Abstract:

Many challenges arise when cementing geothermal wells. Lost circulation and temperature are

the main culprits for increased cost when trying to achieve zonal isolation. At the Puna

geothermal field, extreme lost circulation and bottom hole static temperatures in excess of 500°F

are not uncommon. The extreme conditions, coupled with the remoteness to drilling service

providers, represent a significant challenge. Reverse cementing was used to successfully

complete a job in a challenging environment and also significantly reduce cost in the cementing

phase of well completion. A demonstration of proper planning, designing, and execution of the

job is presented.

Abstract:

Complete cementing of casing strings is critical in geothermal wells to protect the casing and provide mechanical integrity to the well bore. Surface indicators allow drilling personnel to select the best method for remedial cementing. The ‘top fill’ method is selected when cement is observed at the surface during the primary cement job, but the cement subsequently falls down the annulus. The ‘top squeeze’ method is selected when there are no cement returns to surface during the course of the primary cement job. For each case, specific procedures must be followed to successfully complete a remedial cement job. These procedures should be planned in advance. In addition, these procedures are not dependent on the primary cementing technique. Either ‘top squeeze’ and/or ‘top fill’ may be used for any casing string that is run with a previously cemented casing string in place that has an annular preventer installed.

Abstract:

Cement plug setting is one of the most unpredictable and time consuming operations in the drilling process of a geothermal well, thus adding considerable cost and risk to drilling, completion, and workover operations. Setting of ten to twenty consecutive plugs for a single sidetracking job, each requiring up to 8 hours of wait time for the cement to cure, are not unheard of in the industry. Significant risk arises from the inability to support the cement slurry while it cures inside the wellbore.

Perigon’s cement support tool (CST™) was designed to increase the success rate of setting cement plugs by physically separating the plug from the drilling fluid while the slurry cures, just as if it was set at the bottom of a well or above a bridge plug. Another attractive feature of the CST™ tool is its drillability, and foldable aluminum and composite construction (Harestad, 2015), which enables it to be pumped through small diameter tubing and then enlarged in the well bore. This paper summarizes a recent, first-ever and successful plug setting operation using coiled tubing in a large diameter geothermal well casing.

Abstract:

Obtaining fracture gradient data is a critical objective in oil, gas, and geothermal well drilling, from the well construction perspective. Fracture gradient data is important for properly executing many drilling phases and maintaining safe practices. Applying proper well design techniques ensures that a well can be shut in safely, mitigates underground well control issues Availability of fracture gradient data also results in significant improvements to the design and reduces the cost of future wells in the same field by allowing for the determination of the minimum number of casing strings required for safe drilling and completion. Thus, measuring the fracture gradient at relevant depths in a well is critical to reducing well cost, producing a safe well design and reducing the likelihood of downhole well control incidents. The step rate formation integrity test method is a safe and practical method of measuring the fracture gradient and leak-off pressure of a well while minimizing the risk of causing lost circulation.

Abstract:

Drilling and completing geothermal wells involves a number of unique challenges. Included in these challenges is the cementing of various casing strings across what are typically weak formations prone to lost circulation. Not only must the cement systems used on these wells be light enough to be circulated in place, they must also withstand the stresses occurring in the cement sheath from cyclic loading. This paper presents a case history in which foamed cement was used in multiple casing strings of a Hawaiian geothermal well.

Abstract:

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.