Well Logging

Well logging is a mechanism of drilling holes into earth for the sake of extracting oil, gas, minerals, and for geo-ethical studies. The log is generally based on visual inspection of samples brought to surface or based on physical measurements made by instruments lowered into the hole. Today well logging is done electrically. Electric well logging was introduced by Conard and Marcel Schlumberger. They developed a technique for prospecting metal ore deposits. They used surface technique for subsurface applications. The first well log was created by them in 1927. They lowered an electric shonde down a well in Pechelbronn of France and created the first well log.
Geophysical well logs
The oil and gas industry records rock and fluid properties to find hydrocarbon zones in geological formations intersected by a bore hole. They lower a tool onto the end of wire-line into an oil well, to measure the rock and fluid properties and formation. After this an interpretation of this measurement is made to locate potential depth zones containing oil and gas. Logging tools developed measure electrical, acoustic, electromagnetic and radioactive properties of rocks. They also check out contained fluids of these rocks. Once the logging tool is pulled out a record of data is printed out and is called as Well Log. This is transmitted digitally to offices. Well logging is generally performed at various intervals during the drilling of wells. The total depth drilled can range from depths of 300m-8000m.
Logging Measurement Types
Logging measures are quite sophisticated. Their prime target is to measure various geo-physical properties of the subsurface rock formations. They check out porosity, fluid content and permeability.
Porosity is the proportion of fluid filled space found in the rock. This space contains oil and gas. Permeability is the ability of fluids to flow through the rock. Higher the porosity, higher will be the content of oil and gas in the reservoir. If the permeability is high gas flow will be easy and fast from the bored well. Logging tools provide measurements for calculation of these qualities.
Logging measurements also allow interpretation of what kinds of fluids are in pores – oil, brine or gas. They also allow a person to determine mechanical properties of the formations. These mechanical properties determine what kind of recovery methods can be used and what damage to the formation is expected.
Logging instruments used in well logging consist of basic electric logs and spontaneous potential logs. Well and mud logs are usually transferred in real time to the operating company, which analyzes these logs and makes operational decisions about the well. It also analyzes the surrounding wells and makes interpretation of quality of hydrocarbons present. Those specialists who are involved in well log interpretation are called log analysts.