Various type of specimens were exposed at 450°C and 1100 psi in pure supercritical CO2(sCO2) for over 1 month. The exposure was performed in order to assess the effect of various variables on the oxidation of materials used in supercritical CO2 at high temperature.Variable such as temperature and pressure are fairly well covered in the literature. Other identified variables such as contaminants and coatings have been partially addressed. Additional variables of interest such as welding stress corrosion cracking galvanic issues or crevices have not been studied.Welding changes the local microstructure due to the high temperature in the vicinity of the weld. The chromium will diffuse to the grain boundaries and the chromium concentration in the matrix will drop significantly. Consequently the corrosion resistance near the weld will drop. Since welding will likely be used in the manufacturing process it is recommended to test coupons containing the heat affected zone near a weld.Galvanic corrosion occurs when two materials with different electrochemical potentials are in contact with a corrosive environment. There is usually very little change in corrosion rates when materials with similar composition are in contact. However there may be some issue in the case of nickel alloys/stainless steel couples. It has also been suggested in the literature that galvanic corrosion may not be an issue because sCO2is not considered an electrolyte. However it may be of interest to electrically couple two samples of different material (stainless steel and nickel alloy) and measure the weight change of each sample individually after exposure to assess galvanic corrosion.Stress corrosion cracking combines the effect of applied stresses and corrosive environment leading to accelerated crack growth of a susceptible material due to its microstructure.Crevice corrosion may occur within the occluded site of two sandwiched specimens of identical material.Mass loss micro-hardness and SEM/EDS inspection of the specimen cross sections were used to measure the extent of oxidation. The welded specimens wee of both martensitic stainless steel 410 and austenitic stainless steel 310. The galvanic corrosion specimens were stainless steel 410 coupled to nickel alloy 625. The crevice corrosion specimens were two martensitic alloy 410 specimens coupled together. Stress corrosion cracking was studied using C-ring specimens.

The drilling of the second deep geothermal well drilled in the Iceland Deep Drilling Project (IDDP) at Reykjanes geothermal field was successfully completed in beginning of the year 2017. The previously drilled RN 15 production well 2500 m deep at the Reykjanes high temperature geothermal field was used as the base for the IDDP-2 well. The final depth of the IDDP-2 well reached 4650 m depth with a bottom hole temperature measured to be 427°C and a pressure around 340 bar. This made the bottom of the IDDP-2 well reach fluid at supercritical conditions and become the deepest geothermal well in Iceland. The well was then injected with coldwater for stimulation. During the injection the pumping was interrupted and the water in the well was able to heat up. When the injection string (pipe) was retrieved from the well extensive corrosion damages were apparent on the lowest part of the injection string. Cracks were also observed on a 500-meter interval of the injection string pipe starting from the bottom part. The injection string was visually inspected on-site and selected parts were chosen for further failure analysis. Specimens from the pipe and pipe connections were examined using an optical microscope scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) technique. This was done to investigate and discuss the most probably cause of the corrosion damages. Additionally the hardness of specimens of the pipe were measured and compared to the NACE MR 0175/ISO 15156 standard. This paper covers the procedure and results of the failure analysis of the injection string from IDDP-2 well.

In order to make the world’s energy consumption sustainable there is a need for reducing emissions of CO2 and to shift towards renewable energy sources. Geothermal energy has a large potential in certain parts of the world. One example is Iceland where the reservoir in IDDP-2 is around 450°C and 270 bar. This makes it attractive as a geothermal reservoir of high enthalpy supercritical water with the potential for conversion of large amounts of environmentally friendly energy.The IDDP-2 geothermal well has not been produced yet and hence the fluid composition is not known. Using available data for nearby wells and in particular IDDP-1 an estimate can still be made. A combination of high temperature and pressure the presence of corrosive agents (such as HCl and H2S) a low pH and (at least initially) reducing conditions gives rise to challenges related to materials selection.This paper summarizes part of a desktop case study that addresses corrosion and scaling issues for conditions relevant for the IDDP-2 geothermal well. Based on measured water pressure a depth of 4500 meters and assuming a hydrostatic model is valid the temperature and pressure profile along the well is estimated. Knowledge gaps such as lacking solubility data and corrosion rates at supercritical conditions are pointed out.