What is the formula for calculating the demand for oil well casing?
Geological factor
Formation movement: the plastic flow of rock in the formation, salt collapse, fault activity and formation creep will cause damage to the casing. For example, the plastic flow of salt paste layer or salt layer under high temperature and pressure will compress the casing, resulting in deformation or even fracture of the casing.
Formation pressure: Abnormal high pressure in the formation can produce uneven compression of the casing, resulting in casing deformation and fracture. In addition, the increase of slip and shear force in the formation will also aggravate the stress degree of the casing and make it easy to break.
Chemical corrosion
Formation water and chemicals: Corrosive substances such as CO2, H2S, and salt contained in formation water will react with casing materials, resulting in casing corrosion. These corrosive substances accelerate the corrosion process at the point of wear and damage on the casing surface.
Electrochemical corrosion: Microorganisms such as hydrochloric acid reducing bacteria in formation water will accelerate the electrochemical corrosion rate of casing under the condition of hypoxia.
Physical stress
High-pressure water injection and fracturing: In the process of oil production, high-pressure water injection will reduce the effective stress of the formation, make the formation volume expand, produce a large shear stress on the oil layer boundary, resulting in the adjacent casing is vulnerable to damage. At the same time, the pressure change during fracturing will also aggravate the stress degree of casing.
Drilling and cementing: Friction and collisions during drilling and poor perforation accuracy during cementing can cause casing to crack or deform.
Human factor
Improper design: the material and strength of the casing do not meet the requirements of field construction, or the unreasonable combination of casing leads to local extrusion damage.
Improper production: Lack of protective film during casing manufacturing, excessive gap between connection threads, small cracks during processing or uneven casing wall thickness will reduce the service life of casing.
Improper use: In the process of downhole operation, due to inadequate operation or management, the downhole objects or the selected downhole tools are unreasonable, resulting in friction, collision and other damage to the casing.
Other factors
Sand production of oil well: the sand production of oil reservoir can cause the overlying rock mass to rush upward and the underlying rock mass to sink, which will produce transverse supporting force on the oil well casing and may bend or break the casing.
Environmental factors: Formation freezing and thawing caused by seasonal changes will change the formation volume and squeeze the casing.
