Oil Well Cement Production
Oil well cement is one kind of special cement just like white cement and refractory cement.
What is oil well cement? Oil well cement is used for cementing of oil well and gas well, also known as plugging cement. In the oil or natural gas exploration and production, set the steel tube into the hole, reinjection cement slurry, the main function of oil cement is to cement and seal steel tube with the surrounding strata, the packer in the formation of oil, gas, water, prevent string approach each other, in order to form an oil flow channel with good insulation from the reservoir to cut off the ground.
Oil well cement features
The physical properties of oil well cement include water-cement ratio, the specific surface area of cement, initial consistency within 15 to 30 min, thickening time at specific temperature and pressure, and compressive strength at a specific temperature, pressure, and curing age.
- With suitable density and setting time, low consistency, the prepared premixed oil well concrete has good settlement resistance and pumpability.
- When the oil well cement is injected into a predetermined (temperature, pressure) interval, it can quickly set and harden and produce a certain mechanical strength. Concrete has good impermeability, stability, and corrosion resistance after curing.
- Oil well cement is special cement, which is made of Portland cement clinker with calcium silicate hydrate as the main component, adding a proper amount of gypsum and grinding aid.
How To Make Oil Well Cement?
There are two production processes for oil well cement. One is to produce clinker composed of specific minerals to meet the chemical and physical requirements of a certain grade of cement. The other is to use the basic oil well cement (grade G or Grade H cement), adding the corresponding admixture, in order to meet the technical requirements of grade cement. The former approach tends to bring more difficulties to the cement plant, so the second approach is widely used.
Oil well cement manufacturing process is the same as Portland cement manufacture, but there are some basic requirements to be meted in some production process.
- In the raw materials of oil well cement, calcium oxide content of limestone should be high, potassium and sodium content of clay should be low, finished raw meal should be sent into homogenization to ensure the composition of the raw meal into kiln.
- During the process of clinker calcining, the proportion of clinker and the content of free calcium oxide must be strictly controlled, and the specified control indexes must be reached.
- After the cement is put into a storage silo, it should be fully homogenized to ensure that the quality of products from the cement factory all meet the technical requirements stipulated in the standard.
In a short, oil well cement production can be divided into five steps:
- Raw materials preparation
- Raw meal grinding
- Clinker production
- Cement grinding
- Storing or bagging
Firstly, cement crusher helps break raw materials into a smaller size, there are jaw crusher, hammer crusher, cone crusher, impact crusher to choose, cement conveyor and vibrating screen and other equipment transfer raw materials into raw mill.
Thirdly, preheater and precalciner preheating and pre-calcining raw meal, then rotary kiln will calcine raw meal into cement clinker, grate cooler, dryer, bag filter, or electrostatic precipitator will provide support for rotary kiln system.
Oil well cement uses
Notes: The situation of oil well and gas well is very complicated, in order to adapt to the specific conditions of different oil and gas well, it is necessary to add some admixtures in cement, such as a weight-adding agent, lightening agent, or retarder.
The basic requirements of oil well cement are as follows:
- The cement slurry should have certain fluidity and suitable density in the process of well injection
- After the cement slurry is injected into the well, it should condense quickly and reach a certain strength in a short time.
- The hardened cement slurry shall have good stability, impermeability and corrosion resistance.
Classification of oil well cement
In general, the temperature and pressure at the bottom of the well increase with the increase of the well depth. For every 100 m, the temperature increases by about 3℃, and the pressure increases by 1.0 ~ 2.0mpa. Therefore, the influence of high temperature and high pressure, especially high temperature on various properties of cement is the most important problem in the production and use of oil well cement. The high temperature makes the strength of Portland cement decrease significantly,
Therefore, different concentrations of oil Wells should use cement in different compositions. According to GB 10238-98, China’s oil well cement is divided into nine grades, including ordinary (0), medium sulfate resistant (MSR), and high sulfate resistant (HSR). The application scope of oil well cement at all levels is as follows:
- Class A: For cementing from surface to 1830 m depth without special performance requirements are required. Only the normal type.
- Class B: Suitable for demanding downhole conditions and early strength, suitable for cementing from surface to 1830 m well depth. It is divided into two types: medium sulfate resistant and high sulfate resistant.
- Class C: Suitable for downhole conditions with the high requirement in the early strength, apply for cementing from surface to 1830 m depth. It can be divided into three types: common type, moderate type, and high type.
- Class D: Suitable for use under medium temperature and pressure downhole conditions, divided into two types: medium and high sulfate resistance.
- Class E: Suitable for use under high temperature and pressure conditions include two types: medium and high sulfate resistant.
- class F: Suitable for ultra-high temperature and pressure conditions, divided into medium and high sulfate resistance type.
- Class G, Class H: Basic oil well cement, divided into medium sulfate resistant type and high sulfate resistant type.
- J-class: Suitable for cementing 3 660 ~ 4 880 m well depth under ultra-high temperature and pressure conditions.