IDDP-2 DEEPEGS Drilling Experience and Lesson Learned
Ari STEFANSSON, Gudumundur O. FRIDLEIFSSON, Þor GISLASON, Omar SIGURÐSSON
[HS Orka, Iceland]
The drilling of the deepest high-temperature geothermal well in Iceland, IDDP-2, was completed at 4,650 m depth in January 2017. The well is inclined below 2.75 km depth so true vertical depth is closer to 4.5 km below surface. Drilling began by deepening an existing 2.5 km deep well, RN-15 to 3 km depth, and case it with 9 7/8”– 9 5/8” casing and cement it to the surface by reverse cementing method. To reach the main up-flow zone of the Reykjanes system it was necessary to build inclination from 2.75 km with an azimuth of 210°deg. Below 3 km depth total loss of circulation was experienced to the end of drilling. A 7” perforated liner was run into hole and then a 7” production (sacrificial) casing to 1,300 m and cemented to surface. This was followed by running in a 6” rotary assembly to drill out casing shoes for the sacrificial casing and the liner. A 6” pilot hole, 8 m long, was then drilled before pulling out for running in 3 successive 6” coring tools to final depth. The well was left with 3 ½” drill pipe to 4,590 m for long term stimulation and tracer injection. Several lessons learned from the drilling operation are addressed in the paper. To name a few, we recommend not to directionally drill such deep wells, as it involves all sort of problems with increasing depth, and increased risk of failure. This was well known before we began the drilling of IDDP-2, so other reasons ruled. Necessity to reach the center of the up-flow zone at Reykjanes called for our decision to directionally drill IDDP-2. The biggest problems in our drilling related to keyholes that kept the string stuck for days damaging several drill pipes. Next to mention, is the mitigation we used for cleaning the well by bleeding HT polymer and Guargum continuously while drilling, basically using cold water as drilling fluid throughout the drilling. The polymer helped greatly keeping the well clean and the standpipe pressure much lower than by drilling with pure water alone. In the paper we attempt to analyze the coring problems we had in the 8 ½” section. Coring with 8 ½” core bit and 7 1/8” core barrels was presumably far too stiff BHA for smooth run into 8 ½” inclined bore hole, and slimmer tools like the 6” core bits on 4 ½ core barrel like we used in the end is recommended. Our experience shows that cooling of superhot wells during drilling does not appear to be a problem, provided sufficient cooling fluid is available on surface for continuous cooling. Total loss of circulation throughout such drilling as ours, evidently calls for a rich surplus of cooling fluid. Good example of cooling efficiency was seen from the LWD logging tool below 4,000 m, which we tripped in at the end of drilling never experiencing more than 50-60°C heating, in an environment over 500°C hot. Cementing and casing integrity is and will be one of the most sensitive and risky part of a drilling operation for endurance. In the paper we address this sensitive issue and provide some advice for our future deep drillings.
|        Topic: Drilling and Completion Technology||Paper Number: 21025|