Abstract
Steel casing pipes used in underground gas storage or in oil fields are subjected to corrosion. Corrosion frequently causes some pitting or wall thinning to the internal or external of casing pipes. More serious corrosion would form holes on the casing pipes and induce serious operational problems. Hence, corrosion monitoring and early detection of field oil pipe is considerably important to the gas and petroleum industry. We will introduce in this paper a new version of the Direct Current (DC) electromagnetic induction system which is capable of detecting small, isolated corrosion pits and holes on the casing wall. A sensor system based on the DC electromagnetic induction instrument is coupled to an updated data acquisition system. Unlike the conventional DC induction instrument this system transmits all the measured flux leakage (FL) signals and eddy current (EC) signals to the computer logging system (CLS) on surface. To transmit the information represented by enormous data acquired by the downhole instruments to the CLS on surface, a wavelet data compression technique is incorporated. A VLSI integrated circuit (IC) realizing wavelet transform has been designed so that the real time mode can be achieved during the logging operation. The circuit has been designed using a CMOS n-well 2 /spl mu/m technology and has been fabricated by MOSIS.
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