RU2270914C1 - Method for watered carbonate fractured porous waterproofed reservoir treatment - Google Patents

Abstract

FIELD: oil production industry, particularly for water isolation, oil inflow intensification and reservoir recovery increase.

SUBSTANCE: method involves preliminarily saturating highly-watered channels with coagulant, namely 20% calcium chloride solution; injecting buffer fresh water layer; supplying givpan, namely polyacrylonitrile fiber or web waste hydrolyzed in alkali; injecting fresh water and performing hydrochloric acid treatment by injecting mixture of hydrochloric acid and magnesium chloride heated to 85°C into well bottom zone. The magnesium chloride concentration in the mixture is 4.9-11.2%.

EFFECT: increased efficiency of reservoir treatment.

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Description

The invention relates to the oil industry, in particular to a technology for isolating water, intensifying the flow of oil and increasing oil recovery.

During the exploitation of carbonate deposits, various types of treatment are used to increase oil inflow into the wells: simple hydrochloric acid, thermoacid, foam acid, oil acid and others. Their experience has shown that with an increase in water cut of produced products by more than 20-50%, the efficiency of well treatments decreases sharply and their implementation becomes unprofitable.

Watering wells is usually associated with the creation of a water flooding system for productive reservoirs. Carbonate reservoirs are extremely heterogeneous in porosity and permeability. Under such conditions, most wells are quickly flooded. This process is further exacerbated due to fracturing of the formation. At the same time, water breaks through to the wells through cracks, and oil is not forced out of the porous elements of the formation (matrices). For oil production in such conditions, it is necessary to solve the problem of creating such methods of processing wells that simultaneously allow shutting off water channels, increasing the permeability of matrices, and ultimately reducing water flow and increasing oil production.

A known method of acid treatment of wells with preliminary injection of a solution of hydrolyzed polyacrylonitrile with a concentration of from 5 to 20 wt.% (Auth. Certificate No. 840309, 09/27/1979).

The disadvantage of this method is the reverse removal of the precipitate due to the gradual dissolution in desalinated water of an elastic mass of polymer capable of unlimited dissolution in water.

The closest method of the same purpose to the claimed invention in terms of features is a method of acid treatment of fractured-porous hydrophobized reservoirs with high water content, including saturation of high-water channels with an aluminum-containing coagulant liquid - waste from the production of isopropylbenzene, followed by pumping a buffer layer of fresh water, pumping hydrolyzed waste fiber or tissue polyacrylonitrile, and then the injection of fresh water and hydrochloric acid, moreover, as vecoagulant also noted the use of a 20% solution of calcium chloride (RF Patent No. 2171371, 07.27.2001).

The disadvantage of this method is the impossibility of efficiently extracting oil from hydrophobized matrices (porous elements of the formation), since the hydrophobic oil film (substrate) covering the pore surface prevents the contact of hydrochloric acid with carbonate rock, as well as the low reliability of overlapping highly porous channels and fractured water channels, due to the volatility of the content of aluminum chloride (playing the role of a coagulant) in the waste of an aluminum-containing liquid, which reduces the predictability of ultatov reduce water production and processing efficiency and, consequently, the inflow of oil into a well.

The objective of the invention is to increase the processing efficiency of hydrophobized fractured porous carbonate reservoirs with high water content.

This problem is solved by the fact that in the method for treating flooded carbonate fractured-porous hydrophobized reservoirs, which includes pre-saturating highly flooded channels with a coagulant — a 20% solution of calcium chloride, followed by pumping a buffer layer of fresh water and then polyacrylonitrile fiber or tissue hydrolyzed in alkali ( givpana), then the injection of fresh water and hydrochloric acid exposure, according to the invention, the hydrochloric acid effect is carried out by pumping into the bottomhole zone of a mixture of hydrochloric acid with magnesium chloride heated to 85 ° C at a concentration of 4.9-11.2% in the mixture. Alkaline hydrolyzed non-recyclable wastes of polyacrylonitrile fibers or fabrics (hydrolyzed fibrous polyacrylonitrile) is available and is manufactured by the Ufa Chemical and Industrial Complex Khimprom according to TU 49560-04-02-90 under the trade name Givpan, the physicochemical parameters of which are given in Table 1, or gipan "- hydrolyzed polyacrylonitrile having the same chemical formula as givpan.

Table 1
Physico-chemical characteristics of the givpan polymer No. Name of indicator Norm Test method one. Appearance Homogeneous water mass without mechanical impurities Visually 2. PH value 12-14 pH meter 3. Conditional viscosity, sec 160-200 device СПВ-5 four. Pour point, ° C Not higher - 20 GOST 5. Density at 20 ° С, g / cm ³ , within 1,060-1,150 Pycnometrically

To determine the gel-forming ability of a polymer with various coagulants under laboratory conditions, 3 series of experiments were carried out for the interaction of givpan:

1 - with aluminum-containing waste at 20 ° C (prototype);

2 - with a 20% solution of CaCl ₂ at 20 ° C;

3 - with a mixture of magnesium chloride with hydrochloric acid at 85 ° C at a different ratio of these components.

A generalization of the field experience of treating wells with polymers with coagulants shows that usually the polymer-coagulant ratio is 1: 1 or 2: 1, and only in rare cases, when processing highly fractured highly permeable reservoirs, a 3: 1 or 4: 1 ratio is used. When a larger amount of polymer is used in the PZP, almost instantaneous coagulation of the polymer occurs on contact with the coagulant, forming only a small film in thickness, which interferes with interpenetration, volumetric mixing of the reagents, and the production of a large amount of precipitation. As a result, this leads to a decrease in the technological efficiency of processing, and since a large amount of polymer is used, the economic efficiency with this technology is sharply reduced. Therefore, all three series of experiments were carried out with a polymer – coagulant ratio of 1: 1 to 4: 1. The experimental results are shown in table.2.

In the first and second series, the results of the experiments of the authors almost coincide with the results of the prototype (Pat. 2171371, table 3). It should be noted that when using an aluminum-containing liquid, the volume fraction of the gel decreases after 24 hours, i.e. sediment destruction occurs, which is explained by the presence in the aluminum-containing waste not only AlCl ₃ , but also compounds that destroy the precipitate formed, reducing its volume fraction.

Carrying out the 2nd and 3rd series of experiments showed that all structural changes end in 2-4 hours when using coagulants of stable composition (CaCl ₂ , MgCl ₂ ) in the present invention.

Comparing the results of experiments of series 1 and 2, we can conclude that after 1 hour of interaction, the proportion of the gel as a result of coagulation of the polymer (givpan) is slightly different and the technological efficiency of gelation is almost the same, but the gel formed after the interaction of givpan with CaCl _{2 is} more stable and its destruction in 24 hours not happening. Therefore, the invention proposes to pre-saturate the water ducts with a 20% solution of CaCl ₂ .

The results of the third series of experiments show that the best coagulant is a mixture of magnesium chloride with hydrochloric acid, heated to 85 ° C. From table 2 it is seen that the volume fraction of the gel in this case is 1 hour - 0.5, which is higher than when using calcium chloride 1.67 times or 1.92 times than when using aluminum-containing liquid.

The method is as follows.

After the technological preparation of the well, the absorptive capacity (injectivity) of the reservoir is determined by pumping formation water by the pump unit along the tubing with a packer or annular annular space of the production string, the flow rate of injected water (m ³ / h) and injection pressure are measured at different speeds of the unit. Then, the required volume of an aqueous solution of calcium chloride of 20% concentration is pumped into the tubing to saturate the reservoir cracks. Pumped buffer layer of fresh water 0.5 m ³ and hydrolyzed in alkali fiber or polyacrylonitrile waste 4-5 m. Next pumped buffer layer of fresh water in a volume of 0.5-1.0 m and then a mixture of hydrochloric acid heated to 85 ° C with magnesium chloride.

Get a mixture of hydrochloric acid with magnesium chloride as follows.

The reaction tip (container), in which magnesium is loaded on the surface, descends on the tubing into the well in the interval selected for processing. Through the tubing, 15% hydrochloric acid is pumped through the tip. The pumping rate is selected so that the reaction products are heated to 85 ° C. This is possible when pumping 70 liters of acid per 1 kg of magnesium. This results in 3.92 kg of pure MgCl ₂ , and the residual concentration of hydrochloric acid is 11%.

Conducted hydrochloric acid exposure can be divided into two phases. The first phase is a thermochemical effect, in which hydrochloric acid, reacting with magnesium, heats the pumped solution and the surface of the face to 85 ° C. The introduction of heated MgCl ₂ into the coagulation zone causes an accelerated completion of the reaction with the unreacted polymer and its additional coagulation, as a result of which the sediment fraction increases, its structure is strengthened, and pore and fracture water supply channels are more reliably closed. As a result, accelerated cross-linking with the help of polymer and hot coagulant occurs in the bottom-hole zone of individual collector blocks cut by cracks into a single mass and overlapping highly permeable water-conducting cracks. At the same time, part of the hot hydrochloric acid solution of residual concentration enters, as the water supply channels overlap, into the zone with the hydrophobized surface of the pore channels, melting hydrocarbon sediments in them. In addition, due to a sharp decrease in surface tension at an elevated temperature at the oil - rock - acid solution interface, surface hydrophilization occurs with the hydrophobized layers of heavy oil hydrocarbons being rejected into the pore space. These processes make it possible to increase the reaction area of hydrochloric acid with the surface of pores in the matrices.

The second phase of the acid effect is the usual hydrochloric acid treatment of PZP, but it is more effective due to the influx of high temperature hydrochloric acid only into the pore part of the matrices (excluding highly permeable and fractured water-conducting parts of the collector blocked by a coagulated polymer). The use of hot acid makes it possible to increase efficiency due to the acid effect on the porous, previously hydrophobized surfaces of the reservoir matrices and to increase oil production from them.

At the final stage of the treatment, the injected reagents are sold in the BCP with anhydrous oil or produced water and the well is closed for up to 24 hours. After coagulation and acid reaction with the rock is completed, the packer is torn off, the well is washed with technical water by backwashing, and the tubing with the packer is lifted. Then they lower the pump, develop the well and put it into operation.

Known methods for calculating the parameters of well treatment (for example, Shchurov VI, "Technology and Technique for Oil Production", M .: Nedra, 1983), with which, given the specific conditions of the well, it is possible to calculate the main parameters of the process of thermochemical treatment: the required amount of salt acid, metallic magnesium, acid injection rates to maintain a given temperature, the amount of heat generated.

In addition to these calculations, using the present invention, we calculate the mass of MgCl _{2 formed} and its concentration in solution.

So, when processing a well, after the described sequential injection of coagulant, water, polymer and a buffer volume of water, a hydrochloric acid solution is pumped through a special tip with magnesium (at least 40 kg). The following reaction proceeds:

Mg + 2 · HCl + H ₂ O = MgCl ₂ + H ₂ O + H ₂ +461.4 kJ

From the equation it follows that for the dissolution of 1 kg of magnesium is required:

V = 3004 / 161.2 = 18.61 L of an 18% HCl solution, with 18987 kJ of heat being released (Shchurov V.I., p. 146).

In the reaction, 1 kg of magnesium to maintain the temperature of the reaction products at 85 ° C requires pumping through the tip of 70 l of 18% hydrochloric acid (Schurov V.I., ibid.), And for the reaction of 40 kg of magnesium it is necessary to pump 2800 l of acid ( V _acid = 70 L · 40 = 2800 L = 2.8 m ³ ).

In this case, a significant amount of heat is released:

18987 kJ · 40 = 759480 kJ or 759.48 MJ of heat.

It can be seen from the equation that when 1 kg of Mg is dissolved, 3.92 kg of pure magnesium chloride is obtained, and when 40 kg is dissolved, 157 kg of magnesium chloride in 2800 liters are obtained, i.e. the concentration of the resulting solution of magnesium chloride is 157 / 2.8 = 56.07 kg / m ³ or 56.07 g / L.

The introduction of heated MgCl ₂ accelerates the reaction with the unreacted polymer and additional coagulation, as a result of which the proportion of sediment increases, its structure is hardened and pore and fractured water channels are more reliably closed. As a result, accelerated cross-linking with the help of polymer and hot coagulant occurs in the bottom-hole zone of the individual collector blocks dissected by cracks into a single mass and overlapping highly permeable water-conducting cracks.

At the same time, the use of hot acid allows one to increase the efficiency of acid exposure on porous hydrophobized surfaces of the collector matrices and increase oil production from them.

In reference manuals for calculating the parameters of hydrochloric acid treatment, it is recommended to use 1 m ^{3 of} 18% hydrochloric acid per 1 m of effective formation thickness. For low-power conditions of carbonate reservoirs is usually recommended to use 6 m ³ of the acid solution for thick layers of up to 6 m. Then for givpano thermoacid-exposure after the reaction with magnesium, 2.8 m ³ of the acid solution will have a residual concentration of 11% at a temperature of 85 ° C, which contains 157 kg of MgCl ₂ . The remaining part of the acid solution (3.2 m ³ ) entering the reservoir has a concentration of 18%.

The method was tested on high-water well watering wells of the Kopey-Kubovskoye field of Bashkortostan. When choosing a well for processing, the duration of its operation at pressures below the saturation pressure was taken into account, which promotes the formation of a dense hydrocarbon film and hydrophobization of the pore surface of the carbonate formation. The method allowed to obtain savings, which is formed by creating a better closure of water-permeable channels, more effective exposure to heated hydrochloric acid, which is expressed by providing additional oil and reducing the selection of associated produced water.

Examples of well treatment by the proposed method with high water cut of products (80-86%) and data on the prototype are shown in table 3. Compliance with the technological parameters during the treatment of the bottom-hole zones of the proposed method allows to provide a significant technological effect. The effectiveness of the SCR and the comparison of the results from the performed treatments according to the prototype and the invention are given in table 4. According to the prototype, additional oil production at OPZ No. 1 and 2 is given for 14 months, although the effect of the treatments continued. According to the invention, the duration of the effect on treatments No. 1 and 2 is also more than 14 months. To compare the results of the SCR, the amount of additional oil production in both cases was calculated for 14 months of well operation after treatment, although the effect on them continued. For the remaining refineries, additional oil production is calculated before the end of the effect, if the duration is less than 14 months. As a result, according to the prototype, the average value of additional oil production is 379.5 tons per well. The same indicator according to the invention is 496.2 tons, which is 1.3 times more than the prototype.

The method is recommended for processing wells developing fractured porous hydrophobized reservoirs with high water cut and operated at bottomhole pressures below the saturation pressure.

table 2
Gel-forming properties of the compositions Experiment Series Number The ratio (givpan: aluminum-containing waste) at 20 ° C The concentration of AlCl ₃ in the mixture,% The volume fraction of the gel at the following intervals 1 hour 24 hours Gelation using reagents of the prototype one 4: 1 5.2 0.50 0.38 3: 1 6.5 0.50 0.34 2: 1 8.5 0.42 0.32 1: 1 12.6 0.26 0.20 Givpan gelling with CaCl ₂ used in the invention for pre-saturation of the collector with calcium chloride 2 (givpan: 20% CaCl ₂ solution) at 20 ° C The concentration of CaCl ₂ in the mixture,% The volume fraction of the gel at the following intervals 1 hour 2 hours 4 hours 24 hours 4: 1 4.2 0.50 0.50 0.55 0.50 3: 1 5.3 0.45 0.50 0.45 0.50 2: 1 6.9 0.35 0.35 0.40 0.40 1: 1 10,4 0.30 0.35 0.35 0.40 Gelation of givpan with a mixture of HCl and MgCl ₂ used in the invention for additional gelation at the final stage of polymer coagulation and temperature increase in the pore space of a hydrophobized carbonate reservoir 3 (givpan: mixture of HCl and MgCl ₂ ) at 85 ° C The concentration of MgCl ₂ in the mixture,% The volume fraction of the gel at the following intervals 1 hour 2 hours 4 hours 4: 1 4.9 0.72 0.72 0.75 3: 1 5.1 0.67 0.75 0.75 2: 1 7.6 0.65 0.70 0.70 1: 1 11.2 0.50 0.60 0.65

Table 4
SCF effectiveness SCR Number Oil production, t / day Water cut,% Additional oil production, t Duration of effect, months * Reduction in water production, m ³ The duration of the effect, months Before SCF After SCF Before SCF After SCF According to the prototype one 1,0 3.0 84.2 48.9 795 fourteen - - 2 1,1 2,4 91.0 75.0 563 fourteen - - 3 1.9 4.0 65.5 53.0 32 3 - - four 1,2 2.2 91.7 91.0 128 5 - - Total 1.3 2.9 83.1 67.0 1518 9 - - According to the invention one 0.8 2,8 86 68 760 fourteen 397 24 2 0.8 2.9 85 59 950 fourteen 339 fourteen 3 0.8 1,6 80 64 133 10 171 24 four 0.2 0.8 85 46 142 eleven 88 12 Total 0.7 2.0 84.0 59.3 1985 12.3 995 18.5 * Note. Since the prototype gives the effect of additional oil production for 14 months, then according to the invention the effect is also calculated for this period.

Claims (1)

A method of treating flooded carbonate fractured-porous hydrophobized reservoirs, comprising pre-saturating highly flooded channels with a coagulant — a 20% solution of calcium chloride, followed by pumping a buffer layer of fresh water and then polyacrylonitrile fiber or tissue hydrolyzed into the alkali, injecting fresh water and hydrochloric acid characterized in that the hydrochloric acid effect is carried out by pumping into the bottomhole zone a mixture of hydrochloric acid with chloris heated to 85 ° C with magnesium at its concentration in the mixture 4.9-11.2%.