In the process of drilling, special solutions are used to wash out sludge and local rock development products. This operation is necessary to increase the efficiency of the mechanical impact of the rig and to clear the face. Washing is done using grouting mortars, which are prepared using special technologies.
Purpose of drilling mixtures
Water circulation in the well helps to clean the hole, which helps the drilling and sealing processes. Provided that an active composition with additional operational properties is used, one can count on a number of other effects, including the following:
- The formation of a filter cake on the walls of an open trunk. As a result, unstable deposits, clay rocks and loose formations are strengthened.
- Pore pressure counteraction is created.
- Additional hydraulic energy is transmitted to the downhole power unit and bit.
- Drilling and grouting fluids transport the developed rock and, after completion of the circulation, keep this mass in suspension.
- The risks of complications, differential sticking, oil and gas manifestations and well absorption are prevented.
- Collapses and talus are prevented.
- It has a lubricating effect on drilling equipment.
- The tool is cooled and lubricated.
The basis for the composition of the cement mixture
To create drilling fluids, plastic and finely dispersed clays with minimal sand inclusions are used, which together with water can form a viscous suspension with a long settling period. When developing gas and oil wells, experts recommend using alkaline types of montmorillonite clays, as well as clay powders. In addition, the composition of the grouting mortar includes industrial water, hydrogels and salt components. Modern blends include an invert emulsion, a lime-bitumen base, and polymer components. The relationship between the ingredients and their specific set depends on the effect that must be achieved, and the conditions of use of the solution. In any case, impurities like gypsum and soluble minerals, which reduce the stability of viscous clay raw materials, are undesirable components.
Rules for creating a solution
The preparation of grouting mixtures is carried out using cement mixing units in accordance with the regulated regimes. Depending on the tasks set and the raw materials used, different technological solutions can be introduced into the preparation scheme. For example, if stale cement is used, it is necessary to provide for its activation. The dry mixture is fed into the tank with stable operation of the water supply pump. The combination of liquid and dry components should be carried out under conditions of maintaining pressure at the level of 12-15 MPa. This is the optimal medium for the preparation of grouting mortars from the point of view of mixing and setting of the structure. Next, it is necessary to wait for the stabilization period of the mixture, for which a special mode in the cement mixing machine is provided.
Properties of grouting mixtures
The technical and operational properties of drilling mixtures are determined by the selected formulation and in practice, the application determines the quality of interaction with the materials of the wellbores. The following properties of cement slurry are taken into account:
- Water loss. Under conditions of pressure drops, the process of water separation from the active phase of the solution occurs. Depending on the parameters of the wellbore, the indicator of the rate of water loss can be different, it is adjusted individually. For example, if it is planned to strengthen the structure, then the fluid loss of the solution should be close to zero.
- Sedimentation stability. The process of separating water from a solution, in which the cement mass moves down and the liquid moves up.
- Thickening. It is determined by many factors, including the degree of grinding of the components of the solution and the presence of materials that increase the viscosity. The stimulation of this property is affected by an increase in the proportion of water, and by a decrease, an external thermal effect.
- Grasping. As a rule, technologists strive to increase this quality to the maximum in specific conditions. For this, temperature increase with pressure is used, as well as barrel insulation in conditions of high humidity.
Modification of mud properties
Correction of certain qualities is not always possible with conventional means and materials, so it is more advisable to use special additives and additives that effectively and precisely change the desired properties. Among them, the following modifiers are noted:
- Sodium carbonate. Used to reduce setting time. Using this accelerator get quick-setting solutions suitable for use at temperatures up to 55-65 ° C.
- Bentonite. Increases the initial mobility of the washing solution, optimizing the measures for its injection. This modifier is recommended for use with cement slurries, the density of which varies from 1.5 to 2.2 g / cm 3 .
- Gypsum cement suspensions. Improve the ability of the solution to water loss. The base becomes more resistant to dissolution in water. For flushing compositions, the use of suspensions is meaningless, however, in order to strengthen the barrel - it is completely acceptable.
- Cement-resinous additives. A type of plasticizer with epoxy resins that are used for flushing wells with complications of aquifers.
Types of drilling fluids
In practice, the following types of grouting mixtures are usually distinguished:
- Lignite drilling. An alkaline-based solution that is modified by lignites.
- Lime-bitumen solution. Petroleum products are used as a basis - a combination of a dispersion medium from oil or diesel fuel, as well as bitumen and calcium oxide as a dispersed phase.
- Lightweight flushing mixture. It is a cement slurry reduced in weight with minimal density indicators. Used in the development of low pressure wells.
- Polymer solution. The composition is based on water containing high molecular weight linear polymers. Commonly used in hard rock drilling processes.
Check for compliance with GOST
According to GOST 26798.1-96, the parameters of drilling fluids are determined without taking into account possible influences that may occur during operation of the material in real conditions with the connection of casing strings. For compliance with the regulations, the thickening time of the mixture, density and viscosity are checked. Moreover, for different compositions, both technical indicators and the list of evaluation criteria may vary. So, to determine the properties of expansion and strength in the case of cement grout, GOST 1581-96 is used, requiring that tests be carried out at an ambient temperature of about +30 ° C. During the hardening of cement stone mixtures in a limited volume, strength indicators can be higher than when using a similar composition in mass when filling the well. And, on the contrary, the permeability of the solution decreases.
Grouting technology
For the use of drilling fluids, special equipment is used that provides the technical feasibility of circulation operations. In the process of application, cement slurries perform the following process cycle:
- The composition is kneaded and stored in a special container.
- Pumping equipment through the drill pipe string begins to pump the solution from the tank to the well.
- Through pipes, the mixture is directed to the bottom of the borehole, where the drill bit develops another layer of rock.
- The solution returns to the surface, carrying with it rock particles separated by a chisel.
- The mass rises up the annulus, passing between the drill pipe and the walls of the borehole.
- On the surface, the operation of filtering and cleaning the solution from sludge is performed. To do this, use a vibrating sieve.
Conclusion
Grouting mixtures are necessary consumables for the development and construction of wells. However, their improper use together with positive effects can lead to negative consequences. In particular, errors in the production of grouting mortar in the future can result in rock collapses and even damage to drilling equipment. Therefore, a flushing project is initially drawn up, the composition of which is carefully calculated. In general, it is necessary to determine what will be the volume of dry components, water, the total amount of the mixture, the characteristics of cementing aggregates, etc.