Prediction of Reservoir Parameters of Cambrian Sandstones Using Petrophysical Modelling—Geothermal Potential Study of Polish Mainland Part of the Baltic Basin

Important factors controlling the effective utilization of geothermal energy are favorable reservoir properties of rock formations, which determine both the availability and the transfer opportunities of reservoir fluids. Hence, crucial to the successful utilization of a given reservoir is the preliminary recognition of distribution of reservoir parameters as it enables the researchers to select the prospective areas for localization of future geothermal installations and to decide on their characters. The objectives of this paper are analyses and discussion of the properties of quartz sandstones buried down to a depth interval from about 3000 to under 5000 m below surface. These sandstones belong to Ediacaran–Lowery Cambrian Łeba, Kluki and Żarnowiec formations. The source data from the Słupsk IG-1 provided the basis for 1D reconstruction of burial depth and paleothermal conditions as well as enabled the authors to validate of the results of 2D models. Then, porosity distribution within the reservoir formation was determined using the modelings of both the mechanical and chemical compactions along the 70 km-long B’-B part of the A’-A cross-section Bornholm-Słupsk IG-1 well. The results confirmed the low porosities and permeabilities as well as high temperatures of the analyzed rock formations in the Słupsk IG-1 well area. Towards the coast of the Baltic Sea, the porosity increases to more than 5%, while the temperature decreases, but is still relatively high, at about 130 °C. This suggests the application of an enhanced geothermal system or hot dry rocks system as principal methods for using geothermal energy.

Experimental Study on the Heat Exchange Mechanism in a Simulated Self-Circulation Wellbore

Self-circulation wellbore is a new technique for geothermal development in hot dry rocks (HDR), which uses a U-shape channel composed of tubing and casing as the heat exchanger. In this study, a self-circulation wellbore in HDR on a laboratory scale was built, and a serial of experiments were conducted to investigate the heat exchange law and the influencing factors on the heat mining rate of the wellbore. A similarity analysis was also made to estimate the heat-mining capacity of the wellbore on a field scale. The experimental results show that the large thermal conductivity and heat capacity of granite with high temperature can contribute to a large heat-mining rate. A high injection rate can cause a high convective heat transfer coefficient in wellbore, while a balance is needed between the heat mining rate and the outlet temperature. An inner tubing with low thermal conductivity can significantly reduce the heat loss to the casing annulus. The similarity analysis indicates that a heat mining rate of 1.25 MW can be reached when using a 2000 m long horizontal well section in a 150 °C HDR reservoir with a circulation rate of 602.8 m3/day. This result is well corresponding to the published data.