Drilling large holes on all kind of surfaces whether, it’s a seabed or a rock, need precision and planning. One small mistake can result in downtime, which causes heavy losses in petroleum industries, and you have to take every precaution to prevent these situations.
Wireline services are beneficial in this field of work to find the situation of your wellbore with logging and take every decision according to it, but every drilled well need casing before, and all your reading of your open logs can change. In such situations, your only option is cased hole logging.
What Is Cased Hole
Cased-hole logging is the process of retrieving measurements through the metal casing of a wellbore or the metal pipe inserted during the completion operation. It is a rare activity, but it is Known to provide very crucial information about your drilled oil well.
Cased-hole logging services are for a completed hole like if you want to find why the oil flow hampered or what lies beyond the casing. It can also give you the necessary information in case you want to close the wellbore.
Purpose Of Cased Hole Logging Services
It is possible that the open hole logging have a slight mistake that can affect the wellbore working condition or the wellbore conditions have changed after the casing was set. The only way to ensure, that the well is safe and reliable for use is through cased hole logging services. It is necessary that you can identify the new condition of the well and make your strategies according to it and avoid downtime.
Cased-hole logging involves the use of various tools and methods that you can use, but some necessary tools remain the same.
Gamma rays are a very great option for cased hole measurements as they can pass through steel with ease. The gamma ray tools response to naturally occurring gamma radiation and gives you values that you can correlate with open hole measurements, and also differentiate between sand and shale. The problem that you might encounter with this device is its response to salts. The salts can precipitate and hinder the working of the gamma tools. You can use spectral gamma tools for salts like predominated uranium, but potassium present may need some work.
Compensated Neutron Tools
This tool is used to measure the hydrogen index of the well with the help of radioactive neutrons source. The high-speed neutrons are bombarded and collide with atoms of formation and transfer of energy takes place. The mass of hydrogen is very close to the mass of the neutron, and hence a very efficient transfer of power takes place.
Two detectors count the number of de-energised neutrons, and the ratio of this detectors count rate is primarily related to hydrogen index or water-filled porosity. The tool is not much affected by steel casing and serves best to estimate porosity when lithology is known, but its performance can change with gas in the formation.
Pulse Neutron Tools
Pulse neutron tools generate a high energy neutron pulse that collides with the atom of rocks and loses energy. The energy loss at a point becomes very high; the neutrons get captured and emit a gamma ray. The detectors in pulse tool detect the gamma-ray and thus find the cross-section of the formation.
This tool is also flexible to process in the same manner as compensation neutron tool, and finds porosity, with a little adjustment. This estimate of porosity is very reasonable when the water is salty, and the gas presence of the formation is low. This dual operation functionality makes this tools more preferred for cased hole evaluation.
The demand for petrochemical are increasing, and so is the need for sustainable technologies for them. There are new technologies like pulse neutron spectroscopy that provides a better way to measure lithology, porosity and saturation through the casing and that too in the presence of fresh water. Companies are also using advance resistive devices that are capable of finding formation resistivity through the casing. There are also acoustics that helps to measure the velocity of compression and shear wave behind the housing.
Many companies provide the latest technology and the best solutions for all kind of drilling works. The cased-hole wireline services can help you with finding all the aspects of your wellbore and decrease the downtime to a considerable extent.