What are the influencing factors of logging?

 Any scientific method is not absolutely accurate. Therefore, many factors may cause the measured value to deviate from the actual geological value in the oil logging. In many cases, it also needs to be corrected using the actual strata. What are the factors that affect logging?

1. Influence of Logging Instrument

A logging instrument is a metering tool. Therefore, it must be accurate, and the error must be within the permitted range. Otherwise, the tested data will not be accurate. The ground recording instrument and downhole measuring instrument used in logging have specific requirements. In general, they must be "Three unifications", namely, stability, linearity, consistency, and standardization.

 

1. Stability means that when other conditions remain unchanged, the measurement results of the instrument shall not exceed the permitted indicators during continuous operation.

2. Linearity refers to the linear relationship between the input signal and the output signal within the specified condition range, and the error does not exceed the specified range.

3. Consistency means that when different similar instruments are used for measurement, as long as the measurement conditions are the same, the relative error of the measurement results must be within the range specified by the standard.

4. Standardization refers to the standard scale and standard verification of the instrument. The logging instrument can be used only when the standard volume is used for calibration. data without standard scale logging cannot be used.

2.Impact of Drilling Construction

In the drilling process, when the drilling fluid and the layer pressure are poor, the movable part of the fluid in the formation near the borehole wall flows up, a ring belt washed by the drilling fluid is formed on the borehole wall. Generally, when the pressure of the fluid column in the borehole is higher than the formation pressure, the drilling fluid filtrate is immersed in the permeable sand layer or powder layer. At this time, on the one hand, the mud particles in the drilling fluid form a mud cake in the permeability of the formation area; on the other hand, the drilling fluid filtrate squeezed out part of the original fluid contained in the penetration layer, the formation of a ring belt called intrusion. The resistivity of these rings are called mud pie resistivity, washing band resistivity, and immersed band resistivity. The resistivity of the formation that has not been infiltrated by the drilling fluid filtrate is called the formation resistivity. the resistivity of these loops has an impact on the measurement results of the formation resistivity. In addition, the actual measurement results will be affected if the well diameter is enlarged or irregular, and the drilling fluid resistivity is too high or too low.

3.Formation thickness

The formation thickness is different. Some layers have a thickness of dozens of meters, while others have a thin thickness of dozens of centimeters. Some strata are well-balanced, while others are not. A thick and even formation is easy to measure the physical parameters of the formation. It is difficult to determine various physical parameters for thin and uneven layers. For example, when performing common resistivity logging. There is also a high-impedance layer near the target layer, which is called the adjacent layer. The existence of this adjacent layer has a great impact on the distribution of current, making the Resistivity Test of the Target layer inaccurate.

There are many factors that affect the measurement results, but they are regular. through research and analysis, appropriate measures can be taken to reduce or eliminate these effects, make the obtained measurement data more accurate to the actual value. For example, to measure the resistivity of a high-impedance thin layer, the method of lateral logging is better than that of common resistivity logging, and the effect of irregular well diameter or instrument skew on the measurement result can be eliminated by dual-producer and double-collector acoustic logging, in addition, some feature models and mathematical methods can be used for data correction using correction formulas.