Temperature log simulations in high-enthalpy boreholes

Abstract

Temperature logs have important applications in the geothermal industry such as the estimation of the static formation temperature (SFT) and the characterization of fluid loss from a borehole. However, the temperature distribution of the wellbore relies on various factors such as wellbore flow conditions, fluid losses, well layout, heat transfer mechanics within the fluid as well as between the wellbore and the surrounding rock formation, etc. In this context, the numerical approach presented in this paper is applied to investigate the influencing parameters/uncertainties in the interpretation of borehole logging data. To this end, synthetic temperature logs representing different well operation conditions were numerically generated using our newly developed wellbore simulator. Our models account for several complex operation scenarios resulting from the requirements of high-enthalpy wells where different flow conditions, such as mud injection with-and without fluid loss and shut-in, occur in the drill string and the annulus. The simulation results reveal that free convective heat transfer plays an important role in the earlier evolution of the shut-in-time temperature; high accuracy SFT estimation is only possible when long-term shut-in measurements are used. Two other simulation scenarios for a well under injection conditions show that applying simple temperature correction methods on the non-shut-in temperature data could lead to large errors for SFT estimation even at very low injection flow rates. Furthermore, the magnitude of the temperature gradient increase depends on the flow rate, the percentage of fluid loss and the lateral heat transfer between the fluid and the rock formation. As indicated by this study, under low fluid losses (< 30%) or relatively higher flow rates (> 20 L/s), the impact of flow rate and the lateral heat transfer on the temperature gradient increase can be ignored. These results provide insights on the key factors influencing the well temperature distribution, which are important for the choice of the drilling data to estimate SFT and the design of the inverse modeling scheme in future studies to determine an accurate SFT profile for the high-enthalpy geothermal environment.

A new method for correcting temperature log profiles in low-enthalpy plays

“…However, such numerical models (e.g. Espinosa-Paredes and Garcia-Gutierrez 2003;Espinosa-Paredes and Espinosa-Martínez 2009;Yang et al 2015;Wang et al 2019) require detailed information about the well (e.g. well geometry) and its drilling process (e.g.…”

“…mud flow rate, mud properties) to provide good results. However, especially in high-enthalpy regions, where the difference between measured temperature logs and true formation temperature can be very high due to occurring convection, numerical modelling which takes convection into account can deliver better corrected temperatures than analytical models (Wang et al 2019).…”

Modelling borehole flows from Distributed Temperature Sensing data to monitor groundwater dynamics in fractured media

“…They suggested that the dimensionless time function by Kutun et al (2014) as given in equation ( 5) would be sufficiently accurate for engineering purposes for most values of flow time. This approach is frequently used in petroleum engineering as well as in geothermal reservoir (Nian et al, 2018;Song et al, 2018;Wang., 2019). In the following, we demonstrate its applicability in hydrology by performing numerical validation and also showing its field application.…”

Appraising Mahallat Geothermal Region using thermal surveying data accompanied by the geological, geochemical and gravity analyses

“…After exploration, a wide variety of methods can be exerted to model and simulate the hot underground reservoir. Temperature, pressure, flow regime, fracture network are known as the most important factors [14][15][16][17][18] .In the most simplified cases, a geothermal reservoir can be explored merely because of observable surface evidence such as hot springs. But, sophisticated exploration procedures are required to make a reliable prediction on the geothermal potential of a prospect.…”

“…After exploration, a wide variety of methods can be exerted to model and simulate the hot underground reservoir. Temperature, pressure, flow regime, fracture network are known as the most important factors [14][15][16][17][18] .…”