RU2451788C2 - Method to suppress spills from emergency oil and gas wells during field development - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to the oil and gas industry, namely, to methods for suppression of spills from emergency oil and gas wells and may be used to eliminate accidents with the help of shut-off plugs during field development, arranged at water reservoir bottoms, on the day surface, in underground mines, and also in continental shelves. During realisation of the method, using a cut casing pipe, a discrete material that is easily deformed under its own weight, having size and specific weight that ensure material falling in an ascending flow of oil and gas, is supplied in a quantity sufficient to form a shut-off plug in the well, which makes it possible to suppress the reservoir fluid of oil or gas. The shut-off plug may be formed in intervals, where first the discrete material of larger fraction is filled, then fractions with reducing size of solids are serially filled. The discrete material may be used in the form of solids of revolution. The material may be supplied via a hopper, which is installed above the cut casing pipe. After formation of a shut-off plug, the hopper is filled with a hardening mud. Discrete particles are made either from a homogeneous material or from composite materials.

EFFECT: invention provides for safety of a technological process and reduced impact at environment.

6 cl, 2 dwg

Description

The invention relates to the field of the oil industry and can be used to eliminate accidents by means of shut-off plugs by suppressing spills from emergency oil and gas wells when developing fields located on the bottom of the ocean, sea, lake, day surface or in underground mine workings, and on continental shelves.

The bulk of oil fields are confined to domed geological structures in which oil and gas are under high pressure. Opening these structures with wells is accompanied by great difficulties associated with the development of complex special blowout preventers (preventers, sealants) and the use of special solutions, including weighted ones.

From the technical level there is a known method for eliminating accidents in oil wells by inserting a second trunk. Ensuring the efficiency of the well with the second wellbore is provided by predicting the flow rate of the well for oil and the correct selection of insert parameters. A preliminary decision on the appropriateness of the insertion of the second wellbore is taken according to the amount of residual recoverable reserves attributable to the emergency well. After that, the insertion direction, the offset of the second barrel relative to the emergency one are determined, taking into account the fact that at the supposed opening point of the second barrel, the formation should have maximum oil saturation, minimum water cut and reduced filter coverage. They draw maps of development status, fractions of residual recoverable oil reserves, residual oil saturation, water cut and filtration flows. The initial production rate of the well with the second wellbore is predicted and the final decision on the appropriateness of drilling the second wellbore is made based on the well’s work with the predicted production rate. Moreover, to determine the predicted flow rate, field and laboratory studies are additionally carried out with the construction of curves [patent for invention RU No. 2087670].

The disadvantage of this method is the high capital costs for the construction of discharge wells, the complexity and duration of its construction.

There is also a method of killing deep and superdeep wells and pipelines by freezing the emergency flow of well products by injecting magnetic or electroactive particles into them with an external electromagnetic field, magnetic or electric, including injecting magnetic or electroactive particles together with oil, water, gas or a thermosetting resin, or refrigerant, with the curing of the specified composition under the influence of the temperature of the deepest flow, and, if necessary, with the application of external heating. The method allows you to quickly slow down the emergency flow with electromagnetic particles in the zone of action of a magnetic or electric (electromagnetic) field or freezing, or hardening a colloidal dispersed liquid, or a gas suspension with magnetic particles in a given rupture, or with the formation of a "goat" inside the well or pipeline in as a shut-off plug, or cured inclusions in the zone of elevated temperatures in the wellbore during injection of epoxy-diane resin or monomer with magnetically or electroactive particles in the form of a powder or colloidal dispersed suspension or additives of a curing agent to the FAM monomer of benzenesulfonic acid or paratoluene sulfonic acid [patent for invention RU No. 2100567].

The disadvantages of the method include its narrowed functionality, which excludes its use in case of rupture of the casing under water.

In the known technical level is not found the closest analogue (prototype).

The objective of the invention is to develop an optimal method of suppressing oil spills from emergency oil and gas wells by forming a shut-off plug in the well.

Technical results that can be obtained by implementing the claimed invention are:

- A gradual decrease in oil flow through the well with its subsequent cessation.

- Creating backpressure on the reservoir in the opening area of the oil and gas reservoir.

- Ensuring process safety.

- Reducing the burden on the environment.

The solution of the above problem and the achievement of the expected technical results became possible due to the fact that the method of suppressing spills from emergency oil and gas wells during field development is characterized by trimming the damaged casing of the well and supplying a discrete material with coarseness and specific gravity that is easily deformed under its own weight, which ensures the fall of the material in an upward flow of oil or gas in an amount sufficient to form about tseka plugs, providing the ability to extinguish the reservoir pressure of oil or gas and suppress spills.

In particular examples of the method, the shut-off plug is formed at intervals in which the discrete material of the larger fraction is first filled in, then the fractions with decreasing body size are successively filled to increase the hydraulic resistance of the material to be filled, the discrete material is used in the form of rolling bodies, the material is fed through the hopper, which is additionally set above the cut casing, after the formation of the shut-off tube, the hopper is filled with a hardening solution, and discrete parts gical or operate from a homogeneous material or of composite materials.

An inventive step is the supply to the emergency well of easily dispersed material with a high specific gravity of particles of material in an amount that is sufficiently deformable under its own weight to create a shut-off plug in the form of a column of material with a height h, which ensures that the reservoir pressure of the oil is extinguished. Column height h is determined from the condition

,

,

where ρ is the density of the material of the balls, kg / m ³ ;

ρ _W - oil density, kg / m ³ ;

H _H - hydrostatic pressure of the oil reservoir, m;

n is the porosity of the medium formed by the filling material.

The calculated value of the material column in the well will actually be less, since the filled discrete bodies are made of easily deformable material (for example, lead, which is characterized by a high specific gravity and high ductility) and as the weight of the shut-off plug increases over the lower intervals of the material, the discrete particles composing the material, deform, which leads to the formation of a durable and almost impermeable shut-off tube. A favorable factor contributing to the deformation of the material is the elevated temperature in the well.

The inventive method is illustrated by the figures (for a particular example of the location of the well on the continental shelf):

Figure 1 shows the flow of material into the emergency well, cut-off well, discrete particles of filling material.

Figure 2 shows the flow of material into the emergency well, cut-off well, particles of material, storage hopper.

The inventive method of suppressing spills from an emergency oil (gas) well during field development is as follows. Before starting work, the nature of damage to the casing 1 of the well is examined (Fig. 1). A known casing (not shown in FIG.) Is cut off from the damaged casing 1 below the damage. Mount the pipeline 3, direct it to the emergency well (not shown in Fig.) And feed through it into the well the discrete material 4, easily deformable under its own weight, of the required size and specific gravity, ensuring the material 4 is lowered in the upward oil flow down the emergency well in an amount sufficient to form a shut-off plug 5 in it, which makes it possible to suppress the spill of oil and to extinguish reservoir pressure.

In a particular embodiment, when using discrete material of different fractional composition, the material of the larger fraction is first filled in, then the fractions with decreasing particle size are successively filled to reduce filtration properties and increase the hydraulic resistance of the wellbore.

Thanks to the fractional formation of the shutoff plug 5, conditions are created that provide a smooth change in stresses in the casing 1 and eliminate the danger of concentrated stresses in it that can cause its destruction.

In a particular embodiment of the method, a storage bin 6 is installed over the cut-off section of the casing pipe 1 (Fig. 2) and a pipe 2 is directed into it through which discrete material 4 is supplied to the storage bin 6, and the storage bin is used to measure the volume of incoming into the well of the material. After the shut-off plug 5 is formed and the oil spill is stopped from the emergency well, the storage hopper is filled with a hardening solution 5, for example, cement, which, after solidification, closes the well mouth, which further increases the reliability of emergency operations associated with oil leakage from the emergency well.

The practical applicability of the proposed method is shown in the following simulated examples.

Example 1

An emergency well located on the continental shelf is cut off at a level of 1.2-1.5 m from the surface of the ocean floor. In this particular embodiment of the method, lead balls of the same diameter _dw = 0.01 m are fed into the well as discrete material for forming a cut-off plug.

The initial data adopted for the calculation:

The speed of the upward movement of oil along the wellbore ν _B

,

,

where d _c is the diameter of the well; Q - oil consumption.

The height of the column of the cut-off plug from lead balls must satisfy the condition:

In this example, lead balls of the same diameter _dw = 0.01 m are fed as discrete material and the wellbore is filled to a height h = 1400 m. The diameter of the balls _dw = 0.01 m satisfies the condition of overcoming the oil backflow and free movement (without jamming) of the balls in the bore wells

,

,

where Q is the oil flow from the well, m ³ / s;

µ — oil viscosity, Pa · s;

ρ is the density of the material of the balls, kg / m ³ ;

ρ _W - oil density, kg / m ³ ;

d _W - the diameter of the balls, m;

d _c - well diameter, m;

g is the acceleration of gravity g = 9.81 m / s ² .

The falling velocity ν ₀ of lead balls of diameter d _w , density ρ in a liquid at rest with a density ρ _w

.

.

Ball diameter, m Velocity ν ₀ (m / s) at oil viscosity (Pa · s) 0.119 0.05 0.027 0.01 0.001 0.05 0.12 0.21 0.57 0.002 0.19 0.46 0.85 2.29 0.004 0.77 1.83 3.39 9.15 0.005 1.20 2.86 5.29 14.29 0.008 3.08 7.32 13.55 36.59 0.01 4.80 11.43 21.17 57.17 0.02 19.22 45.74 84.70 228.68

The ball sinking speed is ν = ν ₀ -ν _B = 11.43-0.37 = 11.06 m / s≈11.1 m / s.

When oil moves along the wellbore through a porous medium created by balls, the flow will overcome the hydraulic (filtration) resistance.

The pressure loss to overcome this resistance is ∇Р = Q · Ф, where Ф is the hydraulic resistance of the wellbore filled with balls; Q - oil consumption.

Filtration resistance is calculated according to

,

,

where h is the length of the wellbore filled with balls;

µ is the oil viscosity;

c is the permeability coefficient of the pore space formed by the balls;

d _c is the diameter of the well;

S is the cross-sectional area of the well.

The permeability of the porous medium in the borehole with a ball diameter d _W = 0.01 m is s = 8 · 10 ^-9 m ² . With the length of the shutoff plug h = 1400 m, the diameter of the well 0.2 m, the viscosity of the oil µ = 0.05 Pa · s and the diameter of the balls d _W = 0.01 m, the filtration resistance will be

.

.

The resistance of the free (unfilled material) interval of the wellbore is neglected due to its smallness.

We calculate what flow rate the well missed filled with balls d _Ш = 0.01 m at reservoir oil pressure Р = 1000 atm = 10 ⁸ Pa. The pressure drop across the shutoff plug will be equal to the difference between the reservoir pressure and the pressure of water columns with a height of Н _B = 1500 m and oil in the wellbore above the shutoff plug L = 5000-1400 = 3600 m: Δр = Р-γ _B · Н _B -γ _H L = 1.0 · 10 ⁸ -0.15 · 10 ⁸ -0.30 · 10 ⁸ = 0.55 · 10 ⁸ Pa.

.

.

.Thus, the flow of oil spill has decreased and amounts to 1.7% of the initial flow rate of 1000 m ³ / day. The speed of the upward movement of oil in this case will be

.

If in the considered example we assume that the wellbore is filled with balls throughout the depth, then the filtration resistance will be Ф = 0.99 · 10 ¹² Pa · s / m ³ , and the oil spill flow rate will be Q = 0.85 · 10 ⁸ /0.99·10 ¹² ≈0.86 · 10 ^-4 m ^{3 / s} = 7.42 m ³ / day, which is 0.74% of the initial flow rate.

The calculations did not take into account the deformation of lead balls under the action of their own weight. In the present example, the material at the bottom of tube cutoff will be under a pressure of about 100 MPa (for lead limits the compressive strength of _{compression channel} σ = 50 MPa and a tensile σ _p = 12 ... 13 MPa). At this pressure, due to their own weight and high ductility of lead balls, they will be deformed, and the porosity and permeability of the pressed material will be practically zero, i.e. the well will be completely shut off.

. Если материал представлен свинцовыми шарами, то масса заполняющего материала составит m=ρV(1-n)=11340·44·0.7≈350000 кг=350 т.The average time for lowering the balls to depths of 3600 ... 5000 m (h = 1400 m) is t _avg = 4300 / 11.1 = 6.5 min, i.e. the construction time of the shutoff plug will be determined by the technology of feeding the balls into the well. So, with a plug height of h = 1400 m, it will be necessary to supply a volume of filling material into the well with a diameter of d _c = 0.2 m

. If the material is represented by lead balls, then the mass of the filling material will be m = ρV (1-n) = 11340 · 44 · 0.7≈ 350,000 kg = 350 t.

Example 2

The initial data for this particular example of the execution of the method will be the same as in example 1.

As a discrete material for forming a shut-off plug, balls with a density of 8300 kg / m ³ are fed into the well (material consisting of 70% volume of lead and 30% of ordinary rubber with a density of 1200 kg / m ³ in volume). Balls are used in two fractions: 50% with a diameter d _Ш = 0.01 m and 50% with a diameter d _Ш = 0.005 m. First, balls with a diameter of 0.01 m and then balls with a diameter of 0.005 m are fed, forming two zones, the lower of which is represented by a large fraction, and the upper one shallow.

The height of the column of the shut-off plug must satisfy the condition:

Due to the fact that the porosity of the medium, composed of balls of the same diameter, does not depend on the size of the balls, but is determined by their packing, for the lower and upper zones we take the same porosity value n = 0.3.

In this case, the wellbore is filled to a height of h = 1960 m, and the lower interval h _H = 980 m is filled with balls with d _Ш = 0.01 m, and the upper interval h _B = 980 m with balls with d _Ш = 0.005 m.

, скорость погружения шаров диаметром 0.01 м составляет 7.75 м/с; скорость погружения шаров диаметром 0.005 м составляет 1.66 м/с.The diameter of the balls d _W = 0.01 mi d _W = 0.005 m satisfies the condition

, the speed of immersion of balls with a diameter of 0.01 m is 7.75 m / s; the speed of immersion of balls with a diameter of 0.005 m is 1.66 m / s.

The permeability of the porous medium in the wellbore with the diameter of the balls d _W = 0.01 m is s = 8 · 10 ^-9 m ² ; permeability when the diameter of the balls d _W = 0.005 m is c = 2.42 · 10 ^-9 m ² .

According to the dependence, we determine the filtration resistance of the lower and upper intervals of the shutoff tube:

.

.

.

.

The total filtration resistance of the shut-off plug will be

Ф = Ф + Ф = (0.195 + 0.644) · 10 ¹² Pa · s / m ³ = 0.84 · 10 ¹² Pa · s / m ³ .

Let us calculate the flow rate that a well filled with balls d _Ш = 0.01 m (lower interval of 980 m) and balls d _Ш = 0.005 m (upper interval of 980 m) at an oil reservoir pressure of P = 1000 atm = 10 ⁸ Pa.

The pressure drop across the shutoff plug will be equal to the difference between the reservoir pressure and the pressure of water columns with a height of Н _B = 1500 m and oil in the well bore above the shutoff plug L = 5000-1960 = 3040 m: Δр = Р-γ _B · Н _B -γ _H L = 1.0 · 10 ⁸ -0.15 · 10 ⁸ -0.26 · 10 ⁸ = 0.59 · 10 ⁸ Pa.

those. the oil spill flow rate after filling the well table with balls of composite material of two fractions (50% with a diameter d _Ш = 0.01 m and 50% with a diameter d _Ш = 0.005 m) decreased and amounts to 0.6% of the initial flow rate of 1000 m ³ / day.

The speed of the upward movement of oil in the free interval of the well (above the cutoff plug) will be

As can be seen from the simulated examples, the inventive method of suppressing spills from an emergency oil well during field development allows us to solve the problem. Using the proposed method, the following results are achieved:

- A smooth decrease in the flow of oil from an emergency well with its subsequent cessation due to an increase in the hydraulic resistance of the wellbore with a gradual increase in the height of the shutoff plug. At the same time, the speed of the upward oil flow in the free (unfilled) interval of the well gradually decreases, which allows feeding smaller fractions of material with low permeability into the well.

- Creating backpressure on the formation in the opening zone of the oil and gas reservoir due to the weight of the material and its compaction during deformation under the influence of its own weight in the lower part of the wellbore (in the opening zone of the reservoir) until the well is completely blocked.

- Ensuring the safety of the process due to the lack of shut-off equipment at the wellhead and a smooth mode of well repayment by a gradually increasing cut-off plug. The gradual formation of a shut-off plug creates conditions that ensure a smooth change in stress in the casing, and eliminate the danger of the formation of concentrated stresses that can cause its destruction.

- Reducing the load on the environment by reducing and completely suppressing accidental oil spills.

Claims (6)

1. The method of suppressing outflows from emergency oil and gas wells during field development is characterized by trimming the damaged casing of the well and supplying to the well of a discrete material that is easily deformable under its own weight with particle size and specific gravity, which ensures the fall of the material in an upward flow of oil or gas, in an amount sufficient to form a shut-off plug in the well, which provides the possibility of extinguishing the reservoir pressure of oil or gas and suppressing outflow in (emissions). 2. The method according to claim 1, characterized in that the cut-off tube is formed at intervals in which the discrete material of the larger fraction is first filled in, then successively fractions with decreasing body size to increase the hydraulic resistance of the filled material. 3. The method according to claim 1, characterized in that the discrete material is used in the form of rolling bodies. 4. The method according to claim 1, characterized in that the supply of material is carried out through the hopper, which is additionally installed above the cut casing. 5. The method according to claim 1, characterized in that after the formation of the shut-off plug, the hopper is filled with a hardening solution. 6. The method according to claim 1, characterized in that the discrete particles are made either from a homogeneous material, or from composite materials.

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