Enhanced geothermal systems and methods

Abstract

The invention relates to a method of designing an enhanced geothermal system and characterising at least one fracture in an enhanced geothermal system. The enhanced geothermal system comprises at least one well combination of at least one injector well and at least one production well. The method comprises forming at least one stage fracture from at least one well of the well combination according to a fracture treatment design and injecting at least one tracer into the at least one stage fracture. The method comprising circulating fluid from at least a first well to at least a second well of well combination via the at least one stage fracture; wherein the circulated fluid carries at least one circulation tracer and collecting samples of fluid from at least one well and analysing tracer concentrations with respect to sampling time. The method comprises calculating at least one fracture characteristic from the analysis of the tracer concentrations.

1 . A method of characterising at least one fracture in an enhanced geothermal system comprising at least one well combination of at least one injector well and at least one production well, the method comprising:
 forming at least one stage fracture from at least one well of the well combination according to a fracture treatment design;   injecting at least one tracer into the at least one stage fracture;   circulating fluid from at least a first well to at least a second well of well combination via the at least one stage fracture; wherein the circulated fluid carries at least one circulation tracer;   collecting samples of fluid from at least one well and analysing tracer concentrations with respect to sampling time;   calculating at least one fracture characteristic from the analysis of the tracer concentrations.   
     
     
         2 . The method according to  claim 1  comprising forming two or more stage fractures from at least one well of the well combination; injecting at least one distinct tracer into each stage fracture and circulating fluid through each stage fracture. 
     
     
         3 . The method according to  claim 1  comprising injecting the at least one tracer into the stage fracture during the formation of the fracture. 
     
     
         4 . The method according to  claim 1  comprising, for each fracture, calculating a respective fracture circulation efficiency from a calculated flow characteristic and at least one fracture geometry parameter. 
     
     
         5 . The method according to  claim 1  comprising injecting at least one stage tracer in fracturing treatments in more than one well. 
     
     
         6 . The method according to  claim 1  comprising circulating fluid from at least the first well to at least the second well at two or more flow rates. 
     
     
         7 . The method according to  claim 1  comprising collecting samples of fluid from the at least first and/or second well during a period of stable flow. 
     
     
         8 . The method according to  claim 1  wherein the at least one tracer comprises two or more tracers in a distinct combination or ratio. 
     
     
         9 . The method according to  claim 1  comprising measuring surface flow rate, measuring surface pressure, measuring downhole pressure, measuring pressure at a stage hydraulic fracture, calculating downhole pressure for each stage fracture and/or measuring pressure at each stage hydraulic fracture. 
     
     
         10 . The method according to  claim 1  wherein the at least one fracture characteristic is selected from the group comprising fracture geometry; fracture width; hydraulic width; fracture aperture; cross-sectional area of flow; hydraulic cross-sectional area; percentage flow distribution; percentage flow distribution per stage; proppant transport capacity; fracture circulation volume; fracture circulation volume per stage; permeability; permeability per stage; hydraulic fracture conductivity; and/or hydraulic fracture conductivity per stage. 
     
     
         11 . The method according to  claim 1  comprising designing an enhanced geothermal system comprising calculating a fracture circulation efficiency metric from a calculated flow characteristic and at least one fracture geometry parameter;
 based on the fracture circulation efficiency metric, determining at least one design parameter for the enhanced geothermal system. 
 
     
     
         12 . The method according to  claim 11  wherein the at least one design parameter is selected from the group comprising the number of and placement of further injection and/or production wells; proximity of further injection and/or production wells from existing wells; pattern or distribution of further wells in the geothermal reservoir, selection of cased hole completion; selection of open-hole completion; selection of well geometry; perforation clusters per stage; fracture geometry; fracture fluid viscosity; proppant type and/or mass; fracture fluid volume; fracture width; hydraulic width; fracture aperture; cross-sectional area of flow; hydraulic cross-sectional area; percentage flow distribution; percentage flow distribution per stage; proppant transport capacity; fracture circulation volume; fracture circulation volume per stage; permeability; permeability per stage; conductivity; conductivity per stage; post-fracture treatments such as fracture plugging and/or acidization; fracture hydraulic conductivity, the rate of circulation of a circulated heat transfer fluid; circulation fluid type and/or the viscosity of a circulated heat transfer fluid. 
     
     
         13 . The method according to  claim 11  wherein the flow characteristic used for calculating a fracture circulation efficiency metric is selected from the group comprising a flow rate allocation for at least one of the stage fractures, a flow rate allocation for each stage of a multistage fracture, an average fracture circulation volume between the first and second wells, a fracture circulation volume for at least one of the stage fractures and/or a fracture circulation volume for each stage of a multistage fracture. 
     
     
         14 . The method according to  claim 11  wherein the at least one fracture geometry parameter is selected from the group comprising a parameter derived from measured data, stimulated reservoir volume (SRV); fracturing fluid treatment volume; and/or proppant pack porosity volume; hydraulic fracture surface area and/or propped fracture surface area. 
     
     
         15 . The method according to  claim 1  comprising injecting the at least one fracture tracer into at least one fracture and/or circulating the at least one circulation tracer from a tracer source installed, arranged or positioned in the first well. 
     
     
         16 . The method according to  claim 1  comprising measuring and/or monitoring arrival time of each tracer in the second well. 
     
     
         17 . The method according to  claim 1  comprising calculating a mathematical derivative of a tracer response curve. 
     
     
         18 . The method according to  claim 1  wherein the calculated derivative is characterized by means of Residence Time Distribution (RTD) analysis. 
     
     
         19 . An interpretation method of characterising at least one fracture in an enhanced geothermal system, the method comprising:
 providing tracer data, the tracer data previously obtained by analysis of samples of fluid collected from at least one well in a well combination comprising at least one injector well and at least one production well, at least one fracture from least one well in the well combination according to a fracture treatment, wherein each fracture has at least one distinct tracer in the fracture;   wherein fluid has been circulated fluid from at least one well to at least a second well of the well combination via the at least one fracture, and wherein the circulated fluid carries at least one circulation tracer to at least the second well;   calculating at least one characteristic from the tracer data.   
     
     
         20 . A method of designing an enhanced geothermal system, the method comprising:
 in a well combination comprising at least one injector well and at least one production well,   forming at least one stage fracture from at least one well of the well combination according to a fracture treatment design;   injecting at least one tracer into the at least one stage fracture;   circulating fluid from the at least one well to at least a second well of well combination via the at least one fracture; wherein the circulated fluid carries at least one circulation tracer;   collecting samples of fluid from the at least one well and analysing tracer concentrations with respect to sampling time;   calculating a flow characteristic from the analysis of the tracer concentrations;   calculating a fracture circulation efficiency metric from the calculated flow characteristic and at least one fracture geometry parameter;   based on the fracture circulation efficiency metric, determining at least one design parameter for the enhanced geothermal system.