Oil-well cement: marks, composition and fields of application

One of the varieties of Portland cement is oil well cement. This type of Portland cement can be used in the widest range when carrying out oil well works. It occupies one of the most important places due to a good combination of technical and building properties.

What is this material and how does it differ from the usual cement mortar? About this - further.

Specific features

What is different from portland cement cement oil cement - the composition: for its production in the crushed clinker base with gypsum additives are made.

For oil and gas wells, different types of mixtures are made, which are divided into the following subspecies:

1. Hygroscopic. To obtain the material in a dry mass, a hydrophobizer of triethanolamine is introduced.
2. Weighted. For manufacturing, mix cement clinker with gypsum and weighting additives. These can be iron ore in the form of heavy tie, hematite, magnetite.
3. Sandy. To obtain the material of this subspecies, quartz sand with gypsum is added to the mixture. The number of components should not exceed 50% for "hot" wells and less than 20% for "cold" wells.
4. Resistant to salt. It is used where the salts in groundwater have a high concentration. This leads to corrosion, but the addition of finely divided quartz sand eliminates this drawback.

The technical characteristics of each type depend on the proportions and properties of the components. Such can be quartz sand, minerals, limestone, slag.

Application technology

Since oil-well cement must be poured not manually, but pumped with pumps, the mass is made sufficiently liquid. For this, 1 part of water is added to 2 parts of the dry mixture. The resulting mass is called pulp. If the temperature is high, the pulp can harden within 1.5-10 hours. The higher the temperature, the faster the cement will tighten. Application in cold wells (or if the mass is used in waterproofing works on building buildings in the cold season) leads to the fact that the process of solidification begins in 2-3 hours and ends in 20-22 hours. The longest is the salt-resistant cement.

The bending strength index after two days after full hardening is as follows:

1. If there is no heating - approximately 62 kg / cm.
2. If the temperature is stable high - 27 kg / cm.

But this is only if high-quality oil well cement was used. How to check its quality? There is a very simple and reliable way - to carry out the sample through a sieve. To do this, carefully sift through the sieve a little dry powder. If the sieve has left ¾ part of the initial volume, the material is qualitative. You can check for an eye, but this can only be done by those who have extensive experience working with oil well cement. Otherwise, you have to trust the seller. But at the same time it's worth paying attention to the composition of the dry mix - the amount of gypsum should not be more than 3.5%.

Characteristics

The main features of the material are the following:

1. High curing speed. But at the same time the mobility of the mixture mixed with water remains long enough.
2. Water resistance. The solution can harden even under water.
3. Combination with different fillers. And it can be also the surfaces having a physical and chemical nature, including steel.
4. Regardless of the environmental conditions, the solidified mixture retains its strength and integrity for a long time.

Classification features

Oil-well cement is of several types. All of them differ in different parameters. So, the composition of substances material is of these types:

• I - without additives;
• II - with additives;
• III - with special additives. They are used to regulate the density of the solution.

Material type III is weighted (W) and light (Ob). In addition, each type of material is divided into species intended for use at normal (25-50), low (15-24), moderate (51-100) or elevated (101-150) temperatures.

Conventional notation

To determine the brand of material, special labeling is used:

1. Cement plugging - PC.
2. Sulfate resistance - SS.
3. Average density.
4. The maximum permissible temperature during work.
5. Plastification or hydrophobization. Indicated as Pl, Gf.
6. Standard rate.

Example: PCT-I-SS-100. The designation carries such information: the material is a cement-encapsulated Portland cement, not containing additives, is sulfate-resistant. Designed for use at temperatures from 51 to 100 degrees.

PCT-III-UT1-100. This is a plugging type of portland cement, a lightweight type with a density of 2.1 g / cm ³ . You can work with the material at a moderate temperature.

PCT-III-Ob5-50 - cement slurry. Is a light type. Has a density of 1.5 g / cm ^3. Allowed to work at normal temperatures.

Quality checking

This material is designed to create waterproofing wells, but often used plugging cement in construction when erecting some residential or industrial facilities. But for the material to be able to fulfill the intended task, to ensure the integrity and reliability of the created structure and at the same time to be environmentally safe, it must be of high quality, and the composition - in accordance with the complexity and features of the tasks. For this, the created mixtures are tested.

There are different methods of testing oil well cement, which is what specialized laboratories do. They determine the following indicators:

1. Density (specific gravity).
2. Rheological properties.
3. Time of thickening.
4. Water separation.
5. Filtration losses.
6. Strength limit.
7. Stability before ultrasound.
8. Permeability of frozen material with liquids, gas, air.