WO2017030916A1 - Inline viscosity determination technique - Google Patents

Abstract

A method for determining viscosity of a fluid in an inline, substantially real-time, fashion while the fluid is being utilized in an application. The method includes routing a portion of the fluid to a rotary disk viscometer where the portion is directed toward at least one disk surface. Thus, the fluid at the disk surface may shear and induce rotation at a given rate depending on viscosity characteristics and the rate at which the fluid is directed at the surface. Accordingly, with known fluid flowrate and pre-stored viscosity information available, determination of the resulting angular velocity of the disk provides viscosity information about the particular fluid. This may be particularly beneficial for acquiring continuous viscosity information for a non-Newtonian fluid being utilized in the application. However, Newtonian fluids may also be analyzed for viscosity in this fashion.

Description

INLINE VISCOSITY DETERMINATION TECHNIQUE

CROSS REFERENCE TO RELATED APPLICATIONS)

[0001] This Patent Document claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application Serial Number 62/205,179, entitled Rotary Disc Inline Viscometer, filed on August 14, 2015, which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. As a result, over the years, well architecture has become more sophisticated where appropriate in order to help enhance access to underground hydrocarbon reserves. For example, as opposed to wells of limited depth, it is not uncommon to find hydrocarbon wells exceeding 30,000 feet in depth. Furthermore, today's hydrocarbon wells often include deviated or horizontal sections aimed at targeting particular underground reserves. Indeed, at targeted formation locations, it is quite common for a host of lateral legs and fractures to stem from the main wellbore of the well toward a hydrocarbon reservoir in the formation.

[0003] The above described fractures may be formed by a fracturing operation, often referred to as a stimulation operation. The stimulation or fracturing operation, involves pumping of a fracturing fluid or slurry at high pressure into the well in order to form the fractures and stimulate production of the hydrocarbons. The fractures may then serve as channels through the formation through which hydrocarbons may reach the wellbore. The indicated fracturing fluid generally includes a solid particulate or aggregate referred to as proppant, often sand. The proppant may act to enhance the formation of fractures during the fracturing operation and may also remain primarily within fractures upon their formation. In fact, the fractures may remain open in part due to their propping open by the proppant.

[0004] In order to deliver proppant to the fractures in the application as indicated, a non- Newtonian solution, generally of water and a polymer, which is referred to as a "gel", is provided which is tailored to suspend proppant therein. That is, the proppant may be mixed into the gel solution to form the slurry that is utilized in the above described stimulation application. Of course, in order to properly suspend and transport proppant to downhole fractures, the characteristics of the gel should be within certain tolerances, particularly in terms of viscosity. For example, the linear fluid gel solution is often formed by the addition of guar and other potential additives to water at a blender. Once at the blender, the linear fluid may undergo cross-linking and become a highly viscous, more gel-like character for suspending later added proppant and other constituents therein. Thus, the intended fracturing fluid is rendered. Utilizing fracturing fluid with this character provides a level of control over the proppant to help ensure that it is delivered to a targeted downhole location, such as a fracture, as opposed to merely falling out of suspension and dropping to the bottom of the well or other unregulated location.

[0005] In order for the fracturing fluid gel to take on this proper character and hold the proppant, the linear fluid that is provided to the blender should be of a predetermined viscosity. That is, to ensure that the proper cross-linking takes place during forming of the slurry, it is important that the solution be of the proper pre-determined viscosity. So, for example, the application may call for a solution that includes 30 lbs. of guar per every thousand gallons of water. In this example, a mixer may be used where the guar and other constituents are mixed with water as called for to form the solution in advance of it being sent to the blender for combining with proppant and forming the fracturing fluid.

[0006] As indicated, the application may call for a particular protocol of a predetermined amount or rate of guar and other constituents to be added to the water in forming the linear fluid. Of course, there is always the possibility of operator or equipment error in carrying out the protocol or even the possibility that the called for protocol itself is in error. As alluded to above, if this happens, the linear fluid may end up being too thin or not viscous enough to ultimately provide a fracturing fluid capable of properly "holding" the proppant. When this occurs, the application may not only fail but it could result in dropping a sufficient amount of proppant into the well so as to require stopping operations and performing a cleanout at a cost of a day or more in lost time, not to mention added application expenses of a million dollars or more. Alternatively, if the linear fluid becomes too viscous, it may be more difficult on pumping equipment and inefficient to work with, not to mention the likelihood that the increased viscosity reflects wasted guar material cost.

[0007] In order to help ensure that operations are not halted or worse, the linear solution is periodically sampled during operations and evaluated. Specifically, the sampled fluid is checked for viscosity being within tolerances. Additionally, other characteristics such as temperature and acidity may be checked. Regardless, evaluating the sample involves taking the sample from the mixer for evaluation at a separate locale. This is because checking the solution is a non-Newtonian fluid. Therefore, conventional modes require that a discrete amount of the solution be placed within an isolated cup or chamber where an implement may be rotated or moved therein and monitored for torque. In this way, the torque reading may be translated into a useful viscosity reading for the operator. [0008] Unfortunately, taking the sample to another locale for sake of ascertaining the viscosity reading means that operations are proceeding in the interim with the linear fluid as is. That is, should the operator determine that there is a significant viscosity or other issue, it won't likely be until ten to fifteen minutes have passed and the sample has been fully evaluated. During this sample period, tens of thousands of gallons of the solution and ultimately faulty slurry may have been pumped downhole. Indeed, as a practical matter, it is often more likely that the operator will be alerted of an issue with the fracturing fluid due to a noticeable fluid pressure change or other event as opposed to being alerted of an out of spec linear fluid sample. Thus, at best, the sampling may only be of value if it provides information regarding a trend of the linear fluid away from called for specs. That is, once the solution is determined to be fully out of specification by conventional viscosity related sampling, it is likely too late to prevent the pumping of potentially catastrophic amounts of improper fracturing fluid downhole. Furthermore, the inability to ascertain inline, real-time viscosity for a non-Newtonian fluid may be problematic for any oilfield application in which such a fluid is circulated and is not limited to stimulation operations.

SUMMARY

[0009] A method of determining viscosity of a circulating fluid is described. The method includes injecting a portion of the circulating fluid toward a disk at a known flowrate to rotate the disk. As a result, the angular velocity of the rotating disk may be measured and compared to angular velocity and flowrate information for known pre-stored viscosity data to establish the viscosity of the circulating fluid. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Fig. 1 is a side cross-sectional view of an embodiment of an inline rotary viscometer unit for establishing a viscosity of a circulating fluid at an oilfield.

[0011] Fig. 2A is a schematic view of the unit of Fig. 1 shown incorporated into a system for placement at the oilfield.

[0012] Fig. 2B is a perspective view of a disk array within the unit of Fig. 1 for acquiring an angular velocity from interfacing a portion of the fluid at a known flowrate.

[0013] Fig. 3 is an overview of an oilfield accommodating the system of Fig. 2A coupled to oilfield fluid circulating equipment and a control unit.

[0014] Fig. 4 is a chart reflecting angular velocity against flowrate for both a non- Newtonian oilfield fluid and pre-stored Newtonian fluid data.

[0015] Fig. 5 is a flow-chart summarizing an embodiment of utilizing an inline viscometer unit to establish viscosity of a circulating fluid at an oilfield.

DETAILED DESCRIPTION

[0016] In the following description, numerous details are set forth to provide an understanding of the present disclosure. However, it will be understood by those skilled in the art that the embodiments described may be practiced without these particular details. Further, numerous variations or modifications may be employed which remain contemplated by the embodiments as specifically described.

[0017] Embodiments are described with reference to certain embodiments of oilfield operations. Specifically, stimulation operations involving fracturing of a well are detailed herein. However, other types of oilfield operations may benefit from the equipment and techniques detailed herein. For example, tools and techniques as described herein may be directed at the analysis of application fluids introduced into the well as well as production fluids, mud, gravel packing, coiled tubing cleanout fluids, cementing or other fluid types retrieved from the well or otherwise circulated in the well and/or at the oilfield. Indeed, such tools and techniques may be incorporated into downhole equipment or interventional tools. Regardless, so long as fluid characteristic information is monitored in a substantially continuous and real-time manner during the fluid-related application, appreciable benefit may be realized. Along these lines, the terms "continuous", "real-time" and/or "circulating" are meant to infer the dynamic ongoing nature of the viscosity determinations attainable through the tools and techniques detailed herein. That is, as opposed periodic sampling of fluid for remotely ascertaining viscosity, the fluid may continue ongoing circulation as realtime dynamic determinations of viscosity are made inline without interruption. Further, the term "circulating" is not meant to require re-circulating or similar requirements but rather is meant to infer the moving nature of the fluid.

[0018] Referring now to Fig. 1, with added reference to Fig. 3, a side cross-sectional view of an embodiment of an inline turbine-type of rotary viscometer unit 100 is shown for establishing a viscosity of a circulating fluid 102. In the embodiment shown, the fluid 102 is circulated to the unit 100 in an inline fashion through an entry line 105. So, for example, rather than intermittent sampling and offsite analysis of a fluid gel 102 being provided to a mixer 350 at an oilfield 301, a portion of the gel 102 may be routed to the unit 105 in a substantially continuous fashion. That is, the routing of this portion of the gel 102 to the unit 100 as shown in Fig. 1 takes place while other portions of the gel 102 are simultaneously being routed to the mixer 350 as shown in Fig. 3. Thus, as detailed below, an indicator of fluid viscosity for the gel 102 may be ascertained in real-time as it is being fed to the mixer 350. Further, as noted above, while the embodiments depicted are directed at a gel being provided to a mixer 350 for a stimulation application, a host of other fluid types for varying applications may also be evaluated in this manner.

[0019] Continuing with reference to Fig. 1, the rotary viscometer unit 100 acquires a portion of the fluid 102 from an injector 185 having ports 190 aligned with spaces 195 between "blades" or disks 170-178. The ports 190 are angled in a way to provide a predominantly tangential flow with respect to the disks 170-178. Though five disks 170- 178 are depicted, one or more may be utilized depending on operator preference or fluid properties. The fluid 102 is injected at a known flowrate and results in the rotation (167) of the entire array of disks 170-178 at an angular velocity which may be measured. More specifically, the radial component of velocity of the entering fluid 102 accounts for the flow rate while the tangential component of velocity results in a torsional force on the disks 170- 178 which causes the rotation (167) at a given angular velocity. Since the disks 170-178 are substantially frictionless, the rate of rotation thereof is comparable to that of the tangential velocity of the fluid 102. As a result, the relative tangential velocity of the fluid flow at the point of entry with respect to the disks 170-178 exhibits a laminar flow. This laminar flow is of particular benefit where the fluid 102 is non-Newtonian in nature and the viscosity is to be determined as a result of the shearing.

[0020] Ultimately, as described further below, this angular velocity measurement or rpm in light of the known flowrate may be correlated to pre-stored viscosity information so as to ascertain the viscosity of the fluid 102 itself. This type of correlation is particularly beneficial for ascertaining viscosity where the fluid 102 is non-Newtonian in nature which may otherwise require offsite sampling to determine viscosity. However, the viscosity of Newtonian fluids may also be ascertained in this manner.

[0021] The disks 170-178 are centrally mounted to a rotatable shaft 165 within a housing 180. Thus, the rotation (167) is supported within an isolated chamber 181. As the fluid 102 effects the rotation (167) and continues filling the chamber 181, it is also spiraling and circulated out of the chamber 181 through an exit line 107. It is worth noting that due to the centripetal flow displayed by the disks 170-178, all of the fluid 102 is encouraged out of the line 107. This includes particulate and debris associated with the fluid 102. Thus, in a sense, the unit 100 may be considered self-cleaning. In the embodiment shown, with the exception of the uppermost disk 170, the others are outfitted with somewhat centrally located channels 175 to provide a passageway for the fluid 102 toward the exit line 107. The uppermost disk 170 may not include such passageways given that the inj ector 185 may avoid delivering fluid 102 thereabove due to the static nature of the housing 180 adjacent this particular disk 170. Regardless, even the portion of the fluid 102 that is being run through the unit 100 may be returned to circulation and, for example, sent on to the blender 390 for addition of proppant as shown in Fig. 3.

[0022] Once the fluid 102 is injected at a known flowrate and has effected the rotation (167) of the disks 170-178, the unit 100 is equipped with features for detecting the rate of the rotation (167). Specifically, in the embodiment shown, the unit 100 includes an encoder 125 which detects the rotation of a reflective strip or other suitably detectable feature 127 that rotates in alignment with the disks 170-178 and shaft 165 as discussed above. More specifically, the detectable feature 127 is incorporated into a rotatable head 130 that is positioned below the encoder 125 and magnetically coupled to an extension 160 of the shaft 165. Thus, the head 130 rotates in alignment with the shaft 165 in a manner detectable by the encoder 125 (via the detectable feature 127).

[0023] While the rotation may be detected in a variety of manners, in the embodiment shown, magnetic interactions are utilized between the head 130 and the extension 160. Thus, the head 130, extension 160 and an intervening covering 150 there between may all be constructed of a polymer or other suitable non-magnetically interfering material. In the embodiment shown, the head 130 is positioned at a space 135 between the encoder 125 and the extension 160. More specifically, this space 135 is defined by a shroud 140 over the noted recessed covering 150, each mounted to the housing 180 with the shroud 140 accommodating the encoder 125 and the covering 150 defining a space into which the extension 160 is received. The head 130 is rotatable within this space 135 and, as alluded to above, does rotate in alignment with the extension 160 as the disks 165 are rotated by the injected fluid 102.

[0024] In the embodiment of Fig. 1, rotation of the head 130 by the rotating extension 160 is achieved through the interaction of magnets 1 10, 1 11, 1 15, 1 17. More specifically, the extension 160 is outfitted with a bearing magnet 115 which interacts with bearing magnets 1 17 of the head 130 in a magnetically polar manner to effect "floating" thereof. With these magnets 1 15, 1 17 acting as bearings and effecting a floating of the head 130, other magnets 110, 1 11 may serve to keep the floating head 130 in alignment with the rotating extension 160 as discussed above. Specifically, the extension 160 is outfitted with a rotor magnet 1 10 which attractively magnetically couple to rotor magnets 11 1 of the head 130 to locks its orientation in place relative the extension 160. Thus, as the extension 160 rotates, so to does the head 130, correspondingly presenting a rotating detectable feature 127 to the encoder 125.

[0025] As indicated above, other forms of tracking rotation may be utilized. For example, where concern over metallic particles in the fluid 102 are present, it may be more advantageous to utilize a more conventional architecture with sealed bearings. Additionally, the unit 100 may be utilized for more than ascertaining the rotation speed achieved by the injecting of the fluid 102. For example, in one embodiment, the encoder 125 may be replaced with a torque sensor or a generator which more directly interfaces the rotating shaft 165, drawing power therefrom. While this may add a load, information may also be garnered based on the amount of power attained from the rotating shaft 165. Furthermore, this embodiment may be readily scalable to larger sizes for greater power production with more identifiable signals and resilience against particle laden flows.

[0026] In another embodiment, a motor may interface the rotating shaft 165 in place of the encoder architecture shown. In this embodiment, the unit 100 may serve as a pump with the rpm of the rotating disks 170-178 actively controlled by the motor. That is, rather than fixing a known flowrate and measuring the angular velocity of the rotating disks 170-178, the angular velocity may be fixed at a known rate and the flowrate of the introduced fluid monitored for determining viscosity. For such a configuration, the unit 100 would serve as a discflo-type of pump with the entry line 105 more central and the exit line 107 more tangential to the housing 180. Regardless, based on the amount of RPM or power exhibited by the motor in achieving a known flowrate or pressure drop, dynamics of the fluid 102 circulating through the unit 100 may still be ascertained, including viscosity. [0027] Referring now to Fig. 2 A, a schematic view of the unit 100 of Fig. 1 shown incorporated into a system, for example to be positioned at an oilfield 301 as shown in Fig. 3. The unit 100 includes the housing with the shroud 140 and encoder 125 thereover as described above. Additionally, the entry line 105 for injecting fluid 102 into the housing 180 is shown along with the exit line 107. For the system shown, the unit 100 is of a modular configuration and readily coupled to a pump 200 which acquires the portion of the circulating fluid 102 to be drawn into the unit 100 via a circulation line 250. The circulation line 250 may lead from a mixer 350 at the oilfield 301 where the fluid is being prepared and circulated to a blender 390 for use in preparing a slurry 310.

[0028] Continuing with reference to Figs. 2A, with added reference to Figs. 1 and 3, a return line 255 is also shown for returning analyzed fluid 102 back to use at the oilfield 301. For example, this line 255 may lead to the noted blender 390. Thus, in this sense, the unit 100 may be characterized as inline as indicated above. Further, in the embodiment shown, before the analyzed fluid 102 is circulated into the return line 255, it is first collected in a tank 225 below the housing 180. The tank 225 is cooled by a chiller 275 which helps to regulate temperature and encourage the circulation and collection of the analyzed fluid 102 therein.

[0029] In addition to the modular manner in which these equipment pieces may be coupled together, additional instrumentation for monitoring other conditions of the circulating fluid 102 may be added. For example, pressure, temperature and flowrate instrumentation may be included. This may include, a pressure monitor to confirm a substantially consistent pressure drop across the unit 100 of up to about 50 PSI is utilized. Additionally, a flowmeter to confirm a substantially consistent, predetermined flowrate of fluid 102 into the unit 100 of between about 0.1 and 100 GPM may also be utilized. By the same token, temperature compensation may be imparted on the fluid 102 in order to heat or cool the fluid 102 in conjunction with taking other measurements thereof. For example, electric heaters, an extended recirculating period at the unit 100, pumping of coolant and other measures may be employed to attain a target temperature of the fluid 102 in advance of determining viscosity.

[0030] Referring now to Fig. 2B, with added reference to Fig. 1, a perspective view of the array of disks 170-178 within the unit 100 is shown. This view provides a brief illustration of the manner in which a fluid 102 interfaces and circulates relative the disks 170-178. In the embodiment shown, the distance (d) between the disks 170-178 may be 0.5 - 2 mm with the disks 170-178 each having thicknesses of less than about 1 mm with diameters substantially equivalent to each other and less than about 12 inches. Of course, the particular dimensions utilized may a matter of operator preference, for example, factoring in the types of fluids being analyzed by the unit 100. Along these lines, in other embodiments where larger solids are present in the fluid 102, the use of larger distances (d) between the disks 170-178 may be beneficial.

[0031] As described above, the tangential injection of fluid 102 at a known flowrate toward spaces 195 between the disks 170-178 results in a shearing of the fluid 102 across disk surfaces. The resulting non-turbulent laminar flow imparts a torque that translates into rotating of the entire array of disks 170-178 at a measurable rate, with the flow eventually exiting channels 175 near the bottom of the shaft 165 on the way out of the unit 100.

[0032] Referring specifically now to Fig. 3, an overview of an oilfield 301 is shown that accommodates the system and unit 100 of Fig. 2A which is coupled to oilfield fluid circulating equipment. As noted above, this equipment includes a mixer 350 where a linear gel fluid is formed and a blender 390 where proppant is added to the gel to form a stimulation slurry 310. So, for example, in the embodiment shown, a portion of the gel fluid that is formed at the mixer 350 may be continuously circulated to the unit 100 for analysis and back over to the blender 390 for combining with proppant to form the slurry 310. In this way, the unit 100 is considered to be "inline" for providing real-time continuous information regarding the gel fluid, particularly regarding viscosity (even though the fluid is most likely of a non-Newtonian type).

[0033] The overview of Fig. 3 provides an example illustration of the benefits of having such an inline viscometer unit 100 available for oilfield operations. In the embodiment shown, a series of pumps 330 are connected to a wellhead 355 through a manifold 375 in order to deliver a stimulation slurry 310 to a well 325. More specifically, the slurry 310 is directed at high pressure to a reservoir containing formation 315 likely having perforations and fractures. Thus, the slurry 310 may enhance these downhole features and ultimately improve recovery from the reservoir. However, in order to ensure performance of the slurry 310, its viscosity should be appropriately tailored to suspend proppant obtained at the blender 390 while at the same time avoiding becoming too viscous and impairing the pumping equipment or hampering delivery of the slurry 310 as intended.

[0034] Continuing with reference to Fig. 3, the viscosity readings are determined based on analysis of an angular velocity obtained from the unit 100 as described above. More specifically, a processor equipped control unit 300 monitors the angular velocity obtained by the unit 100. This angular velocity may be analyzed in an ongoing, real-time fashion with reference to the injection flowrate of the fluid into the viscometer unit 100 which is compared against pre-stored viscosity data at the processor of the control unit 300.

[0035] The control unit 300 may consist of an operator's laptop directed at monitoring real-time viscosity of the gel fluid. Alternatively, it may be incorporated into a larger CPU for controlling other operations at the oilfield 301 beyond tracking viscosity, such as a unit exerting control over pump rates, blender speeds and acquiring a host of data apart from gel viscosity. Regardless, the unit 300 may be configured to control and keep track of flowrate into the unit 100, pressure, temperature and other factors that may have an impact on the viscosity analysis.

[0036] Whatever the case, once the viscosity analysis is available to the operator, a realtime manner of adjusting the viscosity may be available. That is, with viscosity tolerances set for a given application, the operator may monitor viscosity in real-time for trending of the gel to a state that is too viscous or not viscous enough. Thus, as the gel is determined to be too viscous or trending in that direction, a reduction in the rate of adding guar or other viscosifying agent at the mixer 350 may be called for. By the same token, as the gel is determined to be not viscous enough or trending in that direction, the operator may initiate an increase in the rate of adding viscosifying agent at the mixer 350. Either way, a real-time manner of assuring proper viscosity of the gel has been provided.

[0037] Referring now to Fig. 4, a chart is shown that reflects an example of measured angular velocity obtained from the unit 100 of Fig. 3 at given flowrates. This measurement provides a correlation that may be plotted (480) and analyzed by the unit 100 to determine whether this correlates with a viscosity for the fluid that is too low (e.g. above 485), too high (e.g. below 487) or within tolerances as shown. More specifically, pre-stored data at the processor of the unit 100 corresponding to different known flowrate and velocity curves for fluids of known viscosities may be relied upon. These may be referred to as calibration curves. For example, the unit 100 or another equivalent rotary disc viscometer may be utilized to develop and store a range of viscosity data for different fluids of known viscositites. These values may be correlated to those attained from conventional viscometers and units such as a Fann 35. Regardless, in this particular circumstance, even for non- Newtonian fluids having viscosities established through other means, when run through a rotary or turbine viscometer, the fluid behavior will be consistent for a given fluid viscosity. This includes consistency in terms of shearing, yield stress, strain rate and other viscosity characteristics, all of which may be stored at the control unit 300. Of course, this also includes the correlation between flowrate and angular velocity for a fluid of a given viscosity run through a given viscometer unit 100. Thus, reliable correlations may be made.

[0038] In practice, these correlations may be used to establish tolerances and monitor viscosity on light thereof. So, for example, where a lower end of acceptable viscosity is being detected (e.g. 485), an increased rate of guar may be supplied to the mixer 350 at Fig. 3 in an effort to raise the viscosity from the current level. Of course, there would also be an ongoing effort to avoid raising viscosity beyond an upper tolerance (e.g. 487).

[0039] With added reference now to Fig. 3, an operator having real-time insight into viscosity information as displayed at the control unit 300 now has the ability to adjust viscosity of the fluid gel as needed by changing the rate of guar being added at the mixer 350. Continuing with the example, above, when the readings indicate that the viscosity is closer to the lower end of tolerances (e.g. 485), the rate of guar being added may be increased and when the readings indicate that the viscosity is trending higher (e.g. 487), the rate of add may be reduced. Either way, even for a non-Newtonian fluid such as the forming gel, the operator is provided with a real-time indicator of viscosity due to the inline viscometer provided.

[0040] Continuing with reference to Fig. 4, a Newtonian fluid such as a glycerine-based fluid of known concentration may be plotted (490). In the example shown only one plot of glycerine concentration 490 is depicted for ease of illustrating a single known viscosity reference point 495. However, a host of additional concentration information may be pre- stored such that viscosity for the entirety of the non-Newtonian fluid plot 480 may be acquired by reference. By the same token, in an embodiment where the viscosity of the non- Newtonian fluid 480 is already known as a function of shear rate, the shear rate of the Newtonian fluid 490 may similarly be determined by the reference point 495. Thus, given the intersection of the non-Newtonian fluid 480 with the Newtonian fluid 490 at the reference point 495, a shear rate may now be assigned to the reference point 495.

[0041] With the above in mind, a complete data set with reference points 495 distributed throughout the entirety of the chart of Fig. 4 may be established and pre-stored for later use, each point having a unique viscosity and shear rate associated with it. For example, based on the intersection of a multitude of differing concentrations of Newtonian and non- Newtonian fluids, a complete set of reference points 495 for shear rates and viscosities may be pre-stored. Thus, the unit 100 of Fig. 1 may serve as a true rheometer at the oilfield 301 of Fig. 3, providing true viscosity (and shear rate) measurements for any non-Newtonian (or Newtonian) fluid 102.

[0042] Referring now to Fig. 5, a flow-chart is shown summarizing an embodiment of utilizing an inline viscometer unit to establish viscosity of a circulating fluid at an oilfield. As indicated, fluid viscosity information is stored at a processor (see 515). Thus, a given oilfield fluid may be directed at a rotatable disk at a known flowrate as shown at 530 to effect an angular velocity thereon as noted at 545. With angular velocity information available, a comparison to stored viscosity information at the processor may be made to help determine the viscosity of the oilfield fluid (see 550). Once more, this determination may be made in an ongoing, real-time manner as an oilfield application is being performed with the same fluid as indicated at 580. In certain embodiments, such as for the stimulation operations detailed hereinabove, an operator with access to the viscosity information, may even make real-time adjustments to the viscosity of the oilfield fluid (see 565).

[0043] Embodiments described above allow for the ascertaining of viscosity information of a circulating fluid without the requirement of remote, offsite analysis even where the circulating fluid is non-Newtonian in nature. This is particularly advantageous where the fluid is a gel for use in generation of a proppant slurry for oilfield stimulation operations. That is, the availability of substantially real-time viscosity information may allow operators to alter the viscosity of the gel in a near immediate fashion as necessary to assure the desired properties of the proppant slurry being formed. Thus, the circumstance of utilizing substantial amounts of gel having out of tolerance viscosity due to offsite analysis delay in obtaining viscosity information may be avoided. Of course, such real-time viscosity information and adjustment may be beneficial in a variety of other oilfield applications as well.

[0044] The preceding description has been presented with reference to presently preferred embodiments. Persons skilled in the art and technology to which these embodiments pertain will appreciate that alterations and changes in the described structures and methods of operation may be practiced without meaningfully departing from the principle, and scope of these embodiments. Furthermore, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.

Claims

CLAIMS We Claim:

1. A method of determining viscosity of a circulating fluid at an oilfield, the method comprising:

injecting a portion of the circulating fluid toward at least one disk at a known flowrate to rotate the disk;

measuring the angular velocity of the rotating disk;

comparing the angular velocity of the disk in light of the flowrate against known pre-stored fluid viscosity information to establish the viscosity of the circulating fluid.

2. The method of claim 1 further comprising adjusting the viscosity of the fluid based on results of the comparing.

3. The method of claim 1 further comprising performing an application relative a well at the oilfield with the oilfield fluid.

4. The method of claim 3 wherein the application is one of a stimulation application, a production application, a mud circulation application, a gravel packing application, a coiled tubing cleanout application and a cementing application.

5. The method of claim 1 wherein the injected portion of the circulating fluid is returned to circulation in an inline fashion after the comparing.

6. The method of claim 5 wherein the fluid includes particulate and the disk is cleaned thereof by encouraging of the particulate to return to circulation with the fluid.

7. The method of claim 1 wherein the fluid is a non-Newtonian fluid, the method further comprising determining shear rate information for a Newtonian fluid based on the established viscosity of the non-Newtonian fluid.

8. The method of claim 1 further comprising introducing a temperature compensating measure to attain a target temperature of the portion of the fluid in advance of the injecting thereof.

9. A method of circulating a linear gel at an oilfield to form a stimulation slurry for use in a well at the oilfield, the method comprising:

combining a viscosif ing agent with a fluid in a mixer at the oilfield to form a linear gel;

sending a portion of the gel to a viscometer with a plurality of rotatable disks therein;

injecting the portion of the gel to a space between disks of the viscometer at a predetermined flowrate to induce rotation thereof;

measuring the angular velocity of the rotating disks;

comparing the angular velocity in light of in light of the flowrate against pre-stored fluid viscosity information to establish the viscosity of the linear gel.

10. The method of claim 9 further comprising developing calibration curves of flowrate against angular velocity for viscosities of known linear gel fluids for the pre-stored fluid viscosity information.

11. The method of claim 9 further comprising:

directing the linear gel to a blender for combining with a proppant to form a stimulation slurry during the sending of the portion thereof to the viscometer; and

returning the portion of the linear gel from the viscometer to the blender.

12. The method of claim 11 further comprising pumping the stimulation slurry into the well for a stimulation application therein.

13. The method of claim 12 further comprising:

establishing the viscosity of the linear gel as below a predetermined level; and increasing a rate of adding the viscosifying agent to the mixer.

14. The method of claim 12 further comprising:

establishing the viscosity of the linear gel as above a predetermined level; and reducing a rate of adding the viscosifying agent to the mixer.

15. A rotary disk viscometer unit for inline use at an oilfield circulating a fluid, the unit comprising:

a plurality of disks;

a rotatable shaft accommodating the disks; a housing accommodating the shaft and disks;

an injector for directing a portion of the circulating fluid to a space between disks of the plurality at a known flowrate to induce rotation of the shaft;

a detector secured to the housing adjacent the shaft for monitoring the rotation of the shaft to establish a viscosity of the circulating fluid.

16. The rotary disk viscometer unit of claim 15 wherein the housing is configured for one of positioning at a surface of the oilfield and incorporating into a downhole tool for use in a well at the oilfield.

17. The rotary disk viscometer unit of claim 15 wherein the detector is one of an encoder, a torque sensor, a generator and a motor.

18. The rotary disk viscometer unit of claim 17 wherein the detector is the encoder, the unit further comprising a detectable feature coupled to the shaft and readable by the encoder to establish a rate of rotation of the shaft for the establishing of the viscosity.

19. The rotary disk viscometer unit of claim 18 further comprising a rotatable head over the shaft to accommodate the detectable feature, the rotatable head physically separated from the shaft and magnetically coupled thereto.

20. The rotary disk viscometer unit of claim 18 further comprising:

a rotatable head over the shaft to accommodate the detectable feature; and sealed bearings at an interface between the head and the shaft.

21. A rotary disk viscometer unit for inline use at an oilfield circulating a fluid, the unit comprising:

a plurality of disks;

a rotatable shaft accommodating the disks;

a housing accommodating the shaft and disks;

a motor to rotate the shaft and disks at a predetermined speed as a portion of the circulating fluid is introduced to a space between the disks; and

a detector secured to the housing adjacent the shaft for monitoring the introduced flowrate induced by the motor to establish a viscosity of the circulating fluid.