Hydraulic fracture analysis method

• US 4,802,144 A
• Filed: 03/20/1986
• Issued: 01/31/1989
• Est. Priority Date: 03/20/1986
• Status: Expired due to Term

• Current Assignee: Pinnacle Technologies, Inc. (Carbo Ceramics Incorporated), Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Applied Geomechanics Inc. (Carbo Ceramics Incorporated)
• Inventors: St. Lawrence, William, Holzhausen, Gary R.
• Primary Examiner(s): Moskowitz, Nelson
• Assistant Examiner(s): SWANN, TOD R
• Application Number:
  US06/841,645
• Time in Patent Office: 1,048 Days
• Field of Search: 181/105, 181/30, 367/25, 367/35, 367/73, 367/86, 73/155, 364/421, 166/250, 166/254, 175/48
• US Class Current: 367/35
• CPC Class Codes: E21B 43/26 by forming crevices or fractures
• CPC Class Codes: E21B 49/006 Measuring wall stresses in the borehole
• CPC Class Codes: E21B 49/008 by injection test; by analysing pressure variations in an injection or production test, e.g. for estimating the skin factor measuring pressure E21B47/06
• CPC Class Codes: G01V 1/133 using fluidic driving means, e.g. highly pressurised fluids; using implosionG01V1/104 takes precedence
• CPC Class Codes: G01V 1/46 Data acquisition

Abstract

The growth of a hydraulic fracture increases the period of free oscillations in the well connected to the fracture. Simultaneously, the decay rate of free oscillations decreases. The properties of forced oscillations in a well also change during fracture growth. All of these effects result from the changing impedance of the hydraulic fracture that intersects the well. Hydraulic fracture impedance can be defined in terms of the hydraulic resistance and the hydraulic capacitance of a fracture. Fracture impedance can be determined directly by measuring the ratio of down hole pressure and flow oscillation or indirectly from well head impedance measurements using impedance transfere functions. Well head pressure measurements can also be used to evaluate fracture impedance by comparing them to pressure oscillations computed with hydraulic models that include fractures with different impedances. Because impedance is a function of fracture dimensions and the elasticity of the surrounding rock, impedance analysis can be used to evaluate the geometry of the fracture by analyzing the data which results from free and forced oscillations in the well, and looking for a match between the data and theoretical models of projected shapes of the fracture.

Claims

1. A method of determining the geometry of a hydraulic fracture in the earth communicating with the surface of the earth through a well bore or the like comprising the steps of

(a) perturbing fluid in the well bore to induce oscillation in a fluid in said well bore, said oscillation extending to the surface of the well bore,

(b) measuring the resulting pressure oscillations at at least one point in the well bore,

(c) calculating the theoretical shape of the fracture in the earth based on the oscillations detected in the well bore.

2. A method as in claim 1 including the step of providing a source of oscillations at the surface of the well bore.

3. A method as in claim 1 including the step of providing a plurality of sources of oscillations within the well bore.

4. A method as in claim 1 wherein said calculating step comprises calculating the theoretical oscillations that would result at that measurement point from the applied perturbation from a reasonable estimation of the fracture shape, and

comparing the measured pressure oscillations with the theoretically calculated oscillations to estimate the shape of the fracture.

5. A method as in claim 4 including the step of determining the geometric growth of a hydraulic fracture by repeated application of the method of claim 4 and comparing the estimate of fracture shape and dimension with the measurement of actual oscillations.

6. A method as in claim 4 wherein theoretical oscillations are calculated for a variety of reasonable fracture shapes, and the fracture shape is selected which yields pressure or flow oscillations most closely resembling the measured pressure or flow oscillations as the best approximation of the true shape and dimensions of the hydraulic fracture in the subsurface.

7. A method as in claim 6 including the step of determining the growth of a hydraulic fracture by repeated application of the method of claim 4 and comparing the estimate of fracture shape and dimension with the measurement of actual oscillations.

8. The method of claim 1 and further comprising the step of perturbing fluid in the well bore to induce oscillation in a fluid in said well bore, said oscillation extending to the bottom of the well bore.

9. A method of estimating hydraulic fracture geometry from transient pressure oscillations in a well bore, comprising the steps of

providing a well bore in communication with the fracture region to be examined,

determining properties of a fluid in the well bore or fracture which influence oscillatory response of the fluid,

determining geometry of the well bore and location of potential fluid flow from the wall into the fracture,

perturbing the fluid in the well bore to create transient pressure and flow in the well bore extending to the surface of the well bore,

measuring the transient fluid behavior of the fluid in the well bore,

estimating the hydraulic fracture geometry that best explains the measured pressure or flow oscillations.

10. A method as in claim 9 in which the property determining step includes the step of determining the wave speed and viscosity of the fluid.

11. A method as in claim 9 wherein the perturbation is produced by rapidly removing a slug of fluid from the pressured well bore.

12. A method as in claim 9 wherein the perturbation is caused by rapidly injecting a slug of fluid in the well bore.

13. A method as in claim 9 wherein the perturbation is caused by oscillatory action of reciprocating pumps.

14. A method as in claim 9 including the step of measuring the transient fluid behavior at the well head.

15. A method as in claim 9 including the step of measuring the transient fluid behavior in the well.

16. A method as in claim 9 and further comprising the step of perturbing the fluid in the well bore to create transient pressure and flow in the well bore extending to the bottom of the well bore.

17. A method of determining the orientation of a hydraulic fracture plane in the earth comprising

positioning an array of sensors for measuring seismic ground motion above a region which includes the fracture,

providing a well bore having fluid therein communicating with the fracture to be defined,

perturbing the fluid to cause transient pressure or flow oscillations in the fluid column in the well bore,

measuring seismic ground motion induced by the transient pressure and flow oscillations in the fracture,

calculating, using theory of wave propagation, the ground motion expected of fractures of different orientations,

comparing the measured ground motion with the calculated ground motion patterns representing fractures of different orientations,

selecting the fracture orientation that yields calculated seismic ground motions must closely resembling the measured seismic ground motions as the most probable fracture orientation, and

calculating a probable fracture orientation based on the seismic motion of the ground;

wherein the measuring step includes the step of measuring particle motion in a plane that is not perpendicular to the fracture plane, and

wherein only first motion or particles is measured in said measuring step.

18. A method as in claim 17 wherein the measurement step includes measuring particle motions in a horizontal plane, the particle motion to be measured being upward and/or downward.

19. A method of determining the orientation of a hydraulic fracture plane in the earth comprising

positioning an array of sensors for measuring seismic ground motion above a region which includes the fracture,

providing a well bore having fluid therein communicating with the fracture to be defined,

perturbing the fluid to cause transient pressure or flow oscillations in the fluid column in the well bore,

measuring seismic ground motion induced by the transient pressure and flow oscillations in the fracture,

calculating, using theory of wave propagation, the ground motion expected of fractures of different orientations,

comparing the measured ground motion with the calculated ground motion patterns representing fractures of different orientations,

selecting the fracture orientation that yields calculated seismic ground motions most closely resembling the measured seismic ground motions as the most probable fracture orientation, and

calculating a probable fracture orientation based on the seismic motion of the ground,

wherein the measuring step includes the step of measuring particle motion in a plane that is not perpendicular to the fracture plane, and

wherein the measuring step measures the history of oscillatory particle motion, and said calculating step studies the symmetry of oscillatory particle motion.

20. A method of determining the orientation of a hydraulic fracture plane in the earth comprising

positioning an array of sensors for measuring seismic ground motion above a region which includes the fracture,

providing a well bore having fluid therein communicating with the fracture to be defined,

perturbing the fluid to cause transient pressure or flow oscillations in the fluid column in the well bore,

measuring seismic ground motion induced by the transient pressure and flow oscillations in the fracture,

calculating, using theory of wave propagation, the ground motion expected of fractures of different orientations,

comparing the measured ground motion with the calculated ground motion patterns representing fractures of different orientations,

selecting the fracture orientation that yields calculated seismic ground motions most closely resembling the measured seismic ground motions as the most probable fracture orientation, and

calculating a probable fracture orientation based on the seismic motion of the ground,

wherein the measuring step includes the step of measuring particle motion in a plane perpendicular to the fracture plane,

wherein the measuring step measures the history of oscillatory particle motion, and said calculating step studies the symmetry of oscillatory particle motion, and

wherein the fracture to be studied is vertical, and the particle motions are horizontal in a plane that is also horizontal and perpendicular to the fracture.