One of the varieties of Portland cement is well cement. This type of Portland cement can be used in the widest range during plugging operations. It occupies one of the most important places due to the good combination of technical and construction properties.
What kind of material is this and how does it differ from the usual cement mortar? More on that later.
Special Features
What makes well cement different from Portland cement is its composition: for its manufacture, certain additives are added to the crushed clinker base with gypsum.
For oil and gas wells, different types of mixtures are produced, which are divided into the following subspecies:
- Hygroscopic. To obtain the material, triethanolamine water repellent is introduced into the dry mass.
- Weighted. For manufacturing, cement clinker is mixed with gypsum and weighting additives. These can be iron ore in the form of heavy sp alts, hematites, magnetites.
- Sandy. To obtain the material of this subspecies, quartz sand with gypsum is added to the mixture. The number of components should not be more than 50% for "hot" wells and less than 20% for "cold" ones.
- S alt resistant. It is used where s alts in ground waters have a high concentration. This leads to corrosion, but the addition of finely ground quartz sand eliminates this disadvantage.
Technical characteristics of each type depend on the proportions and properties of the components. These can be quartz sand, minerals, limestone, slag.
Application technology
Since well cement has to be poured not by hand, but by pumps, the mass is made sufficiently liquid. To do this, add 1 part of water to 2 parts of the dry mixture. The resulting mass is called pulp. If the temperature is high, the pulp can harden already in 1.5-10 hours. The higher the temperature, the faster the grout cement will set. Application in cold wells (or if the mass is used for waterproofing work on the construction of buildings in the cold season) leads to the fact that the hardening process will begin in 2-3 hours and end in 20-22 hours. S alt-resistant cement takes the longest to set.
The index of bending strength two days after complete solidification is as follows:
- If there is no heating - approximately 62 kg/cm.
- If the temperature is consistently 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 -test through a sieve. To do this, carefully sift a little dry powder through a sieve. If ¾ of the original volume remains in the sieve, the material is of high quality. You can check it by eye, but only those who have extensive experience with well cement can do this. Otherwise, you will have to trust the seller. But at the same time, it is worth paying attention to the composition of the dry mixture - the amount of gypsum should not be more than 3.5%.
Features
The main features of the material are the following indicators:
- High curing speed. But at the same time, the mobility of the mixture mixed with water is maintained for a long time.
- Water resistant. The solution can harden even under water.
- Combination with different fillers. Moreover, it can also be surfaces that have a physical and chemical nature, including steel.
- Regardless of environmental conditions, the hardened mixture retains strength and integrity for a long time.
Classification features
Well cement is of several types. All of them differ in different parameters. So, according to the composition of substances, the material can be of the following types:
- I - no additives;
- II - with mint additives;
- III - with special additives. They are used to regulate the density of the solution.
Type III material can be weighted (Ut) and lightened (Ob). In addition, each type of material is divided into types intended for use at normal (25-50), low(15-24), moderate (51-100) or elevated (101-150) temperatures.
Symbols
Special marking is used to determine the grade of the material:
- Oil well cement – PCT.
- Sulfate resistance - CC.
- Average density.
- Maximum allowable temperature during work.
- Plastification or hydrophobization. Designated as Pl, Gf.
- Standard.
Example: PCT-I-SS-100. The designation carries the following information: the material is Portland cement, containing no additives, and is sulfate-resistant. Designed for use at temperatures from 51 to 100 degrees.
PCT-III-UT1-100. This is a backfill type of Portland cement, a lightweight type with density indicators of 2.1 g/cm3. You can work with the material at moderate temperature.
PCT-III-Ob5-50 - backfill cement. It is a lightweight type. It has a density of 1.5 g/cm3. Allowed to operate at normal temperatures.
Quality check
This material is designed to create waterproofing of wells, but well cement is often used in construction in the construction of some residential or industrial facilities. But in order for the material to be able to fulfill its intended task, to ensure the tightness and reliability of the created structure and at the same time be environmentally friendly, it must be of high quality, and the composition must be appropriate to the complexity and characteristics of the tasks. Created for thismixtures are tested.
There are different methods for testing oil well cement, which is what specialized laboratories do. They determine the following indicators:
- Density (specific gravity).
- Rheological properties.
- Thickening time.
- Water separation.
- Filtration losses.
- Strength limit.
- Ultrasonic resistance.
- Permeability of solidified material by liquids, gas, air.
