Dual-tube flooded reverse circulation drilling has been successfully applied to drill and run casing through a lost circulation/cross flow zone at Rye Patch, NV. The zone drilled and cased had previously resulted in the temporary abandonment of the well after conventional cement plugs had been unsuccessful in plugging the zone. A Lang Exploratory Drilling dual-tube reverse circulation rig was successfully used for the job. Dual-tube flooded reverse circulation uses air to lift the cuttings out of the hole. Reverse circulation drilling, while not customarily used in geothermal drilling, is standard practice in mining, water well, and large borehole drilling.
Polyurethe grouting has been successfully applied to a lost circulation zone in a geothermal well at Rye Patch, NV. Previously, this zone had resulted in the temporary abandonment of the well after conventional cement plugs had been unsuccessful. The techniques applied to grouting with polyurethane were adapted from civil engineering technology where polyurethane is becoming the grout of choice for sealing boreholes with large voids and high cross flows.
Foam cement i s a versatile and economical light weight cementing slurry that can be used in geothermal wells. Ultralight foam cement slurries develop useful compressive strength and can be used for primary cementing infragile formation intervals and lost circulation areas. Successful circulation of a full column of cement is practically assured with the proper use of foam cement. Geothermal foam cementing success is dependent upon proper applications, slurry design, and cementing procedures. These points will be covered along with the result s of foam cementing at The Union Geothermal Of Indonesia, Gunung Sal ak Project, West Java, Indonesia.
Three wells were drilled at Puna Geothermal Venture, Hawaii in 2005 – a production well redrill, a new production well, and a new injection well. Several innovative procedures were used to deal with difficulties and successfully complete the wells. A casing patch was used to repair parted casing. Foam cement was used for the intermediate casing and foam cement was reverse circulated for the production casing. Mud motors were used for most of the drilling to increase rate of penetration. Micronized cellulose lost circulation material (LCM) was used to protect moderate permeability zones in the injection well and a hydrostatic bailer was used to swab cuttings and mud back out of the zones.
During the drilling of injection well KS-13 in 2005 at the Puna Geothermal Venture (PGV) wellfield, on the island of Hawaii, a 75-meter interval of diorite containing brown glass inclusions was penetrated at a depth of 2415 m. At a depth of 2488 m a melt of dacitic composition was encountered. The melt flowed up the wellbore and was repeatedly redrilled over a depth interval of ~8 m, producing several kilograms of clear, colorless vitric cuttings at the surface. The dacitic glass cuttings have a perlitic texture, a silica content of 67 wgt.%, are enriched in alkalis and nearly devoid of mafic minerals with the exception of rare pyroxene phenocrysts and minor euhedral to
amorphous magnetite. The melt zone is overlain by an interval of strong greenschist facies metamorphism in basaltic and dioritic dike rock. The occurrence of an anhydrous dacite melt indicates a rock temperature of approximately 1050oC (1922oF) and sufficient residence time of underlying basaltic magma to generate a significant volume of highly differentiated material. Heat flux from the magma into the overlying geothermal reservoir is ~3830 mW/m2, an order of magnitude greater than for mid-ocean ridges. The geologic conditions at PGV combine tensional tectonics with magmatic temperatures at readily drillable depths (<2500 m).
Geothermal wells in the Blue Mountain area of Nevada have experienced problems caused by losses during primary cementing of well casings, often requiring top jobs to
complete. Conventional cement designs were not effective in solving the problem. Also, as deeper casing setting depths were required because of reservoir characteristics, the risk of not achieving good cement jobs increased. Analysis of cement jobs in this geothermal field led to the need for developing nontraditional cement designs. This paper documents the analysis, planning, and execution of foamed-cementing operations used to successfully perform primary 13 3/8-in. casing cement work. Previous cementing practices are presented, as well as the advantages and design of foamed cementing for this application. A post-job analysis and cost comparison of foamed versus conventional cementing is also presented.
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