Well cementing: methods and technologies for cementing

After drilling a well in loose sandy soils, a stage is set up to strengthen the casing pipes. At the same time, the barrel should be protected from damage, corrosive effects of groundwater, corrosion and other negative phenomena. We are talking about such a process as well cementing.

It is quite difficult to perform the cementing work independently, but it is possible, if you have knowledge about the technology of the event. We will tell you about why you need to carry out cementing and what you need to pay attention to when working. For clarity, the material contains themed photos and videos.

Why cement the well?

Well cementing is a process that follows immediately after completion.

drilling operations. The cementing procedure is that in the annular or annular (if the casing is placed in turn in polyethylene wider pipe) is introduced cement mortar, which over time hardens, forming a monolithic barrel wells.

Cement mortar in this case is called “cementing”, and the process itself is “plugging”. A complex engineering process, called well cementing technology, requires certain knowledge and special equipment.

In most cases, water sources can be tamponed with your own hands, which is much cheaper than attracting specialists.

Properly performed plugging of water wells contributes to:

• ensuring the well structure strength;
• protection of the well from ground and upper waters;
• strengthening the casing and protecting it from corrosion;
• increase the life of the water source;
• elimination of large pores, voids, gaps through which undesirable particles can get into the aquifer;
• displacement of drilling mud cement, if the first was used during drilling.

The quality of the produced water and the operational characteristics of the well will depend on how well cementing is carried out. Also, cementing is performed for the wells being liquidated, which will no longer be operated.

Stages of water source cementing

The whole process of cementing consists of several stages, each of which has its own nuances:

1. Preparation of cement slurry to fill the annulus.
2. Feed the prepared cement to the well.
3. Injection of cement slurry into the annulus.
4. The hardening period of the cement mortar.
5. Check the quality of cementing.

Each stage requires the use of certain tools and special equipment. Calculations of the necessary materials are best done before the beginning of the grouting works, since the process of plugging should last continuously and if you, for example, do not have enough cement mortar, then it will most negatively affect the quality cementing. We will consider the most important stages in more detail.

Stage №1 - equipment preparation

All work on cementing wells should be carried out strictly in accordance with the technical requirements, the violation of which will lead to poor-quality cementing.

When starting plugging a well, you should know that it is an irreversible process, fix something after the start of the solution supply into the annulus wells is impossible, so the preparatory work, namely the preparation of cementing solution and the choice of equipment, you need to approach the maximum responsibly!

The easiest and most effective way is to rent equipment on a vehicle platform. Such a complex will be able to prepare a cement mortar and pump it under pressure under pressure, while the source of energy for the operation of the equipment is a powerful automobile engine.

If the use of units based on special vehicles is not possible, then you will need:

• mixer for the preparation of cement mortar;
• high-pressure pump pumping the solution to the well;
• cementing head for injection of the solution into the well;
• priming plugs (the amount depends on the method of cementing);
• various small inventory (hoses, measuring tanks).

As a hose, many experts recommend that instead of traditional HDPE pipes with a diameter of 32 cm use a flexible fire hose. It is flat and passes perfectly into the annular space, providing an effective solution flow.

Stage 2 - preparation of the solution

Cement slurry for cementing a well must meet a variety of requirements and have:

• high adhesive properties with surfaces of any type;
• high strength after curing, resistance to mechanical stress;
• ductility and good fluidity to fill all cracks and voids;
• chemical neutrality with respect to plugged soil layers;
• resistance to erosion by groundwater;
• no shrinkage during hardening.

Also, the solution must have a consistency so that it can be delivered to the well without problems and pumped. The solution should be well washed off the equipment, not chemically aggressive towards it and have a minimum loss coefficient during transportation to the well.

The process of preparing cement mortar for tampon is the uniform mixing of the components, its constituent, followed by pouring water into it, with special additives.

The simplest solutions that you can prepare yourself are:

1. Portland cement + quartz sand (1: 1) + special additives and water to obtain the desired consistency. Such a solution has a low density, and its preparation is difficult, because sand that is part of the composition often precipitates and the application of the solution becomes impossible.
2. Portland cement + barite (1.1: 1) + special additives and water. The disadvantage of this solution is low strength.
3. Portland cement + filler. Asbestos is used as a filler (on sandy soils), fibrous materials.

For the preparation of the cementing mixture is best to use grouting Portland cement, which is a kind of cement based on silicates.

Such cement, of course, is more expensive than ordinary Portland cement, but its strength characteristics are much higher than that of ordinary. Barite is a heavy mineral that increases the density of the solution. Barite can be purchased at a hardware store selling bulk building materials.

Under special additives that are part of cementing solutions, understand the various substances that give the solution special properties.

These include:

• setting accelerators cement (calcium chloride, soda ash, potash), used if cementing occurs at temperatures below +5 degrees;
• setting retardersused to prevent rapid hardening (these are calcium or sodium chlorides, sodium nitrite, etc.);
• plasticizers for optimum viscosity (polymer modifiers);
• frost-resistant additives (silicone compounds, coupled with plasticizers);
• moisture-absorbing additives (substances derived from compounds belonging to the groups of sugar, citric, tartaric and tetraoxyadipic acids) and others.

Special additives are stirred in water, which is subsequently used to prepare the cement slurry. Mix the solution using special machines - mixers. Sometimes manual mixing is allowed, but it requires a certain skill and great effort.

Stage number 3 - pouring the solution into the well

The main methods of cementing wells are:

• solid or single-stage;
• two-stage;
• cuff;
• the opposite.

All methods of cementing water wells are based on one principle - injection of cement slurry into the annulus. At the same time, the choice of cementing technology depends on specific conditions: soil type, well depth, casing material, climatic and hydrogeological conditions of the area.

The selected technology for plugging a well into water should provide:

• filling the entire well bore with the solution to the full depth;
• completely displace the flushing fluid (if any);
• the creation of high-strength cement stone, resistant to physical, mechanical and chemical influences;
• high adhesion rate with soil walls of the well, casing pipes.

For deep wells, segmental cementing is used, i.e. not the entire borehole is cemented at once, but only its individual segments.

This process is very complex and practice shows that it is almost impossible to execute it on your own. Therefore, we take a closer look at the technology of one-and two-stage and lip cementing.

Single stage or solid cementing

This method is most often used for cementing domestic water bearing wells. During its implementation, cementing solution is pumped into the annulus.

The solution is pumped under pressure using equipment that is installed on the platform of a special car or stationary near the well. Cementing solution under its own gravity moves to the base “cushion” of the casing, filling all the annular cavities.

Before starting work on cementing is carried out well flushingand then the lower plug is inserted, which will act as a stopper. The concrete pump is turned on and injection of the plugging solution begins, under the influence of which the cork descends until it reaches the casing “shoe”.

After injection of the solution, the upper plug is installed and the cement mix begins to compact, until the upper plug rests on the lower plug. This will mean that the solution has filled the entire annulus. Compaction is carried out by vibropress by pumping the solution with a concrete pump.

The cemented well is left at rest for 36-48 hours for complete solidification of the solution. This method is only suitable for shallow wells with equal configuration. The disadvantage of this method is the inability to track the moment when the cement mortar has reached the lowest point of the wellbore.

Two-stage fill system

This cementing method was developed for oil industry wells. Due to the fact that it requires the use of serious industrial equipment (high-powered concrete pump), it is not often used in the construction of wells. Two-stage cementing is used in the following cases:

• the cement slurry sets so quickly that cementing cannot be completed in one cycle;
• when it is necessary to distinguish two areas in the annulus, which are separated by a considerable distance;
• with a large depth of the well, when it is impossible to carry out work in one cycle.

In other cases, the use of a two-stage method is impractical because of the duration of the process and economic indicators.

The principle of two-stage cementing is based on the fact that cement is pumped into the annulus in two steps.

The first portion of the cement slurry is loaded and pressed. The lower stopper is lowered, which, by the action of the solution, drops the plug to the bottom. The second portion of the solution is pumped in 12-36 hours, after the final solidification of the first portion.

The use of a sleeve method

This method of cementing is used if it is necessary to reinforce only the upper part of the well. In this case, the initial task will be to determine the level to which cementing will be carried out.

The level is marked on the casing by installing a special cuff. The lower part of the alignment is reliably protected by a cuff from penetration of the plugging solution.

The solution is pumped in the same way as in single-stage cementing. The cuff method is used if the upper part of the well is located on sandy soils, and the lower part is on clayey soils. This is quite rare, so this method has not found wide application.

The process of formation of cement stone

The process of formation of cement stone begins immediately after the injection of the plugging solution and lasts from 12 to 36 hours. The main factors affecting the duration of the solidification of the solution to the state of cement stone:

• properties of the components included in the solution;
• soil, casing material;
• hydrogeological and climatic conditions on the site;
• injection density, the correct implementation of the plugging process.

During the period of solidification, it is necessary to leave the well at rest. It is forbidden to use cables, crowbars, wire to assess the quality of cementing, because This may compromise the integrity of the resulting cement stone.

Cement quality assessment

It is worth noting: in spite of the fact that the assessment of the quality of cementing of water-bearing wells is a very important stage, it is impossible to conduct it yourself.

For its implementation requires special laboratory equipment, which is very rarely found even in organizations that are engaged in drilling.

If you still intend to make an assessment of the plugging, you can order the quality control service in one of three ways:

• acoustic, based on knocking the walls of the casing, with subsequent processing of the data obtained by computer programs;
• radiological, when measuring with radio devices;
• thermal, based on the principle of measuring the heat released during the hardening of cement mortar.

In “home” conditions, you can use the simplified thermal method by measuring the temperature at the walls of the well. When it becomes equal to the ambient temperature and becomes lower by 0.5-1.5 degrees, then we can talk about complete solidification. However, even after that, it is recommended to wait for 2-3 days and only then to put the well into operation.

After completing the test, the wellhead is cleaned of the cement slurry using zhelonka. Then a leak test is performed, for which high-pressure water is pumped into the well pipe for 30 minutes. The criterion of tightness will be a decrease in pressure of about 0.3-0.5 MPa. Now the well is completely ready for use.

Conclusions and useful video on the topic

In the videos below, we are talking about wells in the oil and gas industry, but the principle of the production technology is the same as for aquifers.

Procedure for single-stage well cementing:

Specificity of production of cuff cementing:

Technological features of two-stage cementing:

Cementing is a complex process that requires the use of specialized equipment. However, this does not mean that it is impossible to hold it yourself. Having chosen and correctly prepared the cement slurry, using a minimum set of units, it is quite possible to cope with the work yourself.

In any case, the operation of the well without strengthening the stem with cement will not be long, and the cost of drilling a new water source will be no less.

If after studying the material you still have questions about how to properly cement a well after drilling, or you have valuable knowledge on this subject, please leave your comments below. block.