RU2382174C1 - Well absorption zone sealing method - Google Patents

Abstract

FIELD: oil-and-gas industry.

SUBSTANCE: well absorption zone sealing method includes viscoelastic composition and cement slurry gradual pumping into the well, at that pump into the well absorption zone a reagent concentrated water solution, which able to create a three dimension structure in the reservoir, and then the cement slurry, solving with the reagent thin water solution. Use following reagents for the three dimension structure creation in the reservoir: chloride aluminium, carbamide, urotropin, at the following components ratio wt %: chloride aluminium - 4-8, carbamide - 5-30, urotropin - 0-6, the rest is water. As cement grouting liquid used 3-20 times reagent water solution.

EFFECT: well absorption zones sealing efficiency increase.

2 cl, 3 tbl

Description

The invention relates to the oil industry, in particular to the isolation of absorption zones in the well, both during the elimination of rejects in drilling after cementing the casing, and during overhaul.

A known method of isolating the absorption zones in the well (US Pat. No. 2141029, publ. 10.11.99, BI No. 31), including the injection of a water-swelling polymer, however, the effectiveness of this method is insufficient.

Known compositions for blocking aquifers, for isolating absorption zones and permeable layers, for shutting off the layers (respectively, US Pat. No. 2142422, publ. BI No. 1, 1999; US Pat. No. 2120547, publ. BI No. 29, 1998), containing sawdust as a filler, pre-impregnated with special solutions, or sawdust modified with a suspension of magnesium powder, etc. However, all these compositions have low mechanical strength, and in the case of creating alternating depressions in the well, they are washed out of the pores.

Also known compositions (US Pat. No. 2120538, publ. BI No. 29, 1998; Pat. No. 2107156, publ. BI No. 8, 1998), including polyacrylamide (or another water-soluble polymer) and various fillers: bentonite , clay powder, bromel, etc.

Closest to the proposed is a method of isolating the absorption zones in the well (US Pat. No. 2111337 of the Russian Federation, IPC EV 33/13, publ. BI No. 14, 1998), which includes sequential injection into the well of the absorption zone of a viscoelastic composition and then cement mortar. However, this method requires mandatory exposure of the viscoelastic composition in the well to gelation, which increases the repair time, therefore, its cost. The disadvantages are also low mechanical strength, insufficient, for example, for fixing weakly cemented and crumbling rocks or for building cement stone behind the casing; low penetration, not providing long-term overlap of the pore channels of the absorbing layers or cracks in the cement stone behind the casing; multicomponent (more than three) compositions and the complexity of their preparation.

The objective of the invention is to provide a method for isolating the absorption zones in the well, capable of permanently plugging pores and cracks in the absorbing formation, cracks in the annular cement stone with sufficiently deep penetration into them and possess the necessary mechanical strength (after hardening), successfully resisting operational loads due to temperature changes in well and works in it with alternating depressions.

The technical result is achieved by sequentially injecting into the absorption zone of the well a concentrated aqueous solution of reagents capable of forming a three-dimensional structure in the formation, and then a cement mortar that is shut on a dilute reagent solution. As reagents for the formation of a three-dimensional structure in the formation, aluminum chloride, urea and urotropine are used in the following ratio, wt.%:

Aluminum Chloride 4-8

Carbamide 15-30

Urotropin 0-6

Water - Else

As a liquid mixing cement use a concentrated aqueous solution of reagents, diluted 3-20 times.

To prepare a concentrated reagent solution capable of forming a three-dimensional structure in the formation, aluminum chloride and urea, or aluminum chloride, urea and urotropine, the amount of which is selected depending on the reservoir temperature, are dissolved in water (Table 2). The obtained concentrated aqueous solutions of the reagents are divided into two specific parts (portions): the first part is used to obtain a three-dimensional structure in the formation, and the second part, after 3-20-fold dilution with water (depending on the absorption capacity of the well), is used as a grouting cement .

The technical result - depending on the absence or presence of a defect (not tightness) of the casing - is achieved as follows:

a) if there is no defect in the column, technological holes are created by any perforation method, water throttle response is determined, sequentially injected: 1.5-5.0 m ^{3 of} concentrated aqueous reagent solution, cement mortar in which cement is closed with an aqueous reagent solution diluted with water in 3-20 times, in the amount of 0.1-0.5 hour injectivity of the well (the amount of concentrated reagent solution capable of forming a three-dimensional structure in the formation, as well as the rate of dilution for the cement mixing process, select ayutsya depending on the absorption intensity);

b) if there is a defect in the column, all the work listed in paragraph a) is carried out without creating technological holes.

The method was tested in field conditions both in wells with defects in production casing and in wells without defects. At the same time, repeated attempts to eliminate the absorption by the prototype method did not lead to positive results.

The process at the well is carried out in the following sequence. After determining the geometric characteristics of the absorption zone of the well and its injectivity, the necessary total volume of a concentrated aqueous solution of reagents capable of forming a three-dimensional structure in the formation for a given temperature threshold of the well is calculated. After preparation, part of the required volume of the concentrated reagent solution is pumped into the well (in the tubing, lowered to the technological holes, or to the place of the defect of the production string) and followed by a cement mortar. To obtain a cement mortar, the remainder of the concentrated reagent solution diluted as many times as necessary is used as a mixing liquid. Then, all injected solutions are forced into the reservoir by a squeezing fluid with a volume equal to the internal volume of the tubing. The well is left alone at a pressure equal to the burst pressure for the time required to harden the cement.

When the cement slurry is not raised to the design height due to its (solution) absorption by the formation, with the technical feasibility of building up the cement stone from the mouth, proceed as follows. They pressurize the annular space with water and, having determined the geometric characteristic of the absorption and absence of cement stone zones, calculate the necessary total volume of a concentrated aqueous solution of reagents capable of forming a three-dimensional structure in the formation for a given temperature threshold of the well and the volume of cement mortar (Table 3). Having prepared the required volumes of a concentrated aqueous solution of reagents and a solution diluted a required number of times, a concentrated aqueous solution of reagents capable of forming a three-dimensional structure in the formation and cement grout mixed in a diluted solution are pumped sequentially into the annulus of the well. Squeezing a concentrated aqueous solution of reagents capable of forming a three-dimensional structure in the reservoir, and a cement mortar prepared on its basis, is carried out by squeezing liquid with a volume equal to the required (technical specifications, well construction project) volume of free annular space above the cement mortar.

In both described cases of elimination of absorption and marriage to a concentrated aqueous solution of reagents capable of forming a three-dimensional structure in the formation, the role of a reducer of the absorption capacity of the formation is assigned.

A concentrated aqueous solution of reagents creates a screen in the pore space of the absorbing formation, which prevents the dispersion and erosion of the grouting mixture throughout this formation; the mortar diluted to the required multiplicity on which the cement is cemented increases the initial viscosity of the cement mortar (increasing in time the more intensively, the lower the dilution rate of the mortar on which cement is cemented), reduces the filtration capacity of this cement mortar, increases the stability of the insulating barrier.

As can be seen from the data given in table 1, when using the prototype, the absorption began at 4.0-8.0 MPa, and when using the proposed method, there is no absorption at a pressure of up to 15.0 MPa.

Thus, the advantages of this method are:

- no need to prepare plugging mixtures with inert fillers to reduce the intensity of the injectivity of the absorbing layer;

- reducing the time for gelation of a viscoelastic composition in the well, which reduces the repair time (elimination of marriage);

- the ability not to use quick-setting mixtures (BSS), which in the event of unforeseen stops during their preparation and pumping at the intended interval can lead to sticking of the filling pipes;

- with a sharp unforeseen drop in injectivity when injecting the composition into the intended interval to the minimum value (300-400 dm ³ / min = 18-24 m ³ / h), excess composition and cement mortar can be washed out of the well by backwashing without the risk of sticking of the filling pipes;

- high stability of the insulating barrier.

table 2 Name of components For reservoir temperature, ° С twenty 40 60 80 Aluminum chloride four four four 8 Urea 16 fifteen 16 thirty Urotropin 6 four 2 - Water 74 77 78 62

Claims (2)

1. The method of isolating the absorption zones in the well by sequentially injecting a viscoelastic composition and a cement slurry into the well, characterized in that a concentrated aqueous solution of reagents capable of forming a three-dimensional structure in the formation is pumped into the well absorption zone, and then a cement solution closed on a dilute reagent solution , while as the reagents for the formation of a three-dimensional structure in the formation using aluminum chloride, urea and urotropine in the following ratio, wt.%:
Aluminum chloride 4-8 Urea 15-30 Urotropin 0-6 Water rest 2. The method according to claim 1, characterized in that the cement reagent is diluted 3-20 times with an aqueous solution of the reagents.