High temperature, wireless seismometer sensor for Venus
Space agency mission plans state the need to measure the seismic activity on Venus. Because of the high temperature on Venus (462°C average surface temperature) and the difficulty in placing and wiring multiple sensors using robots, a high temperature, wireless sensor using a wide bandgap semiconductor is an attractive option. This paper presents the description and proof of concept measurements of a high temperature, wireless seismometer sensor for Venus. A variation in inductance of a coil caused by the movement of an aluminum probe held in the coil and attached to a balanced leaf-spring seismometer causes a variation of 700 Hz in the transmitted signal from the oscillator/sensor system at 426°C. This result indicates that the concept may be used on Venus.
An estimate of the surface conditions of Venus
Recent spectroscopic observations of the cloud layer region of Venus give good relative pressure data on CO2, CO, H2O, HCl, and HF. From these data and the assumption that the atmosphere is in chemical equilibrium with the lithosphere, it is possible to deduce lower limits on the temperature and pressure of the coolest part of the surface of the planet, and to state an upper limit on the temperature in this coolest region. 
 
For Venus with an isothermal surface and with an adiabatic atmosphere, the surface pressure is found to be ≧ 1.8 bars and the surface temperature ≧ 514°K for all models considered. For Venus with a maximum surface temperature of 700°K and an adiabatic lapse rate above the hottest point, a surface pressure ≧ 5.4 bars and a cold-region temperature T ≧ 540°K were found. A probable upper limit on the temperature in the coolest region, derivable from the observational upper limits on COS and H2S, is about 560°K.
Prevention of Barite Sag in Oil-Based Drilling Fluids Using a Mixture of Barite and Ilmenite as Weighting Material
Drilling high-pressure high-temperature (HPHT) wells requires a special fluid formulation that is capable of controlling the high pressure and is stable under the high downhole temperature. Barite-weighted fluids are common for such purpose because of the good properties of barite, its low cost, and its availability. However, solids settlement is a major problem encountered with this type of fluids, especially at elevated downhole temperatures. This phenomenon is known as barite sag, and it is encountered in vertical and directional wells under static or dynamic conditions leading to serious well control issues. This study aims to evaluate the use of barite-ilmenite mixture as a weighting agent to prevent solids sag in oil-based muds at elevated temperatures. Sag test was conducted under static conditions (vertical and inclined) at 350 °F and under dynamic conditions at 120 °F to determine the optimum ilmenite concentration. Afterward, a complete evaluation of the drilling fluid was performed by monitoring density, electrical stability, rheological and viscoelastic properties, and filtration performance to study the impact of adding ilmenite on drilling fluid performance. The results of this study showed that adding ilmenite reduces sag tendency, and only 40 wt.% ilmenite (from the total weighting material) was adequate to eliminate barite sag under both static and dynamic conditions with a sag factor of around 0.51. Adding ilmenite enhanced the rheological and viscoelastic properties and the suspension of solid particles in the drilling fluid, which confirmed sag test results. Adding ilmenite slightly increased the density of the drilling fluid, with a slight decrease in the electrical stability within the acceptable range of field applications. Moreover, a minor improvement in the filtration performance of the drilling fluid and filter cake sealing properties was observed with the combined weighting agent. The findings of this study provide a practical solution to the barite sag issue in oil-based fluids using a combination of barite and ilmenite powder as a weighting agent to drill HPHT oil and gas wells safely and efficiently with such type of fluids.