Oil casing is pipe usually larger in diameter and is used to line the hole. Casing operations occur periodically throughout the drilling process starting with the surface casing, intermediate casing, and ending with production string which takes place during well completion. Today, the four major properties of oil casing will be introduced in detail in this article.
(1) Anti-jamming performance
According to standard requirements, oil casing threaded joints need to be buckled and unfastened tested. It is stipulated that each joint must be put up and down 6 times. Tighten to the maximum torque recommended by the manufacturer, then loosen and check the adhesion of the internal and external threads of the oil casing. The adhesion and tightening of oil and casing threads are related to factors such as thread quality, thread surface hardness, tightening speed, surface friction coefficient and contact stress (coupling torque). In order to improve the anti-sticking performance of oil casing threads, the smoothness of the threads and the hardness and uniformity of the threads should be improved, the buckling speed should be reduced and the tightening torque should be controlled. At the same time, the surface of the internal threads of the coupling should be coated with a soft metal or non-metallic film to separate the oil casing body from the coupling, prevent the metal surfaces between the two threads from adhering, and prevent the threads from detaching. to be torn or even torn apart. Before tightening the coupling, thread grease needs to be applied to the thread surface to prevent the threads from adhering after tightening the coupling and improve the sealing performance of the threads.
There are many coating methods for the coupling thread surface: such as galvanizing process, phosphating process, etc.; for some special materials and special connecting threads, copper plating is often required. Gluing factors related to the factory: thread parameters (pitch, thread height, taper, tightening torque, thread half angle, etc.), internal and external thread fit (surface treatment, surface finish, phosphating, galvanizing, copper plating, etc.). ), thread grease (function: lubrication, filling and sealing, etc., composed of metal powder and grease), hook-up control (lock-up torque, hook-up speed, etc.), material factors, etc.
Factors related to oilfield operations: no wire protection during hoisting, partial buckling (the pipe swings in the air and the well buckles are not concentric), no or few buckles, thread grease (not meeting standard requirements, sand and debris), tightening speed, Tightening torque, clamp clamping force, etc.
(2) Collapse (pressure) resistance
As the drilling depth increases, the pressure on the oil and casing in oil and gas wells also increases, especially in deep wells, ultra-deep wells, or formations that need to isolate plastic flow (such as rock salt, salt gypsum, shale, etc.) and soft rock formations. ), etc., are more obvious in oil and gas wells with complex formations. When the external pressure endured exceeds a certain limit, the oil well pipe body will undergo groove-like or elliptical deformation, which is called oil well pipe collapse.
(3) Corrosion resistance
Some oil and gas fields contain a large amount of corrosive media such as hydrogen sulfide, carbon dioxide or chloride ions. The corrosion resistance requirements for oil and casing include resistance to sulfide stress corrosion, CO2 and Cl- corrosion, etc. The performance of oil casing is mainly related to factors such as the chemical composition of the steel and the residual stress value of the steel pipe. Reducing the content of non-metallic inclusions and harmful elements in steel, increasing Cr, Ni and other corrosion-resistant elements, reducing the residual stress of steel pipes, and increasing the yield-to-strength ratio of steel pipes are all conducive to improving the oil corrosion resistance of casings.
(4) Perforation performance
The oil production portion of the reservoir casing (multiple layers of oil wells producing oil individually) needs to be perforated to allow crude oil to flow from the designated oil-bearing oil sand layer into the casing. For this reason, petroleum requires the casing to have good perforating performance. Especially when gun-less perforating operations are used, the requirements for the perforating performance of the casing are higher.
The perforating performance of the casing is obtained through the perforation test, that is, the tested casing is suspended in a simulated well, and a series of shaped energy perforating bombs in a certain number, a certain distance, and in different directions are suspended in the casing. Then make holes. After perforating, if there are basically no cracks around the test casing hole, the perforation performance is evaluated as good; if there are a few small cracks around each hole, but their number and length do not exceed the specifications specified in the technical conditions, the perforation performance is evaluated as good. If the number or length of cracks around each hole exceeds the specification, especially if the cracks between two adjacent holes are connected, the perforation performance will be judged to be unqualified.