Modelling Geothermal Reservoirs in CMG Simulation Suites

Reza Malakooti

Energi Simulation Summit 2021, September 30 – October 1

Outline

• Overview of Geothermal Systems

• Introduction to CMG simulators (STARS, GEM and CoFlow)

• Case examples of modelling of various geothermal systems

• Summary

• Hydrothermal (Conventional) Resources• Deep volcanic systems, dual permeability, faults, etc.• Water & steam production, water injection for reservoir

management

Geothermal Systems

Source: GeoVision Analysis 2019, US DOE

Source: US DOE, 2016

• Enhanced Geothermal Systems (EGS)• Hot Dry Rock (HDR), hydraulic fracturing to

enhance permeability of basement rock• Cold water circulation → Hot water production

• Fluid Flow in porous media• Generally naturally fractured reservoirs

• Heat Transfer:• Conduction• Convection • Dispersion

• Thermodynamics of mixtures, water, gases and solids (salts)• Geochemistry and reactions

• Heat and pressure drops along the wellbores• Wellbore conduction and convection for temperature drop• Wellbore hydraulics calculations for pressure drop

Physics in Geothermal Reservoirs

• Industry leading three-phase multi-component thermal and steam additive simulator

• Different gridding systems, naturally fractured and faulted reservoir systems

• Advanced well management options• Stable adaptive implicit formulation, high

performance, dynamic gridding• Geomechanics, geochemistry

Multiple training courses on STARS including ‘Introduction to Thermal EOR Modelling’and ‘Geothermal with STARS’

Source: cmgl.ca

CMG STARS

• Conventional Geothermal Reservoir Model• Geo-pressured reservoir with typical POR and PERM is built in

STARS to evaluate the effects of heat transfer and quantify the amount of energy produced

SCENARIO 1: Producers only SCENARIO 2: Adding Water injectors

Standard Geothermal System

• Task 1: Compare energy production rate for the 2 scenarios

Standard Geothermal System

• Task 2: Examine which reservoir properties most affect the produced enthalpy: use STARS+CMOST to build your Tornado Plot

Standard Geothermal System

Hot Dry Rock

Use the Builder Hydraulic Fracture Wizard to create an HF around the Wells Doublet:

• Closed systems• In very early stage – R&D and pilot projects• Small scale power generation but potentially very reliable• Very promising – no process water, no emissions, small footprint

• Geologic Thermal Energy Storage (GeoTES)

• Geothermal energy and geologic CO2 storage (GCS)

Geothermal Systems

GEM• Industry leading compositional simulator with full

energy equation.• Different gridding systems, naturally fractured and

faulted reservoir systems.• Stable adaptive implicit formulation, high

performance, dynamic gridding.• Geomechanics, geochemistry

CoFlow• Implicitly coupled reservoir and network

environment.• Multi-fidelity option of pressure/temperature

modelling in well/network facility• Building detailed facility infrastructure including

pipes, chokes, heat exchanger, pumps, etc to add geothermal reservoir/well systems

Source: cmgl.ca

CMG – GEM & CoFlow

Closed Loop Model Features

• Reservoir (and overburden) model in GEM• Vertical and build-up sections in CoFlow• Surface network in CoFlow• Multiple laterals, explicitly modeled in GEM (High fidelity)

= +

Case Example: GEM – CoFlow

Modelling Details in Coupled GEM – CoFlow

How Far Does the Temperature Front Go?

T = 20 years50m spacing, near wellbore temperature fronts (delta T > 20 C) collapse into each other

T = 20 years100m spacing, near wellbore temperature fronts (delta T > 20 C) don’t fully collapse into each other

Initial Results – Tubing Temperature

Bottom-Hole

Well-Head

Near wellbore effects leading to a lower BH and TH temperatures in 20m spacing case (dashed lines)

Follow Up Scenarios

• Increased number of laterals• Counter current flow in alternating laterals• NPV optimization including surface facilities• Alternate fluids e.g brines vs fresh water

• Optimization of both lateral length and spacing• Non-uniform lateral spacing

Single Well Closed Loop using CoFlow (No Reservoir Model)

Injection pressure = 20 atmProduction pressure = 10 atmInjection temperature = 20 C

Proxy for reservoir

Closed Loop Geothermal Modelling

STARS✓ Single well (annulus-tubing)

systems✓ Double well (U-configuration)✓ Easy to set-up horizontal

section for heat transfer

❖ Can’t attach to surface network (CoFlow)

❖ Artificial lift very basic

GEM✓ Double well (U-configuration)✓ Can attach to surface network

(CoFlow)

❖ Requires to set-up horizontal section for heat transfer

❖ Single well system can be modeled with analytical model only (using CoFlow)

Summary• Understanding the physics and chemistry of the interaction of rocks and fluids

in the subsurface domain is fundamental to the geothermal energy processes. • CMG’s compositional, thermal reservoir simulation suites such as STARS and

GEM enables modelling the various geothermal energy extraction techniques from hydrothermal (conventional) resources and enhanced geothermal systems (EGS).

• The heat extraction can be modelled by either producing hot water from and injecting cold water into hot geo-pressured reservoirs or recirculation of fluid throughout the U-tube wells configuration in hot dry rocks (closed systems).

• The advanced wellbore transient and integrated reservoir production modelling capabilities in CMG’s simulation suite also facilitates capturing relevant hydraulic and thermal interactions between the reservoir, wellbore and surface facility equipment.

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