RU2111345C1 - Method of killing oil and gas wells - Google Patents

Abstract

FIELD: oil and gas production. SUBSTANCE: when killing wells, solution pumped into the well contains 0.4-0.8 wt.-% of polyacrylamide and is radialyzed by the dose 0.5 to 2.5 Mrad. Solution is forced through by column of liquid providing bottom pressure exceeding formation pressure. Before aqueous solution of radialyzed polyacrylamide is applied, demuding fluid is pumped in. The latter is forced through into formation by buffer liquid. Volume of demuding fluid is twice as large as that of buffer liquid. Volume of solution of radialyzed polyacrylamide is superior to that of demuding fluid by a factor 1.5-2.5. EFFECT: prevented pollution of productive zone of formation and reduced consumption of material. 1 tbl

Description

 The invention relates to the oil and gas industry and can be used for killing wells before carrying out repairs.

 A known method of killing wells, based on the crushing of polymers - thickeners of aqueous solutions, such as polyacrylamides [1].

The disadvantage of such stunning methods is that the polymers used in them create a high adhesive ability on the surface of the rock. This negatively affects the filtration characteristics of the bottomhole zone of the well. The bottomhole zone is clogged with a polymer solution and significantly reduces the productivity of the well after killing it. In addition, the preparation and use of aqueous polymer solutions in borehole conditions and at temperatures of -40 ^o or lower requires the use of special equipment, which significantly complicates and increases the cost of killing wells.

 Known methods of killing and blocking bottom-hole zones of wells using chemically cross-linked polymer materials, such as polyacrylamide and hypane [2].

 The disadvantages of these methods of jamming is that they use multicomponent liquids. The implementation of chemical crosslinking in near-well conditions requires an accurate dosage of chemical reagents throughout the volume of the solution. Such kill fluids have high adhesion to the rock surface and chemically cross-linked spatial structures are not stable over time against the effects of downhole temperature, mechanical mixing, and the preparation of such solutions at low temperatures and directly at the well is problematic.

The technical result of the invention is to prevent contamination of the productive part of the formation in the near-wellbore zone of the well, work at the wellhead at low temperatures (up to -40 ^o C) and reduce the consumption of polymer material.

 The necessary technical result is achieved by the fact that in the method of killing oil and gas wells by pumping into the well an aqueous solution of polyacrylamide, according to the invention, a solution containing 0.4-0.8 wt.% Polyacrylamide radiated by radiation with a dose of 0.5 is pumped into the well - 2.5 Mrad, which is squeezed into the bottom by a liquid with a column providing bottomhole pressure exceeding the reservoir pressure, and before pumping an aqueous solution of radialized polyacrylamide into the well, decolming liquid from the squeeze is pumped it is added to the reservoir with a buffer fluid, the volume of decolating fluid being two volumes of buffer fluid, and the volume of an aqueous solution of radialized polyacrylamide is 1.5 - 2.5 volumes of decolming fluid.

 Upon completion of the well repair, its development is carried out. After reducing the pressure in the wellbore, the buffer fluid, together with the decolming fluid, is brought to the surface under the influence of reservoir energy.

 When implementing this method, the formation is cleaned and the well production rate is increased, which reduces the downtime of the well and there is no need for additional technological operations to clean the formation. For the kill fluid, a γ-irradiated polyacrylamide is used with the qualities required for the kill fluid. It is obtained from an aqueous solution of polyacrylamide containing 0.4 - 0.8 wt.% Of the basic substance by irradiation with a dose of 0.5 - 2.5 Mrad. With this dose of radiation, the polyacrylamide solution acquires a gel-like, non-flowing structure that can swell in water without dissolving in it, increasing its volume by 6.8 - 10.8 times.

 When an aqueous solution of polyacrylamide is irradiated with less than 0.4 wt.% At an irradiation dose of 0.5 Mrad, the spatial structure does not form and the polyacrylamide does not lose its ability to dissolve in water.

 Radialized polyacrylamide obtained from a solution of polyacrylamide with a concentration of more than 0.8% or when irradiated with a dose of more than 2.5 Mrad forms a structure of a high degree of crosslinking and significantly loses the ability to absorb water, i.e. swell in water.

 This characteristic of polyacrylamide thus radiated is low adhesion to the rock, which is explained by the absence of free polar groups, due to which the formation of the bulk structure of the polymer occurred.

 The concentration of radialized polyacrylamide in water to obtain a buffer fluid is chosen so that after swelling it fills the entire wellbore in the interval of the productive part of the reservoir.

 For radialized polyacrylamide, this concentration is in the range of 0.3 - 1.0 wt.% Calculated on the dry matter.

 The table shows the results of studies of radialized polyacrylamide.

 An example of a specific implementation of the method.

 Before the repair, killing a well with a depth of 1640 m is carried out with a filter interval length of 100 m, the diameter of the production string is 146 mm. The reservoir pressure is 15.0 MPa.

First, decolming fluid is pumped into the well, for example, a 3-10% aqueous solution of sodium pyrophosphate Na ₄ P ₂ O ₇ or sodium orthophosphate Na ₃ PO ₄ and 0.2-1.5% surfactant in a volume of 5-10 m ³ at the volume of the wellbore 30 - 40 m ³ .

 The decolming liquid is isolated with a buffer liquid containing, depending on geological factors, either a 0.2 - 0.4% aqueous solution of a surface-active substance (SAS), or a 5 - 10% aqueous solution of methanol.

 Then, killing fluid is fed into the well, which pushes decolmating fluid into the formation. Killing fluid is an aqueous solution of radialized polyacrylamide.

 To create a bottomhole pressure, a weighted liquid is then pushed to the bottom of the well, the column of which in the well provides bottomhole pressure.

The volume of decolming fluid is equal to two volumes of buffer fluid, and the volume of the kill fluid (aqueous solution of radialized polyacrylamide) is 1.5 to 2.5 volumes of decolming fluid:
V ₁ = 2V ₂ ; V ₃ = 1.5 - 2.5V ₁ ,
Where
V ₁ - the volume of decolming fluid,
V ₂ - the volume of the buffer fluid,
V ₃ - the volume of the fluid kill.

 Thus, in order to create a bottomhole pressure exceeding the reservoir pressure, the kill fluid is pushed to the bottom of the well with a heavier fluid, the column of which in the well provides a bottomhole pressure of 16.4 MPa. Radialized polyacrylamide swells within a few hours, so pumping it and delivering it to the bottom of the well is not accompanied by complications. After swelling, radialized polyacrylamide fills the entire volume of the well and reliably separates the formation.

 This sequence of operations allows you to simultaneously clear the formation of mud and to kill the well without clogging it, because after the swelling of the radialized polyacrylamide, it fills the entire volume of the filter part of the wells and reliably separate the reservoir from the fluid on it.

Claims (1)

 A method of killing oil and gas wells by pumping an aqueous solution of polyacrylamide into a well, characterized in that a solution containing 0.4-0.8 wt.% Polyacrylamide radiated by irradiation with a dose of 0.5-2.5 Mrad, which they are pushed to the bottom with a liquid with a column providing a bottomhole pressure exceeding the reservoir pressure, and before the aqueous solution of radialized polyacrylamide is pumped into the well, the decolming fluid is pumped into the well with the buffer fluid being poured into the reservoir, the volume of decolming The amount of liquid in solution is two volumes of buffer liquid, and the volume of an aqueous solution of radialized polyacrylamide is equal to 1.5 - 2.5 volumes of decolating liquid.

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