RU2094608C1 - Method for detecting damaged spot in technological bore-hole strings - Google Patents

Abstract

FIELD: oil and gas production industry. SUBSTANCE: this is intended for checking tightness of technological pipe strings in extracting oil and gas. According to method, injected into annular space is liquid which is insoluble in water and is of specific gravity less than specific gravity of water with subsequent measuring of steady-state gauge pressure at well head in tubular and annular spaces. Depth of damaged spot is determined according to following relation: H = 10(P₁-P₂)/(γ₁-γ₂),, where P₁ - steady-state pressure in annular space at well head, kgf/sq.m; P₂ - steady-state pressure in tubular space at well head, kg/sq.m; γ₁ - specific gravity of water in tubular space, kg/cu.m; γ₂ - specific gravity of liquid injected into annular space, kg/cu. m; H - depth of damaged spot in string, m. If gauge pressure drops to zero, measured are static levels of liquid in tubular and annular spaces of well, and depth of damaged spot in string is determined according to following relation: H = (H₁γ₁- H₂γ₂)/(γ₁-γ₂),, where H₁ - depth of static level of water in tubular space, m; H₂ - depth of static level of liquid injected into annular space. EFFECT: high efficiency. 1 dwg

Description

 The invention relates to mining, in particular to methods for monitoring the tightness of technological columns of wells in oil and gas production and can be used in downhole mining.

A known method of testing the casing for leaks, including the injection of the working agent, crimping the column with internal pressure and, after changing the pressure, the column is additionally filled with a working agent, until the initial pressure is restored and, by the amount of injected agent, the tightness of the string is judged [1]
The disadvantage of this method is the long simple wells associated with preparatory work and the high complexity of the work, and, in addition, it does not allow to determine the depth of the damage site in the column.

Closest to the invention is a method for determining damage to production casing strings, including injecting into the space between the casing and working casing a liquid immiscible with water with a specific gravity of less than one, pushing it with air to the depth of the casing string, then bleeding the air and returning the fluid to the surface , and damage to the column is judged by a decrease in fluid volume [2]
The disadvantage of this method is the inapplicability in oil and gas producing wells, where an explosive mixture of pyrophoric compounds is possible in a mixture with oxygen, which can subsequently lead to self-ignition and explosion.

 The purpose of the invention is to simplify the process of determining the location of damage to technological columns of wells and to increase the safety of work.

In the described method for determining the location of damage to the production casing of a well, including injecting liquid insoluble in water and having a specific gravity less than the weight of water into the annular space, followed by measuring pressure at the wellhead, it is new to determine the steady-state overpressure at the wellhead in the pipe and annular spaces, and the depth of the damage site is determined based on the following ratio:
H = 10 (P ₁ -P ₂ ) / (γ ₁ -γ ₂ ),
where P ₁ steady-state pressure at the mouth in the annulus, kg / m ² ;
P ₂ steady-state pressure at the mouth in the pipe space, kg / m ² ;
γ ₁ is the specific gravity of water in the pipe space, kg / m ³ ;
γ ₂ - the specific gravity of the fluid pumped into the annulus, kg / m ³ ;
H column breaking depth, m;
in this case, in the case of reducing the overpressure to zero, measure the static fluid levels in the pipe and annular spaces of the well, and the depth of the damage site is determined based on the following ratio:
H = (H ₁ γ ₁ - H ₂ γ ₂ ) / (γ ₁ -γ ₂ ),
where H _{1 the} depth of the static water level in the pipe space, m;
H _{2 the} depth of the static level of the fluid pumped into the annulus, m

 The drawing shows a longitudinal section of an oil injection well.

 The invention is illustrated by the example of determining the tightness of the production casing of an oil injection well, through which water is pumped into the reservoir.

An injection well includes: a production string 1, where, for example, the presence and location of damage 2, the annulus 3, the tubing string 4, the tubular space 5, the wellhead 6 with valves 7 and 8 on the pipe and annular spaces are determined and with pressure gauges 9 and 10. The piping is connected to a pump unit 11 and a capacity of 12. The level of H ₁ and H ₂ in the pipe and annular spaces is measured with an echo sounder.

 The method of the example of an oil injection well is as follows.

Water is pumped into the pipe space of the well 5 by the aggregate 11 and the pipe 5 and the annular space 3 are washed into the container 12 to a constant specific gravity (γ ₁ kg / m ³ ).

Then, in the annulus through the valve 7 is pumped, to a depth of H ₂ , where it is necessary to determine the tightness of the column, a portion of the liquid with a lower specific gravity (γ ₂ kg / m ³ ), which does not dissolve in the previously pumped liquid, for example, oil produced in the field or other fluid satisfying these conditions. After the injection, steady-state overpressure in annulus 3 and tube 5 spaces is recorded using manometers 9 and 10. If there is damage in the production string, for example, at a depth H located above the watershed, first a lighter fluid below the damage will flow, and then water will be established, so that the watershed will be established at this depth.

The overpressure at the wellhead will decrease until the pressure is balanced at the level of the watershed in the pipe space 5, the annular space 3 and the static pressure in the reservoirs, where fluid flows through damage 2. At this point, the pressure in the pipe and annular spaces stabilizes. After the termination of the pressure change, measure their value and calculate the depth of damage according to the following relationship:
H = 10 (P ₁ -P ₂ ) / (γ ₁ -γ ₂ ).
Similarly, the depth of the hole is determined if the pressure in the tube and annulus decreases to zero, i.e. fluid levels dropped below the wellhead.

 Sounder measure steady (static) levels in the pipe 5 and annular 3 spaces.

In this case, the calculation is made according to:
H = (H ₁ γ ₁ - H ₂ γ ₂ ) / (γ ₁ -γ ₂ ).
where H ₁ static level in the pipe space, m;
H ₂ static level in the annulus, m

 The proposed method allows you to check the tightness of the production string and determine the depth of the location of the damage through which fluid leaks from the well without significant labor and material costs, allows you to ensure occupational safety and improve the efficiency of work related to environmental protection.

Information sources:
1. USSR author's certificate N 829867, cl. E 21 B 43/00.

 2. Copyright certificate of the USSR N 1218080, cl. E B 41/00, 1984.

Claims (1)

A method for determining the location of damage to a production string of a well, including pumping a liquid insoluble in water and having a density less than the density of water into the annulus followed by measuring pressure at the wellhead, characterized in that steady-state overpressure at the wellhead in the pipe and annular spaces is determined, and the depth of the damage site is determined on the basis of the following ratio:
H = 10 (P ₁ -P ₂ ) / (γ ₁ -γ ₂ ),
where R ₁ steady-state pressure at the mouth in the annulus, kg / m ² ;
P ₂ steady-state pressure at the mouth in the pipe space, kg / m ² ;
γ ₁ - the density of water in the pipe space, kg / m ³ ;
γ ₂ - the density of the fluid pumped into the annulus, kg / m ³ ;
N the depth of the violation of the column, m,
in this case, in the case of reducing the overpressure to zero, measure the static fluid levels in the pipe and annular spaces of the well, and the depth of the damage site is determined based on the following ratio:
H = (H ₁ γ ₁ - H ₂ γ ₂ ) / (γ ₁ -γ ₂ ),
where H _{1 the} depth of the static water level in the pipe space, mm;
H _{2 the} depth of the static level of the fluid pumped into the annulus, m