Device and method for evaluating fracture initiation and propagation, and stress sensitivity of propped fracture

Patent metadata

Field	Value
Publication number	US-11313775-B2
Application number	US-202016879156-A
Country	US
Kind code	B2
Filing date	May 20, 2020
Priority date	Oct 9, 2019
Publication date	Apr 26, 2022
Grant date	Apr 26, 2022

Abstract

A device and method for evaluating fracture initiation and propagation, and a stress sensitivity of a propped fracture is provided. The device includes a core part, a confining pressure loading part, a fracturing fluid pumping part, a stress sensitivity testing part and a fracture monitoring part. The method evaluates fracture initiation and propagation, and a stress sensitivity of a propped fracture using the above device and is reliable and simple to operate and guides optimization of construction parameters of hydraulic fracturing, thus achieving improvement in productivity of an oil and gas well.

First claim

What is claimed is:

1. A device for evaluating fracture initiation and propagation, and a stress sensitivity of a propped fracture, comprising a core part, a confining pressure loading part, a fracturing fluid pumping part, a stress sensitivity testing part and a fracture monitoring part, wherein the core part comprises a core ( 42 ), a wellbore casing ( 24 ), an uncased wellbore ( 27 ) and a core supporting plate ( 38 ), the core is located on the core supporting plate, at most 16 acoustic emission probes ( 35 ) are installed in the core, a borehole is arranged in a middle of the core, the wellbore casing is arranged at an upper end of the borehole, and the uncased wellbore is arranged at a lower end of the borehole;
wherein the confining pressure loading part comprises triaxial hydraulic pumps, an oil tank ( 21 ), a confining pressure cover plate ( 23 ) and a confining pressure base ( 30 ), inlet ends of the triaxial hydraulic pumps are connected with the oil tank ( 21 ) and outlet ends of the triaxial hydraulic pumps are respectively connected with triaxial oil cylinders, the core part is located in a space formed by the confining pressure cover plate and the confining pressure base, the oil cylinders, backing plates, seepage plates and the core are respectively arranged in the space from outside to inside, the seepage plates are fixed and sealed with the core through a sealant rubber sheath ( 36 ), and the triaxial hydraulic pumps apply triaxial confining pressures to the core through the oil cylinders, the backing plates and the seepage plates in X, Y and Z directions respectively;
wherein the fracturing fluid pumping part comprises a CO 2 check valve ( 1 ), a CO 2 intermediate container ( 2 ), a low-temperature bath ( 3 ), a CO 2 pressure regulating valve ( 4 ), a CO 2 gas cylinder ( 5 ), a constant-speed and constant-pressure pump ( 6 ), a first water storage tank ( 7 ), a first intermediate container ( 8 ) and a second intermediate container ( 9 );
wherein the stress sensitivity testing part comprises the constant-speed and constant-pressure pump ( 6 ), the first water storage tank ( 7 ), the first intermediate container ( 8 ), the second intermediate container ( 9 ), as well as an electronic balance ( 11 ), a second water storage tank ( 12 ), an N 2 check valve ( 13 ), a flow controller ( 14 ), an N 2 pressure regulating valve ( 15 ), an N 2 gas cylinder ( 16 ), an X-axis seepage plate ( 28 ), a Y-axis seepage plate ( 40 ) and a Z-axis seepage plate ( 29 ), the X-axis seepage plate, the Y-axis seepage plate and the Z-axis seepage plate are located in three directions of the core, the seepage plates are fixed and sealed with the core through the sealant rubber sheath ( 36 ), so as to measure a gas permeability and a liquid permeability of the core; and
wherein the fracture monitoring part comprises a first computer ( 10 ), the electronic balance ( 11 ), the constant-speed and constant-pressure pump ( 6 ), the triaxial hydraulic pumps, the flow controller ( 14 ), as well as a second computer ( 22 ), an acoustic emission receiving device ( 17 ), the acoustic emission probes ( 35 ) and high-speed cameras ( 26 ) with light sources,
wherein the first computer is connected with the electronic balance, the constant-speed and constant-pressure pump, the triaxial hydraulic pumps and the flow controller, and is used for collecting and recording pressure data and flow data,
wherein the second computer is connected with the acoustic emission receiving device and the high-speed cameras with the light sources, the acoustic emission receiving device receives signals transmitted by the acoustic emission probes, the high-speed cameras with the light sources are respectively located in an X-axis backing plate and a Y-axis backing plate, and the second computer monitors and analyzes fracture initiation and propagation of a hydraulic fracture in the core and an acoustic emission signal.

2. The device for evaluating the fracture initiation and propagation, and the stress sensitivity of the propped fracture according to claim 1 , wherein the triaxial hydraulic pumps comprise an X-axis hydraulic pump ( 20 ), a Y-axis hydraulic pump ( 19 ) and a Z-axis hydraulic pump ( 18 ), and the triaxial oil cylinders comprise an X-axis oil cylinder ( 37 ), a Y-axis oil cylinder ( 41 ) and a Z-axis oil cylinder ( 32 ); and the triaxial confining pressures are applied to the core by the X-axis hydraulic pump through the X-axis oil cylinder ( 37 ), the X-axis backing plate ( 34 ) and the X-axis seepage plate ( 28 ), by the Y-axis hydraulic pump through the Y-axis oil cylinder ( 41 ), the Y-axis backing plate ( 39 ) and the Y-axis seepage plate ( 40 ), and by the Z-axis hydraulic pump through the Z-axis oil cylinder ( 32 ), a Z-axis upper backing plate ( 33 ) or a Z-axis lower backing plate ( 31 ), and the Z-axis seepage plate ( 29 ).

3. A method for evaluating fracture initiation and propagation, and a stress sensitivity of a propped fracture using the device according to claim 1 , sequentially comprising the following steps:
step 1: setting X-axis, Y-axis and Z-axis pressures, and applying triaxial loads to the core;
step 2: testing a permeability of the core before fracturing with clean water or nitrogen, and calculating a uniaxial permeability or an overall triaxial permeability of the core flowing from the wellbore to a reservoir or from the reservoir to the wellbore;
step 3: preparing a required fracturing fluid and taking a proppant, adding the fracturing fluid into the first intermediate container as a prepad fluid, adding the fracturing fluid and the proppant into the second intermediate container and using the mixture as a sand-carrying fluid, and stirring the sand-carrying fluid evenly;
step 4: setting a constant displacement to inject the prepad fluid into the core, determining fracture initiation and propagation in the core through a shooting image, the acoustic emission signal and a pressure at an inlet of the wellbore, and injecting the sand-carrying fluid into the core after the core is fractured; or fracturing the core with liquid carbon dioxide; and
step 5: testing a stress sensitivity of a propped fracture of the core after fracturing with clean water or nitrogen, setting the constant displacement to inject water or gas into the wellbore or the triaxial seepage plates, monitoring a quality of the electronic balance and changes of pressure gauges at the inlet and outlet ends, and calculating the uniaxial permeability or the overall triaxial permeability of the core flowing from the wellbore to the reservoir or from the reservoir to the wellbore; and testing a change of a permeability of the propped fracture under different confining pressures by adjusting the triaxial pressures to evaluate the stress sensitivity of the propped fracture.

4. The method according to claim 3 , wherein the low-temperature bath liquefies CO 2 and then discharges the liquefied CO 2 into the CO 2 intermediate container, the constant-speed and constant-pressure pump provides a displacement pressure to drive the liquefied CO 2 out of the intermediate container, the liquefied CO 2 flows through the CO 2 check valve and then is injected into the core, and facture initiation at an uncased part forms an artificial fracture; or the constant-speed and constant-pressure pump absorbs water from the first water storage tank and provides the displacement pressure, the prepad fluid in the first intermediate container and the sand-carrying fluid in the second intermediate container are injected into the core, the facture initiation at the uncased part forms the artificial fracture, and the proppant is carried into the fracture to prop the fracture.

5. The method according to claim 3 , wherein nitrogen with a constant volume flow is injected into the uncased wellbore t

Assignees

• Univ Southwest Petroleum

Inventors

• Li Yongming
• Chen Bo
• Guo Zixi

Classifications

• G01N2203/0067

  Fracture or rupture · CPC title

• G01N2203/0256

  Triaxial, i.e. the forces being applied along three normal axes of the specimen · CPC title

• E21B49/00

  Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells · CPC title

• G01N33/24 Primary

  Earth materials (G01N33/42 takes precedence) · CPC title

• G01N3/062

  with mechanical indicating or recording means · CPC title