A method for measuring the resistivity of the formation outside the casing through the metal casing

Abstract

Provided is a method for measuring stratum resistivity outside a drivepipe through a metal drivepipe. The method for measuring stratum resistivity outside the drivepipe through the metal drivepipe comprises the following steps: adopting to measure two groups of independent excitation current sources with different frequencies, one group of current source which is used for injecting current to the stratum is exerted on the ground between a well opening drivepipe and a return circuit electrode, and measuring the resistivity of the stratum outside the drivepipe; the other group of current source which is used for measuring uniformity of the drivepipe and eliminating influence while measuring the stratum resistivity is exerted under a well on a measuring drivepipe, the two groups signal sources adopt two signals with different frequencies between 0-15 Hz, simultaneously exert on the drivepipe to measure, and finally utilizes the following formula to calculate a visual resistivity of an objective stratum. By using a double power supply incentive method, the method for measuring stratum resistivity outside the drivepipe through the metal drivepipe avoids transmitting drive signals to the well through well-measuring cables, avoids power damage caused by large current while flowing through the well-measuring cables, and eliminates the influence of measuring signals caused by the drive signals and also caused by mutual connection in a coupling mode between cable cores.

Description

technical field [0001] The invention relates to well logging for oil field exploration and development, in particular to a method for measuring the resistivity of formation outside the casing through a metal casing. Background technique [0002] Formation resistivity is an important parameter for distinguishing oil and water layers in oilfield exploration, and it is of great significance for oil layer identification, crude oil reserves, remaining oil saturation, and reservoir dynamic evaluation. Traditional formation resistivity measurement instruments use electrical logging tools to measure in open holes, but it is difficult to implement electrical logging in cased holes due to the shielding effect of the metal casing on the electric field. Measuring the resistivity of the formation outside the metal casing by electrical logging is an important research field of resistivity logging in recent years. [0003] In 1939, Alpin of the former Soviet Union proposed to use three el...

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Problems solved by technology

[0012] As a result of the above factors, it is difficult to increase the effective excitation current actually injected into the formation, and the low-frequency noise has a greater influence, and it is difficult to improve the detection accuracy of weak signals. Finally, the effective measurement range of formation resistivity is small, usually in the range of 0 to 50 ohmm about

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