RU2256776C1 - Method for restricting water influx into well - Google Patents

Abstract

FIELD: oil and gas industry, particularly methods or devices for cementing and plugging holes, crevices, or the like to isolate water-bearing stratum layers.

SUBSTANCE: method involves pumping sodium silicate solution, separating agent and sodium silicate polymerization initiator into well in the following succession: silicate polymerization initiator, separating agent and sodium silicate. Sodium silicate polymerization initiator includes 20-35 vol% of oil, 5-40 vol% of condensate, 58 vol% of 20-25% nitric acid and 2 vol% of emulsifier. Separating agent is gas condensate.

EFFECT: increased efficiency due to provision of additional porous collector space hydrophobization and increased reliability of created isolation shield.

2 cl, 3 tbl

Description

The invention relates to the oil and gas industry, in particular to methods for limiting and isolating water inflow in gas wells.

A known method of limiting water inflow into a well, comprising sequentially injecting into the well an aqueous solution of sodium silicate and a hardener (initiator of the polymerization of sodium silicate) [see SU 1423726 A1, E 21 B 33/13, 1988]. In this case, an aqueous solution of sodium silicate reacts with a hardener (hydrochloric acid solution), as a result of which silica sol is formed.

The disadvantages of this method include the fact that the injection process causes premature mixing of the injected solutions, and due to the ionic nature of the chemical reaction between them, characterized by almost instant formation of silica sol in the contact zone with the formation of a blocking screen near the injection line and in the wellbore.

These disadvantages are eliminated in the method of limiting water inflow into the well, which we selected as a prototype [see RU No. 2121570 C1, E 21 B 43/32, 33/138, 1998], and including the sequential injection into the well of an aqueous solution of sodium silicate and a 0.5-4.0% hydrochloric acid solution in highly mineralized water of calcium chloride type, with before the injection, a separator is pumped into the well, which is proposed to use light oil.

The disadvantages of the prototype include the fact that the silica formed as a result of the polymerization reaction is not sufficiently resistant to erosion by formation water, which in turn reduces the life of the insulating screen.

It should also be noted that in field practice, there are widely known methods of limiting water inflow into a well by treating a formation with a hydrophobizing pore space with a hydrocarbon-based emulsion [see RU No. 2114990 C1, E 21 B 43/32, 33/13, 1998]. However, a significant drawback of the known method is the fact that the shielding composition under the influence of the pressure of formation water after some time is pushed back into the wellbore.

The technical result of the proposed method to limit water inflow into the well is to increase the efficiency of the method due to additional hydrophobization of the pore space of the reservoir and the creation of a more reliable insulating screen.

This result is achieved by the fact that the method of limiting water inflow into the well includes injecting a sodium silicate polymerization initiator, then a separator and a sodium silicate solution, and a hydrophobic invert emulsion of the following composition, vol.%: Oil - 20-35; condensate - 5-40; nitric acid 20-25% - 58; emulsifier - 2, and gas condensate is used as a separator.

Comparative analysis with the prototype shows that the distinguishing features of a new method of isolating water inflow are a necessary and sufficient condition characterizing the novelty of the object of the invention, namely, the injection sequence and the composition of the sodium silicate curing reagent.

A hydrocarbon-based invert emulsion promotes hydrophobization of the pore space, reducing phase permeability to water, and contains a solution of nitric acid as a dispersed phase, which initiates the polymerization of sodium silicate with the formation of a water-insoluble plugging material in the form of silica sol in the pore space of the reservoir.

To prepare the emulsion using a 20-25% solution of nitric acid - 58, oil - 25, condensate - 15 and emulsifier - 2, which allows the formation of an invert emulsion of the type "water in oil". The acid solution is prepared from non-concentrated nitric acid made according to OCT.113-03-270-90. The emulsifier is pre-dissolved in a small amount of hydrocarbons, then, with vigorous stirring, added to the main part of the oil, after 10 minutes, a solution of nitric acid is added and intensively mixed for another 10 minutes.

A solution of sodium silicate is prepared from liquid glass with a sodium density of 1300 kg / m ³ with a silicate module 3 made in accordance with GOST 13078-81. As a separator that prevents premature mixing of the reagents in the wellbore and near the injection line, gas condensate is used - a mixture of saturated hydrocarbons C ₅ -C ₈ and above.

The objective of the invention is the alternate injection into the flooded interval of the reservoir of a hydrophobic invert emulsion containing as a dispersed phase a solution of nitric acid acting as the initiator of the polymerization reaction for the subsequent sodium silicate solution. In this case, the synergistic effect of the treatment is manifested in the hydrophobization of the pore space in the remote zone of the reservoir, due to the presence of hydrocarbons in the emulsion that reduce the relative phase permeability of the reservoir for water, and the creation of an insulating screen during the chemical reaction of the interaction of nitric acid and sodium silicate. To prevent premature mixing of the reagent solutions, an intermediate injection of a separator chemically inert to these reagents, in particular gas condensate, is provided. Nitric acid is the dispersed phase of the water-in-oil reverse emulsion. Being present in the composition of a hydrocarbon emulsion in a micellar state, the acid has less corrosion activity in relation to downhole equipment and preserves the specified concentration to the maximum. The sodium silicate solution is an effective material for injection into water-saturated rocks because of its high filterability and high adhesive properties. In reservoir conditions, sodium silicate practically does not enter into chemical interaction with the rocks of the reservoir, but has good adhesion to them. The rheological parameters of the emulsion and sodium silicate solution are selected in such a way that when injecting into the formation, the isolation zone is uniformly treated with maximum intrapore ash formation. The viscosity of emulsions is controlled by the ratio of oil, condensate and acid. Ash formation occurs during the interaction of nitric acid and sodium silicate according to the scheme:

2НNO ₃ + Na ₂ SiO ₃ → H ₂ SiO ₃ ↓ + 2 NaNO ₃

As a result of the reaction, a water-insoluble sol of metasilicic acid is formed. Metasilicic acid is unstable and undergoes polymerization: its molecules are enlarged and polysilicic acids of various composition and structure are formed. The general equation for the polymerization reaction can be represented as follows:

nSi (OH) ₄ = (SiO ₂ ) _n +2 _n Н ₂ O

This equation indicates that polymerization causes the condensation of silanol groups (SiOH) to form siloxane bonds (Si — O — Si). The polymerization of Si (OH) ₄ entails the distribution of OH ^- ions between different silicon atoms with the formation of polymer cells in which each Si ⁴⁺ atom is surrounded by six OH ^- ions.

Nitric acid initiates the polymerization of sodium silicate and serves to maintain the acidic reaction of the medium, since the polycondensation rate of the formed silicic acid in the region of pH <2 is accelerated by protons, and in an acidic medium the reaction proceeds by a donor-acceptor mechanism with the formation of a transition complex in which Si temporarily acquires the coordination number 6 instead of 4. The stability of the silicic acid sol depends on the acid concentration and pH of the medium (Table 1). At pH> 7.5, the hydrosol is thermodynamically resistant to coagulation. As a result, under reservoir conditions, the resulting plugging material will be stable.

The method was tested in laboratory conditions. The proposed formulation was tested on printed models of Cenomanian sand, previously saturated with formation water. Initially, the permeability of water-saturated models was measured by gas and water, then reagent solutions were injected and water permeability was re-measured. According to the results of laboratory studies, the insulating effect is 94-98%, while the minimum gradient of water filtration increased up to 10 times (Table 2).

For water inflow restriction methods, the main parameters that determine the volume of formation water filtration into the well per unit time are the permeability coefficient of the bottom-hole reservoir rocks after water isolation and the minimum filtration pressure gradient.

Thus, comparing the proposed method with the prototype, with equal final permeability, after the proposed treatment method, it is possible to operate the wells without the addition of formation water while creating a 1.12-2.81 times greater depression on the productive formations, which increases the production capabilities of the wells (table .3).

table 2
Insulation effect from artificial colmatation of samples Packed Model No. Name of reagents pumped through the sample Model parameters before processing Model parameters after processing Insulation effect,% (K ₁ -K ₂ ) / K ₁ × 100% The increase in the retaining effect,%

МПа/мMin. filtration pressure gradient

MPa / m Water permeability, K1 Min. filtration pressure gradient

MPa / m Water permeability, K2 1 Emulsion No. 1 sodium silicate 0.56 0.294 2.24 0.018 93.9% 300% 2 Emulsion No. 2 sodium silicate 0.56 0.223 5.61 0.004 98.2% 901% 3 Emulsion No. 3 sodium silicate 0.56 0.413 4.17 0.011 97.3% 645%

Table 3 Processing method Permeability after processing, μm ² Minimum gradient of filtration pressure, MPa / m Proposed 0.004-0.018 2.24-5.61 Prototype 0.003-0.013 less than 0.2

Claims (2)

1. A method of limiting water inflow into a well, comprising injecting into a formation a solution of sodium silicate, a separator and a polymerization initiator of sodium silicate, characterized in that the polymerization initiator of sodium silicate is first pumped into the well, then a separator and sodium silicate, and a hydrophobic invert is used as the polymerization initiator an emulsion of the following composition, vol. %: oil 20-35; condensate 5-40; nitric acid 20-25% 58; emulsifier 2. 2. The method according to claim 1, characterized in that gas condensate is pumped into the well as a separator.