Introduction
Well logging also known as borehole logging or wireline logging, is the practice of making a detailed record (a well log) of the geologic formations penetrated by a borehole. Well logging is performed by a trained geologist or geoscientist to obtain the details of the subsurface formations, and to detect commerical hydrocarbon and mineral deposits. A well log can be used to analyze the productivity of subsurface formations and to provide a record of subsurface geological features, fluids, and pressures.
A number of logging methods have been developed to obtain these insights. Logging can be divided into two categories: open-hole logging and cased-hole logging. Open-hole logging is used to create a continuous profile of the subsurface and provide information about locations of formations and other subsurface features. Cased-hole logging is usually conducted to look for leaks, corrosion, or production problems.
Tools
Well logs are acquired using several types of tools. One of the most important is the logging sonde. The logging sonde contains sensors that record parameters such as natural gamma rays, mud resistivity, sonic velocity, and magnetic properties of the wellbore. Data from these sensors can be used to identify lithology, porosity, and fluid saturation.
Other well logging tools include temperature tools, density tools, neutron tools, production logging tools, and natural gamma-ray logging tools. These tools measure parameters such as formation temperature, formation pressure, and hydrocarbon content of formations.
Open-Hole Logging
Open-hole logging is typically conducted when drilling a new well. This method is used to obtain a continuous profile of the subsurface and to provide information about the location of formations and other features. Open-hole logging is a more expensive process than cased-hole logging. It requires more extensive preparation, since the well must be drilled to the required depth before the logging can commence.
Cased-Hole Logging
Cased-hole logging is the practice of using logging tools to measure formation pressure, fluid saturation, and other parameters in a previously drilled well. Cased-hole logging is usually conducted to look for leaks, corrosion, or production problems. The logging tools used in cased-hole logging are usually lower in cost than those used in open-hole logging.
Applications
Well logging can play an important role in oil and gas exploration, development, and production. Logging data can be used to identify the type of material penetrated by the wellbore and to determine the productivity of formations and potential hydrocarbon reservoirs. Logging data can also be used to measure formation pressures, fluid saturations, and temperatures, which can provide valuable information to reservoir engineers during development and production of a well.
Conclusion
Overall, well logging is an effective tool for providing information about subsurface formations and potential hydrocarbon reservoirs. Through the use of logging tools, geoscientists are able to measure a variety of parameters, including lithology, porosity, fluid saturation, natural gamma rays, mud resistivity, sonic velocity, and magnetic properties. Logging data can also be used to measure pressure, fluid saturation, and temperature. The data obtained from well logging can be invaluable for oil and gas exploration, development, and production.
