TECHNOLOGY OF PREPARATION AND APPLICATION OF LIGHTWEIGHT DRILLING FLUIDS FOR DRILLING OIL AND GAS WELLS

ABSTRACT

The article discusses the methods and technology of preparation and application of lightweight drilling fluids used in drilling oil and gas wells. The compositions of lightweight drilling fluids are presented, as well as the technology of their preparation using light minerals and polymer additives. Lightweight drilling fluids are designed to prevent complications in wells when drilling low-pressure and productive formations, in particular, by reducing the hydrostatic pressure in the well.

АННОТАЦИЯ

В статье рассматриваются способы и технология приготовления и применения облегченных буровых растворов, используемых при бурении нефтяных и газовых скважин. Представлены составы облегченных буровых растворов, а также технология их приготовления с использованием легких минералов и полимерных добавок. Облегченные буровые растворы предназначены для предотвращения осложнений в скважинах при бурении низкодавленных и продуктивных пластов, в частности, за счет снижения гидростатического давления в скважине.

Keywords: drilling fluids, well depth, chemical reagents, polymineral compositions, complex conditions, drilling fluid stability, main functions of the solution, drilling tool, flushing process, flushing agent, well walls, vertical direction, closed hydraulic circuit, corresponding interval.

Ключевые слова: буровые растворы, глубина скважины, химические реагенты, полиминеральные композиции, сложные условия, устойчивость бурового раствора, основные функции раствора, буровой инструмент, процесс промывки, промывочный агент, стенки скважины, вертикальное направление, замкнутый гидравлический контур, соответствующий интервал.

I. Introduction. Today, the physicochemical modification of chemical reagents used in the drilling of oil and gas wells, the production of lightweight drilling fluids based on them, and their application in drilling under complex geological conditions is an important task globally. In this regard, the development of highly effective composite chemical reagents based on local raw materials and production waste for the preparation of weighted drilling fluids using mineralized formation waters is both in demand and highly relevant [1].

The above situations that arise when drilling oil and gas wells determine the need for lightweight drilling fluids. The use of lightweight drilling fluids when drilling wells is a critical period that requires great attention. Much attention is paid to the density of drilling fluids [6]. If the density of the drilling fluid is increased when drilling a well, a disaster (accident) will occur in the well - absorption (absorption) of the drilling fluid.

II. Methods. Large-scale work is being carried out worldwide to explore oil and gas fields, develop them and exploit them taking into account the well design and drilling depth [9]. Therefore, the creation of new types of drilling fluids using local clay minerals, chemical reagents and stabilizing additives from synthetic and natural materials is of great importance.

Specific gravity of lightweight drilling mud. The density of the drilling mud creates hydrostatic pressure that counteracts the pressure on the bottomhole and borehole walls. Specific gravity is the ratio of the weight of the liquid and solid phases to the volume. The terms “density” and “specific gravity” are often used in relation to drilling muds. These terms do not mean the same thing.

Specific gravity is the ratio of the weight of a substance measured in the same units of mass and volume to the weight of a volume of water. Temperature is taken into account for accurate measurement of these indicators.

The indicator “Specific gravity 250/200 °C” expresses the ratio of the weight of a liquid or solid to a volume, in the case when the weight of a liquid or solid measured at a temperature of 250 °C is equal to the volume of water at 200 °C. The temperature of water is often taken to be 40 °C, since at 40 °C water has a constant mass.

The weight of a solid or liquid substance relative to its volume: density is a dimensional quantity measured in various units. For clarity, temperature is also taken into account. For example, the density of water at 40°C is 1.0 g/cm³ or 1000 kg/m³. Density and specific gravity are numerically equal when measuring mass in a volume of 1.0 cm³. Let's consider calculating the specific gravity of a drilling mud with a density of 1.20 g/cm³. So, the weight of water is 1.0 cm³, then the specific gravity is:

The specific gravity (density) of the lightweight drilling mud is measured by hydrometers or pycnometers. In the field, the most widely used shoulder hydrometers are VRP-1M (Figure 1), AG-1, AG-2 and AG-3PP [4].

Figure 1. Shoulder scale – density meter VRP-1M

The principle of operation of these devices is based on the comparison of the density of the same volume of the test solution and water.

The shoulder scales used to determine the density of light drilling fluids (Figure 1) consist of a base, a pointed stand, a graduated lever, a measuring cup, a lid, supports, a level with an air bubble, and a rider. The measuring cup is fixed to one end of the graduated lever. The cup and lever lie in a plane perpendicular to the plane of the pointed base at the end of the base, and are aligned by moving the rider along the lever.

If the drilling mud density decreases during well drilling, another disaster (accident) will occur in the well - a blowout (gusher). Therefore, the use of lightweight drilling muds requires theoretical and practical knowledge and skills, many years of experience, special requirements, special rules and great responsibility.

If we classify the difficulties of well drilling, they can be grouped as follows:

1. Drilling in zones with abnormally low formation pressures (ALFP);

2. Drilling in zones with abnormally high formation pressures (AHFP);

3. Drilling vertical and horizontal wells;

4. Drilling wells in strong formations of unstable clay rocks;

5. Drilling wells on heterogeneous mineralized hemogenic deposits;

6. Drilling in permafrost zones;

7. Drilling in high temperature conditions;

8. Oil and gas wells.

In this case, if the rock pressure anomaly coefficient is significantly lower than 1, then hydrocarbon-based solutions are used [8]. Accordingly, the average specific gravity (density) of such a drilling fluid is within 0.88-1.0 g/cm³, and the use of such fluids is considered appropriate mainly in difficult conditions, namely when drilling wells with abnormally low formation pressure (ALRP).

There are several types of drilling fluids, especially hydrocarbon-based ones, which have the following set of technological properties: high dispersion, very low filtration coefficient and good inhibiting properties.

If the difference between the hydrostatic pressure inside the well and the layer of abnormally high formation pressure (AHFP) is not very large, when the well is in AHFP, then it is impossible to drill these layers using hydrocarbon-based solutions. Usually in such cases, it is advisable to drill such formations with aqueous solutions prepared on the basis of bentonite. In some cases, aqueous solutions prepared on the basis of the required amount of marble powder corresponding to the porosity of the reservoirs in the rocks are used as drilling fluids [2].

Experience shows that when drilling in the AHFP zones (formation anomaly coefficient above 1), a drilling fluid with a high specific gravity (density) is used, since back pressure in the AJUKB zone can only be ensured by increasing the specific gravity of the solution to prevent well blowouts. Usually, the specific gravity of polymer drilling fluids does not exceed 1.16–1.18 g/cm³, but various salts (sodium chloride, potassium chloride) are used to prepare heavier solutions. The specific gravity of drilling fluids prepared on the basis of various salts is within the range of 1.18–1.6 g/cm³. In fact, the specific gravity of drilling fluids can be increased to 2 g/cm³ using solid-phase weighting agents. For example, the addition of limestone and dolomite allows you to obtain flushing fluids, increasing the specific gravity of the solution to 1.25–1.35 g/cm³. Such weighting agents dissolve well in acidic environments, therefore such weighting agents are used only during the primary opening of productive formations [10]. Currently, the most common weighting agents for drilling fluids are: heavier reagents such as iron carbonate, barite, hematite, magnetite and galena (lead sulfide), which are used to obtain solutions with a density of 1.4-2.3 g/cm³ and higher for poorly soluble salts.

III. Results and discussion.

In order to maximally preserve the effective oil permeability of reservoirs during the initial formation penetration after drilling, much attention should be paid to the composition of the drilling fluid. Accordingly, during the initial formation penetration, drilling fluids must meet the following requirements:

- Filtration index (temperature and pressure difference in the effective formation interval) under formation conditions - less than 18 cm³;

- API filtration index - less than 4-4.5 cm³;

- Index of inhibiting properties - initial wetting velocity of clay minerals - less than 4 cm/s;

- Interfacial tension at the boundary “drilling fluid filtrate - hydrocarbon phase (heptane)” - less than 10 mN/m;

- Wetting angle of the hydrophilic surface by the drilling fluid filtrate - more than 110°.

It is shown that the drilling fluid during primary formation opening effectively retains the composition of non-ionic PKG - polyalkylene glycols. This PKG drilling fluid filtrate effectively reduces interfacial tension at the hydrocarbon phase interface, effectively hydrophobizes the walls of the reservoir capillaries and maximizes contamination of the liquid phase [7].

Today, oil and gas production specialists have accumulated a certain amount of experience, based on which the main functions of drilling fluids can be described.

1. Removing decomposition products from the well;

2. Cooling the rock-cutting tool and drill pipes;

3. Maintaining the particles of the cuttings in a suspended state;

4. Creating hydrostatic equilibrium in the “well casing – scale” system;

5. Maintaining the permeability of earwax;

6. Transferring energy from pumps to mechanical mechanisms;

7. Ensuring the implementation of geophysical surveys;

8. Protecting the drilling tool and equipment from corrosion and abrasive wear;

9. Sealing channels to reduce the absorption of drilling fluid and water flows;

10. Preventing the appearance of gas, oil and water;

11. Reducing the coefficient of friction.

IV. Discussiоn. During the drilling process, the balance of the rocks that make up the borehole walls is disturbed. The strength of the walls depends on the initial strength characteristics of the rocks and their changes over time under the influence of various factors. The washing process and detergent play a major role in this. The main function of washing is to ensure an effective drilling process, including maintaining the strength of the walls and core of the borehole.

Drilling fluids are divided into the following categories depending on their function:

1) fluids for normal drilling geological conditions (water, some aqueous solutions, normal clay solutions);

2) fluids for complex drilling geological conditions.

A drilling fluid cannot perform all functions to the same extent. And what is important, this is not always necessary. Therefore, for specific drilling conditions, the main functions of a drilling fluid are determined and the properties that ensure their implementation are determined. As can be seen, a wide range of drilling fluids is required when drilling wells in geologically complicated areas of the country. Thick salt deposits, for example, in the areas of the Bukhara-Khiva and Gissar troughs, are located at relatively great depths and at high temperatures, where in addition to salt and temperature aggression, hydrogen sulfide is also encountered. Drilling such wells is only possible with high-quality drilling fluids treated with appropriate chemical reagents and materials [3]. Montmorillonite and other bentonite minerals have the best qualities in terms of preparing drilling mud. Thus, from 1 ton of bentonite clay it is possible to obtain about 15 m³ of high-quality clay mud, while from medium-quality clay - 4-8 m³, and from low-grade clays - less than 3 m³. Montmorillonite minerals include montmorillonite, saponite, nontronite, vermiculite; kaolinite minerals include kaolinite, nacrite, halloysite, dickite, endellite, apoxite; hydromica minerals include illite, hydromuscovite; palygorskite minerals include sepnolite, attapulgite, palygorskite [5]. All work on the selection and adjustment of recipes (ingredients) should be subordinated to the task of obtaining the specified properties. At the same time, it is necessary to maintain the remaining parameters of the detergent at an acceptable level. Method and technology for preparation and technology, preparation of issued solutions for drilling used for drilling and developing wells are shown in figure 2.

Figure 2. Preparation and use of lightweight drilling fluids with 3M glass microspheres

During the drilling process, the drilling fluid interacts with the objects being drilled, formation water, is exposed to temperature, pressure, atmospheric air and precipitation. Internal processes occur in it associated with the decay of electrical charges in particles and the wear of its components. All this leads to a deterioration in the properties of the solution, the loss of its ability to perform the necessary functions. Therefore, during the drilling process, it is necessary to restore and maintain its necessary properties.

In many cases, the change of bodies in the geological section entails the need to change some functions of the drilling fluid. Therefore, if it is impossible to replace the solution, its properties are adjusted during the drilling process as it approaches the appropriate interval.

Thus, the need to adjust the properties of drilling fluid arises in the following cases:

1. When preparing a solution with a given property;

2. Maintain functions required during drilling;

3. Change parameters as geological conditions change during drilling.

The properties of drilling fluid are adjusted:

• • chemical treatment (by introducing special reagents);
  • physical methods (dilution, concentration, dispersion, weighing, introduction of fillers);
  • physicochemical methods (combination of the listed methods).

V. Conclusion. Therefore, when drilling oil and gas wells, decisions for drilling during the development of oil and gas should be rid of. The use of such solutions of sweat in various geological conditions in wells and the use of drilling solutions in a stormy solution gives good results. In addition, if this article is developed in different layers and technologies in different levels and technologies, this technology is convenient, reliable, reliable and economically useful.

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