Stimulation of the RN-15/IDDP-2 Well at Reykjanes Attempting to Create an EGS System
[HS Orka, Iceland]
An overview is given of the stimulation activity carried out in the well RN-15/IDDP-2 at the Reykjanes geothermal field in southwest Iceland. The well was deepened to 4659 m (MD) from the 2507 m deep RN-15 production well in the time interval August 2016 to January 2017. The aim was both to create an EGS system underneath the conventional reservoir as well as to get into supercritical environment. The stimulation activity was divided into stages with the first stage consisting of short pressure and thermal shocking carried out at the end of the drilling operation. The second stage followed and concentrated mainly on cooling and thermal shocking on the deep section of the well. That stage ended in June 2017 by use of fluid blocking material to reduce fluid losses to the more permeable zones and to divert the pressure load to the less permeable zones. Preparation was made for hydraulic fracturing below the liner in the deepest part of the well as the third stage of stimulation but had to be abandoned. However, long term cooling from the top of the well and as far down as fluid blockers and permeability control allowed was maintained until August 2018 when the stimulation operation ended, and warmup was started to prepare the well for discharge testing. The deepening of the well was basically drilled with total loss of circulation the whole time so all cuttings (60 m3) were lost to fractures and fluid loss zones in the well. Though the cuttings are partly blocking the fractures it is considered that they can act as proppants as the well and formation warms-up. Number of fractures accepting fluid losses and the strength of the loss zones below 3000 m depth was more than had been anticipated before the drilling. Several loss zones were in the first 200 m interval below the casing (set at 2941 m) but the main zone was located at about 3360 m (MD). Affirmative loss zones were found down to at least 4550 m as observed from temperature profiles. Simple injection step rate tests were used to measure the effectiveness of the stimulation activity. At the end of the drilling operation the injectivity index was estimated around 1.9 L/s per bar and it increased to about 3.1 L/s per bar during the first stimulation stage. Despite a lot of fluid blocking material had been pumped into the well, the injectivity index was estimated around 2.8 L/s per bar at the end of the stimulation activity. Brief interpretation of temperature recovery during a warmup for thermal shocking indicate temperatures above 400°C in the deepest section of the well and close to 500°C near the bottom of the well.
|        Topic: EGS - Enhanced Geothermal Systems||Paper Number: 31010|