With the rapid development of the petroleum industry, well pipe casings, buried pipelines, storage tank floors, and pup Joints inside oil fields are all subject to external corrosion. In particular, severe corrosion of well pipe casings has brought great problems to the production, development, and production of oil fields. Management as well as the environment have had serious impacts. There is corrosion on both the inner and outer walls of oil and gas well pipe casings, among which internal corrosion is more serious. In addition, in well sections with large changes in well inclination, the mechanical damage of the tubing to the casing during operations accelerates the corrosion and perforation of the casing; welding defects in the welds, gaps in the threads and other parts can easily cause differences in the electrochemical properties of the steel pipe surface. It also leads to more serious corrosion damage.
To solve the corrosion problem of the inner wall of the well pipe casing, we generally add bactericides, corrosion inhibitors, pH adjustment, airtight oxygen isolation technology in the annular space of the oil well, and use low-strength oil casing in sulfur-containing oil and gas fields. To solve the corrosion problem of the outer wall of well pipe casing, cathodic protection technology should be adopted. At present, this has been recognized by people in the anti-corrosion industry at home and abroad. To prevent soil from corroding underground steel structures, cathodic protection is the most economical, reasonable and very effective technical measure. Cathodic protection is a safe and mature anti-corrosion technology. It has the characteristics of strong protection ability, simple construction and low investment. This technology is increasingly widely used in oil and gas, petrochemical, municipal construction and other sectors. It can not only prevent the corrosion of newly built oil well pipe casings, but is also very effective for existing old oil well pipe casings. It can extend the service life and reduce the number of replacements, and the economic benefits are very obvious.
Well pipe casing cathode protection principle
Well pipe casing cathode protection is to drill an anode deep well for every 2-4 oil wells on average in areas with dense oil wells or oil wells. As the anode of the cathode protection system, a forced current is applied through a potentiostat to provide a uniform supply to the casing. , a sufficient amount of cathode protection current flows back to the cathode of the potentiostat through the confluence point next to the wellhead, forming a closed loop to fully cathodic polarize the oil well pipe casing, thereby avoiding or reducing corrosion of the oil well pipe casing.
Compared with other cathode care methods, deep well anode and cathode care has the following advantages:
1. Output is adjustable
The deep well anode and cathode protection accepts a potentiostat as the output power supply of the impressed current cathode protection. It has the functions of constant current and constant potential, which solves the problem of lack of output potential of the sacrificial anode and inability to adjust the output current potential.
2. Wide radiation range
Since the deep well anode is located in deep soil rich in groundwater, it can effectively reduce the ground resistance of the anode body, which can greatly increase the effective radiation range of the anode body and achieve good protection effects for casings buried several kilometers underground. , reducing the cost while reducing the number of anode ground beds. Suitable for places with small space and high soil resistivity.
3. The current distribution is uniform. A certain distance is maintained between the deep well anode body and the oil well casing, so that the cathode protection current distribution on the surface of the casing is more uniform and the interference to other buried metal structures is relatively small.
In addition, deep well anode and cathode protection also has the advantages of being less affected by climate, stable ground resistance, small stray current interference, small footprint, long service life, and convenient installation. It is suitable for oil and gas field production facilities with dense pipeline networks and harsh working conditions. corrosion protection.