Design, testing, and evaluation of an air injection grouting system for geothermal bores. Final report

Technical Report · Wed Apr 01 04:00:00 EST 1998

OSTI ID:362349

The objective of this research was to examine the feasibility of an air injection grouting system for geothermal bores. The system that was researched used a pressurized blow tank and a small diameter hose (3/4 or 1 inch) to pneumatically transport dry bentonite granules into a wet bore. Upon contact with the annular fluid in the bore, water or drilling mud, the particles hydrated and formed a grout. A valve on the bottom of the tank allowed the feed rate of particles into the hose to be adjusted. Granular bentonites that were tested ranged in particle size from four to fifty mesh. The pneumatic conveying properties of granular bentonites were studied in dry injection tests. For a fifty-foot length of three quarter inch hose, mass flow rates up to 50 lb/min were found at a tank pressure of 25 psi with air flow rates ranging from 8 to 17 scfm for pressures of 15 to 25 psi. Mass flow rates of over 100 lb/min at a pressure of 25 psi were reached with a one inch hose. Air flow rates ranged 27 to 50 scfm for pressures of 15 to 25 psi for the one inch hose. Testing simulating wet bore conditions were also performed. A method of removing the injection hose at a constant rate was found to produce a uniform, high solids content grout. A relationship between mass flow rate and the percent solids of the resulting grout was discovered in test with drilling mud as an annular fluid. The mass flow rate and percent solids relationship for tests in water was influenced by the type of granular bentonite. Permeability coefficients of air injected grouts were found to be similar to those of slurry bentonite grouts. Tests with a sand and bentonite mixture had flow rates similar to those found for straight granular bentonites, although the number of possible valve settings was reduced. The sand/bentonite mixture produced an acceptable grout in wet injection tests once the reduced yield of the mixture, due to the sand, was taken into account. A field trial conducted with the Solinst injector confirmed the feasibility of the air injection grouting concept and discovered practical concerns in applying the concept to field conditions.

• Research Organization: Electric Power Research Inst., Palo Alto, CA (United States); South Dakota State Univ., Brookings, SC (United States)
• Sponsoring Organization: Electric Power Research Inst., Palo Alto, CA (United States)
• OSTI ID: 362349
• Report Number(s): EPRI-TR--110481
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
BENTONITE
EXPERIMENTAL DATA
FIELD TESTS
GEOTHERMAL WELLS
GROUTING
MATERIALS HANDLING EQUIPMENT
PERMEABILITY
PNEUMATIC TRANSPORT
SEALING MATERIALS
SOLIDS FLOW