RU2399751C1 - Method of reducing sand ingresses in gas wells with abnormally low formation pressure - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: in method for reducing sand ingresses in gas wells with abnormally low formation pressure, which involves pumping to the formation through production well of the solution of urethane pre-polymer in acetone-containing solvent with displacement of solution to the formation, the above solution contains, as acetone-containing solvent, acetone or its being mixed with gas condensate at the content of the latter of up to 50% of the mixture weight; 5-30% solution is used; displacement is performed by gas pumping, which contains water vapours, with relative humidity of not less than 10% during not less than 1 hour at the above gas pumping pressure exceeding formation pressure by 1.5-5 times. At that, after the above processing there also performed is well perforation.

EFFECT: increasing efficiency of reduction of sand ingresses in the well, reducing the period of well development, simplifying the technology and increasing well flow rate.

2 cl, 4 ex, 1 tbl

Description

The invention relates to the field of gas production and can be used to reduce the removal of sand from a producing gas well with an abnormally low reservoir pressure and increase its flow rate.

The development of gas reservoirs is often accompanied by complications associated with the destruction of the reservoir and, as a result, with the appearance of sand in the produced products. Part of the sand is carried to the surface and destroys the technological equipment due to its abrasive wear. Another part of the sand forms a sand plug in the well and reduces its flow rate due to the overlap of the perforation interval. To combat this phenomenon, in order to increase the current gas production rate, sand plugs are periodically removed.

A known method of removing sand plugs by washing the well with a 25-30% solution of monohydric alcohol in water with the addition of 1-1.5% surfactant using a sleeveless long pipe (BDT) [1].

This method requires the use of expensive equipment and gives only a short-term effect. In addition, the monohydric alcohol-methanol commonly used in gas wells has a toxic effect.

A longer-lasting effect of reducing sand removal into the well is provided by the use of a downhole filter. According to this method, a gravel mixture with a particle size of 0.4 to 1.8 mm is pumped into the well [2]. However, such a filter creates additional hydraulic resistance and thereby reduces the production rate. In addition, such a filter is expensive and makes it difficult to carry out repair work and geophysical research.

Closest to the claimed method is a method of dealing with sand occurrences in gas wells by pumping a solution of a urethane prepolymer in acetone into a well, followed by water displacement. The injection of the urethane prepolymer in a dilute solution of lower ketone into the formation and its subsequent displacement from the pores with water leads to the formation of a spatial polymer network mechanically linking disparate sand grains. Water in this method acts as a hardener and a displacing agent at the same time [3].

The disadvantage of this method is the need for injection into the reservoir of large volumes of liquid to advance the reaction mass into the reservoir. In the future, this fluid must be removed during well development. The task of fluid removal is exacerbated in wells with an abnormally low reservoir pressure, since the pressure energy of the reservoir gas pressure may not be enough to remove it from the reservoir. This leads to a long development period. In addition, this method does not increase the flow rate of the well.

The aim of the invention is to increase the efficiency of reducing sand in the well, reducing the period of well development, simplifying the technology and increasing the current flow rate.

This goal is achieved by the fact that in the method of reducing sand occurrences in gas wells with abnormally low formation pressure, including injecting a solution of a urethane prepolymer in an acetone-containing solvent into the formation through a well, pumping said solution into the formation, said solution contains acetone or a mixture of it as an acetone-containing solvent with gas condensate when the content of the latter is up to 50% by weight of the mixture, and the solution is used 5-30%, it is forced through injection of gas containing steam water, with indication of the relative humidity no less than 10%, for at least 1 hour at a pressure of injection of said gas reservoir in excess of 1.5-5 times.

Moreover, after this treatment, perforation of the well is additionally carried out.

The essence of the claimed method consists in the fact that a solution of a urethane prepolymer in acetone is pumped into a gas well and pumped into the formation with moist gas. Gas can be used in the form of air, natural associated gas, nitrogen. Gas in this case acts as a displacing agent and a carrier of water vapor. Gas displaces excess polymer solution from the pore volume. Volatile acetone is removed from the adsorbed solution during gas pumping and the urethane prepolymer remains. Upon contact with water in a vapor state, the prepolymer cures and forms a spatial network. This grid creates a framework that impedes the movement of grains of sand.

The urethane prepolymer is pumped in the form of a 5-30% solution in acetone or a mixture of acetone with a hydrocarbon solvent - gas condensate. The indicated concentration range of the prepolymer was selected experimentally. At a prepolymer concentration of less than 5%, sand does not bind. At a prepolymer concentration of more than 30%, the gas permeability of sand decreases and, as a result, the productivity of the well decreases. The minimum water content in the gas was also determined experimentally - 10%. For the curing reaction of the urethane prepolymer under these conditions, a time of at least 1 hour is required. To effectively move the solution into the reservoir, it is necessary that the pressure of gas injection exceeds the reservoir by 1.5-5 times. A lower pressure outside this interval does not ensure the advancement of the solution into the formation and can lead to a decrease in well productivity and an increase in the development time of the well. Excess pressure more than 5 times from the reservoir complicates the process of gas injection in the absence of an increase in efficiency.

Example 1

The proposed method is implemented on a laboratory model of the reservoir. For this, a reservoir model in the form of a cylinder with a diameter of 1 cm and a length of 30 cm was filled with sand and the sand permeability was determined. Then a 30% solution of urethane prepolymer in acetone was prepared and sand pores were filled with this solution. Then, air with a humidity of 10% was pumped through the model for 1 hour. The permeability was determined and the strength of the resulting material was tested. As a result, it was found that after such treatment of unbound sand, its permeability decreased by 5%, and the compressive strength was 7 MPa. Thus, the proposed method allows you to bind sand into a solid structure while maintaining filtration properties.

By analogy, we studied the strength of sand obtained after a similar treatment of sand with a prepolymer solution with a concentration of 5 wt.%. It was found that the polymer content below 5% in an acetone solution does not provide sand binding to a strong structure.

Example 2

Analogously to example 1, a 15% solution of a urethane prepolymer in a solvent containing 50% acetone and 50% gas condensate was prepared. As a result, a cured sand sample with a strength of 3 MPa was obtained.

Example 3

A gas well operating on the Cenomanian gas horizon with a reservoir pressure of 21 atm has a flow rate of 75 thousand m ^{3 of} gas per day. In this case, sand is carried out and a rise in the current face is observed. Periodically, the well is stopped to carry out repair work to remove the sand plug.

To reduce sand removal and reduce the growth rate of sand plugs, measures were taken to reduce sand removal from the reservoir. To this end, the perforation zone of the well was cleaned of sand and the current bottom was set 2 m below the lower perforation level. Subsequently, 5 m ^{3 of a} 10% solution of urethane prepolymer in acetone was successively pumped into the well through a tubing - tubing. Then, through the tubing, using a booster installation UNG-8/15, natural gas was supplied with moisture - with a relative humidity of 15% - and at a pressure of 63 atm (3 times higher than the reservoir) for 5 hours. The well was stopped for technological sludge to complete the curing reaction of the urethane prepolymer (resin). Further, the well worked on the flare line for 48 hours, after which it was transferred to the operating mode.

According to the results of operational data, sand removal decreased to 10 g per day. The overhaul period for removing sand plugs increased from 3 to 7 months. Gas production rate has not changed.

In a similar way, gas wells No. 2 and No. 3 were processed. For control, gas well No. 4 was used, on which washing of the sand plug was carried out, but no processing was carried out using the proposed technology.

The results are presented in the table.

Table Test results of a method for reducing sand occurrences in gas wells. SLE No. Perforation interval, m The initial face, m Sand plug removed after repair, m Sand cork growth in 3 months The amount of polymer, kg Debit, thousand m ³ Before repair After repair one 1145-1172 1232 34 fifteen 350 75 83 2 1130-1190 1192 32 24 450 76 76 3 1151-1199 1301 6 one 400 114 116 four 1047-1095 analogue 1238 94 96 0 105 102

Example 4

One of the wells was treated according to the method described in example 3. After pumping 800 kg of a urethane prepolymer into the well in the form of a 20% solution in acetone, then through the tubing into the well using a booster unit UNG-8/15 for supplying moisture-saturated with a relative humidity of 15% of natural gas at a pressure of 63 atm (3 times higher than the reservoir) for 5 hours. The well was stopped for technological sludge to complete the curing reaction of the urethane prepolymer (resin). After 1 month, the well was perforated. As a result, it was found that the sand production rate has stopped, and the gas production rate has increased by 2 thousand m ³ per day.

From the above examples it is seen that the proposed method allows to achieve the goal - to reduce sand removal while maintaining and even increasing the current gas flow rate compared to the control experiment (well No. 4, table, where the sand plug completely for the same period of 3 months recovered and gas production decreased).

Information sources

1 RU 2188304, 12.28.2001, E21B 37/00, E21B 19/22. The method of washing sand plugs.

2. RU 2206719, 2001.12.26. A method of constructing a gravel filter in a well.

3. RU 2285791, 2005.11.21. The way to deal with sand in gas wells.

Claims (2)

1. A method of reducing sand occurrences in gas wells with an abnormally low formation pressure, comprising injecting a solution of a urethane prepolymer in an acetone-containing solvent into the formation through a borehole by selling said solution into the formation, characterized in that said solution contains acetone as its acetone-containing solvent or a mixture thereof gas condensate when the content of the latter is up to 50% by weight of the mixture, the solution is used 5-30%, squeezing is carried out by injection of gas containing water vapor, with relative humidity of at least 10% for at least 1 h at a pressure of injection of the specified gas exceeding the reservoir by 1.5-5 times. 2. The method according to claim 1, characterized in that after said processing, the well is also perforated.