The Research On Field Distribution Of Constant-current Source And Mental Casing Defect Detection

Metal casing support and protect the borehole wall and equipment in oil and gas wells、separate from the layers of fluid, and guarantee the normal work of oil and gas wells. But ithas been working in the harsh environment of high pressure、high temperature and salinity fora long time, meanwhile because of various formation and the engineering technology factors,the metal pipelines became deformation、dislocation、rupture、leakage. What’s more, the casingwas fixed by the concrete in the well, which is belong to the one-time consumable, thewastage of the casing has reached more than70%of the total oil-well pipes, as a result, the oilfield exploitation caused serious economic loss and environmental impact, so it has greatpractical significance to detecting the casing defects timely manner to avoid productionaccident, reduce the economic loss.At present, there are many kinds of detection methods for casing corrosion defects. Andeach method has its own advantages, disadvantages, and conditions of use.This paper is basedon the field distribution of constant-current source, with the help of the finite element analysissoftware COMSOL Multiphysics simulating for casing detects respectively at the current field(ec) and magnetic and electric field (mef) in the low-frequency electromagnetic fields moduleAC/DC, getting the electric field distribution in the inner wall of the pipe when it has beendamaged. the post-processing technology of COMSOL Multiphysics was used intuitivelyanalyzed the intensity of excitation source, the distribution of exciting and detecting electrodeeffect on the detection resolution. And described the method to distinguish between the innerand outer of the corrosion of the casing in detail, combining with the skin effect, which isgenerated by multi-frequency alternating current excitation. In addition, based on theprogress of theory research, this paper set up the experimental platform, in order to verify thethe detection method on constant current source field distribution. This subject preliminarydiscussed the design of the excitation electrodes and the potential-measuring electrodes,completed the array of signal measurement and the design of the preamplifier circuit, at onetime,through the existed high-precision of data-acquisition instrument PXle-1062Q got thevoltage measure points to calculate the corresponding current density,then, drawn2D graphicsby MATLAB2008,which could response the true form of the casing intuitively andclearly.This paper on how to design the parameters of apparatus,control the magnification times and testing precision of the signal,and achieve the best effect of measurement is veryimportant.