RU2236559C1 - Method for selective treatment of bed - Google Patents

Abstract

FIELD: gas extractive industry.

SUBSTANCE: method includes orderly feeding of buffer liquid into bed - water solution of metal salt and cementing compound with forming in bed conditions with calcium ions of a compound non-soluble in water - alkali sediment, as water solution of metal salt a 10-30% water solution of sodium hydrosulphate is used, and as cementing compound - water solution of chlorine calcium, feeding of each of said solutions is performed in even portions, volumes of which are determined on basis of thickness of productive bed and well diameter or speed of absorption of fed solutions. In bed with penetrability 100 mcm² said sediment is reinforced by cement bridge. Feeding of solutions into bed is performed as in stopped well, as in operating well. For delivery of solutions to given well perforation zone and providing for calculated speed of pumping coltubing is used.

EFFECT: higher effectiveness of isolation due to creation of stable volumetric sediment in watered portions of bed, which prevents influx of bed waters.

4 cl, 2 tbl

Description

The invention relates to the gas industry, in particular to the selective isolation of water inflows in gas and gas condensate wells.

A known method of isolating water inflows in gas wells, including the injection of cement mortar through tubing while maintaining the fluid level in the annulus of the well at a certain depth (SU 1758219 A2, E 21 B 43/32, 1992).

The difficulty in continuously monitoring the liquid level in the annulus of the well and the lack of control over the process of pumping cement in the presence of a packer in the well limit the application of this method in many gas and gas condensate fields.

Also known is a grouting composition for isolating permeable formations containing polymer, acetone and a nonionic surfactant (SAS), the so-called A-formation, used in gas wells (see US Pat. RF 2046180, E 21 B 33/138, 1995) .

However, this method also has a number of drawbacks consisting in technological complexity and requiring the use of special technical means to ensure selectivity in the treatment of water-developing sections of the formation, and in most cases cement bridges are installed to consolidate the effect.

Of the known methods, the closest to the invention is a method for selectively treating a formation in a well, including sequentially injecting a buffer liquid — an alkali metal salt and a plugging composition — into a water-insoluble compound — an alkaline precipitate under formation conditions with calcium ions (SU 1754889 A1, publ. 15.08.1992).

The objective of the invention is to increase the efficiency of isolation by creating a stable volumetric sediment in water-developing areas of the formation that prevents breakthrough of formation water and thereby connecting to the development of stagnant and slightly drained zones of the formation that provide the well operation mode specified by the collection system.

In the method of selective treatment of the formation, which includes sequential injection of a buffer liquid — an aqueous solution of a metal salt and a plugging composition into the formation with formation of a water-insoluble compound — an alkaline precipitate under calcium conditions with calcium ions — a 10-30% aqueous solution is used as the aqueous solution of the metal salt sodium hydrogen sulfate, and as a tamponating composition - an aqueous solution of calcium chloride, the injection of each of these solutions is carried out in equal portions, the volumes of which are determined based on the thickness productive formation and well diameter or absorption rate of injected solutions.

In a formation with a permeability of 100 μm ^{2, the} specified sediment is fixed with a cement bridge.

Solutions are injected into the formation both in a stopped well and in a working well.

For delivery of solutions to a given zone of perforation of the well and to ensure the estimated speed of injection use count-tubing.

The essence of the proposed method is as follows. A solution of sodium hydrosulfate of 10-30% concentration and a solution of calcium chloride with an optimal ratio of gypsum-forming ions are sequentially pumped into the formation, where upon mixing the solutions in the pore volume, a plugging deposit forms in the form of a fine suspension, and on the walls of the pore channels in the form of solid microcrystals. Moreover, this procedure is repeated several times depending on the thickness of the reservoir and the diameter of the well or the absorption rate of the injected solutions.

The selectivity of repair and insulation works (RIR) is provided by the selection of volumes of portions of solutions, based on geological conditions or the corresponding mode of operation of the well during the work. The well operating mode during the isolation work can be calculated using the dispersion-annular flow formulas based on previous gas-dynamic studies (GDI) or it can be selected using the experimental method directly at the well by selecting a diaphragm that ensures the well works in the "flooding" mode. Those. at a certain level of velocity of the gas-liquid mixture, the upward movement of the film and the dispersed system stops (hangs), and from a certain point the liquid begins to slide down and is absorbed by the flooded layer. Thus, plugging solutions delivered to the treatment interval through count-tubing are absorbed by the flooded layer, while the influx of gas from the non-flooded working interval will prevent it from being contaminated during RIR. The speed of transition to the "flooding" mode is called critical and is determined by the formula (1):

where δ is the coefficient of surface tension, N / m;

ρ _W - the density of the liquid phase at the corresponding P and T, kg / m ³ ;

ρ _g - the density of the gaseous phase at the corresponding P and T, kg / m;

g - acceleration of gravity, m / s ² .

Insulation capacity was determined on models simulating a highly permeable reservoir of Cenomanian deposits, for which a printed model of loose Cenomanian core was used. The sand was poured into a cylindrical high-pressure chamber with a coaxially installed tube simulating a perforated section of the well and saturated with formation Cenomanian water. After measuring the initial filtration parameters, the prepared 15% NaHSO ₄ · 2H ₂ O and CaCl ₂ solutions in a ratio of 1: 1 were pumped through a sand sample and kept for 30 minutes under constant thermobaric conditions (P = 1.5 MPa, T = 28 ° C).

The nature of the interaction of the solutions was determined by the equation:

The optimal ratio of dry matter in solutions was determined by stoichiometric calculations of the reaction with the calculation of mass fractions and laboratory studies, for example:

In the interaction of 15% solutions of NaHSO ₄ · 2H ₂ O, CaCl ₂ in a ratio of 1: 1.

Molar mass (M): NaHSO ₄ · 2H ₂ O - 156.09 g / mol

CaCl ₂ - 110.99 g / mol

CaSO ₄ · 2H ₂ O - 172.17 g / mol

Mass of solution (m _p-pa ): NaHSO ₄ · 2H ₂ O - 100 g

CaCl ₂ - 100 g

Mass fraction of substance (w): NaHSO ₄ · 2H ₂ O - 15%

CaCl ₂ - 15%

The mass of salt in solution: m _v-va = w · m _r-ra

m (NaHSO ₄ · 2H ₂ O) = 15 g

m (CaCl ₂ ) = 15 g

The amount of the main substance in the solution: n = m / m

n (NaHSO ₄ · 2H ₂ O) = 0.096 mol

n (CaCl ₂ ) = 0.135 mol

The calculation of the mass of the product was carried out based on the mass of the substance taken in the deficiency, i.e. NaHSO ₄ · 2H ₂ O.

The mass of CaSO ₄ · 2H ₂ O formed was determined: m = n · M

m (CaSO ₄ · 2H ₂ O) = 16.53 g

To confirm the theoretical calculation, a laboratory experiment was conducted _{on the} interaction of NaHSO ₄ · 2H ₂ O and CaCl ₂ . The mass of the obtained gypsum precipitate CaSO ₄ · 2H ₂ O was 14.40 g or 87% of theoretical. In order to optimize the yield of sediment at a ratio of solutions of 1: 1, the following concentrations were calculated (mass fractions of the substance):

As a result of the studies, it was determined that at a pressure drop of up to 6 MPa, the printed model remained impermeable to water. The pressure of the onset of water filtration through the plugged medium was more than 6 MPa. After dismantling the model, it was found that the pore space around the perforated section of the well is gelled with a gel-like mass of gypsum-containing substance, while the grains of sand are covered with precipitated gypsum.

A method for selective formation treatment developed in laboratory conditions has been tested in field practice. For this, the M-10 col-tubing unit and the UNG-8/15 gas booster unit were used, which ensured the selective injection of reagents. When conducting the process under consideration, two stages are distinguished.

At the first stage, the technological preparation of the well for chemical treatment takes place, for this a shoe of a seamless long pipe (BDT) was installed at the bottom of the perforation interval.

The second stage involved the injection of an aqueous solution of sodium hydrogen sulfate of 15% concentration into the lower interlayer of the super collector, and then a 15% solution of calcium chloride. Portions of aqueous solutions of chemical reagents were pumped into the gas well in such a volume that the hydrostatic pressure of the liquid column in the well at the level of the upper holes of the perforation interval did not exceed the reservoir gas pressure. This excluded the absorption of chemicals in the upper part of the gas-saturated formation. At the same time, the fluid pressure at the level of the lower perforation holes exceeded the reservoir pressure by the value of the gravitational component. As a result, there was a process of absorption of chemicals only in the lower part of the perforated supercollector. Punching was carried out by the booster unit UNG-8/15 using gas. Further, the calcium chloride solution was also pressed through with gas until the wellhead parameters were equalized. When using large volumes of chemical reagents, batch injections were performed in a volume of 3-4 m ^{3 of} each solution into the formation with alternation. Then, the bottom-hole zone of the treated section of the formation was fixed with cement mortar.

The method of selective treatment of the reservoir is implemented in wells No. 12213, 9193, the results of the RIR are shown in table 2.

Claims (4)

1. A method of selective treatment of the formation, comprising sequentially injecting into the formation a buffer liquid — an aqueous solution of a metal salt and a plugging composition with the formation of a water-insoluble compound — an alkaline precipitate in the formation environment with calcium ions, characterized in that the metal salt is used as an aqueous solution 10 -30% aqueous solution of sodium hydrogen sulfate, and as a tamponing composition - an aqueous solution of calcium chloride, each of these solutions is injected in equal portions, the volumes of which determined on the basis of the thickness of the reservoir and the diameter of the well or the absorption rate of the injected solutions. 2. The method according to p. 1, characterized in that in the reservoir with a permeability of 100 μm ^{2, the} specified sediment is fixed with a cement bridge. 3. The method according to p. 1, characterized in that the injection of solutions into the reservoir is carried out both in a stopped well and in a working well. 4. The method according to p. 1, characterized in that for the delivery of solutions in a given zone of perforation of the well and to ensure the estimated speed of injection using the number of tubing.