The purpose of the formation of basic evaluation measurements are made through the casing for three basic reasons:
First, to add measurements taken in an open hole. It is essential because oil well conditions may prevent the possibility of safely putting the required open measurements.
Second, to observe the changes in formation properties that have occurred for the casing was set. Changes in the saturation of the pore space by oil, gas, and water may be included by sustained production during the life of a well. These changes may require evaluation of nature to design more effective hydrocarbon recovery strategies.
Third, to give an in-depth reference between the cased hole and open hole measurements and services.
Basic Cased Hole Tools
The basic cased hole tools can be categorized into three general classifications: correlation, saturation, and porosity.
- The correlation device is used to correlate cased hole measurements with open hole measurements and to determine oil shale volume.
- The saturation device is used to estimate water saturation when porosity and water salinity are known.
- The porosity device is used to estimate porosity when lithology is known.
The Applications And Types Of Basic Cased Hole Tools Are As Follows:
Gamma Ray Tool
The gamma-ray measurements provided by the cased hole well services respond to naturally occurring gamma rays for the formation. These gamma rays penetrate steel casing, and this permits the gamma ray to be used in a cased hole for correlation with open hole logs, also to differentiate between sands and shale and to calculate shale volume. Its use is critically identical to its use in an open hole except for small environmental corrections needed for the influence of the steel casing and cement.
A common problem to be seen in the cased hole use of the gamma ray device is scaling of radioactive slats in the casing. However, if the salts are potassium, their effect cannot be corrected, and if the salts are uranium, their impact can be removed using spectral gamma ray.
Compensated Neutron Tool
The compensated neutron measurement is a little bit influenced by the presence of a steel casing. This permits the compensated neutron to be used in a cased hole to determine porosity when lithology is known. However, the presence of gas in the formation will cause the compensated neutron to miscalculate porosity crucially.
Pulsed Neutron Tool
Pulsed neutron devices are electronic devices that produce pulses of high energy neutrons. These high energy neutrons attack the formation, losing energy as they collide with atoms of the rock. Eventually, the neutrons lose a lot of energy that they are captured.
When a neutron is occupied, a gamma ray is emitted. The detectors in the pulsed neutron tool are planned to measure these “capture” gamma rays; therefore, a “capture cross section” of the formation through casing can be estimated.
This formation feature allows one to determine the water saturation when porosity and formation water salinity are known.