In 2010, a geothermal exploratory drilling program was conducted on Akutan Island, Alaska. The purpose of the drilling program was to obtain temperature gradient data to constrain resource capacity. The wells were designed to allow long-term monitoring and possible testing of the Akutan geothermal field. The 2010 drilling operations were carried out using wireline core equipment and were supported by helicopter. Two wells were drilled to respective depths of 253.9 meters and 457.2 meters. The first well (TG-2) was drilled directly above an outflow aquifer(s). A preliminary analysis of the TG-2 well showed that the well made 2-phase flow with a 190 liter per minute liquid phase via a 96 mm hole and from a depth of 177 to 178 m. The second well (TG-4) was drilled at the margins of the modeled outflow in order to conceptualize the size of the outflow resource. That well had very low permeability but displayed a high temperature gradient, with an extrapolated temperature of 164 deg C at 457 m. Some evidence that a deeper, hotter resource exists at or near the TG-4 site was found using mineralogical data. Preliminary analysis of data suggests that a pumped production well at the TG-2 site would be capable of a maximum production of 2.3 MW. Geochemical sampling of the fumarole gasses was carried out on the flank of the Akutan Volcano concurrent with the drilling. The data obtained from drilling will be combined with core and geochemical analysis in order to form a resource model of the field preliminary to
Reverse circulation cementing has been used for a number of years to cement casing in geothermal wells. There are several methods of reverse circulation cementing, all of which send cement down the annulus from surface to the casing shoe. The four most commonly used will be discussed. All of these methods significantly reduce the circulating bottom hole pressure (BHP). Reducing this pressure reduces the risk of loss of circulation while cementing, eliminating the need for costly and time-consuming
secondary cement jobs. Each technique presents different challenges and influences both the circulating BHP and risk of lost circulation while cementing.
The purpose of this paper is to review four commonly used reverse circulation cementing techniques and challenge cementing companies to develop standards to model circulating BHP. Having standardized BHP models will allow for more informed decision-making when it comes to choosing between conventional and reverse circulation cementing techniques. The following topics will be explored: reverse circulation advantages, rheology for conventional and foamed cement, reverse cementing into the shoe, reverse cementing to surface through drill pipe, and displacement options.
The PUNA Geothermal Venture (PGV) wells are located on the Big Island of Hawaii near the Kilauea Volcano. This results in a highly fractured, hard, hot formation, challenging PGV with lost circulation, hole-cleaning, cooling, and stuck pipe issues. With static formation temperatures of 600°F the traditional fluid system incorporates water-based mud, various cooling systems to maintain operation temperature limits < 300°F, micronized cellulose for lost circulation, and mud-pulse measurement while drilling.
Although aerated mud is the preferred drilling fluid for operations performed in areas prone to lost circulation, there are certainly drawbacks and considerations to running aerated fluids.
1. One of the industry standards, mud pulse telemetry better known as Measurement While Drilling (MWD), will not function in aerated fluid.
2. Reduced fluid density hampers the ability to lift cuttings.
3. Aerated fluid adversely affects the ability to power positive displacement mud motors.
4. The thermal capacity of aerated mud is lower, reducing the cooling effect on the hole.
5. Drilling equipment exposed to the high velocities can be quickly eroded.
6. The reduced hydrostatic head can have a detrimental effect on wellbore stability.
PGV along with its contractors managed to complete the 26" hole section flawlessly on aerated mud, which has not been part
of the standard program. The following techniques were used:
1. A pump rate of 350 GPM
2. Foaming agents supplemented with polymers were used to provide rheological properties and gel strengths to facilitate hole cleaning
3. A polymer was used for cuttings encapsulation and lubricity.
4. A controlled rate of penetration (ROP) was employed to allow for proper cuttings disposal and hole cooling
5 . A 9½" performance mud motor equipped with high-temp stator elastomers, provided high torque drilling with temperature resilience.
6. Fixed hole openers were used to further ream and condition the borehole.
This section of the well was drilled successfully and 22" casing was landed with no problems . This is a significant improvement as compared to other offset wells in the area.
Success in drilling can often be traced to adequate planning, including risk identification and response strategies. The traditional framework for planning drilling projects is hierarchical and consists of a small project team. The high complexity of drilling projects, combined with time restraints, often results in a failure to identify risks, provide contingency plans, and effectively monitor project execution. One solution is to create an integrated cross-functional team specifically for planning and iterative project review. The team is composed of representatives of the operator’s drilling, resource, and production groups, representatives of the companies providing major services, consultants, and personnel from the lead regulatory agency. In a cross-functional team, the members have input into the initial drilling plan, and then participate in a drill-on-paper exercise in which a detailed drilling procedure, including risk identification and contingency planning, is developed. The team then establishes iterative review sessions at key milestones of the project, promoting rapid self-correction, accurate lessons learned, and projectspecific heuristics.
Puna Geothermal Venture
Well Name: Kapoho State-11RD (Geothermal Well)
Tests and surveys on the Kapoho State-11RD, a geothermal well near Hilo on the island of Hawaii, indicated a shallow leak into the formation zone. Injection fluid was traveling through the current fractures from the re-drill to the original wellbore, creating interference problems with the production zone of another well. Re-drilling was considered, but the decision was made difficult by previous re-drilling and workovers to the well, and the proximity of any new bore to the previous bores.
A coordinated research effort involving Baker Hughes Integrated Services and the client, Ormat, revealed that the most economical procedure would be to relocate the target and kick-off point, sidetrack the well by performing a casing exit through the two casing strings to increase the separation from any previous wellbores, and then directional drill the hole to the designated target.
A window was milled in 37½ hrs, including drilling 15 ft of formation below an extra long whipstock ramp that was more than 19 ft long. The PDC mills cutting structure allowed milling with lighter weight, which enabled the mill to stay on the face of the whipstock and avoid departing from the ramp prematurely.
Even though the T-95 and T-90 casing grades usually require several runs to mill a window through two strings, and drilling with a PDC formation window mill is also difficult, the window was successfully milled. When running the drilling bottomhole assembly (BHA) through the window, no drag was encountered. The 7-in. casing was also run through without drag and then cemented.
The 5⅞-in. productive interval was drilled 120 ft when it was discovered that the 7-in. liner cement job was fatally flawed, and this entire interval was abandoned.
A second window was milled several hundred feet above the first, through the same two strings of casing, using the same equipment and methods. This window was similarly successfully milled in 30½ hrs. The 8½-in. hole was drilled, and the 7-in. liner was run and cemented. The 6¼-in. productive interval of this sidetrack was successful in encountering the top of production at 5,135 ft and was drilled to 6,872 ft, where pipe was inadvertently stuck in the hole. It was completed with 4.5-in. preperforated liner from 4,755 to 4,755 ft and a combination 7-in. and 5-in. alloy injection hang down string from surface to 3,038 ft.
Job success was attributed to a team effort involving Ormat, Geothermal Resources Group and Baker Hughes Integrated Services. Coordination included the engineering, technical advice and field support services to achieve this task. This paper describes the well condition, the project plan, the equipment/materials used, and the procedure.
Typical geothermal formations are highly fractured or poorly consolidated; these conditions inherently lead to lost circulation. When losses occur, lost circulation material is typically applied first, followed by cement plugs. Cement plugs may be used to seal lost circulation zones, allowing drilling to continue through and below the loss zone with good returns to surface. Innovative drift plug technologies may be used in place of conventional balanced plug methods, achieving better results in severe loss zones.
Please enter your email address to receive a free download of the entire article as well as access to all of our articles.
For additional information please use this form to contact us.
77530 Enfield Lane, Building E
Palm Desert, CA 92211, USA