Three-Dimensional Finite Element Numerical Simulation and Physical Experiment for Magnetism-Stress Detecting in Oil Casing

The casing damage has been a big problem in oilfield production. The current detection methods mostly are used after casing damage, which is not very effective. With the rapid development of China's offshore oil industry, the number of offshore oil wells is becoming larger and larger. Because the cost of offshore oil well is very high, the casing damage will cause huge economic losses. What's more, it can also bring serious pollution to marine environment. So the effective methods of detecting casing damage are required badly. The accumulation of stress is the main reason for the casing damage. Magnetic anisotropy technique based on counter magnetostriction effect can detect the stress of casing in real time and help us to find out the hidden dangers in time. It is essential for us to prevent the casing damage from occurring. However, such technique is still in the development stage. Previous studies mostly got the relationship between stress and magnetic signals by physical experiment, and the study of physical mechanism in relative magnetic permeability connecting the stress and magnetic signals is rarely reported. The present paper uses the ANSYS to do the three-dimensional finite element numerical simulation to study how the relative magnetic permeability works for the oil casing model. We find that the quantitative relationship between the stress' s variation and magnetic induction intensity's variation is: Δδ =K* ΔB, K = 8.04×109, which is proved correct by physical experiment.

Corrosion Rate of Hydrogenation to C110 Casing in High H_2S Environment

The corrosion behavior of C110 bushing at high temperature and high pressure with a high H2S / CO2 was studied, and a basis for the materials selection of sour gas well bushing was provided in H2S, CO2 and saline coexisting environment. Under acidic condiction, hydrogen atoms greatly entered into the material and caused the material properties changed. Weight loss method was used to study the corrosion rate of hydrogen charging samples and original untreated samples in simulated oil field environment. PAR2273 electrochemical workstation was used to examine the electrochemical performance of samples untreated, hydrogen charging after reacting in autoclave. The corrosion product film was observed through SEM. The experimental results show that sample with hydrogen charging has a much more obvious partial corrosion and pitting corrosion than the untreated blank sample even the downhole corrosion speed of bushing is increased after being used for a period of time. Polarization curve shows the corrosion tendency is the same between sample with or without hydrogen charging and corrosion tendency is reduced by corrosion product film. A layer of dense product film formed on the surface of samples provides a certain protective effect to the matrix, but cracked holes which will accelerate partial corrosion of the sample were also observed.

Measurement-While-Milling(MWM):An innovative approach for increasing the casing milling efficiency in deep drilling operations

Deep boreholes are secured by steel tubes(casings)which are run in the hole and cemented in place.In most cases,these casings are considered a permanent installation.However,sometimes they have to be removed in order to repair or abandon the well.As the casing is cemented in place,it cannot be pulled,but needs to be milled to small chips which are flushed out of the borehole by the drilling mud.One of the main challenges in casing milling operations is continuous and complete chip removal.If the metal chips are too long,chip nests will grow around the milling string.As a result,this will restrict the annulus flow area and affect the chip removal in boreholes.The obvious solution in such condition is to do round tripping and clean the chip nest which is associated with the risk of injuries,as well as,increasing the none-productive time.In the worst case,the poor cleaning and circulation of chips can even end up with the milling string stucking problem in boreholes,consequently long-time fishing job.According to the available literatures,hardly any study for identifying the chip shapes and accordingly adapting the operation parameters to the casing milling process environment downhole to keep milling within desired generated chip shapes and sizes could be found.This paper presents an encouraging idea to monitor the milling process in real time by utilizing the acoustic emission signals(vibration modes)accompanied with the milling process to identify the desired chip shape and size range.Initial laboratory tests have been carried out to investigate and study the acoustic emission signals accompanying the casing milling process to identify the chip shapes and sizes.The preliminary test results show very good correlation and agreement between the chip length formed during those specific tests and the observed burst events in the measured signals.The study results have demonstrated the functionality of the new concept,and thus confirmed that it is a very promising idea towards developing a practical real time downhole monitoring system for milling operations.Adapting the milling operation parameters downhole in real time to keep the milling process within the desired generated chip shapes and sizes will offer better cleaning and removal of the chips and will prevent the development of chip nest around the drill string and its consequences such as round tripping,risk of drilling crew injury,none-productive time and even milling string stucking problems.

Slurry erosion behaviors of P110 steel and chromizing coating in liquid-solid two-phase flow

A chromizing coating was formed on P110 oil casing tube steel (P110 steel) via pack cementation to improve its performance and increase the lifetime during operation. The slurry erosion behaviors of the P110 steel substrate and the chromizing coating were assessed in a liquid-solid two-phase flow condition. The results showed that the obtained coating exhibited higher surface hardness, lower mass loss, and lower slurry erosion rate than those of P110 steel. The chromizing treatment has significantly improved the surface hardness and slurry erosion resistance of P110 steel.