RU2285791C1 - Method to prevent sand appearance in oil and gas wells - Google Patents

Abstract

FIELD: oil and gas production, particularly to perform repair-and-renewal operations in wells to reduce sand ingress in well and to consolidate geological formations, including artificial ones after hydraulic formation fracturing.

SUBSTANCE: method involves injecting water-free liquid in well, wherein water-free liquid contains polyurethane pre-polymer and solvent; injecting water in well; hardening thereof. The polyurethane pre-polymer is hydrophobic polyurethane pre-polymer. The solvent is lower ketone. Above substances are taken in the following amounts (% by weight): hydrophobic polyurethane pre-polymer - 5.0-15.0, lower ketone - 85.0-95.0. Volume of the liquid is equal to 0.4-5.0 pore volumes. Injection time does not exceed 3 hours. After liquid injection the injection is stopped and well is left as it is for not less than 10 hours in static conditions to provide liquid hardening.

EFFECT: increased efficiency of sand appearance control without noticeable collecting properties decrease.

1 ex, 1 tbl

Description

The invention relates to the field of oil and gas production and can be used when carrying out repair and restoration work in wells to reduce sand removal into wells, as well as to strengthen geological formations, including artificial ones after hydraulic fracturing operations.

There is a method of strengthening geological formations by injecting fixing solutions based on polyisocyanates in them, in which at the first stage a polyisocyanate is injected, which reacts with the water in the rock to form polyurea, and at the second stage, a polyisocyanate and polyhydric alcohol are injected (1).

The disadvantage of this method is its complexity and multi-stage. At the same time, the filtration resistance of the rock increases sharply, which can lead to a complete loss in the productivity of the production well.

A known method of fastening solid particles, including sand, a composition containing, parts by weight: perlite and sand 0.65, hydrophilic polyurethane prepolymer 1.1, acetone 0.8 and water 1.0, by mixing them (2).

The closest analogue to the claimed method is a method of controlling sand formation in oil and gas wells, comprising injecting into the well a composition containing 75% viscous oil and 25% diesel fuel, then an anhydrous liquid containing a polyurethane prepolymer and a solvent dimethylformamide, propylene carbonate, dimethyl sulfoxide, and then a catalyst from the group of quaternary amines, water, and curing (3).

A disadvantage of the known methods is the reduction of rock permeability up to complete isolation.

The objective of the invention is to increase the effectiveness of sand control in wells without significantly reducing their reservoir properties.

The problem is solved in that in a method of controlling sand formation in oil and gas wells, including injecting an anhydrous fluid containing a polyurethane prepolymer and a solvent, injecting water and curing into the well, a hydrophobic PPG polyurethane prepolymer is used, and lower ketone is used as the solvent, with their ratio, wt.%:

BCP 5.0-15.0 lower ketone 85.0-95.0

carry out the injection of the specified liquid in a volume equal to 0.5-1.5 pore volume, and the injection of water in an amount of 0.4-5.0 pore volume for a time not exceeding 3 hours, after which the injection is stopped and exposure is carried out under static conditions at least 10 hours for curing.

The essence of this method lies in the fact that it implements a three-stage treatment scheme for the formation with a urethane prepolymer solution, including:

- filling the pore space with a prepolymer solution;

- planting polymer on the surface of the rock;

- curing the precipitated polymer.

Each stage is characterized by its optimal parameters. For the first stage, this is the injection into the pore space of a highly diluted - 85-95% solution in ketone. The use of ketone as a solvent is due to the fact that it is a solvent that does not contain active hydrogen. In addition, it mixes equally well with both water and non-polar hydrophobic fluids, including oil hydrocarbons and gas condensate and a hydrophobic prepolymer. It is possible to use acetone as well as its homologs as a ketone. The use of a hydrophobic urethane prepolymer in this method leads to a significant reduction in rock permeability. In the process of injection into the pore space, this allows you to clean the rock surface from high molecular weight hydrocarbons adsorbed on its surface for subsequent precipitation of the prepolymer from the solution onto the rock surface. For the second stage, it is important that the total planting time does not exceed 3 hours, more precisely, the polymer curing time. The rate of water displacement of the ketonopolymer system affects the prepolymer film thickness and, consequently, the permeability of the collector. For the third step, the required cure time should not be less than 10 hours. With these parameters, a polymer layer forms on the rock surface with a minimum thickness and maximum strength, which leads to the preservation of the total permeability of the reservoir. The method achieves optimal results when injecting water in an amount of 0.4-5 pore volumes, i.e. 0.4-5 of the volume of the polymer solution. At volumes less than 0.4, polymer precipitation on the surface occurs near the well and leads to a significant decrease in permeability, at volumes greater than 5, the effectiveness of rock consolidation is reduced, since the formation regions remote from the well are strengthened, and the adjacent ones remain sand-producing.

Example.

The method was tested in laboratory conditions on a model of a gas field formation. Model dimensions: length 175 mm, diameter 33 mm. The model is filled with a disintegrated core of Cenomanian deposits. The model was connected to a source of compressed gas and a container with reagents. In a separate container, a solution of a urethane prepolymer (urethane resin) in acetone was prepared with an acetone content of 92%. Then we performed the following operations:

- conducted filtration through the model of produced water in order to saturate it;

- conducted a reverse filtration and measurement of core permeability in produced water;

- purged the model for determining gas permeability;

- pumped 0.8 pore volume of a solution of urethane in acetone over a period of 0.5 hours;

- 0.4 pore volumes of water were pumped into the sample;

- the sample was held for 20 hours;

- conducted formation water filtration and permeability measurement;

- purged the reservoir model and measured gas permeability;

- created excessive gas pressure up to 10 atm for 10 minutes and control over the removal of sand.

By analogy, experiments were carried out on the implementation of the proposed method with other parameters.

The results of measurements of permeability and sand development are presented in the table. The results (experiment 1) show that water permeability decreased by 36%, gas permeability - by 61%. This is many times lower than in the prototype. As can be seen from the above data, the use of this method allows to prevent the removal of sand with a limited decrease in permeability.

Information sources

1 Patent SU No. 1776321, 09 K 8/502, publ. 15.11.1992.

2. US patent No. 3805532, E 21 B 33/138, publ. 23.04.1974.

3. US patent No. 5048608, E 21 B 43/04, publ. 17.09.1991. The way to combat sand in oil and gas wells

Table No. Solvent content PPG injection in solvent Kolich. water / water injection time Holding time Before processing After processing Sand removal Core Condition % parts of pore volume parts from the pores. volume / hour hour Sq Mkm ² Kg mkm ² Sq Mkm ² Kg mkm ² one 92 (acetone) 0.5 0.4 / 0.5 twenty 0.22 0.58 0.14 0.23 no connected 2 95 (acetone) one 2/1 twenty 0.31 0.66 0.09 0.18 no connected 3 85 (acetone) 0.5 3/2 10 0.41 0.81 0.22 0.32 no connected four 85 (methyl ethyl ketone) 1,5 5/3 twenty 0.13 0.59 0.02 0,07 no connected Note: Kv - water permeability coefficient; Kg is the gas permeability coefficient.

Claims (1)

A method of controlling sand manifestation in oil and gas wells, including injecting an anhydrous fluid containing a polyurethane prepolymer and a solvent into the well, injecting water and curing, characterized in that the polyurethane prepolymer is hydrophobic PPG, and the lower ketone is used as the solvent in their ratio, wt .%: BCP 5.0-15.0 Lower ketone 85.0-95.0 this liquid is pumped in a volume equal to 0.5-1.5 pore volumes, and water is pumped in an amount of 0.4-5.0 pore volumes for a time not exceeding 3 hours, after which the pump is stopped and the mixture is kept in static conditions of at least 10 hours for curing.