Simulating corrosion condition of air foam drilling, corrosion inhibition performance and foaming properties of stable foam are evaluated. Corrosion product layer images and composites are investigated by scanning electron microscope, energy dispersion spectrometer and x-ray diffraction analysis. The results show that corrosion pitting with sodium chloride crystalline grain forms on the surface of steel corroded by formation water. Foam can retard corrosion, particles in foam uniformity, thinness and tightness. After adding foam and inhibitor no obvious corrosion phenomenon happens but existing tiny trace originating from washing and erosion. Foam corrosion inhibition mechanism is first put forward through laboratory data and theoretical analysis, which mostly consists in foam agent absorption on steel surface; viscosifier complexing characteristic; oxygen isolation; foam enwrapping sands, reducing erosion. Adding inhibitor and oxygen scavenger, foam corrosion inhibition ability is improved further. Indoor experiment and field application show foam drilling substituting for dry air drilling and adjusting pH value and adding inhibitor reduce sharply corrosion of drilling tools. Special formula in Western Gasfield of China X-14 well is 2.0%F4 +0.3%HPAM + 0.2%XC + 0.5%CT2 + 0.05%Na2SO3. Practice proved that this method effectively restrained drilling tools corrosion and improved economic benefits.
This paper is the first in a series of studies designed to bring forward foam corrosion inhibition in air foam drilling. The goal is to better understand the mechanism of foam corrosion inhibition, to be able to select the proper inhibitor and extend air foam drilling techniques in suit region.