Two main issues occur during the well testing activity:
a) Release in the atmosphere of hydrogen sulfide around the well head during the first well opening phase (typical duration up to around half an hour). In this phase, it is important to maintain in-air concentration level which allows the work site personnel to continue executing normal operations.
b) Release in the atmosphere of both hydrogen sulfide and VOC during the well test (typical duration 2 – 10 days).
The well testing begins by opening the well head valve, leading to the discharge in the atmosphere of both non-condensable gas and liquids accumulated in the upper part of the well, i.e., non-condensable gases, water and environmental friendly lubrication oil residuals; the duration of this phase depends on the well characteristics and varies from several seconds to some minutes.
Once both gas and liquids present in the upper part of the well have been completely released through the head valve, the geothermal fluid coming from the reservoir, composed by water steam and non-condensable gases, reaches the well head;
The test facility (see picture) is composed of two lines in a parallel configuration, used sequentially: the cyclon separator line and silencer line. When the test operator closes the head valve and opens the cyclon separator line valves, the geothermal fluid, still characterized by a significant amount of liquid fraction, starts to flow in the facility. In this line, two pieces of equipment are installed: a remotely controlled regulation valve and the James tube. The regulation valve leads pressure value dropping below a typical absolute value of about 6 bar while the James tube allows the measurement of the fluid flow rate. Fluid exiting the James tube flows through a cyclone separator which releases the gas fraction in the atmosphere and discharges the liquid fraction in a tank. The liquid content gradually decreases during the test; once it is considered negligible, the operator performs the line switch: the cyclon separator line is closed while the silencer line is gradually opened. As well as the cyclon separator line, the silencer line is equipped with a pressure regulation valve. Nowadays, the duration of the well tests varies between two and ten days. During the test, air quality monitoring campaign is performed through stationary and mobile stations capable to measure the hydrogen sulfide concentration in air with the aim to verify the respect of threshold limits indicated by the WHO (World Health Organization).
Previous preliminary tests were carried out by Enel regarding the in-well injection of hydrogen peroxide through coil tubing. While the abatement of hydrogen sulfide was largely successful, this solution was not permanently implemented due to significant plant complexity along with the large amount of effort needed to commercialize this procedure. Moreover, in some cases a compressor is used before starting the test to push gases accumulated in the upper part of the well within the reservoir fractures; in this way, when the head valve is opened, in the initial phase the gas release is considerably reduced.
A preliminary commercial scouting analysis conducted in early 2022 did not identify technical solutions suitable for the proposed applications. However, it was recognized that dry granular media scavengers, mixtures of iron oxides and/or mixed metal oxides, or an inert inorganic carrier may be suitable components of a feasible solution. Acceptable methods may separate the hydrogen sulfide from the water stream or treat the whole fluid.
Identify and test a solution able to eliminate or at least strongly reduce the olfactory impact produced during geothermal well testing with particular regard on hydrogen sulfide and other VOC. The solution must be applicable to wells having different characteristics in terms of fluid flow rate, temperature, pressure, gas content and chemical composition. The preferred method does not involve in-well treatment. Finally, the solution must be transportable to different testing locations.
Submissions should address the following Solution Requirements.
The proposed solutions must:
- TRL ≥7
- be compliant with European safety standards, especially regarding pressure vessel and piping;
- be transportable by trucks;
- reduce the hydrogen sulfide and other gaseous olfactory emissions released in the atmosphere of at least 90%;
- process the fluid during all test phases described above (gas discharge through the head valve, flow through the cyclon separator line, flow through the silencer line);
- be suitable for wells whose fluid has the following characteristics:
- pressure in the range 1 – 40 bar ( values refer to fluid at well head upstream the regulation valve);
- temperature in the range 100 – 300°C
- typical chemical fluid composition as follows (by volume): water 88 – 98%, non-condensable gas: 2 – 12%; non condensable gas has the following typical composition (by volume): carbon dioxide 87 – 97%; methane 0.4 – 4%; hydrogen 0.3 – 6%; hydrogen sulfide 0.4 – 4.5%; nitrogen 0.5 – 4.5%;
- presence of VOC (Volatile Organic Compounds)
- condensate, as possible representative example, described a possible chemical composition as follows:
- mass flow rate: 10 – 100 t/h (50 t/h to be considered as average statistically representative value);
Moreover, the solution should:
- not require pressurized vessels to store by-products.
- work on fluid downstream the pressure regulation valves mentioned above;
- reduce the hydrogen sulfide and other gaseous olfactory emissions released in the atmosphere of at least 98%;
The submitted proposal should include the following:
- An explanation of the proposed solution addressing specific Solution Requirements along with a well-supported rationale and pertinent data
- Schematics that illustrate important aspects of the design
- A cost assessment and implementation strategy for geothermal fields in Italy
- Application references of the proposed technologies/processes with focus on industrial plants.
The proposal should not include any personal identifying information (name, username, company, address, phone, email, personal website, resume, etc.) or any information the Solvers may consider as their Intellectual Property they do not want to share.
This challenge provides contribution to the following sustainable development goals (SDGs) to transform our world:
- SDG 11: Sustainable Cities and Communities
- SDG 13: Climate Action
- SDG 17: Partnerships to achieve the Goal.