D3203 - Electromagnetic and magnetometer work, mapping, dynamometer, measurement while drilling, instrumentation service, gravity metering, flow evaluation, oilfield safety

Operational Details
The fact the earth has a strong magnetic field has been turned to good use by the petroleum industry in search for minerals. Through applying the principle that like rocks have the same magnetic fields enables a comparison in the magnetism by the minerals in the rocks. Igneous rock. Frequently found underneath sedimentary layers often contains magnetic minerals. There are arches and folds in the so-called “basement” rock that can be measured, giving a fairly good picture of the geological formations. A formation out of place with its surroundings is an indicator of a fault that may be associated with petroleum deposits.

Measuring instruments used to determine if petroleum is present include a field balance instrument that is used on the earth’s surface and measures the difference in magnetism rather than the true or absolute magnetic variation of an area. The magnetometer records variations in the magnitude of the earth’s total magnetic field. These variations are principally associated with the burial depth of magnetized rocks.
Micromagnetic and/or electromagnetic survey and mapping include the airborne readings taken from low- altitude surveys, normally flown 300 feet above the earth’s surface. Magnetic field tapes from the aircraft are computer processed, producing a total magnetic field map, a flight line plot and total field magnetic profiles. These profiles are then used to produce a fracture interpretation of the basement rock and characteristics of overlying sediments. The net result is an efficient exploration method that defines relatively small areas for seismic surveys or drilling.

With some rocks denser than others, the gravitational force they exert is more powerful than that of a layer of very light rocks. The difference in mass for equal volumes of rocks is due to variations in specific gravity. A gravity meter is a sensitive weighing instrument for measuring such variations in the gravitational field of the earth. Although the basic principle of the gravitational method remains the same, new technology and instruments continue to improve data collection. A small, portable, highly accurate gravity meter is used for land work.

Dynometers are instruments used on the surface to test downhole pumps and pumpjack performance. An Echometer is a downhole instrument used to log fluid levels and requires the discharge of blank shells to generate shock waves, which are then
recorded.

Measurement While Drilling (MWD) is described as a type of well logging that incorporates the measurement tools into drillstring and provides real time information to help with steering the drill.


Gravity meter readings can also be taken for aircraft or from on board a boat. Interpreters now use digital computers to relate gravity to geological causes. Gravity maps and models help geologists examine large areas of development and provide guidelines for planning a seismic exploration program.

Tools used also include: scintillometers, transits, gravity meters, magnetometers and other measuring instruments. When analytical reports are provided by those taking the measurements, it forms part of this industry.

There is a strong association with the work undertaken by geophysicists and much of the data prepared by those operating the measuring devices and instruments. In fact, geophysicists may be hired by employers in this subcode to operate the measuring instruments. Geophysical companies also contract these same employers top provide them with data. However, they usually do the interpretation and pass the information along to the prospective oil and gas companies.

Often, because of the sensitive nature of the information, oil firms do not want the people taking the measurements to know who the work is being done for. By using a geologist or geophysicist as the "middle man", their confidentiality is ensured.

SIC Codes
000000327 - Electromagnetic and magnetometer wo
000000331 - Oilfield safety
000000328 - Mapping
000000329 - Dynamometer, instrumentation service, measurement while drilling (MWD)
000000330 - Gravity metering, flow evaluation