Microgravity-Hybrid Microgravity

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Exploration Technique: Microgravity-Hybrid Microgravity

Exploration Technique Information
Exploration Group: Geophysical Techniques
Exploration Sub Group: Gravity Techniques
Parent Exploration Technique: Gravity Techniques
Information Provided by Technique
Lithology:
Stratigraphic/Structural: Ground subsidence can be mapped using microgravity
Hydrological: Monitoring net mass changes of a geothermal reservoir due to production and reinjection processes
Thermal: Changes in liquid density due to temperature changes in the reservoir
Cost Information
Low-End Estimate (USD): 50.005,000 centUSD
0.05 kUSD
5.0e-5 MUSD
5.0e-8 TUSD
/ station
Median Estimate (USD): 61.676,167 centUSD
0.0617 kUSD
6.167e-5 MUSD
6.167e-8 TUSD
/ station
High-End Estimate (USD): 115.0011,500 centUSD
0.115 kUSD
1.15e-4 MUSD
1.15e-7 TUSD
/ station
Time Required
Low-End Estimate: 0.30 days8.213552e-4 years
7.2 hours
0.0429 weeks
0.00986 months
/ 10 stn
Median Estimate: 0.36 days9.856263e-4 years
8.64 hours
0.0514 weeks
0.0118 months
/ 10 stn
High-End Estimate: 1.20 days0.00329 years
28.8 hours
0.171 weeks
0.0394 months
/ 10 stn
Additional Info
Cost/Time Dependency: Location, Size, Resolution, Terrain, Weather
Dictionary.png
Microgravity-Hybrid Microgravity:
Microgravity measurements precisely monitor subtle changes in gravity with time in order to understand mass gain or loss in a subsurface reservoir.
Other definitions:Wikipedia Reegle


 
Introduction
Reservoir monitoring during the exploitation of a geothermal field is imperative for the sustainable and environmentally responsible management of a geothermal resource. Microgravity is a powerful reservoir monitoring tool which enables an understanding of changes in mass in the subsurface.
 
Use in Geothermal Exploration
The intent of a microgravity survey at a geothermal field is to understand net mass changes of the geothermal reservoir over time. The changes in gravity are caused by: vertical ground movement (mainly subsidence); changes in shallow groundwater levels; liquid drawdown or saturation changes in the two-phase zone; and changes in liquid density resulting from temperature changes. Vertical ground movement and shallow groundwater levels need to be surveyed separately using GPS and shallow well data and corrected for in the microgravity survey to obtain net mass change. [1]

Microgravity surveys produce contour maps of gravity changes, through which regions of net mass loss or gain can be identified over a specified time period in between measurements.

For instance, at the Wairakei geothermal field in New Zealand, the ground subsidence achieved a maximum vertical ground movement of 11 m in one area of the field. Additionally, the maximum subsidence rate (in mm/yr) between gravity measurements may be calculated. [1]


 
Field Procedures
Microgravity measurements require that the precise location of the gravity measurement be reoccupied for consistency within the dataset. For additional information on the gravity survey, refer to Ground Gravity Survey.
 
Environmental Mitigation Measures
Microgravity provides a means to monitor environmental effects of the production of a geothermal field, namely ground subsidence. Through the application of microgravity surveys, the extent of subsidence may be monitored and corrected for in the production/reinjection strategy of the field.
 
Physical Properties


 
Best Practices
• Prior to the development of the geothermal field, a baseline data set should be established to record pre-exploitation conditions.
• Microgravity measurements should be recorded outside the boundary of the known geothermal field as well in order to characterize the fluid flow upon reinjection.
• The frequency of reoccupation of the microgravity stations should be greater during the initial production of the field, when the largest changes may be anticipated.
• Microgravity data should be applied in conjunction with numerical reservoir simulation models. [1]










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