Mechanically assisted fracture initiation

Abstract

Systems and methods are described for controlling the location where a fracture initiates and the fracture direction at the initiation point. A mechanical device is positioned in a main wellbore or partially or fully in a side hole off of the main wellbore. The mechanical device is actuated so as to contact the formation walls and induce stress in the formation. According to some embodiments, fractures are also initiated using the mechanical device. A hydraulic fracturing process is then carried out to fracture and/or propagate fractures in locations and/or directions according to the actuation of the mechanical device.

What is claimed is: 
     
         1 . A system for inducing fractures in a subterranean rock formation surrounding a wellbore, the system comprising:
 an expandable mechanical device configured to make physical contact with two or more rock surfaces on the subterranean rock formation and to apply force on the two or more rock surfaces thereby inducing stress in the subterranean rock formation; and   a hydraulic fracturing sub-system configured to isolate a subterranean zone including the mechanical device and to pump fluid into the isolated zone thereby inducing further stress in the rock formation such that one or more fractures are induced and/or propagated in the formation, wherein the one or more fractures are in a location and or direction that is based in part on the force applied from the expandable mechanical device.   
     
     
         2 . A system according to  claim 1 , wherein the force applied on the two or more rock surfaces is in a direction that is not perpendicular to a central axis of the wellbore. 
     
     
         3 . A system according to  claim 1 , wherein the force applied on the two or more rock surfaces initiates a first fracture which is thereafter propagated by the pumped fluid from the hydraulic fracturing sub-system. 
     
     
         4 . A system according to  claim 1 , wherein the expandable mechanical device is further configured so as to be at least partially positionable in a side hole formed off of the wellbore, wherein at least one of the two or more rock surfaces are in the side hole. 
     
     
         5 . A system according to  claim 4 , further comprising a drilling sub-system configured to form the side hole using a drilling process. 
     
     
         6 . A system according to  claim 4 , wherein the side hole has a central axis perpendicular to a central longitudinal axis of the wellbore. 
     
     
         7 . A system according to  claim 4 , wherein the side hole has a central axis that is not perpendicular to a central longitudinal axis of the wellbore. 
     
     
         8 . A system according to  claim 1 , wherein the expandable mechanical device is further configured such that actuation of the device causes a first end piece to move towards a second end piece thereby causing two or more rods to move away from a central longitudinal axis of the device, and wherein at least portions of the two or more rods are configured to contact the two or more rock surfaces. 
     
     
         9 . A system according to  claim 8 , wherein the two or more rods includes a first pair of rods and a second pair of rods, and the mechanical device is further configured to expand asymmetrically such that the first pair of rods move away from the central axis of the device at a greater rate than the second pair of rods. 
     
     
         10 . A system according to  claim 1 , wherein the expandable mechanical device is further configured such that actuation of the device causes a first end piece to move away from a second end piece in a direction parallel to a central longitudinal axis of the device, and wherein the first and second end pieces are configured to contact the two or more rock surfaces. 
     
     
         11 . A system according to  claim 10 , wherein the actuation is caused by turning a nut in a direction about the central longitudinal axis of the device. 
     
     
         12 . A system according to  claim 10 , wherein the actuation is caused by turning a nut in a direction about a secondary axis that is perpendicular to the central longitudinal axis of the device. 
     
     
         13 . A system according to  claim 1 , wherein the expandable mechanical device includes one or more sensors for measuring one or more parameters while deployed in the wellbore. 
     
     
         14 . A system according to  claim 13 , wherein the one or more parameters includes stress in three orthogonal directions. 
     
     
         15 . A system according to  claim 13 , wherein the one or more parameters is selected from a group consisting of temperature, pressure, acoustic, and fluid flow. 
     
     
         16 . A system according to  claim 13 , wherein the expandable mechanical device is further configured to store measurements from the one or more sensors. 
     
     
         17 . A system according to  claim 13 , wherein the expandable mechanical device is further configured to transmit measurements from the one or more sensors directly or indirectly to a surface analysis system. 
     
     
         18 . A system according to  claim 1 , wherein the expandable mechanical device forces fluid into a hydraulic cylinder for expansion. 
     
     
         19 . A system according to  claim 1 , wherein the expandable mechanical device includes one or more non-expandable spacers positioned between the two or more rock surfaces on the subterranean rock formation. 
     
     
         20 . A system according to  claim 1 , wherein the mechanical device is further configured with a sharp edge for making physical contact with at least one of the rock surfaces so as to initiate a fracture in the at least one of the rock surface. 
     
     
         21 . A method for inducing fractures in a subterranean rock formation surrounding a wellbore, the method comprising:
 positioning an expandable mechanical device in the wellbore;   expanding the mechanical device so as to make physical contact with two or more rock surfaces on the subterranean rock formation;   further expanding the mechanical device so as to induce stress in the subterranean rock formation; and   pumping hydraulic fluid into an isolated zone of the wellbore including the expandable mechanical device so as to induce and/or propagate one or more fractures in the formation, wherein the one or more fractures are in a location and/or direction that is based in part on the force applied from the expandable mechanical device.   
     
     
         22 . A method according to  claim 21 , further comprising forming a side hole off of the wellbore, wherein the expandable mechanical device is positioned at least partially in the side hole and at least one of the two or more rock surfaces is in the side hole. 
     
     
         23 . A method according to  claim 22 , wherein the side hole is formed using a drilling process. 
     
     
         24 . A method according to  claim 22 , wherein the side hole has a central axis perpendicular to a central longitudinal axis of the wellbore. 
     
     
         25 . A method according to  claim 22 , wherein the side hole has a central axis that is not perpendicular to a central longitudinal axis of the wellbore. 
     
     
         26 . A method according to  claim 22 , wherein the force applied on the two or more rock surfaces is in a direction that is not perpendicular to a central axis of the wellbore. 
     
     
         27 . A method according to  claim 21 , wherein the expanding and the further expanding include actuating the mechanical device such that a first end piece moves towards a second end piece along a central longitudinal axis of the device thereby causing two or more rods to move away from the central longitudinal axis of device, and wherein at least portions of the two or more rods make contact with the two or more formation rock surfaces. 
     
     
         28 . A method according to  claim 27 , wherein the two or more rods includes a first pair of rods and a second pair of rods, and the expanding is asymmetric such that the first pair of rods move away from the central axis of the device at a greater rate than the second pair of rods. 
     
     
         29 . A method according to  claim 21 , wherein the expanding and the further expanding include actuating the mechanical device such that a first end piece moves away from a second end piece in a direction parallel to a central longitudinal axis of the device, and wherein the first and second end pieces make contact with the two or more formation rock surfaces. 
     
     
         30 . A method for mechanically inducing fractures in a subterranean rock formation surrounding a wellbore, the method comprising:
 positioning an expandable mechanical device in the wellbore;   expanding the mechanical device so as to make physical contact with two or more rock surfaces on the subterranean rock formation;   further expanding the mechanical device so as to initiate one or more fractures in the subterranean rock formation; and   pumping hydraulic fluid into an isolated zone of the wellbore including the expandable mechanical device so as to further propagate the one or more fractures in the formation.   
     
     
         31 . A method according to  claim 30 , further comprising forming a side hole off of the wellbore, wherein the expandable mechanical device is positioned at least partially in the side hole. 
     
     
         32 . A method according to  claim 30 , wherein said further expanding includes providing an acceleration of the mechanical device towards at least one of the two or more rock surfaces so as to impart a shock to the subterranean rock formation thereby facilitating the initiation of the one or more fractures in the subterranean rock formation. 
     
     
         33 . A method according to  claim 30 , wherein said further expanding includes vibrating part of the mechanical device so as to impart vibrational energy into the subterranean rock formation thereby facilitating the initiation of the one or more fractures in the subterranean rock formation. 
     
     
         34 . A method according to  claim 30 , further comprising introducing chemically reactive fluids so as to selectively weaken the subterranean rock formation in specific directions thereby facilitating the initiation of the one or more fractures in the subterranean rock formation.