Methods For Establishing A Subsurface Fracture Network

Abstract

A method of creating a network of fractures in a reservoir is provided. The method includes designing a desired fracture network system, and determining required in situ stresses to create the desired fracture network within the reservoir. The method further includes designing a layout of wells to alter the in situ stresses within the stress field, and then injecting a fracturing fluid under pressure into the reservoir to create an initial set of fractures within the reservoir. The method also includes monitoring the in situ stresses within the stress field, and modifying the in situ stresses within the stress field. The method then includes injecting a fracturing fluid under pressure into the reservoir in order to expand upon the initial set of fractures and to create the network of fractures. A method for producing hydrocarbons from a subsurface formation is also provided herein, wherein a fracture network is created from a single, deviated wellbore production.

What is claimed is: 
     
         1 . A method of creating a network of fractures in a reservoir, the reservoir having an in situ stress field, and the method comprising:
 designing a desired fracture network system using geomechanical simulation;   determining required in situ stresses to create the desired fracture network within a reservoir having an in situ stress field;   designing a layout of wells to alter the in situ stresses within the stress field;   injecting a fracturing fluid under pressure into the reservoir in order to create an initial set of fractures;   monitoring the in situ stresses within the stress field;   updating the geomechanical simulation based on the monitored in situ stresses;   designing a program of modifying the in situ stress within the stress field using geomechanical simulation;   modifying the in situ stresses within the stress field by implementing at least one aspect of the program; and   injecting a fracturing fluid under pressure into the reservoir in order to expand upon the initial set of fractures and to create the desired fracture network.   
     
     
         2 . The method of  claim 1 , wherein the reservoir has a permeability less than 10 millidarcies. 
     
     
         3 . The method of  claim 2 , wherein:
 at least two wells in the layout of wells are completed for the production of hydrocarbon fluids; and   the network of fractures is designed to optimize production of the hydrocarbon fluids.   
     
     
         4 . The method of  claim 3 , wherein injecting a fracturing fluid under pressure into the reservoir comprises injecting the fluid through the at least two wells completed for the production of hydrocarbon fluids. 
     
     
         5 . The method of  claim 3 , wherein at least two wells in the layout of wells are completed for the injection of fluids as part of enhanced oil recovery. 
     
     
         6 . The method of  claim 5 , wherein injecting a fluid under pressure into the reservoir comprises injecting the fluid through the wells completed for the injection of fluids. 
     
     
         7 . The method of  claim 6 , wherein the fluids represent an aqueous fluid. 
     
     
         8 . The method of  claim 4 , further comprising:
 producing hydrocarbon fluids from the wells completed for the production of hydrocarbon fluids after the initial set of fractures is created.   
     
     
         9 . The method of  claim 8 , wherein modifying the in situ stresses comprises the producing of hydrocarbon fluids. 
     
     
         10 . The method of  claim 8 , wherein modifying the in situ stresses comprises injecting a fluid into at least a portion of the reservoir in order to increase pore pressure within the in situ stress field. 
     
     
         11 . The method of  claim 2 , further comprising:
 after monitoring the in situ stresses within the stress field, again injecting a fracturing fluid under pressure into the reservoir.   
     
     
         12 . The method of  claim 1 , wherein:
 at least two wells in the layout of wells are completed for the production of geothermally-produced steam;   injecting a fluid under pressure into the reservoir comprises injecting the fluid through selected wells completed for the production of the geothermally-produced steam; and   the network of fractures is designed to optimize heat transfer for geothermal applications.   
     
     
         13 . The method of  claim 2 , wherein
 at least two wells in the layout of wells are completed for the injection of acid gases; and   injecting a fluid under pressure into the reservoir comprises injecting the fluid through selected wells completed for the injection of acid gases.   
     
     
         14 . The method of  claim 13 , wherein:
 the acid gases primarily comprise carbon dioxide; and   the carbon dioxide is injected as part of an enhanced oil recovery project.   
     
     
         15 . The method of  claim 13 , wherein:
 the acid gases primarily comprise carbon dioxide;   the carbon dioxide is injected as part of a sequestration operation; and   the network of fractures is designed to optimize CO 2  storage capacity.   
     
     
         16 . The method of  claim 2 , wherein:
 at least two wells in the layout of wells are completed for the injection of drill cuttings; and   injecting a fluid under pressure into the reservoir comprises injecting the fluid through selected wells completed for the injection of drill cuttings.   
     
     
         17 . The method of  claim 2 , wherein determining required in situ stresses to create the desired fracture network comprises (i) reviewing downhole pressure measurements from existing wells, (ii) reviewing micro-seismic monitoring conducted in existing wells, (iii) conducting downhole stress modeling, (iv) reviewing tiltmeter readings, or (v) combinations thereof. 
     
     
         18 . The method of  claim 2 , wherein:
 injecting a fluid under pressure into the reservoir comprises injecting a fluid through a plurality of wells that are part of the layout of wells; and   modifying the in situ stresses comprises injecting a fluid under pressure into each of the plurality of wells either (i) simultaneously, or (ii) in stages such that fluid is injected into one or more wells sequentially.   
     
     
         19 . The method of  claim 18 , wherein modifying the in situ stresses further comprises (i) specifying a length of time for injecting for selected wells, (ii) specifying a viscosity of fluid for injection into selected wells, (iii) modifying a temperature of the reservoir, or (iv) combinations thereof. 
     
     
         20 . The method of  claim 19 , wherein modifying a temperature of the reservoir comprises (i) injecting a heated gas into the reservoir, (ii) applying resistive heat to a rock matrix comprising the reservoir, (iii) actuating one or more downhole combustion burners, (iv) injecting a cooler fluid into the reservoir, or (v) combinations thereof. 
     
     
         21 . The method of  claim 2 , wherein modifying the in situ stresses comprises providing new perforations into the reservoir from selected wellbores, with the perforations being shot at a non-transverse angle relative to the wellbores. 
     
     
         22 . The method of  claim 2 , wherein modifying the in situ stresses comprises producing hydrocarbon fluids from the reservoir. 
     
     
         23 . The method of  claim 2 , wherein modifying the in situ stresses comprises injecting a fluid into the reservoir to increase pore pressure. 
     
     
         24 . The method of  claim 2 , wherein modifying the in situ stresses comprises establishing an assistive fracture path (i) by creating a plurality of radially offset perforations into the reservoir through a plurality of wells, (ii) by injecting an acidic fluid through a plurality of wells to create worm holes in the reservoir, or (iii) combinations thereof. 
     
     
         25 . The method of  claim 2 , wherein injecting a fluid into the reservoir to create the network of fractures comprises determining pump rates and associated shear rates for selected wells. 
     
     
         26 . The method of  claim 2 , wherein:
 the reservoir comprises two or more zones; and   the network of fractures is created within at least two different zones, such that:
 designing a desired fracture network system comprises designing a fracture network system in each of the at least two zones, and 
 injecting a fluid under pressure into the reservoir comprises injecting a fluid into each of the at least two zones so as to create the network of fractures within the at least two zones. 
   
     
     
         27 . A method of producing hydrocarbons from a subsurface formation, the formation having a permeability less than about 10 millidarcies, and the method comprising:
 providing a wellbore in the subsurface formation, the wellbore having been completed as a deviated wellbore, and the wellbore having been perforated within the subsurface formation along at least a first zone and a second zone;   fracturing the subsurface formation along the first and second zones to form substantially vertical fractures extending from the wellbore;   producing hydrocarbon fluids through the vertical fractures along the first and second zones;   monitoring the wellbore to determine when a change in orientation of the maximum principal stress occurs within the subsurface formation along the first and second zones;   injecting a fracturing fluid into the subsurface formation through perforations in the first and second zones, thereby creating a first new fractures within the subsurface formation that at least partially extends from the vertical fractures along a plane that is substantially transverse to the vertical fractures; and   producing hydrocarbons through the first new fractures and through the vertical fractures along the first and second zones.   
     
     
         28 . The method of  claim 27 , wherein:
 the deviated wellbore is completed as a substantially horizontal wellbore within the subsurface formation; and   the vertical fractures extend substantially transverse to the wellbore.   
     
     
         29 . The method of  claim 28 , wherein:
 monitoring the wellbore comprises (i) determining when a designated volume of hydrocarbon fluids have been produced from the wellbore; (ii) determining when a designated reduction in reservoir pressure within the subsurface formation has taken place; (iii) determining when a selected period of time of production has taken place; (iv) determining whether micro-seismic readings indicate a change in in situ stresses; (v) or combinations thereof.   
     
     
         30 . The method of  claim 28 , wherein:
 the wellbore has further been perforated within the subsurface formation along a third zone;   fracturing the subsurface formation further comprises fracturing the subsurface formation along the third zone to form additional vertical fractures extending from the wellbore;   producing hydrocarbon fluids through the vertical fractures further comprises producing hydrocarbon fluids along the third zone;   monitoring the wellbore further comprises monitoring the wellbore to determine when a change in maximum principal stress may occur within the subsurface formation along the third zone;   injecting a fracturing fluid into the subsurface formation to create the first new fractures further comprises injecting a fracturing fluid through perforations in the third zone; and   producing hydrocarbons through the first new fractures further comprises producing hydrocarbons through the vertical fractures along the third zone.   
     
     
         31 . The method of  claim 30 , further comprising:
 injecting a fracturing fluid into the subsurface formation through perforations in the first, second, and third zones, thereby creating second new fractures within the subsurface formation that at least partially extend from the (i) vertical fractures, (ii) the first new fractures, or (iii) both, along a plane that is substantially transverse to the vertical fractures; and   producing hydrocarbons through (i) the second new fractures, (ii) the first new fractures, and (iii) the vertical fractures along the first, second, and third zones.   
     
     
         32 . The method of  claim 31 , wherein the perforations along the first zone, the second zone, and the third zone are separated by a distance of between about 20 feet (6.1 meters) and 500 feet (152.4 meters). 
     
     
         33 . The method of  claim 31 , wherein the vertical fractures extend a distance of about 100 feet (30.5 meters) to 500 feet (152.4 meters) from the wellbore. 
     
     
         34 . The method of  claim 31 , further comprising:
 perforating the wellbore to create new perforations along a selected zone, wherein the new perforations are shot at a non-transverse angle relative to the wellbore;   injecting a fracturing fluid into the subsurface formation through the new perforations in the selected zone in order to fracture the subsurface formation along the selected zone; and   producing hydrocarbon fluids through perforations along the selected zone.   
     
     
         35 . A method of producing hydrocarbons from a subsurface formation, the formation having a permeability less than about 10 millidarcies, and the method comprising:
 providing a wellbore in the subsurface formation, the wellbore having been completed as a deviated wellbore, and the wellbore having been perforated along at least a first zone and a second zone;   fracturing the subsurface formation along the first and second zones to form substantially vertical fractures extending from the wellbore;   producing hydrocarbon fluids through the vertical fractures along the first and second zones;   injecting a fluid into the subsurface formation through perforations in the second zone, thereby raising reservoir pressure in the subsurface formation along the first zone and causing a change in the in situ stresses within the subsurface formation along the first zone;   injecting a fluid into the subsurface formation through perforations in the first zone, thereby causing a propagation of fractures in the subsurface formation along the first zone at least partially towards the second zone; and   producing hydrocarbons through the perforations along the first zone.   
     
     
         36 . The method of  claim 35 , wherein:
 the deviated wellbore is completed as a substantially horizontal wellbore within the subsurface formation; and   the vertical fractures extend substantially transverse to the wellbore.   
     
     
         37 . The method of  claim 36 , further comprising:
 producing hydrocarbons through the perforations along the second zone along with the production of hydrocarbons from the first zone.   
     
     
         38 . The method of  claim 36 , further comprising:
 monitoring the wellbore to determine when a change in maximum principal stress may occur within the subsurface formation along the first zone as a result of injecting the fluid into the second zone.   
     
     
         39 . The method of  claim 36 , wherein:
 monitoring the wellbore comprises (i) determining when a designated volume of hydrocarbon fluids have been produced from the first zone; (ii) determining when a designated reduction in reservoir pressure within the subsurface formation along the first zone has taken place; (iii) determining when a selected period of time of production has taken place; (iv) determining whether micro-seismic readings indicate a change in in situ stresses; (v) determining any changes in in situ stresses; (vi) determining when a selected volume of fluid has been injected into the subsurface formations through the perforations in the second zone; or (vii) combinations thereof.   
     
     
         40 . The method of  claim 36 , wherein:
 the wellbore has further been perforated within the subsurface formation along a third zone;   fracturing the subsurface formation further comprises fracturing the subsurface formation along the third zone to form additional vertical fractures extending from the wellbore;   producing hydrocarbon fluids through the vertical fractures further comprises producing hydrocarbon fluids along the third zone;   injecting a fluid into the subsurface formation through perforations in the second zone further raises reservoir pressure in the subsurface formation along the third zone, and further causes a change in the in situ stresses within the subsurface formation along the third zone; and   the method further comprises:
 injecting a fluid into the subsurface formation through perforations in the third zone, thereby causing a propagation of fractures in the subsurface formation along the third zone at least partially towards the second zone; and 
 producing hydrocarbons through the perforations along the third zone. 
   
     
     
         41 . The method of  claim 40 , further comprising:
 producing hydrocarbons through the perforations along the first and second zones along with the production of hydrocarbons from the third zone.   
     
     
         42 . The method of  claim 36 , wherein the perforations along the first zone and the second zone are separated by a distance of between about 20 feet (6.1 meters) and 500 feet (152.4 meters). 
     
     
         43 . The method of  claim 36 , wherein the fractures extending substantially transverse to the wellbore extend a distance of about 100 feet (30.5 meters) to 500 feet (152.4 meters) from the wellbore. 
     
     
         44 . The method of  claim 36 , further comprising:
 discontinuing production of hydrocarbons from the first zone;   injecting a fluid into the subsurface formation through perforations in the first zone, thereby raising reservoir pressure in the subsurface formation along the second zone and causing a change in the in situ stresses within the subsurface formation along the second zone;   injecting a fluid into the subsurface formation through perforations in the second zone, thereby causing a propagation of fractures in the subsurface formation along the second zone at least partially towards the first zone; and   producing hydrocarbons through the perforations along the second zone.   
     
     
         45 . The method of  claim 40 , further comprising:
 discontinuing production of hydrocarbons from the third zone;   injecting a fluid into the subsurface formation through perforations in the third zone, thereby raising reservoir pressure in the subsurface formation along the first zone and causing a change in the in situ stresses within the subsurface formation along the first zone;   injecting a fluid into the subsurface formation through perforations in the second zone, thereby causing a propagation of fractures in the subsurface formation along the second zone at least partially towards the third zone; and   producing hydrocarbons through the perforations along the second zone.   
     
     
         46 . The method of  claim 36 , further comprising:
 perforating the wellbore to create new perforations along a selected zone, wherein the new perforations are shot at a non-transverse angle relative to the wellbore;   injecting a fracturing fluid into the subsurface formation through the new perforations in the selected zone in order to fracture the subsurface formation along the selected zone; and   producing hydrocarbon fluids through perforations along the selected zone.   
     
     
         47 . A method of creating a network of fractures in a reservoir, the reservoir having an in situ stress field, and the method comprising:
 monitoring the in situ stresses within the stress field;   injecting a fracturing fluid under pressure through a first set of perforations into the reservoir in order to create an initial set of fractures;   producing native fluids from the reservoir to change in situ stresses within the stress field; and   injecting a fracturing fluid under pressure through a second set of perforations into the reservoir in order to expand upon the initial set of fractures and to create the network of fractures.   
     
     
         48 . The method of  claim 47 , further comprising:
 designing a desired fracture network system;   determining required in situ stresses to create the desired fracture network within the reservoir; and   designing a layout of wells to alter the in situ stresses within the stress field.