Drilling and Logging in Space; an oil-well perspective

摘要

Growing interest in extraterrestrial subsurface exploration has prompted an examination of advanced technologies for drilling slim holes and obtaining geophysical data in these holes. The borehole surveys with geophysical measurements called "logging", complement, and under favorable conditions, replace soil sampling. Very shallow drilling systems were used extensively during the Apollo lunar missions, and are in the planning stages for use on Mars. The prime objective is to gather scientific data, but these data could eventually provide a basis for the commercial use of space mineral resources. Given the strong scientific interest in water on Mars and the Moon, subsurface characterization with geophysical methods is attractive, because these methods can cover a much larger volume than soil sampling. Space technology has boosted the development of borehole geophysical instruments because both in space and in boreholes the instruments have to function in hostile environments, in confined spaces, and to be able to withstand large g-forces. This paper reviews oil industry drilling and geophysical borehole techniques that could be adopted for space applications. Coiled tubing drilling has many advantages because the surface facilities are compact, and an electrical cable in the tubing can transmit power and data. Moreover geophysical sensors can be embedded in the drill collars, which ensures that measurements are carried out while drilling, and this avoids risky reentry of geophysical tools in the hole. If kevlar is used for the coiled tubing, a laser beam could be transmitted via optic fibers in the coiled tubing wall. Using this beam to cut the rock would virtually eliminate mud and downhole motor requirements, and save a lot of weight. The quest for water and the strict requirements for redundancy, simplicity, and rugged instruments led to the selection of electromagnetic wave resistivity, natural gamma radiation, geophones, and induced epithermal neutron instruments as detectors. All these detectors can in principle be fitted into a coiled tubing string, and a combination of these measurements can provide quantitative information on the porosity, water-saturation, seismic velocity, and lithology of the Martian or Lunar soil.