals to monitor the torque. After the torque is detected by the torque sensor272, the controller232may change the rotation speed/shear rate of the cylinder246and measure additional torques on the torsion bob252.

FIG.3is a cross-sectional side view illustrating an embodiment of a rheometer310for use within a hazardous location (e.g., controlled location106). The rheometer310includes a torsion bob352that receives a rotational force from a rotating fluid within the rheometer310. A monitoring fiber318is connected between the torsion bob352and a torque sensor372that sends and receives optical signals (e.g., light pulses) through the monitoring fiber318. The rheometer310also includes a mirror380that reflects the signals sent by the torque sensor372through the monitoring fiber318back through the monitoring fiber318to the torque sensor372.

The rotational force on the torsion bob352rotates the torsion bob352in a direction354until the rotation force is balanced by a torsion spring element374that surrounds the monitoring fiber318. A strain sensor376is a portion of the monitoring fiber318that is secured between fiber securing points at the torsion bob352(point378a) and at a housing340of the rheometer310(point378b). Thus, any rotation of the torsion bob352results in rotation of the strain sensor376. The strain sensor376includes stress elements that change the signal propagating from the torque sensor372through the monitoring fiber318. The stress elements include, for example, attenuating elements that reduce the strength of the optical signal based on how much the strain sensor376is rotated. That is, if the strain sensor376is rotated further, the signal from the torque sensor will be further attenuated. The torsion spring element374and the torque sensor372are thus calibrated to establish the relationship between signal attenuation and a torque on the torsion bob352.

FIG.4is a flow chart of an embodiment of a method400that may be used to monitor the rheological properties of a fluid within a hazardous location. The method400is used, for example, by the controllers (e.g.,132,232) above to determine a torque and a shear stress for a fluid within a rheometer. At step402the method starts and then asks404whether it is time to test the fluid for the torque and/or shear stress. If it is not time, the method400ends406. If it is time to test, the method400sets408a desired shear rate. The shear rate depends on the rotation speed and the geometry of the cylinder within the rheometer. Once the shear rate is set, the method rotates410the cylinder and the fluid, which imparts a force on the torsion bob. The cylinder is rotated without sending electrical signals. For example, the cylinder is rotated using a fluid motor that receives a pressurized fluid from a safe area outside of the hazardous location. The method400monitors412a speed of rotation of the cylinder and adjusts414the pressure delivered to the fluid motor. The monitoring412can be done optically using a monitoring fiber and an optical signal reflecting from the rheometer. The method400will ask416whether the shear rate has been achieved, and if not418the method400will monitor412and adjust414the pressure again until the correct rotation speed for the shear rate is achieved420.

Once the correct shear rate is reached, the method400determines422the shear stress as a function of the shear rate. The shear stress is measured as dependent upon a torque on a torsion bob within the rheometer. The torque is measured, for example, by the rheometer310described above. Specifically, a controller (e.g., controller132,232, or torque sensor372) may send a signal (e.g., light pulse) through a fiber (e.g.,318) to the rheometer310. The signal returns to the controller with an adjustment that indicates a torque imparted on the rheometer310. In response to the determining the shear stress as a function of the shear rate, the method400includes changing424operating parameters for a drilling operation in order to stay within an operating window for a drilling operation. The operating window is the pressure range that is acceptable for drilling a wellbore, and is determined largely by the rheological properties of the fluid in the wellbore. The lower pressure limit is driven by the formation pore pressure which depends largely on the lithology and depth of the formation. Thus, the pressure exerted by the drilling fluid must be higher to prevent formation fluid influx. The lower limit may also be impacted by the required mud weight to support the wellbore and to prevent wellbore collapse. The upper pressure limit is commonly known as the “fracture gradient” which depends largely on the wellbore trajectory, formation properties and formation stresses. When the shear stress for the first shear rate is determined, the method400includes asking426whether another shear rate test is desired. If yes, the method400starts again, if no, the method ends406.

FIG.5is a cross-sectional side view illustrating an embodiment of a rheometer510for use within a hazardous location (e.g., controlled location106ofFIG.1). The rheometer510may be used to measure a torque to determine a shear rate as according to the method400ofFIG.4and includes a torsion bob552that receives a rotational force from a rotating fluid within the rheometer510. A monitoring fiber518is connected between a rotary joint582and a torque sensor572that sends and receives optical signals through the monitoring fiber518. The rheometer510also includes a strain sensor576that is a portion of the monitoring fiber518between the rotary joint582and the torsion bob552. As with strain sensor376above, the strain sensor576includes a mirror580and a torsion spring element574. The strain sensor576is rotatably coupled to the torsion bob552and the rotary joint582, however, such that when the torsion bob552is rotated, the strain sensor576does not rotate. For example, the torsion spring element574may change a length584of the strain sensor576rather than rotating the strain sensor576. That is, a rotation in the rotation direction554due to the force from the fluid may extend the length584, or contract the length584. Changing the length584of strain sensor576changes the signal from the torque sensor572by attenuating the signal, changing the spectrum of the signal, changing the timing of the return of the signal, changing an encoding of the signal, or other adjustments.

As one example, the strain sensor576may include a fiber Bragg grating that propagates a light pulse through the strain sensor576at a primary wavelength.FIGS.6A and6Bare schematic views of a fiber optic cable600having a Bragg grating602that may be used as part of the strain sensor576ofFIG.5. At a first position604, the fiber optic cable600is unstrained and a light signal transmitted through has a first signature606having a first primary wavelength608. At a second position610, the fiber optic cable600is strained to increase a length612. The light signal that propagates through the fiber optic cable600in the strained position will have a second signature614with a second primary wavelength616. A difference618may be detected, for example, by the torque sensor572ofFIG.5, and used to determine a degree of rotation by the torsion bob552.

FIG.7is a cross-sectional side view illustrating an embodiment of a rheometer710for use within a hazardous location (e.g., controlled location106ofFIG.1). As with the embodiments described previously, the rheometer710includes a torsion bob752that receives a rotational force from a rotating fluid within the rheometer710. A monitoring fiber718is connected between a rotary joint782and a torque sensor772that sends and receives optical signals through the monitoring fiber718. The rheometer710includes a first strain sensor776athat is rotatably coupled to the torsion bob752and a second strain sensor776bthat rotates with the torsion bob752. A light pulse is sent from the torque sensor772that passes through the first strain sensor776aand the second strain sensor776bsimultaneously, bounces off a mirror780, and returns to the torque sensor772.

The combination of the first strain sensor776aand the second strain sensor776bcan enable more precise rheological measurement of the fluid within the rheometer710. For example, the first strain sensor776aor the second strain sensor776bmay include a fiber Bragg grating as described above. If the fiber Bragg grating is incorporated into the second strain sensor776b, the rotation of the strain sensor776belongates (or contracts) the Bragg grating to adjust the primary wavelength of the light pulse. If the fiber Bragg grating is incorporated into the first strain sensor776a, the fiber Bragg grating may be lengthened or contracted by a torsion spring element774.

Additionally or alternatively, the first strain sensor776amay detect temperature changes within the rheometer710. For example, the torsion spring element774may not extend or contract with the rotation of the torsion bob752, and thus the first strain sensor776aextends or contracts instead based on the conditions within the rheometer710. For example, a higher temperature within the rheometer710may extend the first strain sensor776a. The extending of a length784of the first strain sensor776adue to conditions, and the accompanying adjustment to the light pulse, may be compared with a change in the light pulse detected by the second strain sensor776bto eliminate any effect on the torsion bob other than the rheological properties of the fluid.