Hydrostatic Testing of Oil Casing and Tubing

Date:2024-07-15Tags:Casing and Tubing, casing pipe, Hydrostatic Testing, Oil-specific pipes, API SPEC 5CT, Forming process, Heat treatment

Oil-specific pipes are primarily used for drilling and transporting oil and gas in wells. During drilling, oil casing plays a crucial role, primarily serving as a wall support in the drilling process to ensure the smooth progression of drilling and the normal operation of the entire well after completion. Oil casing and tubing is the lifeline for maintaining well operation. Given the complex geological conditions and the diverse stress states underground—such as tensile, compressive, bending, and torsional stresses—stringent quality requirements are imposed on the casing itself. If the casing and tubing is damaged for any reason, it can lead to reduced production or even abandonment of the entire well. To ensure the quality and performance of oil casing and tubing , hydrostatic testing becomes an essential inspection method.


1.Classification and Application of Oil Casing and Tubing

Oil casing and tubing can be classified into different steel grades and uses based on the usage conditions and environment. Common steel grades include J55, K55, N80, L80, C90, T95, P110, Q125, and V150. Different well conditions and depths require casings of different steel grades. In corrosive environments, the casing and tubing needs to have anti-corrosion properties, while in complex geological conditions, the casing and tubing must have anti-collapse properties. The main categories of oil casing and tubing include conductor casing and tubing,surface casing and tubing,intermediate casing and tubing,and production casing and tubing, each with its own purpose and function.


2.Conductor casing and tubing: Used at the beginning of drilling to provide a guide.

Surface casing and tubing: Used to seal shallow, loose formations in the ground, preventing collapse and instability of the wellbore.

Intermediate casing and tubing: Used to seal off deeper, more complex formations, providing wellbore stability.

Production casing and tubing: Used to seal the production zone, preventing wellbore collapse and ensuring the smooth extraction of oil and gas.

Casing and Tubing


3.Importance of Hydrostatic Test of Oil Casing and Tubing

Hydraulic test of oil casing and tubing is an important means to detect its pressure bearing capacity and sealing performance. Hydrostatic test is mainly used to detect whether the casing and tubing can withstand the complex stress environment downhole in actual use, and to ensure that it does not leak or deform. The oil casing and tubing hydrostatic tester is a professional equipment used to detect the pressure bearing capacity of the casing and tubing. The test pressure can reach 70MPa. It is suitable for casings and tubing of different specifications, such as 9 5/8", 7", 5 1/2", 5", 4 1/2", 3 1/2", 2 7/8", etc., meeting the API SPEC 5CT standard. During the test, the booster cylinder method is used to increase the pressure. The booster method is fast and reliable, and is equipped with an automatic control system, which can display the pressure curve in real time, output the test report, and save the test data.


4.Casing and tubing water pressure test standard

The casing and tubing water pressure test standard mainly refers to the industry standard "SY/T 6194-2017 Oil and Gas Well Casing Test Method". In the test, the inner diameter and outer diameter of the casing and tubing are tested separately to ensure its stability and safety under high pressure environment.

Casing and tubing pressure test standard:

The inner diameter test pressure is 1.5 times the maximum use pressure, and the test time is 30 minutes.

The outer diameter test pressure is 1.1 times the maximum use pressure, and the test time is 30 minutes.

Casing leakage test standard:

The inner diameter test pressure is 1.5 times the maximum use pressure, and the test time is 30 minutes.

The outer diameter test pressure is 1.1 times the maximum use pressure, and the test time is 30 minutes.

Process of casing water pressure test

The process of casing water pressure test includes four steps: preliminary preparation, casing material preparation, test process and data processing and analysis.

Preliminary preparation:

Prepare the required test instruments and equipment, such as test pumps, pipelines, water tanks, etc.

Inspect and maintain the test pumps and pipelines to ensure the normal operation of the test equipment.


5.Casing  and tubing material preparation:

Select casing materials that meet the requirements of the specifications, carry out cleaning and docking work, and ensure the cleanliness of the test casing and the tightness of the connection.

Test process:

Send the water flow in the test pump into the casing, and apply the test pressure according to the standard.

During the test, observe and detect the appearance of the casing, whether there is water leakage inside, whether there is deformation, etc.

Data processing and analysis:

Process and analyze the data obtained from the test to determine whether the casing meets the use requirements.

If problems are found, correct and deal with them in time to ensure the quality and performance of the casing.


6.Other detection methods for oil casing and tubing

In addition to the water pressure test, the detection of oil casing also includes the following methods:

Ultrasonic detection:

Use ultrasonic probe to detect defects inside the casing, such as cracks, pores and inclusions.

Ultrasonic detection has high precision and high sensitivity and can detect subtle defects.

Magnetic particle detection:

Use magnetic particle flaw detector to detect defects on the surface of the casing.

Magnetic particle detection is mainly used to find cracks and other surface defects on the surface of the casing.

Radioscopic detection:

Use radiographic flaw detector to detect the inside of the casing.

Radioscopic detection can detect defects such as pores, inclusions and cracks inside the casing.

Hardness test:

Use hardness tester to test the hardness of the casing.

Hardness test can reflect the strength and wear resistance of the casing material.


7.Manufacturing process and quality control of oil casing and tubing

The manufacturing process of oil casing includes multiple links such as steel selection, forming, heat treatment and subsequent processing. Each link requires strict quality control to ensure that the casing has excellent mechanical properties and service life.

Steel selection:

Casing is usually made of carbon steel or alloy steel.

The chemical composition and impurity content of steel directly affect the mechanical properties and corrosion resistance of casing.

Forming process:

The forming process of casing includes hot rolling, cold drawing and seamless steel pipe forming.

The hot rolling process can improve the density and uniformity of steel, while the cold drawing process can improve the dimensional accuracy and surface finish of casing.

Heat treatment:

Through processes such as annealing, tempering and normalizing, the metallographic structure of steel can be optimized, and its strength and wear resistance can be improved.

The selection of heat treatment process needs to be optimized according to the material and application requirements of the casing to ensure its reliable performance in high stress environments.

Subsequent processing:

The subsequent processing of casing includes processes such as turning, grinding and surface treatment.

Surface treatment processes such as galvanizing and coating can improve the corrosion resistance of the casing and extend its service life.


8.Actual Case of Casing  and tubign Hydrostatic Test

In practical applications, casing hydrostatic test has become a standard inspection method in oil drilling operations. The following is a practical case that shows the important role of casing hydrostatic test in ensuring drilling safety.

In the drilling process in Xinjiang, China, a batch of newly purchased J55 steel grade casing was used. Before the casing was lowered into the well, a strict hydrostatic test was carried out. The test results showed that several casings had slight leaks under the test pressure. Through further testing, it was found that these casings had small manufacturing defects. Timely discovery and replacement of these defective casings avoided possible downhole accidents and ensured the smooth progress of drilling operations.


9.Conclusion

Oil casing plays a vital role in the drilling and production of oil and gas wells. In order to ensure that the casing can withstand high pressure and variable stress states in a complex downhole environment, hydrostatic test has become an indispensable means of detection. Through strict hydrostatic test and other detection methods, the defects and problems of the casing can be discovered in time to ensure its quality and performance. At the same time, the manufacturing process and quality control of the casing are also the key to ensure its reliability. Only through comprehensive testing and strict quality control can we produce high-quality casing that meets the requirements and ensure the safety and smooth progress of oil drilling operations.


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