First EAGE/IGA/DGMK Joint Workshop on Deep Geothermal Energy

Magnetotelluric (MT) measurements are of particular value in volcanic-hosted, high-enthalpy geothermal exploration, since electrical resistivity depends dramatically on the mineral composition of the hydrothermally altered rock, which is in turn a function of temperature. We present an integrated study from the Darajat geothermal field in West Java – a vapor-dominated field associated with an eroded andesitic stratovolcano, currently producing at 271MW capacity. Besides MT data, also gravity and micro-earthquake event data from seismic monitoring were incorporated in the workflow. A cross-gradient approach was followed in the joint inversions to structurally link the different domains. An additional cross-gradient link to porosity from a geological model was further used to promote structural similarity. The 3D joint inversion modeling resulted in mutually consistent resistivity, density and velocity models, in agreement with the current understanding of the field. We expect that similar joint inversion workflows employed both early in and during the lifetime of the field would strengthen the building of a concept model for exploration, and later updates guiding development drilling programs.

Recent development in wireless recording technology together with a dramatic increase in the productivity derived from the O&G industry such as blended vibroseis acquisitions made the seismic surveys more attractive and in accordance with geothermal budgets. The increased quality due to a broadband recording makes a huge difference even with the most recent surveys. This paper presents the acquisition of the first 3D survey recorded in a suburban environment south of Munich (Germany) with such technology and for geothermal object.

Percussion drilling system, combining a mud hammer with drill bits, has been developed to increase drilling performances in hard formations. This system is based on a high-power down-the-hole hammer (Power output of 30 kW), capable of delivering high-energy impacts at high frequency (35 Hz) used with mud pressure as the power source. The drill bit is a key performance element because it is the one that is in contact with the rock and destroys it. It must be designed to optimize the cutting process. Numerous elementary tests of the insert-rock contact and the development of a model of the performances have been performed. It makes it possible to show the importance of the bit design parameters and the need to adapt the design to the drilling conditions. A new generation of bits optimized for performance has thus been developed and manufactured. The 6” mud hammer and the new drill bit have been then tested on a full scale drilling test bench. The performances comparison with roller cone bit showed an improvement of 100 to 300% of Rate of Penetration (ROP). The set was ultimately used in field drilling operations and validated the large improvement in ROP of 300%.

Around 12 000 boreholes have been listed in France according to an overview performed by INERIS (Lafortune, 2015, Lahaie and Bouffier, 2017). This paper describes the assessment study of abandoned oil and gas wells conversion for geothermal energy recovery. To that purpose, a multi-criteria analysis of key parameters is conducted to classify and grade wells according to their geothermal potential. The analysis accounts for surface information, parameters associated to the wells along with geological and geothermal properties (e.g. land use, existence of aquifers, temperature, transmissivity, depth reached, and drilling years). A case-by-case investigation is propose for a sample of high potential wells to ensure that all appropriate conditions are met to consider the conversion.

The induced seismicity recently observed in Rittershoffen and in Soultz-sous-Forêts highlights the need to perform a seismic monitoring, even during the exploitation phase of power plants, which is now explicitly required by the French mining authorities for getting the exploitation license.

An extensive wireline logging campaign has been carried out in the Rittershoffen geothermal doublet in Eastern France. In particular, dipole sonic logs and wellbore image logs were acquired in the open hole over the target fractured aquifer. The interpretation of image logs allowed the characterization of the geometry (dip and azimuth) and the properties of the natural fracture network. The combination of density and sonic logs served as a base for geomechanical analysis. The near-wellbore results were then integrated and applied to the reservoir scale to build a 3D geological, hydrothermal and geomechanical model of the site.

CPG systems have been compared with conventional hydrothermal power plants based on thermodynamic simulation calculations. Especially at moderate reservoir depths and permeabilities, significant performance benefits for CO2 system were observed which validates the results from literature.Considering the surface power plant layout a less complex CO2 cycle with less equipment and a smaller footprint in comparison to brine based systems can be derived.

The oil and gas industry has accumulated decades of experience characterizing and accessing deep and ultra-deep formations, including in challenging conditions which are commonly found in geothermal sites (high temperature, pressure, salinity, corrosion…). Oilfield service companies, in particular, have been developing innovative and efficient solutions to explore, map and produce these resources. Geophysical surveying, notably with electromagnetic methods, and integrated subsurface modeling in multi-disciplinary software platforms allow the characterization and quantification of the resource prior to drilling. Dedicated technologies for high pressure, high temperature drilling, including muds and bits, are used to realize highly deviated wellbores. Wellbore logging, either wireline or while drilling, provides the data to characterize the properties of the reservoir rock (porosity, permeability, presence of fractures) and to analyse well integrity. Production can be enhanced by stimulation treatments and by the installation of surface or downhole pumps. The combination of these services under a single provider may optimize the efficiency of well construction and resource characterization.

The assessment of the stress orientations is the first step for geomechanical modelling and for the understanding of the relationships between fractures, stress and fluid flow. Furthermore, an understanding of the stress regime and stress field orientation is crucial for optimizing planning of boreholes with a view to minimizing the risks. In the present publication, the results of a borehole image interpretation performed for the National Cooperative for the Disposal of Radioactive Waste (NAGRA) from a geothermal borehole in Northern Switzerland are presented. The borehole was drilled in Upper Jurassic carbonates that are partly intensively fractured and also contain vugs. It is shown that analysis and interpretation of borehole images contribute to a better understanding of reservoirs and that these data are important for efficient drilling and effective development of adjacent boreholes. The interpretation adds detail to the regional structural and present-day stress picture of the Upper Jurassic strata in the area. The main stress orientation matches results from nearby measurements. The fractures are potentially governed by local or regional structural elements, i.e. faults or folds.

Corrosion of construction materials in geothermal brine environments is of great concern in the long-term operation of geothermal power plants. In case of geothermal energy production there are many site-specific factors influencing corrosion processes e.g. high salinity, pH, high temperature, presence of non-condensable gases, fluid velocity, corrosion products, geometry of the power plant, acid treatment and acid cleaning procedures (Guerra & Jacobo 2012). To prolongate the lifetime and thus decrease downtime periods and economic losses, a careful material selection at acceptable costs is essential (Carter & Cramer 1992). Nogara & Zarrouk (2018b) summarized the results of 172 tested metals and alloys for the use in geothermal environment. Among low cost carbon steels, stainless steels, alloys and titanium are employed for functional parts as turbine blade or heat exchanger material respectively (e.g. Ravier et al. 2016). In geothermal power plants up to 12 types of corrosion may occur depending on the corrosiveness of the produced brine (e.g. Nogara & Zarrouk 2018a).