Table 2 Review of common cement placement methods in geothermal wells

Stage cementing: single stage, multi-stage

Suitable once expected cement column pressure is too high; lower possibility of casing collapse; method can be used as a back-up for other cementing methods

Not preferred when circulation losses occur; volume of cement mixture cannot be flexibly adjusted; continuous cementing is not allowed; rather long operation time; possibility of premature cement setting; applicable only when selective intervals are to be cemented or require different cement composition

Inner-string (stinger method)

Advisable for wider casing sections; smaller cement contamination and waste; decreased displacement time; continuous cementing possible

Long tripping time of cementing string; possible failure of stage collars due to temperature conditions; potential hole packing off; possible fracturing and drilling kicks propagation; possible cement residues inside the work string and premature cement setting

Reverse circulation

Greatly reduced bottom hole pressures; reduced or eliminated need for cement retarder use; lower costs of consumables and secondary cementing jobs; not all cement slurry is exposed to high temperatures; increase early cement compressive strength; decrease pumping and cement setting time; lower hydraulic horsepower of pumps required; lower cement waste; allows for continuous pumping

Cement job relies on the quality of the radioactive tracers or other dyeing products; possibly long residues of hardened cement inside the casing and at the well bottom; uncertainty of cement reaching the casing shoe; complex cementing procedures; specialized simulation software and need for cementing specialists; unconventional and custom made cementing tools necessary; long-term effects in geothermal wells are not known

Tie-back

Easy job execution; no elastomer and temperature sensitive parts; can be used for casing repair

Possible separation from the liner pipe; problems with placing due to debris from previous cementing jobs; additional tubing costs; possible collapse due to water pockets

Lightweight cement

Reduced pressures, fluid loss, and formation fracturing; higher compressive strengths and decreased permeability of cement; good gas migration protection; better protection against cyclic loads

High market price; additional rig equipment needed; complex cementing procedure; long-term effects in geothermal wells are not known

Cementing through annulus packer

May be positioned above loss zone to prevent migration of cement into the loss zone; easily implemented into the conventional drill string; can be activated from the surface once needed

Include elastomer parts which might fail under high temperatures; packer failure and leaking