RU2187635C1 - Method of cleaning of bottom-hole formation zone - Google Patents

Abstract

FIELD: oil producing industry, particularly, methods of cleaning of bottom-hole formation zone from colmatant and asphalt-resinous-paraffin accumulations. SUBSTANCE: method includes successive injection into bottom-hole formation zone of gas- evolving solution and aqueous solution of hydrochloric acid forming carbon dioxide as result of reaction; process holding for reaction and pressure drop at bottom hole. Gas-evolving solution is used in form of aqueous solution of neutral salt of carbonic acid. After process holding, pressure is built-up at bottom hole corresponding to supercritical state of carbon dioxide with subsequent pressure drop at bottom hole. EFFECT: higher efficiency of cleaning and safety in operation. 3 dwg

Description

 The invention relates to the oil industry, in particular to methods for cleaning the bottom-hole formation zone (PZP) from colmatant and asphalt-tar-paraffin deposits.

 There is a method of cleaning the bottom-hole zone of the formation, which includes sequential injection of a gas-emitting solution and an aqueous solution of hydrochloric acid into the bottomhole formation zone, which produce carbon dioxide as a result of the reaction, technological exposure to the reaction, and pressure relief at the bottom of the well (1).

 In the known method, the effect of the treatment is obtained from the temperature released during the reaction. At the same time, it is extremely difficult to regulate the temperature distribution over the treated area.

 The method is significantly laborious in the implementation and regulation of the process due to the reaction in 2 stages.

 High pressures (up to 20 MPa) generated during the reaction are hazardous from a safety point of view.

 The purpose of the invention is to increase the efficiency of the method and the safety of its implementation.

 The goal is achieved by the fact that in a method comprising sequentially injecting a gas-emitting solution and an aqueous solution of hydrochloric acid into the bottomhole formation zone, forming carbon dioxide as a result of the reaction, technological exposure to the reaction and depressurization of the bottom hole, an aqueous solution of medium salt is pumped into the bottom-hole zone carbonic acid, after technological exposure at the bottom of the well, create a pressure corresponding to the supercritical state of carbon dioxide, followed by depressurization of the bottom.

Carbon dioxide (CO ₂ ) at certain values of temperature and pressure goes into a new phase state. The gas property acquired during this transition is characterized by significant density fluctuations, while its viscosity remains the same. Carbon dioxide acquires the property of a strong solvent.

 At the same time, it becomes possible to use this state and the property of carbon dioxide in the processes of suffusion (leaching) of deposits from the porous PZP environment, in particular in the processes of cleaning the bottom-hole zone of the formation from colmatant and asphalt-resin-paraffin deposits.

The minimum value of pressure and temperature (critical point) necessary for the gas to go into a supercritical state is 31 ^o С and 7.5 MPa (2).

 It is known that carbon dioxide can be generated directly in reservoir conditions.

As a result of a chemical reaction between the aqueous solutions of the middle salt of carbonic acid and hydrochloric acid injected into the PPP, CO _{2 is formed} . As the middle salt of carbonic acid, for example, calcium carbonate CaCO ₃ or sodium carbonate Na ₂ CO ₃ can be used.

 Laboratory studies were conducted of the effect of carbon dioxide generated under formation conditions at various pressure levels on the process of cleaning the bottom-hole formation zone.

 Figure 1 shows a diagram of the reservoir model of the reservoir.

 The model consists of a vacuum line 1, a column with a two-layer model of a porous medium 2, a column casing 3, model pressure gauges 4, valves 5, a PVT bomb 6, a bomb casing 7, a separation piston for a PVT 8 bomb, a barrel for displacement fluid 9, a distribution manifold 10, metering pump 11, ultra-thermostat 12, pressure sensors 13, recorders 14, pressure regulator 15, beakers 16.

 A bulk model of the porous medium was prepared by vibration packing of a steel column with a diameter of 0.032 m and a length of 1.0 m. Part of the porous medium was composed of quartz sand (90%) and montmorillonite clay (10%), and the initial section (1/3 of the volume) was filled from mixtures of silica sand and silica dust.

Transformer oil was used as a model of oil. The experiments were carried out with thermostating of the system at a temperature of 32 ^o C. A qualitative assessment of the hydrodynamic state of the system after cleaning was carried out by taking pressure recovery curves (HPC). At all stages of the experiment, the HPC was taken at a pressure drop ΔP = 2.0 MPa (P _input = 10.0 MPa; P _output = 8.0 MPa).

 After tying the experimental setup and saturating it with transformer oil, the background HPC was taken on an uncontaminated initial section of the porous medium (Fig. 2, curve 1). Then artificial contamination of the initial section of the porous medium with asphalt-resin-paraffin oil (30%) was carried out in an amount equal to 0.3 of the pore volume of the model. Again made the removal of the HPC (figure 2, curve 2).

In order to clean the zone of the initial section, a portion of a 15% aqueous solution of sodium carbonate and a 12% aqueous solution of hydrochloric acid in equal volumes were sequentially pumped to the model inlet. Under injection pressure, the system was left to react (technological shutter speed). After technological exposure to the response, the system was pressurized to a certain level (4 series of experiments) - P _1inx = 7.0 MPa; P _2in = 8.0 MPa; P _sv = 9.0 MPa; P _4in = 10MPa.

 In each experiment, when the pressure drop was recorded, the pressure at the inlet to the model was released to atmospheric pressure and the volume was measured using a beaker.

Then, in order to assess the hydrodynamic state of the system after cleaning and to compare the results of the experiments, after each of the four experiments, an HPC was taken (ΔP = 2.0 MPa; P _input = 10 MPa; P _out = 8 MPa; Fig. 2, curves 4,5,6 , 7).

For experience: P _1in - curve 7; P _2in - curve 6; P _3in - curve 5; P _4in - curve 4.

 For comparison, a portion of a 12% hydrochloric acid solution was pumped into the input of a contaminated model. After technological exposure, a pressure of 10.0 MPa was created in the system, and when fixing the pressure drop in the system at the model inlet, the pressure was reduced to atmospheric.

After that, the HPC was removed at ΔP = 2.0 MPa; P _input = 10.0 MPa; P _o = 8.0 MPa (figure 2, curve 3).

In FIG. 2 illustrates a series of experimental HPCs (P ₁ — output pressure change). As can be seen from the results of the experiment, the pressure recovery time after treatment of a contaminated reservoir model with CO ₂ -generating solutions is different, depending on the level of pressure created at the model inlet after technological exposure.

It is obvious that the pressure recovery time after treatment with hydrochloric acid medium is less than in a contaminated environment, but much greater pressure recovery time after processing model CO ₂ - generating solutions.

To compare the results of HPC during the treatment of a porous medium with CO ₂ generating solutions, Fig. 3 shows the dependence of the rate of change of pressure on the level of pressure created after technological exposure. As can be seen from the curve, the highest rate of pressure recovery is observed at the inlet pressure P _2in = 8.0 MPa.

Thus, the thermobaric conditions for the manifestation of the supercritical properties of CO ₂ significantly affect the hydrodynamic characteristics of the porous medium.

 The method at the well is carried out in the following sequence.

 The corresponding volumes of aqueous solutions of a medium carbonic acid salt and an acidic solution are prepared at the solution site or wellhead.

An aqueous solution of a medium salt of carbonic acid, for example, Na ₂ CO ₃ , is pumped with a pump unit with a closed annulus into the tubing, the shoe of which is installed at the upper holes of the filter. Then, a buffer liquid, such as water and an aqueous solution of hydrochloric acid, is pumped into the well. Injected fluids are pushed into the bottom-hole zone with water, and the well is left at rest at the injection pressure (technological exposure).

 Technological exposure is considered complete after fixing, according to the reading of the wellhead pressure gauge, the beginning of the fall, which increased during the in-situ pressure reaction.

 After technological exposure on the bottom of the well create a pressure corresponding to the supercritical state of carbon dioxide (minimum - 7.5 MPa).

 The change in pressure at the wellhead is recorded and, when it decreases, the pressure at the wellhead is sharply dropped, thereby relieving pressure at the bottom, causing the removal of sediment from the bottomhole zone into the well.

Sources of information
1. RF patent 2068086 E 21 V 43/27, 1996.

 2. Ibragimov G.Z., Sorokin V.A. and others. Chemical reagents for oil production. Reference worker. M .: Nedra, 1986, p. 207.

Claims (1)

 A method of cleaning the bottom-hole zone of a formation, including sequentially injecting a gas-emitting solution and an aqueous solution of hydrochloric acid into the bottom-hole zone of the formation, which produce carbon dioxide as a result of the reaction, technological exposure to the reaction and depressurization of the bottom of the well, characterized in that as a gas-emitting solution into the bottom-hole zone the reservoir is injected with an aqueous solution of a medium salt of carbonic acid, after technological exposure at the bottom of the well create a pressure corresponding to the supercritical state carbon dioxide, followed by pressure relief at the bottom of the well.

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