Methods and systems to control flow and heat transfer between subsurface wellbores connected hydraulically by fractures

Abstract

A controlled rate of propagation of the fluid saturation front or thermal front is desired in may oil and gas and geothermal operations. Natural fractures and fractures created during hydraulic stimulation may have heterogeneous hydraulic properties resulting in uneven flow distributions, therefore leading to short-circuiting and breakthrough issues. The present invention relates to wellbores connected hydraulically by multiple fracture zones; methods are directed to control for even flow distribution among fractures, regardless of heterogeneities in fracture hydraulic properties, and to control propagation of saturation fronts and thermal fronts in subsurface reservoirs.

1 .- 20 . (canceled) 
     
     
         21 . A method to enhance thermal sweep efficiency, comprising:
 determining a fracture spacing for a formation containing a natural source, wherein the fracture spacing is based on a characteristic distance of investigation of a temperature transient for the formation;   creating one or more fractures in the formation between an injection well and a production well based on the fracture spacing, wherein the fracture spacing provides reduced mass flow rate within the one or more fractures; and   flowing a fluid between the injection well and the production well through the one or more fractures.   
     
     
         22 . The method of  claim 21 , wherein determining the fracture spacing comprises:
 calculating the characteristic distance of investigation of the temperature transient based on a characteristic time; and   setting a fracture half-spacing equal to the characteristic distance of investigation.   
     
     
         23 . The method of  claim 21 , wherein determining the fracture spacing comprises:
 calculating an increase in thermal sustainability based on a reduction in the mass flow rate caused by a reduction in the fracture spacing.   
     
     
         24 . The method of  claim 21 , wherein determining the fracture spacing comprises:
 calculating a rate at which a thermal front propagates through the formation based on the fracture spacing.   
     
     
         25 . The method of  claim 21 , wherein creating the one or more fractures comprises:
 performing characterization tests to determine formation properties of the formation;   determining a perforation pattern based on the formation properties; and   hydraulically fracturing the formation based on the perforation pattern.   
     
     
         26 . The method of  claim 25 , wherein the formation properties comprise at least one of a potential for splay fractures, a potential for the one or more fractures to terminate against preexisting fractures, a potential for the one or more fractures to propagate through the preexisting fractures, or a potential for conductivity of the formation. 
     
     
         27 . The method of  claim 25 , wherein the characterization tests comprise at least one of a pressure transient test, a constant rate injection test, a shear stimulation test, a diagnostic fracture injection test, a step-rate injection test, or a step-pressure injection test. 
     
     
         28 . The method of  claim 21 , further comprising:
 monitoring a temperature profile between the injection well and the production well; and   adjusting a fluid flow rate based on detected variations in the temperature profile.   
     
     
         29 . The method of  claim 28 , wherein the temperature profile is monitored using distributed temperature fiber optics. 
     
     
         30 . The method of  claim 21 , further comprising:
 increasing fracture intensity of the one or more fractures to reduce the mass flow rate.   
     
     
         31 . The method of  claim 21 , wherein creating the one or more fractures comprises:
 calculating a perforation pressure drop in the injection well based on expected flow rates; and   determining a configuration of perforation clusters to achieve even flow distribution over the one or more fractures.   
     
     
         32 . A system for recovery of geothermal energy, the system comprising:
 an injection well in a formation containing a natural resource;   a production well in the formation; and   one or more fractures created between the injection well and the production well based on a fracture spacing, wherein the fracture spacing is determined based on a characteristic distance of investigation of a temperature transient for the formation, the fracture spacing providing reduced mass flow rate within the one or more fractures.   
     
     
         33 . The system of  claim 32 , further comprising:
 monitoring equipment comprising at least one of: a distributed network, a distributed fiber optic network, a pressure sensor, an acoustic sensor, a temperature sensor, a distributed temperature fiber optic network, or a distributed acoustic sensing fiber optic network.   
     
     
         34 . The system of  claim 32 , further comprising:
 an intelligent completion comprising one or more downhole sensors, one or more surface-controlled downhole flow control valves, and a well control platform to maintain, increase, or decrease flow through the injection well and the production well.   
     
     
         35 . The system of  claim 32 , wherein the characteristic distance of investigation of the temperature transient is calculated based on a characteristic time, a fracture half-spacing being equal to the characteristic distance of investigation. 
     
     
         36 . The system of  claim 32 , wherein the fracture spacing is determined based on an increase in thermal sustainability associated with a reduction in the mass flow rate. 
     
     
         37 . The system of  claim 32 , wherein the fracture spacing is determined based on a rate at which a thermal front propagates through the formation. 
     
     
         38 . The system of  claim 32 , wherein the one or more fractures are created based on a perforation pattern, the perforation pattern determined based on formation properties of the formation, the formation properties determined based on characterization tests performed on the formation. 
     
     
         39 . The system of  claim 38 , wherein the formation properties comprise at least one of a potential for splay fractures, a potential for the one or more fractures to terminate against preexisting fractures, a potential for the one or more fractures to propagate through the preexisting fractures, or a potential for conductivity of the formation. 
     
     
         40 . The system of  claim 38 , wherein the characterization tests comprise at least one of a pressure transient test, a constant rate injection test, a shear stimulation test, a diagnostic fracture injection test, a step-rate injection test, or a step-pressure injection test.