Device and method for determining static settling velocity of proppant in fracturing fluid

Abstract

A method for determining the static settling velocity of a proppant in a fracturing fluid. The proppant carrying capabilities of different drag reducer products can be compared, so that a proper drag reducer product can be selected for hydraulic fracturing operation. The influence of the concentration of the drag reducer in the fracturing fluid, the salinity and hardness of the fracturing fluid and the size of the proppant on the static settling velocity of the proppant is researched, the chemical structure of the drag reducer in the synthesis process can be optimized, and the hydraulic fracturing operation can be optimized, for example, the proper drag reducer concentration is determined according to the salinity and the size of the proppant.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority and benefit of co - pending U.S. Patent Application No. 17 / 941,633, filed on September 9, 2022, and titled "Apparatus and Method for Determining Static Settling Velocity of Proppant in Fracturing Fluid", the entire disclosure of which is incorporated herein by reference in its entirety for all purposes. Background Technical Field

[0004] The present disclosure generally relates to fracturing fluid formulations, and more particularly to using proppant settling time to determine the optimal drag - reducing agent formulation for fracturing fluids. Background Art

[0005] Hydrocarbons such as oil and gas can be produced from wells drilled into hydrocarbon reservoirs. For low - permeability or formation - damaged reservoirs, the flow rate of hydrocarbons into the production well may be very low. In such cases, the well is typically stimulated by a hydraulic fracturing operation. For a hydraulic fracturing treatment, first, a viscous fluid without proppant (pad fluid) is pumped in at a high enough rate and pressure to break the formation and create fractures. Subsequently, a fracturing fluid (proppant - carrying fluid) is pumped in to transport proppants such as sand and ceramic particles into the fractures to keep the fractures open so that hydrocarbons can flow into the wellbore. The ability to carry proppant is one of the most important properties of the proppant - carrying fluid. These fluids can be guar - based linear gels and polyacrylamide - based drag - reducing agent solutions. A proppant - carrying fluid with high proppant - carrying capacity can transport proppants into fractures far from the wellbore to increase the surface area in contact with the wellbore. The temperature of the reservoir, the concentration and chemical structure of the polymer in the proppant - carrying fluid, the salinity and hardness of the proppant - carrying fluid, and the size and density of the proppants all affect the settling of proppants in the proppant - carrying fluid.

[0006] Therefore, determining the correct concentration and formulation of the drag - reducing agent in the proppant - carrying fluid is crucial for efficient hydrocarbon production. Currently, there are two methods for qualitatively estimating the properties of proppants in fracturing fluids. The first method is to estimate the settling of proppants by visual observation. The second method is also to conduct a proppant transport test through simulation to visually observe the settling of proppants in the fractures. Neither of these two methods can provide quantitative data for measuring these settling characteristics. Therefore, there is an urgent need in the prior art for a method for determining the optimal drag - reducing agent loading and formulation for different reservoir properties. Summary of the Invention

[0007] An embodiment of the present invention can provide an apparatus for measuring the settling velocity of proppants. The apparatus may include a transparent container filled with fracturing fluid. The apparatus may further include a camera to record multiple images at set time intervals. The apparatus may also include a computer to analyze the images captured by the camera.

[0008] In some embodiments, the transparent container can be circular, triangular, square, or hexagonal. The fracturing fluid can also include a proppant and a friction reducer. The size of the proppant can be 8 - 140 mesh, and the concentration present in the fracturing fluid can be 0.25 - 6 lb m / gal. The friction reducer can be a polyacrylamide - based friction reducer, and the concentration present in the fracturing fluid can be 0.01 - 30 gpt.

[0009] In some embodiments, the camera can take images at intervals from once per second to once every 6 hours. The computer can also include image - analysis software. In some embodiments, the software is ImageJ. In other embodiments, the fracturing fluid can also include a guar - based linear gel.

[0010] The second embodiment of the present technology provides a method for determining the settling height of a proppant. First, a fracturing fluid containing a proppant and a friction reducer can be placed in a transparent container. Then, the fracturing fluid is photographed at a predetermined time interval. The images can be uploaded to a computer, and the images can be analyzed in the computer to determine the settling height of the proppant.

[0011] In some embodiments, the pictures can be cropped before analyzing the images. The analysis can include color - threshold measurements to determine the saturation value of the images. These measurements can also include generating a saturation histogram. In other embodiments, the analysis can be brightness analysis. The determination of the settling time and height can be performed by one or more macros.

[0012] The third embodiment of the present invention provides a method for determining the settling velocity of a proppant in a fracturing fluid. In this method, images of the proppant in the fracturing fluid are taken over time. These images can be analyzed by a computer to determine the settling height in each image. The settling velocity can be determined by identifying the period of constant change in the settling height for each time period.

[0013] In some embodiments, the analysis can be color - threshold measurements to determine the saturation value of the images. The image - taking interval can vary from 1 second to 6 hours. In some embodiments, a second period with an accelerating velocity can be identified. Additionally, a third period with a decelerating velocity can be identified. Both of these periods can be excluded from the calculation of the settling velocity. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present technology can be better understood by reading the following detailed description of non - limiting embodiments of the present technology and referring to the accompanying drawings, wherein:

[0015] Figure 1 is a device for measuring the settling velocity of a proppant according to an embodiment of the present disclosure.

[0016] Figure 2 is a method for determining the proppant settlement height according to an embodiment of the present technology.

[0017] Figure 3A is an exemplary embodiment showing the initial image, the cropped image, and the generated saturation evaluation.

[0018] Figure 3B is an exemplary embodiment showing the settlement height measurement based on the saturation evaluation.

[0019] Figure 4 is an exemplary proppant settlement curve over time according to an embodiment of the present technology.

[0020] Figure 5 are the experimental results of different types of drag reducers in the method of the present invention.

[0021] Figure 6 are the experimental results of different concentrations of drag reducers in the method of the present invention.

[0022] Figure 7 are the experimental results of different types of proppants in the method of the present invention.

[0023] Figure 8 are the experimental results of different fracturing fluid brines in the method of the present invention. Detailed implementation manners

[0024] When referring to the following description of the preferred embodiments and the accompanying drawings, the above aspects, features, and advantages of the present technology will be further understood, where like reference numerals represent like elements. When describing the preferred embodiments of the technology shown in the drawings, specific terms will be used for clarity. However, the present technology is not intended to be limited to the specific terms used, and it should be understood that each specific term includes equivalents that operate in a similar manner to achieve a similar purpose.

[0025] When introducing the elements of the various embodiments of the present invention, the articles "a", "an", "the", and "said" are intended to indicate the presence of one or more elements. The terms "comprising", "including", and "having" are intended to be inclusive, meaning that there may be additional elements in addition to the listed elements. Any examples of operating parameters and / or environmental conditions do not exclude other parameters / conditions of the disclosed embodiments. In addition, it should be understood that when referring to "an embodiment", "embodiments", "certain embodiments", or "other embodiments" of the present invention, it is not intended to be construed as excluding the existence of other embodiments that also include the described features. In addition, when referring to terms such as "above", "below", "upper", "lower", "side", "front", "rear", or other terms related to orientation, they are relative to the illustrated embodiments and are not intended to limit or exclude other orientations.

[0026] The present invention relates to an apparatus and method for analyzing an image generated by static settlement of proppants in a fracturing fluid having a drag reducer. In particular, the provided apparatus and method can be used to determine the static settlement velocity of proppants in a fracturing fluid. This can be used to optimize the concentration of the drag reducer in the fracturing fluid in field applications. This can also be used to optimize the chemical structure of the drag reducer (such as a polyacrylamide-based drag reducer) during the synthesis of the drag reducer.

[0027] Generally, an apparatus and method for determining the static settlement velocity of proppants in a hydraulic fracturing fluid are described as follows. A uniformly mixed fracturing fluid containing proppants is poured into a transparent container. A fixed camera can be used to continuously capture static settlement images of the proppants in the fracturing fluid, and the camera can be set to automatically capture images. By analyzing the images of a specific proppant concentration determined using a selected saturation range, the position is tracked to determine the velocity of the static settlement of the proppants.

[0028] Figure 1 is an embodiment of an apparatus according to an embodiment of the present technology. The apparatus can include a transparent container 102 and a camera 104. The transparent container 102 can be of any shape, such as circular, triangular, square, hexagonal, or any other suitable configuration.

[0029] The transparent container 102 can be filled with a fracturing fluid as Figure 1 shown. The fracturing fluid can include proppants and a drag reducer. The proppants can be sand, ceramic particles, glass beads, or any other solid particles known in the art used as proppants. In an embodiment of the present invention, the size of the proppants can be 8 - 140 mesh (105 µm - 2.38 mm), 16 - 30 mesh (595 µm - 1190 µm), 20 - 40 mesh (400 µm - 841 µm), 30 - 50 mesh (297 µm - 595 µm), 40 - 70 mesh (210 µm - 400 µm), or 70 - 140 mesh (105 µm - 210 µm). The concentration of proppants in the fracturing fluid can be any value between 0.25 lb m / gal US to 6 lb m / gal US (30 kg / m³ - 719 kg / m³).

[0030] The drag reducer in the fracturing fluid can be a polyacrylamide-based drag reducer or any other suitable drag reducer known in the art. The concentration of the drag reducer in the fracturing fluid can be any value between 0.01 gpt and 30 gpt (gallons per thousand gallons). The fracturing fluid can also be a linear gel fracturing fluid.

[0031] The camera 104 can be any suitable camera capable of taking images at regular time intervals either on its own or through an external controller connected to the camera. The time interval between each image can be from about 1 second to about 6 hours.

[0032] Figure 2 is an embodiment for determining the proppant settlement method according to an embodiment of the present invention. In step 202, the system can be set up by mixing the fracturing fluid sample to be tested and setting the image interval of the camera. In step 204, the sample can be poured into a transparent container, and then the camera starts taking images. The images can be taken within a set time period or manually stopped based on visual observation of the fracturing fluid sample.

[0033] In step 206, the images can be imported into a computer for analysis. To analyze the images, first, in step 208, the images can be cropped to include only the part of the image that needs to be analyzed. This can be the area where the proppant has settled within the transparent container. Then, in step 210, a color threshold measurement can be run on the resulting cropped image to determine the saturation values at different heights within the transparent container. This can result in a saturation histogram of the image. The analysis range can be from half of the peak of the previous image to 255. As Figure 3A shown in the example. Here, the image of the transparent container (shown in full) is cropped into the composite image in the lower right corner and saturation analysis is performed. The saturation analysis can be carried out by the ImageJ image processing program or any suitable software known in the art. In other embodiments, instead of saturation analysis, brightness analysis can be performed on the images.

[0034] Saturation analysis can be used to determine the settlement height at the time the image is taken in step 212. As Figure 3B shown in the example. This process can be repeated for each image taken. In some embodiments, one or more macros can be used to determine the settlement height and settlement time of each image. This can generate a chart as Figure 4 shown. The chart can include three independent time periods marked in the figure. Time period (a) can be the initial unstable state at the start of the analysis, when the proppant may accelerate its settlement due to gravity. Time period (b) depicts the interval during which the settlement height changes at a constant rate over time. The slope of this interval (change in height over time) can be the settlement velocity of the proppant. Finally, time period (c) depicts the situation where the settlement velocity may slow down when the proppant reaches its final settlement height.

[0035] Generally, the settlement velocity can be used to evaluate the ability of the fracturing fluid to carry the proppant. A lower settlement velocity can enable the fracturing fluid to have better sand-carrying capacity. This can be used to select appropriate drag reducer products and concentrations for use in fracturing operations.

[0036] Figures 5 - 8 It is an exemplary embodiment of how a device and method determine different settling velocities according to different fracturing fluid conditions. Figure 5 It is an embodiment of how different drag reducers change the settling velocity of proppants. In the experiment, the brine used to prepare the fracturing fluid was 2 wt% KCl. The concentration of the drag reducer was 8 gpt in all cases. The proppant with a concentration of 2 ppg (pounds per gallon) was 100-mesh sand. Four different polyacrylamide-based drag reducers were tested, and the resulting settling velocities were 0.61 - 0.095 cm / s.

[0037] Figure 6 It is an embodiment depicting how the concentration of the drag reducer affects the settling velocity. In this example, drag reducer 104 was selected and its concentration was varied between 2 gpt and 8 gpt, while the proppant and brine conditions remained the same as Figure 5 shown. The change in the concentration of the drag reducer resulted in settling velocities of 0.56 - 0.095 cm / s.

[0038] Figure 7 It is an embodiment where the proppant varies between 40 / 70-mesh sand and 100-mesh sand. In this embodiment, the properties of the brine, the type of drag reducer, and the concentration of the drag reducer remain unchanged. The change in the proppant results in a change in the settling velocity from 0.095 cm / s to 0.38 cm / s.

[0039] Figure 8 It is an embodiment of the change in brine concentration between experiments. Here, the salt concentration in the brine varies between 7 wt% and 1 wt% of the solution. The type and concentration of the drag reducer and the proppant remain unchanged. The experimental results show that the settling velocities are 0.032 cm / s to 0.29 cm / s.

[0040] Although the techniques herein have been described with reference to embodiments, it should be understood that these embodiments are only for illustrating the principles and applications of the techniques. Therefore, it should be understood that various modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the techniques defined by the appended claims.

Claims

1. An apparatus for measuring the settling velocity of proppants, comprising: A transparent container filled with fracturing fluid; A camera for recording multiple images at a time interval; And A computer for analyzing the multiple images from the camera.

2. The apparatus according to claim 1, wherein the transparent container is circular, triangular, square or hexagonal.

3. The apparatus according to claim 1, wherein the fracturing fluid further comprises: Proppants; And Drag reducer.

4. The apparatus according to claim 3, wherein the proppant is between 8 and 140 mesh, and the concentration of the proppant present in the fracturing fluid is about 0.25 - 6 lb m / gal.

5. The apparatus according to claim 3, wherein the drag reducer is a polyacrylamide-based drag reducer, and the concentration of the drag reducer present in the fracturing fluid is about 0.01 - 30 gpt.

6. The apparatus according to claim 1, wherein the shooting interval of the multiple images is about 1 second to about 6 hours.

7. The apparatus according to claim 1, wherein the computer further comprises image analysis software.

8. The apparatus according to claim 7, wherein the image analysis software is ImageJ.

9. The apparatus according to claim 1, wherein the fracturing fluid further comprises: Guar gum-based linear gel.

10. A method for determining the settling height of proppants, comprising: Placing a fracturing fluid containing proppants and a drag reducer in a transparent container; Taking multiple images at a predetermined interval over a period of time; Uploading the multiple images to a computer; and Analyzing the multiple images by the computer to determine the settling height of the proppants.

11. The method according to claim 10, further comprising: Cropping the uploaded multiple images before the analysis.

12. The method according to claim 10, wherein the analysis of the multiple images is color threshold measurement to determine the saturation value of the multiple images.

13. The method according to claim 12, further comprising: Generating a saturation histogram from the analysis of the multiple images.

14. The method according to claim 10, wherein the analysis of the multiple images is brightness analysis.

15. The method according to claim 10, wherein the settling height and settling time are determined by one or more macros.

16. A method for determining the settling velocity of proppants in a fracturing fluid, comprising: Taking multiple images of the proppants in the fracturing fluid over time; Analyzing the multiple images to determine the settling height of each image; And Determining the settling velocity by finding a first time period during which the settling height changes constantly for each time period.

17. The method according to claim 16, wherein the analysis of the multiple images further comprises: Performing color threshold measurement to determine the saturation value of the multiple images.

18. The method according to claim 16, wherein the shooting interval of the multiple images is about 1 second to about 6 hours.

19. The method according to claim 16, further comprising: Identifying a second time period with an accelerating settling velocity to exclude from the calculation of the settling velocity.

20. The method according to claim 16, further comprising: Identifying a third time period with a decelerating settling velocity to exclude from the calculation of the settling velocity.

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