mkdocs theory added

![Figure description](../images/DC1D_cartoondoublet.png)

*Figure 1: Figure of a doublet system, showing the production well and injection well, with the reservoir in between. The production well extracts hot water from the reservoir, which is then used to produce energy, while the injection well returns cooled water back into the reservoir.*

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*Figure 1: Figure of a doublet system, showing the production well and injection well, with the reservoir in between. 

The production well extracts hot water from the reservoir, which is then used to produce energy, 

while the injection well returns cooled water back into the reservoir.*

The following parameter values are proposed for the doublet model, which can be adjusted in the ThermoGIS configuration file.

The Skin factor of -1 corresponds to having a 45° slanted well in the reservoir and the -3 

corresponds to the situation after well stimulation  (hydraulic or acidication) or drilling horizontal or multilateral sections 

in the reservoir.

The well distance is optimized in such a way that the maximum cooling of the production water is 1% of ΔT after 50 years. 

This means that the difference between production water and return (injection) temperature after 50 years,

is at least 99% of the original temperature difference.

| Technical parameter                                   | symbol    | value      | unit       |

|-------------------------------------------------------|-----------|------------|------------|

| use Kestin visicosty                                  | kestin    | True       | bool       |

| distance between the two wells  at reservoir          | L         | optimized  | m          |

| pump system efficiency                                | ESPn      | 0.6        | -          |

| production pump depth                                 | ESPz      | 500        | m          |

| pump pressure, limited to 30% of hydrostatic pressure | ΔPtotal   | optimized  | bar        |

| well trajectory curvature factor                      | scurve    | 1.1        | -          |

| calculation segment length                            | Δz        | 50         | m          |

| inner diameter (casing)                               | rw        | 8.5        | inch       |

| casing roughness                                      | m         | 1.38       | milli-inch |

| injector well skin (with stimulation)                 | S         | -1 (-3)    | -          |

| production well skin (with stimulation)               | S         | -1 (-3)    | -          |

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# Economic Model

The ThermoGIS economic model is based on a cashflow calculation which determines

the levelized costs of net geothermal converted energy in ct/kWh and NPV (million€). 

The economic model takes as input the gross power outcome of the DoubletCalc calculation 

and converts this to net power, in agreement with either the direct heat, heat pump, Chiller or ORC scenario 

as described above. The subsurface setting of the reservoir, pumping power requirements,

production parameters and net power produced are used to determine the CAPEX and OPEX for the lifetime of the project.

[well costs and plant costs](cost_model.md) These include well and plant construction Capital Expenditure (CAPEX) 

and operating and maintenance costs (OPEX)

# Modelling Geothermal Doublets

# economic model

## Cost model

The following CAPEX and OPEX items are included in the cashflow model:

- CAPEX<sub>wells</sub>

- CAPEX<sub>stimulation</sub>

- CAPEX<sub>plant</sub>

##  Well costs

*CAPEX<sub>wells</sub> = 375,000 + 1050 ∙s<sub>curve</sub>∙ z<sub>tvdtop</sub> +  0.3∙ ∙s<sub>curve</sub>∙  z<sub>tvdtop</sub>^2*

## stimulation costs

If stimulation is activated, the stimulation costs can be  included in the CAPEX modell, e.g.:

*CAPEX<sub>stimulation</sub> = 0.75 million€*

## Plant costs

*CAPEX<sub>plant</sub> = CAPEX<sub>base</sub> + CAPEX<sub>other,var</sub> ∙ P<sub>net</sub>*

where:

- CAPEX<sub>base</sub> is the base capital expenditure, which includes the cost of the geothermal plant and other fixed costs.

- CAPEX<sub>other,var</sub> is the variable capital expenditure, which includes the cost for scaling to a certain capacity of geothermal power

- P<sub>net</sub> is the net power output of the geothermal plant, which is the geothermal power output  

corrected for the conversion efficiency any parasitic power losses. For direct heat (including heat pump) it does not include conversion to heat of the ESP power,

and added heat in the heatpump from the compressor.

## Operating Expenditure (OPEX)

accounts for yearly operational expenses of the geothermal plant, which include maintenance, repairs, and other ongoing costs.

*OPEX = OPEX<sub>base</sub> + OPEX<sub>power</sub> ∙ P<sub>net</sub> + OPEX<sub>heat,var</sub> ∙ Hprod<sub>y</sub>*

where:

- OPEX<sub>base</sub> is the base operating expenditure, which includes the cost of operating and maintaining the geothermal plant.

- OPEX<sub>power</sub> is the scaling of operating expenditure per unit of net power capacity.

- OPEX<sub>heat,var</sub> is the additional operating expenditure per unit of net heat output, 

which includes the cost of operating and maintaining the geothermal plant for direct heat applications.

- Hprod<sub>year</sub> is the geothermal energy producted  of the geothermal plant on a yearly basis [kWh].

the proposed values for these parameters are dependent on the energy conversion technology and the type of geothermal resource [directheat](../energyconversion/directheat.md), 

[directheat with heat pump](../energyconversion/directheatHP.md), [chiller](../energyconversion/chiller.md) and [ORC](../energeyconversion/ORC.md) and can be adjusted in the ThermoGIS configuration file.

In the [directheat with heat pump](../energyconversion/directheatHP.md) there are additional CAPEX<sub>hp,var</sub> and OPEX<sub>hp</sub> parameters for the heat pump system, 

which are included in the cashflow model as follows:

*CAPEX<sub>hp</sub> = CAPEX<sub>hp,var</sub> ∙ P<sub>net</sub>*

*OPEX<sub>hp</sub> = OPEX<sub>hp</sub> ∙ P<sub>net</sub>*

## What is a geothermal doublet?

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