RU2554975C1 - Method of water production zone isolation in well - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: method of water production zone isolation in a well involves sequential injection of coagulation agent (25% solution of calcium chloride), buffer layer of fresh water, and Givpan acrylic reagent. Additionally, polyethylene terephthalate production waste product, PET with low polymerisation degree, is added to Givpan as a filler in amount of 18-24 wt %.

EFFECT: reduced core permeability.

1 dwg, 7 tbl, 3 ex

Description

The invention relates to the oil and gas industry, in particular to methods used to isolate water inflows into the well.

Known methods for isolating water inflow zones into a well by pumping compositions based on water glass (sodium silicate) with additives of various mineral and organic substances and water (RF patent No. 2494225, C09K 8/50, publ. 09/27/2013, bull. No. 27; No. 2494229, C09K 8/50, publ. 09/27/2013, bull. No. 27).

A common disadvantage of these methods is the low efficiency of isolation of water inflow due to the low structural and mechanical properties of the compositions.

Known methods of isolating zones of water inflows, carried out by injection into the well of compositions based on cement mortars (RF patent No. 2504640, E21B 33/138, publ. 01.20.2014, bull. No. 2; No. 2352766, E21B 33/138, publ. 20.04 .2009, bull. No. 11; No. 2209928, E21B 33/13, publ. 10.08.2003).

The disadvantages of these methods are the low filterability of cement mortars, a small depth of penetration into the reservoir, as well as insufficient mechanical strength, often leading to cracking of the stone during repeated perforation, etc.

The closest in technical essence and the achieved result is a method of isolating water inflow zones into a well, including preliminary injection of a coagulant - a 20% solution of calcium chloride, followed by pumping of a buffer layer of fresh water and hydrolyzed waste fiber or polyacrylonitrile tissue (givpan), then pumping fresh water and hydrochloric acid exposure (RF patent No. 2270914, E21B 43/27, publ. 02.27.206, bull. No. 6). Givpan-based polymer compositions have a low density, good adhesion to metal and to rock of the collector, are resistant to corrosion, and also have high filtration ability [Shaidullin V.A. The use of polymer-acid exposure in low atmospheric temperatures // Engineering practice. - 7. - 2011. - P.72-74].

The disadvantage of the prototype is the lack of effectiveness of the method associated with a low initial concentration of the coagulant, which does not fully provide polymerization of givpan due to dilution of the solution with a buffer, as well as a slight decrease in the permeability of the rock during the implementation of the method.

The objective of the invention is to increase the efficiency of isolation of zones of water inflow into the well.

The problem is solved in that in a method for isolating water inflow zones into a well, which includes sequential injection of a coagulant — a solution of calcium chloride, a buffer layer of fresh water, and polyacrylonitrile (givpan) wastes hydrolyzed in alkali — 25% calcium chloride solution is used as a coagulant, additionally, waste of production of polyethylene terephthalate (PET) - PET with a low degree of polymerization at the rate of 18-24 wt.% is introduced into the givpan as a filler.

The PET waste, which is the product of the incomplete polymerization of PET, is non-toxic, water-insoluble and chemically neutral with respect to the reagents used.

Hydrolyzed in alkali waste polyacrylonitrile fibers or fabrics are produced according to TU 2216-001-04698227-99 under the trade name "Givpan". Physicochemical parameters for givpan polymer are given in table 1.

A mixture of givpan with PET waste is obtained by mechanical stirring in a mixer for 10 minutes.

The effectiveness of the method was evaluated in laboratory conditions by filtration through bulk and artificial core samples.

To study the filtration processes, an installation was designed to keep a constant pressure drop, the circuit diagram of which is shown in the drawing. The installation contains a gas cylinder for pumping the investigated compounds 1, a gas cylinder for lateral crimping of the core 2, gearboxes 3, manometers 4, a container for pumped liquids 5, a core holder 6, a graduated cylinder 7, valves 8.

The pressure on the lateral crimping of the core holder and at the entrance to the core holder through an intermediate container 5 containing the test compounds is created using nitrogen from cylinders 1 and 2. The pressure at the outlet of the core holder 6 is maintained at atmospheric level. The amount of liquid passed through the core is measured by a measuring cylinder 7. If it is necessary to create high temperatures, the core holder can be placed in a heating cabinet. Filtration of liquids through the core can be carried out in the forward and reverse directions with a constant pressure drop across the core sample.

Bulk cores were prepared as follows: a stopper with a tap for liquid drainage is screwed onto the outlet end of the core holder, then a grate and a grid for holding sand are installed, then 118 g of river sand is packed, it is carefully compacted and a grid with a grate is installed on it. A thrust ring is installed in the empty space and an inlet plug with a tap for fluid supply is screwed on.

Example 1. For the study prepared samples of artificial cores with different porosities: 19, 24 and 27%. The porosity of bulk cores was 34%. Water saturation of the cores was carried out with fresh water.

25 wt.% Solutions of calcium chloride (33 ml), buffer (11 ml) and a mixture of givpan (33 ml) with different percentages of waste were pumped sequentially through the cores: 6, 18, 24, 30 wt.%. Fresh water was used as a buffer. Processing efficiency was evaluated by reducing the core permeability coefficient. The calculation was made according to the Darcy formula [Gimatudinov Sh.K. Physics of the oil and gas reservoir. - M .: "Nedra", 1971]. The results of the study are presented in tables 2 and 3.

As can be seen from tables 2 and 3, the introduction of PET waste contributes to a significant reduction in core permeability due to mechanical clogging of pores. At the same time, the optimal waste content in givpan is 18-24 wt.%.

Example 2. The experiment was carried out according to the scheme of example 1. Calcium chloride solutions, a buffer and a mixture of givpan with waste (24 wt.%) Were pumped sequentially through the cores. The concentration of calcium chloride in solutions was 20 and 25%. The results of the study are presented in tables 4 and 5.

As can be seen from Tables 4 and 5, an increase in the concentration of calcium chloride contributes to a decrease in core permeability, which is explained by more complete polymerization of givpan.

Example 3. The experiment was conducted according to the scheme of example 1. Calcium chloride solutions, a buffer and a mixture of givpan with waste (24 wt.%) Were pumped sequentially through the cores. As a control, core samples processed according to the method specified in the prototype were examined. The results of the study are presented in tables 6 and 7.

As can be seen from table 6 and 7, the application of the proposed method of isolation of zones of water inflow into the well allows to achieve higher values of the reduction in core permeability compared to the prototype.

Thus, on the basis of the data obtained, it can be concluded that the most optimal is the method of isolating water inflow zones into the well, including sequential injection of a coagulant - 25% solution of calcium chloride, fresh water and a mixture of givpan with PET waste (18-24 wt. %).

Claims (1)

A method of isolating water inflow zones into a well, including the sequential injection of a coagulant — a solution of calcium chloride, a buffer layer of fresh water and givpan, characterized in that a 25% solution of calcium chloride is used; additionally, polyethylene terephthalate production waste — PET with a low degree of polymerization — is introduced into the givpan. from the calculation of 18-24 wt.%.