Oil Well Cement Production
What is oil well cement? Oil well cement, also known as plugging cement, is a kind of special cement used in the cementing engineering of oil well or gas well. It consists of Portland cement or blended cement, plus additives. Its performance is consistently stable in well cementing applications at extremes of depth, temperature, and pressure.
In the exploitation process of petroleum and natural gas, when the drilling depth reaches the design requirements, we usually put a steel casing into the borehole and pump cement slurry into the borehole around the casing to cement the casing with the surrounding formation. This process not only blocks the oil, gas, and water layers but also forms an isolated channel from the oil or gas layer to the surface.
Oil Well Cement Features
- Good liquidity. After mixed with water, the oil well cement has low consistency, low free water content, and high sedimentary stability, which is conducive to pumping in operation.
- Appropriate setting time. Under different well temperature and well pressure conditions, the oil well cement slurry has a long thickening time to ensure that it can quickly set after cementing and produce certain mechanical strength. The interval between its initial and final setting time is short.
- Appropriate density. After mixing oil well cement with water, it has appropriate slurry density to meet the needs of cementing operation of various rock formations.
- The intensity is produced rapidly. After well cementing, the oil well cement slurry can harden quickly and ensure long-term stability.
- Good compactness. The hardened oil well cement paste is airtight and waterproof and has good impermeability, stability, and corrosion resistance.
Oil Well Cement Functions
Using oil well cement to fill the void between the casing and the borehole has various functions.
Oil Well Cement Types
The temperature and pressure in the oil well usually rise with the increase of well depth. For every 100 meter depth, the temperature increases by about 3℃ and the pressure increases by 1.0~ 2.0mpa. Under high temperature and pressure, various properties of oil well cement will be greatly influenced. Therefore, different grades of oil well cement should be used in wells with different depths. According to the US API specification, oil well cement can be classified into eight grades. Each grade is further divided into ordinary type (O, C3A < 15%), moderate sulfate resistant type (MSR, C3A ≤ 8%, SO2 ≤ 3%), and high sulfate resistant type (HSR, C3A ≤ 8%).
Grade A: grade A oil well cement only has the ordinary type, which is suitable for shallow cementing operation without special requirements. It is usually directly mixed with water to make slurry. Sometimes, a small amount of admixture such as coagulant can be added according to the need.
Grade B: grade B oil well cement has a moderate sulfate resistant type and high sulfate resistant type. It is suitable for shallow sulfate resistant cementing operations.
Grade C: grade C oil well cement, also called early strength oil well cement, has the ordinary type, moderate sulfate resistant type, and high sulfate resistant type. It is suitable for shallow cementing operations requiring early strength and sulfate resistance.
Grade D, E, F: all of the grade D, grade E, and grade F oil well cement are called retarded oil well cement. They all have a moderate sulfate resistant type and high sulfate resistant type, suitable for cementing operations in medium and deep wells. Grade D oil well cement is suitable for the downhole conditions of medium temperature and medium pressure. Due to the complex manufacturing process, its production cost is high. So it can be replaced by the addition of retarders to grade G and Grade H oil well cement. Grade E oil well cement is suitable for downhole conditions of high temperature and high pressure. And the grade F oil well cement is commonly applied under ultra-high temperature and high-pressure downhole conditions.
Grade G, H: both grade G and grade H oil well cement are called basic oil well cement. They have a moderate sulfate resistant type and high sulfate resistant type, suitable for most cementing operations. They can be mixed with low-density materials (fly ash, bentonite, etc.) to form cement slurry, which is commonly used for sealing and fixing low-pressure and leaky formation. And they can also be combined with the admixture to form conventional density cement slurry for well-cementing projects. In addition, the grade G and grade H oil well cement can be prepared with weighting materials (crystal powder, iron ore powder, etc.) into a high-density cement slurry for deep and high- pressure wells cementing projects.
|Grade||Application Depth(m)||Application Temperature(℃)||Type|
|Ordinary(O)||Moderate Sulfate Resistance(MSR)||High Sulfate Resistance(HSR)|
How to Make Oil Well Cement?
We usually choose to produce basic oil well cement (grade G and grade H oil well cement) and then add corresponding additives to meet the technical requirements of other grades of cement. The production cost of this method is relatively low and the production process is simple.
How to manufacture oil well cement? The production process of oil well cement is basically the same as the ordinary Portland cement. It can be roughly divided into five steps: raw material crushing, raw material grinding, clinker calcination, cement grinding, and cement packing.
Before starting production, the most important thing is to choose raw materials. We should select high-quality limestone with CaO content about 50.0% and MgO content less than 2.0%, hard sandstone with SiO2 more than 90%, Al203 less than 5.0%, and alkali content less than 1.0%. After that, we should select equipment as each step of oil well cement manufacturing requires a lot of professional cement equipment.