RU2520101C2 - Method for prevention of drilling equipment sticking in well - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: method includes suppression of sodium chloride crystallisation on the well walls by treatment of salt-saturated mud with an inhibitor of sodium chloride crystallisation. Glycerine is used as an inhibitor of sodium chloride crystallisation; it is added to the salt-saturated mud in quantity of 5-30 wt % to the volume of the salt-saturated mud depending on the temperature in the well.

EFFECT: enlargement of inventory for sticking prevention, simplified technology, improved characteristics of the drilling mud.

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Description

The invention relates to the oil and gas industry, and in particular to methods of preventing sticking of a drilling tool while drilling saline deposits.

When drilling saline deposits, complications such as narrowing the wellbore often occur, resulting in a sticking of the drill pipe string and the drill tool. The narrowing of the wellbore occurs due to the crystallization of the finely dispersed salt of sodium chloride from oversaturated drilling fluids on the wall of the well, represented by halite, which leads to a decrease in the nominal diameter of the wellbore.

There is a method of eliminating sticks of a rock cutting tool when drilling salt deposits by installing water baths, in which pumping portions of fresh water into the sticking zone allows you to free the tool [Khurshudov V.A., Khurshudov D.V. Characteristic features of the fight against complications in the salt deposits of the Upper Jurassic when drilling superdeep wells in the Eastern Ciscaucasia (struggle against the plastic flow of salts), J. “Construction of oil and gas wells on land and at sea”, “VNIIOENG”, No. 12, 2009, p.16-20].

The disadvantage of this method is the deterioration of the properties of the drilling fluid due to the ingress of fresh water. As a result, the filtration of the drilling fluid increases, its density decreases, which inevitably leads to an increase in material costs caused by additional directed treatments with reagents and weighting agent to restore the design values of the technological parameters of the drilling fluid. In addition, the injection of fresh water into the sticking zone can lead to serious complications: dissolution and erosion of salts and the formation of caverns, the occurrence of landslides and talus.

Closest to the claimed purpose and a set of essential features and adopted as a prototype is a method of preventing sticking of the upper part of the drill pipe string while drilling deep-seated saline rocks, which consists in suppressing the crystallization of sodium chloride on the surfaces of drill and casing pipes by treating the salt-saturated drilling fluid with a chloride crystallization inhibitor sodium, which is used anionic surfactants and mineral oil, while the inhibitor is added to drilling fluid in an amount of 1.0-1.5 vol.% to the volume of drilling fluid [RF Patent No. 2417302, IPC ЕВВ 31/00, s. No. 2009133767, priority 09/08/2009, publ. 04/27/2011].

A significant disadvantage of this method is the need for preliminary preparation of the crystallization inhibitor in a mixing device by adding anionic surfactants to the mineral oil and mixing the composition to a homogeneous mass.

The objective of the proposed technical solution is to expand the arsenal of tools to prevent sticking of drilling tools during drilling of saline rocks by suppressing crystallization of sodium chloride on the walls of the borehole while improving the characteristics of the drilling fluid.

The problem in the claimed method of preventing sticking of a drilling tool in the well, which consists in suppressing the process of crystallization of sodium chloride on the walls of the well by treating a saline drilling fluid with a sodium chloride crystallization inhibitor, is solved by the fact that glycerol is used as an inhibitor of crystallization of sodium chloride in an amount of 5-30 wt.% to the volume of saline drilling fluid, depending on the temperature in the well.

The difference of the claimed technical solution is that glycerol used as an inhibitor of crystallization of sodium chloride is added in an amount of 5-30 wt.% To the volume of saline drilling fluid depending on the temperature in the well.

Glycerin is a chemical compound with the formula HOCH ₂ CH (OH) -CH ₂ OH or C ₃ H ₅ (OH) ₃ , is a representative of trihydric alcohols and is a viscous transparent liquid, unlimitedly soluble in water. The scope of glycerin is diverse: food industry, tobacco production, medical industry, production of detergents and cosmetics, agriculture, textile, paper and leather industries, plastics, paint and varnish, electrical and radio engineering. Technical glycerin is used to fill vibration-resistant pressure gauges of the DM8008 VU type, fill mechanical seals of mixers, etc.

Glycerin is produced by industry according to GOST 6824-96.

It is known that glycerol is used in drilling fluids for other purposes, for example, as a viscosity reducer (USSR AS No. 1125226, 1640137), to reduce the filter cake permeability (USSR AS No. 1661186), to eliminate absorption (RF patent No. 2241818), for isolating water inflow (RF patent No. 2081297), for releasing stuck drill pipes in a well (USSR AS No. 939722, 1744242).

The prior art also knows the use of glycerol as one of the components of an inhibitor of water-soluble salt deposits in gas wells, designed to slow down scaling in cased production wells, which is fed into the annulus of the well (AS USSR No. 791644). The technical result achieved by the use of this inhibitor is to reduce the rate of scaling due to the introduction of sulfoureid and slow down the adhesion process.

The adhesion process occurring in the well is due to the molecular interaction of the walls of the well with salt molecules from the solution while maintaining the boundary between the contacting bodies, as a result of which salt “sticks” to the well walls.

The known inhibitor envelops crystals of sodium chloride and organic high molecular weight components of the reservoir fluid and reduces the rate of further development of deposits on the inner wall of the tubing and thereby slows down the process of molecular interaction of solid phases and the formation of “salt plugs”.

When opening large-scale salt deposits on aqueous drilling fluids, the physicochemical processes of the interaction of the salts of the borehole wall and the drilling fluid medium are caused by an increase in their solubility with increasing temperature as the well deepens, the formation and accumulation of a finely divided solid phase of salts with a decrease in temperature in the upper part of the salt section of the rocks when flushing. The accumulation of small crystals in the drilling fluid medium is accompanied by the transfer of molecules from small crystals from the medium to large crystals, which causes the crystallization of salt on the wall of the well and the narrowing of its bore without maintaining the boundary between the contacting bodies. In this case, the secondary crystallization process corresponds to the well-known physicochemical process of “sludge aging”, the speed of which significantly exceeds the working time of the bit, which creates the conditions for narrowing the wellbore and accidents when raising the drilling tool.

The claimed technical solution is aimed at achieving a new technical result, which consists in suppressing the secondary crystallization of sodium chloride on the walls of the well, represented by salt in the depth range and, accordingly, the temperature range of their occurrence, by adding the estimated volume of glycerol to the drilling fluid to modify its medium and change direction sludge aging process.

In the claimed invention, the authors established a new dependence of the quantitative addition of glycerol to the drilling fluid used for drilling wells in saline deposits, taking into account the conditions of the well, namely the salt bed temperature.

Glycerol supplementation is determined by the solution of the Thomson (Kelvin) thermodynamic equation depending on the temperature in the wellbore

where P ₁ is the vapor pressure of the pure solvent, Pa;

P ₂ is the vapor pressure of the modified solvent, Pa;

σ _tj - surface tension at the crystal-solution interface, J / m ² ;

M is the mass of crystallized salt, kg;

d _W - the relative density of the liquid, b / r;

R is the universal gas constant - 8.134 J / (mol · K);

T is the temperature, K;

r _cp is the average size of small crystals in a saline solution. The solution of equation (1) in a parametric form is carried out by presenting each parameter of the equation as a function of temperature:

where M ₁ and M ₂ are the masses of crystallized salt obtained experimentally, kg

The obtained values of M ₁ and M _{2 are} converted to 1 m ² surface.

The equation for the selection of temperature to achieve the equality M ₂ = M ₁ is:

The study of the crystallization of sodium chloride in the presence of glycerol was carried out according to the method developed by OOO VolgoUralNIPIgaz for assessing the ability of reagents to prevent the growth of crystals of sodium chloride in aqueous solutions.

Studies salt crystallization process for the salt cup wall performed with the application of water-based drilling fluid with the following process parameters: density - 1450 kg / m ^3, relative viscosity - 124, filter component - 2 cm ^3/30 min, pH - 8.3 a dynamic shear stress of 26 Pa, a plastic viscosity of 0.06 Pa · s, and an increase in the weight of a salt beaker by 0.56 g was obtained.

According to this technique, the mass of crystallized sodium chloride salt was determined from the volume of saline drilling fluid on the wall of a salt glass made of halite core after its circulation under conditions simulating the processes occurring in the well.

The formation of crystals on the wall of the salt glass is estimated by the change in the inner diameter and depth of the cylindrical hole in the salt glass, as well as by the change in its mass compared to the original. The results of the studies are shown in table 1, where d _n is the diameter of the cylindrical hole of the salt glass, h _n is the depth of the cylindrical hole of the salt glass.

Table 1 No. Structure Weight, d ₁ d ₂ d ₃ , d ₄ h ₁ h ₂ h ₃ , h ₄ p / p g m m m m m m m m one Boer. p-p 1350.80 0.04 0,042 0,041 0,043 0,052 0.051 0,047 0,048 2 b.p. + 5 wt.% hl 1346.95 0,041 0,043 0,042 0,045 0,052 0.051 0,047 0,048 3 b.p. + 10 wt.% hl 1343.13 0,043 0,044 0,043 0,047 0,052 0.051 0,047 0,048 four b.p. + 20 wt.% hl 1339.05 0,044 0,045 0,044 0,049 0,053 0.051 0,047 0,048 5 b.p. + 30 wt.% hl 1334.71 0,045 0,046 0,045 0,050 0,054 0,052 0,047 0,048

A gradual decrease in the mass of crystallized salt on the surface of the glass walls indicates that glycerin has the ability to prevent scaling.

From table 1 it is seen that the more glycerol was added to the drilling fluid, the smaller the amount of sodium chloride salt crystallized out.

Optimal is the addition of glycerol to the saline drilling fluid in an amount of 5-30 wt.%.

An increase in glycerol content to 35 wt.% In the drilling fluid is impractical because further improvement of indicators does not occur.

Laboratory studies of the process of secondary crystallization of salt and the direction of the mass transfer process when modifying the drilling fluid and using equation (4) determined the limiting temperatures that exclude the processes of mass transfer to the wall of the well from the concentration of glycerol in the drilling fluid.

The dependence of the glycerol addition to the salt-saturated drilling fluid on the salt bed temperature calculated by the thermodynamic equation for the northern side of the Caspian syneclise is presented in table 2.

table 2 No. p / p Structure T, K one Drilling p-p + 5 wt.% Glycerol 309.62 2 Drilling p-p + 10 wt.% Glycerol 314.93 3 Drilling p-p + 20 wt.% Glycerol 337.57 four Drilling p-p + 30 wt.% Glycerol 359.64

Visually, the data of table 2 can be represented in the form of a graph.

The data obtained, reflected in the graph, allowed us to approximate the equation

where Cr is the concentration of glycerol,%;

T is the temperature, K.

The use of this schedule will eliminate a large amount of laboratory research in the development of drilling fluid compositions.

When drilling wells, the walls of which are represented by clay rocks, there are complications associated with the swelling of clays. Clay swelling leads to instability of the walls of the well, the formation of caverns, explorations and accidents.

Clay swelling coefficient is a value determined by the ratio of the volume of swelling of a clay sample to the initial volume of a clay sample. The coefficient characterizes the ability of clay to swell in a given environment. The lower the swelling coefficient, the stronger the properties of the mud filtrate that inhibit the clay rocks of the geological section.

There are several methods for studying the effect of mud filtrate on clay swelling. The most used is the method for determining the coefficient of swelling of clay materials on a Zhigach-Yarov instrument. Studies of the comparative effectiveness of the inhibitory ability of glycerol were carried out by measuring the value of the swelling coefficient of clay samples (STO Gazprom 2-3.2-020-2005 Drilling fluids. Methods of measuring the coefficient of swelling of clays and clay powders).

The results of studies to determine the effect of saline saturated mud filtrate with various glycerol additives on the value of clay swelling coefficient are presented in table 3.

Table 3 No. p / p Structure Clay swelling ratio one mud filtrate 0.371 2 filtrate drill. p-pa + 5 wt.% glycerol 0.216 3 filtrate drill. p-pa + 10 wt.% glycerol 0.195 four filtrate drill. p-pa +20 wt.% glycerol 0.153 5 filtrate drill. p-pa +30 wt.% glycerol 0.152

Analyzing the data of table 3, it can be noted that the addition of glycerol effectively prevents clay swelling, as evidenced by a significant decrease in the swelling coefficient.

An important parameter of the drilling fluid, characterizing its quality, is the value of its filtration rate. The lower the mud filtration, the less likely there are various complications when drilling wells. The results of laboratory studies on the effect of glycerol addition on the value of the filtration rate of saline drilling fluid are presented in table 4, the filtration index was measured on a VM-6 instrument (STO Gazprom 2-3.2-003-2005 Drilling fluids. Method for performing filtration measurements on a VM-6 instrument )

Table 4 Technological parameters of the solution Structure Density, ρ, kg / m ³ Conditional viscosity, T, s Indicator filtration, F, ^cm3 / 30 min pH Static shear stress, Q _1/10 , dPa Plastic viscosity, η, MPa · s Dynamic shear stress, τ ₀ , Pa drilling mud 1420 76 7.0 7.9 25/49 38 16.8 drilling mud + 5 wt.% glyc. 1410 60 5,0 7.9 20/43 33 13.9 drilling mud + 10 wt.% glyc. 1400 56 5,0 7.7 15/25 29th 12.1 drilling mud + 20 wt.% glyc. 1390 53 5,0 7.6 7/16 25 9.8 drilling mud + 30 wt.% glyc. 1380 fifty 5,0 7.6 2/6 22 7.6

As seen from Table 4, introduced into the salt-additive glycerin drilling mud provides filtering index values decrease at 2 cm ^3/30 min.

The authors also found that the formation of coagulation structures that could complicate the process of cementing casing when mixing drilling fluid with cement in a volume ratio of 1: 1 was not detected.

Thus, as a result of the action of glycerol in the solution, the direction of the mass transfer process changes from large crystals (well wall) to small crystals that originate in the drilling fluid, which leads to an increase in the diameter of the wellbore, eliminates accidents when raising a drilling tool and reduces costs.

In this case, the calculated addition of glycerol determines the necessary change in the surface energy of salt on the surfaces "salt-liquid" and "liquid-gas", as well as a decrease in the solubility of salt in the volume of the drilling fluid medium.

From available sources of patent and scientific and technical information, information about technical solutions containing features that match the distinctive features of the claimed invention and give a similar technical result is not identified. This allows us to conclude that the claimed technical solution meets the criterion of "inventive step".

The implementation of the method in an industrial environment consists in the addition of glycerol in an amount of 5-30 wt.% To the volume of saline drilling fluid depending on the temperature in the well, after which the entire thickness of saline deposits is drilled with this solution.

Using the proposed method will eliminate the complications and accidents when drilling terrigenous chemogenic deposits of large thickness by suppressing the secondary crystallization of sodium chloride on the walls of the well, folded by halite deposits, and also significantly improve the technological parameters of the drilling fluid.

Claims (1)

A method of preventing sticking of a drilling tool in a well, comprising suppressing a process of crystallization of sodium chloride on the walls of a well by treating a salt-saturated drilling fluid with a sodium chloride crystallization inhibitor, characterized in that glycerol is used as an inhibitor of crystallization of sodium chloride in an amount of 5-30 wt.% To the volume of saline drilling fluid depending on the temperature in the well.