RU2108445C1 - Method for restoring tightness of casing clearance - Google Patents

Abstract

FIELD: oil and gas production industry. SUBSTANCE: this is applied in repair and isolation operations. According to method, diameter of casing string is enlarged within isolation interval. Diameter of string is increased due to use of non-explosive breaking mixture which increases in volume during hardening. Mixture is injected into casing string so as to create bridge within isolation interval. EFFECT: higher efficiency. 1 cl, 1 tbl

Description

 The invention relates to repair and insulation works (RIR), and in particular to methods for restoring the tightness of annular space.

 A known method of restoring the tightness of the annular space by creating excess pressure inside the casing with respect to the annular space (pumping fluid or blasting the charge). The casing is inflated and the gap between the casing and cement stone is closed [1].

 The disadvantages of the analogue are that, firstly, the creation of excess pressure by pumping liquid causes the destruction of the column not only in the interval in which there is cement in the annular space, but also in the intervals where there is no cement. This is dangerous for the integrity of the casing. Secondly, the blasting of the charge process is uncontrolled, which can lead to disruption of the column and cement stone.

 Closest to the invention in technical essence is a method of eliminating annular flows by increasing the diameter of the column beyond the elastic deformations in the insulation interval [2]. An increase in the diameter of the column is carried out by hydraulically acting on the column in the insulation section.

 The disadvantage of this method is the high complexity of the work due to the need for parquet equipment, which, as a rule, is not very reliable.

 The task is to increase the efficiency of repair and insulation works and to reduce labor costs.

 The problem is achieved in that in the method of restoring the tightness of annular space by increasing the diameter of the column in the isolation interval, the diameter of the column is increased due to the non-explosive destructive mixture (LDC) increasing in volume during hardening [3], which is pumped into the column and a bridge is created in the isolation interval. In this case, as the LDCs use a mixture of lime for mining and drilling (SIGB).

 The success of repair and insulation work to fix the leakage of the cement ring does not exceed 50%. This is because the insulation materials used (mainly cement mortar and resin solutions) have a common drawback - shrinkage.

 During the operation of the well, the tightness of the annulus decreases. This occurs under stress on the casing and cement stone. For example, it was found that when the pressure in the well decreases, the adhesion strength of the cement stone to the column decreases. All types of perforation also lead to deterioration of the cement ring. At the same time, it was noticed that directly in the intervals of perforation, adhesion / contact / cement stone with the column improves. The latter fact is explained by the increase in the pressing force of the column to cement as a result of its deformation. After crimping the casing, as a rule, there is a violation of its contact with cement. In this case, the greatest disturbances of contact are noted in the intervals of the layers with high permeability and caverns. In strata with suspended water, contact disturbances after pressure testing are most often observed in the oil-water contact zone / WOC / [1].

 Let us estimate the throughput for bottom water of the annular micro-gap between the casing and cement stone by calculations. The Darcy – Weisbach formula can be written as follows [4].

где - D-внутренний диаметр цементного кольца, м;
d-внешний диаметр обсадной колонны, м;
p-переппад давления, Па;
λ -коэффициент гидравлических сопротивлений;
H-длина микрозазора, м;
Q-расход воды, м³/сут
Введем обозначения D-d= δ ; P/H = grad P,
где δ - зазор между колонной и цементным камнем, м;
grad P -градиент давления, Па/м.

where - D-inner diameter of the cement ring, m;
d is the outer diameter of the casing, m;
p-pressure difference, Pa;
λ is the coefficient of hydraulic resistance;
H-length of micro-clearance, m;
Q-flow rate, m ³ / day
We introduce the notation Dd = δ; P / H = grad P,
where δ is the gap between the column and the cement stone, m;
grad P is the pressure gradient, Pa / m.

Для определения коэффициента гидравлических сопротивлений необходимо вычислить критерий Рейнольдса

где ν - кинематическая вязкость воды / при 70^oC. ν = 0,5•10^-6 v²/c).Then the formula / 1 / will look like:

To determine the coefficient of hydraulic resistance, it is necessary to calculate the Reynolds criterion

where ν is the kinematic viscosity of water / at 70 ^o C. ν = 0.5 • 10 ^-6 v ² / s).

Зададимся числовыми значениями: ν = 0,5•10^-6м²/с; d = 0,168 м; δ = 0,1 мм = 10^-4 м; grad P = 4•10⁶ Па/м.In turbulent mode, the drag coefficient is determined by the formula:

Let us set the numerical values: ν = 0.5 • 10 ^-6 m ² / s; d = 0.168 m; δ = 0.1 mm = 10 ^-4 m; grad P = 4 • 10 ⁶ Pa / m.

 The system of equations / 2-4 / is solved by the selection method.

Thus, through a gap of 0.1 m with a pressure gradient of 4 MPa / m, about 22 m ^{3 of} water per day can enter the perforation interval.

 The increase in pressure in the casing leads to an increase in its diameter. Calculations show how much pressure is needed in the column so that its outer radius increases by 0.1 mm to close the micro-gap.

μ -коэффициент Пуассона, μ = 0,25;
E -модуль упругости для стали, E = 2.1.10⁵МПа;
P₁ -внутреннее давление, МПа;
P₂ -внешнее давление, МПа;
r₁ -внутренний радиус трубы, м;
r₂ -внешний радиус трубы, м, r₂=d/r.The formula for radial displacements of the outer wall of the pipe according to the Lyame problem has the form / 5 /

μ is the Poisson's ratio, μ = 0.25;
E is the elastic modulus for steel, E = 2.1.10 ⁵ MPa;
P _{1 is the} internal pressure, MPa;
P _{2 is the} external pressure, MPa;
r _{1 is the} inner radius of the pipe, m;
r _{2 is the} outer radius of the pipe, m, r ₂ = d / r.

Let P ₁ = P ₂ + P _huts or P ₁ -P ₂ = P _huts .

Where
P _hull = overpressure in the column compared to external pressure.

отсюда

При δ = 10^-4м; P₂ = 20 МПа; r₁ = 0,075 м; r₂ = 0,084 м.Then the formula / 5 / will look

from here

When δ = 10 ^-4 m; P ₂ = 20 MPa; r ₁ = 0.075 m; r ₂ = 0,084 m.

p_изб. = 33,7 МПа.

p _hut = 33.7 MPa.

 Calculations show that if there is a gap of 0.1 mm between the casing and the cement ring, then it is enough to create a pressure of 33.7 MPa in the string and the gap will be closed by increasing the outer diameter of the string. Such pressure and even more can be created by placing in the column of the bridge of non-explosive destructive mixture / LDC / and in particular a mixture of lime for mining and pine forest / SIGB / [6].

 LDCs are used mainly for the destruction of durable brittle materials (rock), concrete and reinforced concrete products, masonry, for the extraction of natural stone.

 LDCs are most often powdered non-combustible and non-explosive materials that give an alkaline reaction with water (pH = 12). When the LDC powder is mixed with water, a suspension (working mixture) is formed, which, being poured into a hole made in an object to be destroyed, hardens over time, hardens, while increasing in volume. The increase in volume is a consequence of hydration of the components that make up the LDCs, leading to the development of hydration pressure in the hole (more than 40 MPa). Under the influence of hydration pressure, stresses develop in the body of the object, leading to its destruction [7].

 The proposed method of isolation annular space is as follows.

A tubing string is lowered into the well so that the lower end is 10-20 m below the perforation interval of the reservoir. Excite circulation and wash the well with water, cooled to 0-10 ^o C.

Shut LDC in water with a temperature of 0-10 ^o C.

 With an open annulus, a suspension of LDCs is pumped into the tubing in the volume necessary to fill the casing in the range of 10-20 m.

 The LDC suspension is pushed until its levels in the tubing are aligned in the annulus.

 Raise the tubing to the depth of the lower perforation holes and, if necessary, wash the well, washing out the excess volume of the LDCs.

 The tubing is raised above the perforation interval, the annulus is sealed for the time necessary for the expansion and curing of the LDCs.

 Master the well.

 The advantage of the proposed method is that the overlapping of the channels for water to the perforation interval is not due to the hydraulic impact on the string, but due to the creation of a bridge in the casing from the expanding material. This, firstly, removes the need to install a packer; secondly, it reduces the time spent on conducting RIR.

Claims (2)

 1. A method of restoring the tightness of annular space by increasing the diameter of the column in the isolation interval, characterized in that the diameter of the column is increased due to the non-explosive destructive mixture (LDC) increasing in the cage during hardening, which is pumped into the column, and a bridge is created in the isolation interval.  2. The method according to p. 1, characterized in that as the LDCs use a mixture of lime for mining and drilling (SIGB).

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