Patent Application
20210131280
This application is directed, in general, to fracturing of a hydrocarbon wellbore and, more specifically, to a wellbore fracturing system, a method of calculating a friction pressure (CALCFP) in a wellbore and a method of managing a friction pressure in a wellbore.
Hydraulic fracturing or “fracking” is a type of subsurface well stimulation, whereby formation fluid removal is enhanced by increasing well productivity. The process of fracking, also known as induced hydraulic fracturing, involves mixing a formation proppant (e.g., sand) and chemicals in water to form a formation fracturing fluid (i.e., a fracturing fluid) and injecting the fracturing fluid at a high pressure through a wellbore into a subterranean formation. Small fractures are formed, allowing formation fluids (e.g., formation gas, petroleum, and brine water), to migrate into the wellbore for harvesting. Once the hydraulic pressure is reduced back to equilibrium, the sand or other formation proppant particles hold the fractures open.
Multi-stage hydraulic fracturing is an advancement that provides harvesting of fluids along a single wellbore or fracturing string. The fracturing string, usually for vertical or horizontal wellbores, passes through different geological zones. Some geological zones do not require harvesting, since desired natural resources are not located in those zones. These zones can be isolated so that no fracking action occurs in these zones that are empty of desired natural resources. Other zones having natural resources employ portions of the fracturing string to harvest these productive zones.
Instead of having to alternate between drilling deeper and fracturing operations, a system of fracking sleeves and packers can be installed within a wellbore to form the fracturing string in a multi-stage fracturing process. The sleeves and packers are positioned within zones of the wellbore. Fracking can be performed in stages by selectively activating sleeves and packers, thereby isolating particular subterranean zones. Each target zone can then be fracked stage by stage, for example, by sealing off selected zones, and perforating or fracturing without interruptions due to having to drill between each fracturing stage.
The disclosure provides a wellbore fracturing system for a subterranean formation of a wellbore. In one example, the wellbore fracturing system includes: (1) wellbore fracturing resources coupled through a wellbore conveyance to the subterranean formation of the wellbore, (2) a bottom hole pressure gauge that provides a bottom hole gauge pressure, and (3) a processor coupled to the wellbore fracturing resources and the wellbore conveyance that calculates a wellbore friction pressure using a time-series sampling of bottom-hole gauge pressures for a fracturing fluid system after a uniform fracturing fluid condition is achieved in the wellbore.
The disclosure also provides a method of calculating a friction pressure (CALCFP) in a wellbore. In one example, this method includes: (1) determining a uniform fluid condition for a fracturing fluid in the wellbore, (2) sampling time-series bottom-hole gauge pressure data after the uniform fluid condition of the fracturing fluid is achieved, and (3) calculating a friction pressure for each sample of the time-series bottom-hole gauge pressure data.
The disclosure further provides a method of managing a friction pressure in a wellbore. In one example, the method of managing a friction pressure includes: (1) applying a fracturing fluid system to the wellbore, (2) sampling current fracturing job data, (3) calculating a friction pressure for the current fracturing job data, and (4) managing the fracturing fluid system to maintain the friction pressure within selected limits.
Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
This disclosure addresses the problem of determining the friction pressure of a fracturing fluid system in a wellbore during hydraulic fracturing (in both real time and pre-job). This disclosure requires that at least one fracturing stage pumped using a hydraulic fracturing fluid system employ at least one bottom hole gauge pressure (BHGP) time-series measurement somewhere in the wellbore. Effects, such as the influence of source water on friction pressure, can be directly captured by this approach and used to select an optimal fracturing fluid system on location.
This disclosure applies to a hydraulic fracturing fluid system (here fracturing fluid system may refer to one or more combinations of fracturing fluids, proppants and chemicals) where data from at least one fracturing stage is available having a bottom-hole gauge pressure measurement. This disclosure proposes a use of BHGP measurements to determine friction pressure with and without proppant that may then be used to calibrate a chosen friction model with or without proppant, and also to provide scaling of laboratory data to field conditions. This calibrated friction model and/or scaled lab data may then be used to predict friction pressures for any future hydraulic fracturing stages that employ the fluid system under consideration. The accurate prediction of friction pressure can be used to design or select fluid systems to match target operating pressures, diagnose perforation and near-wellbore properties using step-down tests, thereby improving job design and determine pump maintenance and fuel costs for pumping a given fluid system.
The approach may also be used to vary a concentration of friction reducers and/or a type of friction reducers and/or a concentration and/or type of proppant over time (before/flush, during ramp-up, during stage, during ramp-down or after/flush of a wellbore) to determine fluid friction relationships that can be used to optimize treatment pressures in real time either during a current stage or from stage to stage. A real-time control algorithm may be included in the surface equipment control system where various step-up/step-down sequences may be introduced to automatically determine and differentiate fluid friction and proppant friction induced pressure drop. This information can proactively be used to model bottom-hole treating pressure, and select combinations of friction reducers, friction reducer concentration or proppant concentration or type to reach a target bottom-hole treating pressure in real time. The measured data can be shared with real-time models, and the modeled data can be used to determine operating set-points for fracture treatments in real time. A pressure response of the treatment can be measured enabling real-time fracture control and automation.
In one example, the wellbore 130 may extend substantially vertically away from the earth's surface 122 over a vertical wellbore portion 132, or may deviate at any angle from the earth's surface 122 over a deviated or horizontal wellbore portion 134. The wellbore 130 may include one or more deviated or horizontal wellbore portions 134. In alternative operating environments, portions or substantially all of the wellbore 130 may be vertical, deviated, horizontal or curved. The wellbore 130 includes a casing string 140. In the example of
In accordance with the disclosure, the wellbore system 100 includes one or more fracturing zones. While only two fracturing zones (e.g., a lower fracturing zone 160 and upper fracturing zone 170) are illustrated in
In another example, the wellbore system 100 may further include a downhole tool assembly, manufactured in accordance with this disclosure, and positioned in and around (e.g., in one embodiment at least partially between) the lower fracturing zone 160 and upper fracturing zone 170. Again, while the service tool assembly is positioned in a horizontal section 134 of the wellbore 130 in the embodiment of
The present disclosure has recognized that by including the check valve with the packer plug, any excess fluid existing between the packer plug and the lower packer assembly may exit the lower packer assembly as the packer plug is positioned therein. As no excess fluid exists between the packer plug and the lower packer assembly, the packer plug may physically rest upon a no-go shoulder of the lower packer assembly. Accordingly, when a perforating device is discharged up-hole of the packer plug during the fracturing process, any force created by a compression wave resulting therefrom will transfer directly between the packer plug and the lower packer assembly. Moreover, since the packer plug physically rests on the lower packer assembly, the force of the compression wave cannot compress the fluid located there between, and thus does not damage the fluid loss device located directly there below.
While the wellbore system 100 depicted in
The hydrocarbon wellbore fracturing system 100 additionally includes surface equipment such as one or more pumping units 119 and wellbore fracturing resources such as friction fluids 116, fracturing proppants 117 and fracturing fluid systems 118 employing at least a portion of the friction fluids 116 and fracturing proppants 117. In the illustrated example, these fracturing fluid systems 118 are pumped, by the pumping units 119, through the wellbore conveyance 126. The wellbore conveyance 126 may be a drill pipe or another type of conveyance sufficient to handle the pressure used for fracturing. The hydrocarbon wellbore fracturing system 100 further includes wellbore pressure determining means such as pressure gauges. These pressure gauges may include a wellhead pressure gauge 182 that provides a surface wellhead pressure (WHP) and a bottom hole pressure gauge 185 that provides a bottom hole gauge pressure (BHGP) that is communicated to the surface 122.
Additionally included is at least one wellbore pressure gauge (in this example, WP1 through WPn pressure gauges are shown) that determines an intermediate wellbore pressure, which is communicated to the surface 122. These intermediate wellbore pressures may be employed to facilitate verification of a uniform fracturing fluid condition throughout the wellbore 130. In another example, electrical or optical sensors (not expressly shown) may be placed in an annular space between casing and formation where they are typically cemented in place. These sensors are communicatively coupled to an electrical or optical cable (not expressly shown) that is controlled by a processor 120 at the surface 122. The optical cable may include multiple optical fibers that may be used for distributed temperature sensing or distributed acoustic sensing.
The processor 120 additionally calculates a wellbore friction pressure for a selected fracturing fluid system and manages the fracturing fluid system to maintain the wellbore friction pressure within predetermined limits. This wellbore friction pressure may be employed to calibrate or update a friction model that may be employed in fracturing the wellbore 130. The processor 120 may employ or store executable programs of sequences of software instructions to perform one or more of various calculations including a wellbore friction pressure, updating a wellbore friction model or selecting various fracturing fluid systems, for example. The software instructions of such programs may represent algorithms and be encoded in machine-executable form on non-transitory digital data storage media, (e.g., magnetic or optical disks, random-access memory (RAM), magnetic hard disks, flash memories, and/or read-only memory (ROM)), to enable the processor 120 to perform one, multiple or all of the steps of one or more of the described methods, functions, systems or apparatuses described herein. Portions of disclosed examples may relate to computer storage products with a non-transitory computer-readable medium that have program code thereon for performing various computer-implemented operations that embody a part of an apparatus, device or carry out the steps of a method set forth herein.
Non-transitory used herein refers to all computer-readable media except for transitory, propagating signals. Examples of non-transitory computer-readable media include, but are not limited to: magnetic media such as hard disks, floppy disks, and magnetic tape as well as optical media such as CD-ROM disks; magneto-optical media in general and hardware devices that are specially configured to store and execute program code, such as ROM and RAM devices. Examples of program code include both machine code, such as that produced by a compiler, and files containing higher level code that may be executed by the computer using an interpreter.
If real-time BHGP data is available, the processor 120 can employ the methodology of this disclosure and can be utilized for real-time control and optimization of a fracturing fluid system, including selection of a friction reducer and proppant type and concentration. Note that the disclosed method or approach includes the use of multiple BHGP data if available, which will serve to enhance the accuracy of the real-time calculations and improve operational decisions.
The disclosed approach may also be used to vary the concentration of friction reducers and/or types of friction reducers as well as a concentration of proppant over time (before/flush, during ramp-up, during stage, during ramp-down, after/flush) to determine fluid friction relationships that can be used to optimize treatment pressures in real time either during a current fracturing stage or from stage to stage. A real-time control algorithm may be included in the processor 120 acting as a surface equipment control system, where various step-up/step-down sequences may be introduced to automatically determine and differentiate fluid friction and proppant friction induced pressure drop.
The disclosed approach can additionally be used to also distinguish between friction pressures inside the wellbore and in the near-wellbore region including formation perforations. An example application of this disclosure may be to evaluate an effectiveness of a diversion treatment. All of this information may proactively be used to model bottom-hole treating pressure, and select combinations of friction reducers or a friction reducer concentrations as well as a proppant concentration to reach a target bottom-hole treating pressure in real time. The measured data can be shared with real-time models, and the modeled data can be used to determine operating set-points for fracture treatments in real time. Additionally, the pressure response of a treatment can be measured enabling real-time fracture control and automation.
Friction pressure may be determined from bottom hole gauge pressure for a particular stage from job data by obtaining sample points for calculating the friction pressure using a sweep method (or a sweep approach). For calculating the sample points in the sweep approach or method, it is required that the wellbore be filled with a fracturing fluid system having a uniform condition from the wellhead down to the position of the bottom hole gauge pressure. This uniform condition refers to uniformity in density, chemical composition of the fluid (such as a same concentration of friction reducing fluids), and proppant concentration in the fracturing fluid system. Note that if more than one downhole gauge pressure unit is installed in the wellbore, they can be used to verify the uniform condition, as well as a fully developed flow condition. The following procedure illustrates the use of the sweep approach or method to obtain the sample points.
Choose a target condition: say 0.5 gallons of friction reducer (FR1) per thousand gallons of water (fracturing fluid) that may be generally expressed as 0.5 gpt of friction reducer FR1. Start from a time when this concentration is first introduced and use a fracturing fluid flow rate to determine a first instance where a target fracturing fluid system is consistent from wellhead to the bottom hole gauge location. Then,
where MDBHG is the measured depth at the bottom hole gauge location and MDWH is the measured depth at the well head. The quantity γ is a factor that accounts for mixing and imperfect fluid displacement, and
In
The target condition may also involve proppant concentration, for example, 0.5 gallons of Friction Reducer 1 per thousand gallons of water (fracturing fluid) and 0.25 pounds proppant concentration per gallon (ppg) of water (fracturing fluid) that may be expressed as 0.5 gpt FR1, 0.25 ppg proppant concentration. This condition is illustrated in
In order to determine reliable sample points, some data processing may be necessary. Sometimes, data readings during operations can contain spurious noise such as in some data (e.g., FR concentration) that may have significant impact on the sample values. Passing the data through a low pass filter may provide more accurate sampling for these cases, for example. The density of the fluid pumped may be used to calculate the hydrostatic pressure which affects the calculation of friction pressure. A reliable estimate of fluid density can be obtained by sampling data points (e.g., sample data point 280) after the end of pumping (once a water hammer signature has subsided). This is indicated by line 5 in
For each sample point, friction pressure drop may be calculated using equation (2) below.
ΔPf=WHP−BHGP+PH, (2)
where WHP is the well-head pressure, BHGP is the bottom hole gauge pressure and PH is the hydrostatic pressure at the bottom hole gauge location, given by:
P
H
=ρg(TVDBHG), (3)
where ρ is the density of the fluid system at the target condition, g is the acceleration due to gravity and TVDBHG is the total vertical depth at the bottom-hole gauge location. All of these measured and calculated pressures are plotted in
ΔPm=f(V,A,ρ,n,k,We)ψ(ϕ), (4)
where f is a function of the flow velocity V, cross-sectional area A, density ρ, power-law index n, consistency index k, and fluid Weissenberg number We. The function ψ accounts for the effect of a proppant concentration ϕ (expressed as a dimensionless volume fraction). Friction models are typically developed for certain representative fluids using extensive lab testing and validation. In order to apply them to new fracturing fluid systems, calibration of one or more model parameters is typically required. Setting ΔPf=ΔPm provides for calibration of the model parameters. The function ψ is a less well known effect, and the bottom-hole gauge pressure (BHGP) measurements allow the determination of ψ(ϕ) for particular fluid systems. Then,
where α is a model parameter to be determined from the data. Depending upon the fluid system in question, other types of models may be appropriate.
Another use of the calculated friction pressure is to scale lab measurements to meet actual field conditions. Very often, for a new fluid system, the only measurements available are from laboratory friction testing that is carried out on a much smaller scale than an actual field application. The calculated friction pressure may be used to obtain, validate or calibrate scaling relationships that allow the use of lab data for field applications.
A calibrated friction model and/or scaled lab data may be used to predict friction pressures for a fluid system at any given condition. An accurate prediction of friction in a wellbore may be utilized to design or select fluid systems to meet target operating pressures. Also, an accurate prediction of friction in a wellbore may be employed to diagnose perforation and near-wellbore properties using step-down tests to thereby improve fracturing job design. These properties may be input to a hydraulic fracturing simulator thereby providing accurate estimations that are valuable for high quality job designs. Additionally, pump maintenance and fuel costs for pumping a given fluid system may be determined.
Application of the method 300 allows real-time determination of a wellbore friction pressure drop as it relates to fracturing friction reducers and proppants. This allows real-time control of friction reducers (type and concentration) and proppants to proactively control the impact of a friction reducer and proppant related pressure drop with the objective of controlling the bottom hole treating pressure. This results in lower treatment pressure with associated cost reductions due to fuel, equipment wear and tear, maintenance, time on location and improved hydraulic fracturing treatments.
If the decision step 525 determines that the fluid pressure calculated in the step 520 is not acceptable, another decisional step 530 determines if a new fracturing fluid system is available. If a new fracturing fluid system is available, a need to change the existing fluid system is recognized in a step 535 and method 500 returns to the step 510 where a newly selected fracturing fluid system is applied to the wellbore. New fracturing job data is sampled in real time, and a friction pressure is calculated for the new fracturing job data, in the step 520. This second processing loop continues until the decision step 525 determines that a calculated friction pressure is acceptable, where the method 500 again employs the first processing loop, as before.
In one example, the current fracturing job data corresponds to bottom-hole gauge pressures. In another example, calculating the friction pressure employs CALCFP, as noted. In yet another example, a concentration or a type of a friction reduction fluid is changed to provide an acceptable friction pressure. In still another example, a concentration or type of fracturing fluid proppant is changed to provide an acceptable friction pressure. The method 500 ends in a step 540.
While the methods disclosed herein have been described and shown with reference to particular steps performed in a particular order, it will be understood that these steps may be combined, subdivided, or reordered to form an equivalent method without departing from the teachings of the present disclosure. Accordingly, unless specifically indicated herein, the order or the grouping of the steps is not a limitation of the present disclosure.
The description and drawings included herein are intended to illustrate the principles of the present disclosure. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the disclosure and are included within its scope. Furthermore, all examples recited herein are principally intended expressly to be for pedagogical purposes to aid the reader in understanding the principles of the disclosure and concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles and aspects of the disclosure, as well as specific examples thereof, are intended to encompass equivalents thereof. Additionally, the term, “or,” as used herein, refers to a non-exclusive or, unless otherwise indicated. Furthermore, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used only for convenience in referring to the accompanying drawings. Additionally, it is to be understood that the different embodiments of the present disclosure may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of the present disclosure.
Those skilled in the art to which this application relates will appreciate that other and further additions, deletions, substitutions and modifications may be made to the described embodiments.
Various aspects of the disclosure can be claimed including apparatuses, systems and workflows as disclosed herein. Aspects disclosed herein include:
A. A wellbore fracturing system for a subterranean formation of a wellbore, including: (1) wellbore fracturing resources coupled through a wellbore conveyance to the subterranean formation of the wellbore, (2) a bottom hole pressure gauge that provides a bottom hole gauge pressure, and (3) a processor coupled to the wellbore fracturing resources and the wellbore conveyance that calculates a wellbore friction pressure using a time-series sampling of bottom-hole gauge pressures for a fracturing fluid system after a uniform fracturing fluid condition is achieved in the wellbore.
B. A method of calculating a friction pressure (CALCFP) in a wellbore, including (1) determining a uniform fluid condition for a fracturing fluid in the wellbore, (2) sampling time-series bottom-hole gauge pressure data after the uniform fluid condition of the fracturing fluid is achieved, and (3) calculating a friction pressure for each sample of the time-series bottom-hole gauge pressure data.
C. A method of managing a friction pressure in a wellbore including (1) applying a fracturing fluid system to the wellbore, (2) sampling current fracturing job data, (3) calculating a friction pressure for the current fracturing job data, and (4) managing the fracturing fluid system to maintain the friction pressure within selected limits.
Each of aspects A, B and C can have one or more of the following additional elements in combination:
Element 1: wherein the fracturing fluid system is managed to maintain the wellbore friction pressure within selected limits and at variable fracturing fluid flow rates. Element 2: wherein the fracturing fluid system is managed by the processor in real time. Element 3: wherein the processor calculates a friction pressure for each time-series sampling of the bottom-hole gauge pressure. Element 4: wherein the time-series sampling of bottom-hole gauge pressures employs a CALCFP method of obtaining the time-series sampling and calculating the wellbore friction pressure. Element 5: wherein the fracturing fluid system includes a friction reduction fluid or a fracturing proppant, each at selectable concentrations. Element 6: further comprising a wellhead pressure gauge that provides a wellhead pressure measurement. Element 7: further comprising at least one wellbore pressure gauge corresponding to an intermediate wellbore depth to determine the uniform fracturing fluid condition. Element 8: wherein the processor controls at least one fracture pumping unit to maintain the wellbore friction pressure within selected limits. Element 9: further comprising processing samples of the time-series bottom-hole gauge pressure data to improve data sample quality before calculating the friction pressure. Element 10: further comprising updating a friction pressure model using the friction pressure calculated for at least one time-series bottom-hole gauge pressure data sample. Element 11: wherein managing the fracturing fluid system includes maintaining the friction pressure within the selected limits in real time. Element 12: wherein the current fracturing job data corresponds to a bottom-hole gauge pressure. Element 13: wherein calculating the friction pressure employs a CALCFP method. Element 14: further comprising updating a friction model to reflect a current friction pressure of one or more current fracturing job data samples. Element 15: wherein an updated friction model or field-scaled lab data is used to predict a friction pressure. Element 16: wherein managing the fracturing fluid system includes changing a friction reduction fluid concentration or a type of friction reduction fluid for the wellbore. Element 17: wherein managing the fracturing fluid system includes changing a fracturing fluid proppant concentration or a type of fracturing fluid proppant for the wellbore. Element 18: wherein managing the fracturing fluid system includes managing a fracturing fluid injection rate for the wellbore.
