RU2486334C1 - Method of high-viscosity oil development - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: in the method of development for high-viscosity oil deposit that includes stages of steam injection into injection well, productive stratum heating with creation of steam pocket, oil recovery through recovery well, pumping of produced water to injection well when project value of residual oil saturation is reached and steam injection is cancelled concentration of hydrocarbonate-ions is determined in produced water. Produced water with concentration of hydrocarbonate-ions of at least 3 g/l is subject to pumping into wells. When concentration of hydrocarbonate-is less than 3 g/l at temperature more than 100°C in a steam pocket carbamide is added into produced water. When temperature in the steam pocket drops below 100°C sodium, ammonium or potassium carbonate is added into produced water and these substances decompose with release of carbon dioxide gas under effect of heat accumulated in the steam pocket.

EFFECT: increase in efficiency of thermal-steam treatment during recovery of residual oil due to use of heat accumulated in the steam pocket when steam injection is terminated.

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Description

The invention relates to the oil industry, in particular to methods for developing high-viscosity oil fields using heat at a late stage of development.

There is a method of developing an oil deposit, which consists in the fact that when oil is displaced by steam, carbon dioxide is added to it - CO ₂ (patent Ca No. 2351148, IPC C10G 1/04; ЕВВ 43/16; Е21В 43/34; publ. 21.12.2002 ) The disadvantage of this method is that the application of the method in the field requires high costs associated with obtaining, transporting and supplying carbon dioxide to the injection well.

There is a method of developing deposits of high viscosity oils by heat and steam, including the injection of alternating rims of the reagent solution, under the influence of temperature decomposing with the release of carbon dioxide and steam (patent RU No. 2361074, IPC ЕВВ 43/24, С09К 8/52, publ. 10.07.2009, Bulletin No. 19). As said reagent used urea and additionally introduced into the solution of ammonium nitrate, ammonium thiocyanate, complex surfactant - Neftenol WSC surfactant or mixture of nonionic surfactants -12 _9-AF or NP-40 or NP-50, and anionic SAW volgonate or sulfanol, or NPS-6 in the following ratio of components, wt.%:

Urea 15.0-40.0 Ammonium nitrate 8.0-20.0 Ammonium Rodanisty 0.1-0.5 Neftenol VVD 1.0-5.0 Water rest

Or

Urea 15.0-40.0 Ammonium nitrate 8.0-20.0 Ammonium Rodanisty 0.1-0.5 Nonionic surfactant 1.0-2.0 Anionic surfactant 0.5-1.0 Water rest

The method is applied at the initial stage of development of an oil deposit and is carried out both through a steam injection well and through a production well, into which, after steam injection, the rim of oil is pumped and the specified well is kept for soaking for up to 14 days.

The disadvantages of the method are low efficiency at the late stage of development of deposits of high viscosity oils, as well as the multicomponent composition, which complicates the process of preparing the working solution in the field, prolonged shutdown of the well for treatment also reduces the efficiency of the steam and thermal exposure.

A known method of developing a field of heavy oil or bitumen using double-mouth horizontal wells, including pumping coolant through a double-mouth horizontal injection well, heating the reservoir with the creation of a steam chamber and selecting products through a double-mouth horizontal production well (patent RU No. 2340768, IPC ЕВВ 43/22, published on December 10, 2008, Bulletin No. 34.) This method is applied at the initial stage of development of an oil deposit and does not provide for a change in the thermodynamic conditions of the formation at her late stage of development.

Closest to the technical essence of the proposed method is a method of developing a highly viscous oil field, including pumping coolant into injection wells, oil extraction through production wells, pumping produced water to injection wells at a late stage of field development (patent RU No. 2114289, IPC ЕВВ 43 / 24, published on June 27, 1998). The coolant is injected cyclically into different groups of wells. After processing the bottom-hole zones of the oil reservoir, the selection of oil through production wells begins. At the next stage of development, simultaneously produced hot water is pumped into injection wells, which contributes to the advancement of the thermal rim both in area and in thickness of the formation.

The disadvantage of this method is the alternation of steam injection into injection wells with the selection of oil from production wells, which reduces the uniformity of heating the oil reservoir, which leads to a decrease in the efficiency of the steam-thermal process. Also, the disadvantage is that the pressure in the formation is not maintained after the injection of steam is canceled at a late stage of development, which reduces the effectiveness of steam and thermal exposure at a late stage of development.

The technical task of the invention is to increase the efficiency of heat and steam when extracting residual high-viscosity oil at a late stage of development due to the use of heat accumulated in the steam chamber (reservoir) after the termination of steam injection.

The technical problem is solved by the method of developing a highly viscous oil field, including injecting steam into the injection well, heating the reservoir with the creation of a steam chamber, taking oil through the producing well, injecting produced water into the injection well after reaching the design value of the residual oil saturation and canceling the steam injection.

What is new is that the concentration of bicarbonate ions in produced water is determined, the produced water is pumped with a concentration of bicarbonate ions of at least 3 g / l, and when the concentration of bicarbonate ions in produced water is less than 3 g / l at a temperature in steam urea is additionally introduced into the chamber at a temperature above 100 ° C; after the temperature in the steam chamber is lowered below 100 ° C, sodium or ammonium carbonate or sodium or potassium bicarbonate decomposed with the release of carbon gas under the action of heat accumulated in the steam chamber.

As a urea solution, a 40% solution of urea (NH ₂ ) ₂ CO in fresh water is used (GOST 2081-92). Urea under normal conditions is non-combustible, fire and explosion proof, in terms of exposure to the body, it belongs to substances of the 3rd hazard class.

As the hydrocarbonate and carbonate salts are used:

a) sodium bicarbonate - NaHCO ₃ (GOST 2156-76). At a temperature of 50-60 ° C, aqueous solutions of sodium bicarbonate decompose with the release of CO ₂ .

The solubility of sodium bicarbonate in water is small and with increasing temperature it increases: from 6.87 g per 100 g of water at 0 ° C, to 19.17 g per 100 g of water at 80 ° C;

b) potassium bicarbonate - KHCO ₃ (GOST 4143-78). The solubility of KHCO ₃ in water is 33.3 g per 100 g of solvent at 20 ° C. At 100-120 ° C or boiling aqueous solutions it decomposes into K ₂ CO ₃ and CO ₂ ;

c) ammonium carbonate - (NH ₄ ) ₂ CO ₂ (GOST 9325-79). Ammonium carbonates are colorless crystals that are readily soluble in water. They are very unstable, since even at room temperature they release ammonia, turning into ammonium bicarbonate NH ₄ HCO ₃ . At temperatures above 60 ° C, it quickly decomposes into NH ₃ , CO ₂ and H ₂ O. Ammonium carbonate begins to decompose already at 20 ° C with the release of ammonia and carbon dioxide;

d) sodium carbonate GOST 5100-85 - soda ash Na ₂ CO ₃ . The solubility of Na ₂ CO ₃ in water is 21.8 g per 100 g of solvent at 20 ° C. In an aqueous solution, sodium carbonate is hydrolyzed to form a hydrocarbonate ion.

The process of steam-thermal exposure is aimed at imparting mobility and extracting usually motionless high-viscosity oil. Initially, steam is injected into the injection well at a high viscosity oil field at a high speed, and as a result, a thermal connection is established between the injection and production wells and a steam chamber is created. At the chamber boundary, steam condenses and heat is transferred by conduction to colder surrounding areas. Using temperature sensors, the temperature in the steam chamber is periodically determined. Near the chamber, the oil temperature rises, and it flows with the hot vapor condensate to the producing well. Oil is continuously removed at a point below the steam chamber.

As the highly viscous oil field is depleted at a late stage of development and the design value of the residual oil saturation is reached, when the use of steam and thermal exposure becomes unprofitable, since high production costs of steam for oil production are required, steam injection is stopped. The content of bicarbonate ions (HCO ₃ ^- ) in the produced water is determined. Then, the produced water containing bicarbonate ions is injected through the injection well, which, under the action of heat accumulated in the steam chamber (formation), decomposes with the release of carbon dioxide (CO ₂ ). Gaseous carbon dioxide enters the steam chamber, replaces the condensed steam and thereby maintains the pressure in the steam chamber at the same level and prevents the collapse of the steam chamber after canceling the steam injection. Maintaining pressure in the steam chamber after the cessation of steam injection allows preserving the oil flow rate due to the effect of the gas pressure mode. In addition, part of the carbon dioxide dissolves in oil and thereby reduces the viscosity of residual high-viscosity oil. Together, these processes contribute to increasing the efficiency of the steam and thermal exposure during the extraction of residual high-viscosity oil.

In the reservoir, under the action of the heat of the steam chamber, solutions of urea or carbonate salts hydrolyze (decompose) to form carbon dioxide and ammonia or only carbon dioxide, respectively.

Urea (NH ₂ ) ₂ CO + H ₂ O ^t = CO ₂ + 2NH ₃ , Sodium carbonate Na ₂ CO ₃ + H ₂ O = NaHCO ₃ + NaOH Sodium bicarbonate 2NaHCO ₃ ^t = Na ₂ CO ₃ + CO ₂ + H ₂ O Potassium bicarbonate 2KHCO ₃ ^t = K ₂ CO ₃ + CO ₂ + H ₂ O Ammonium carbonate (NH ₄ ) ₂ CO ₃ + H ₂ O = NH ₄ HCO ₃ + NH ₄ OH Ammonium bicarbonate NH ₄ HCO ₃ ^t = NH ₃ + CO ₂ + Н ₂ О

Based on the equation for the decomposition of a bicarbonate ion under the influence of heat

2HCO ₃ ^-t = CO ₃ ^-2 + CO ₂ + H ₂ O

calculate the amount of carbon dioxide released under the action of heat from produced formation water. The results are shown in table 1.

As can be seen from table 1, when the content of the bicarbonate ion HCO ₃ ^- in the produced water 1-2 g / l is released under reservoir conditions, about 0.1 m ³ carbon dioxide. This amount of CO _{2 is} not enough to maintain pressure in the steam chamber, the volume of which is several thousand m ³ , and to reduce the viscosity of highly viscous oil. Therefore, when the concentration of bicarbonate ions in the produced water is less than 3 g / l, carbonate or bicarbonate salts or urea are additionally introduced into the produced water, decomposing under the influence of temperature with the release of carbon dioxide. At 20 ° C, the solubility of sodium bicarbonate is about 9 g per 100 g of water. Therefore, the working concentration of sodium bicarbonate solutions injected into the formation, taking into account the solubility, should not exceed 10% by weight.

Table 1 The amount of released CO ₂ from 1 m ³ formation water with a different content of bicarbonate ion The concentration of bicarbonate ion in the produced water, g / l The amount of released CO ₂ under normal conditions (NU), m ³ The amount of released CO ₂ in reservoir conditions, m ³ one 0.183 0,041 2 0.367 0,081 3 0.551 0.122 four 0.734 0.163 5 0.918 0,203 10 1,836 0.406 twenty 3.67 0.81 thirty 5.51 1.22 40 7.34 1,63 fifty 9.18 2.03 60 11.02 2.44 70 12.85 2.84 80 14.67 3.25 90 (8.3%) 16.52 3.66 300 69.00 17.0

Significant hydrolysis of urea begins at a temperature of 80 ° C and above. The solubility of urea is higher than the solubility of sodium bicarbonate and is: 51.8 (20 ° C), 71.7 (60 ° C), 95.0 (120 ° C) g in 100 g of solvent. The working concentration of urea solutions injected into the reservoir averages 40 wt.%. In addition, 0.23 m ³ CO ₂ is released from a urea solution with a concentration of 1 g / l under normal conditions (n.o.) (Table 2), and 0.18 m ³ is released from a solution of sodium bicarbonate with the same concentration CO ₂ i.e. 1.3 times more. When injecting working solutions of urea with a concentration of 40 wt.% (Which corresponds to a concentration of 667 g / l), nine times more carbon dioxide is released under reservoir conditions than when injecting a solution of sodium bicarbonate with a concentration of 8.3 wt.%. (or 90 g / l). Therefore, while the temperature in the steam chamber remains high enough (above 100 ° C), a urea solution is pumped. As the steam chamber cools and its temperature drops below 100 ° C, they switch to the injection of solutions of hydrocarbonate or carbonate salts, since their decomposition temperature is lower than that of urea. The choice of carbonate or bicarbonate salts is determined from the most favorable conditions for the supply of these reagents.

Case Study

The experimental section of the high-viscosity oil reservoir with a density of 960 kg / m ^{3 of the} Ashalchinskoye field is developed by the method of heat and steam using a pair of horizontal wells: production No. 232 and injection No. 233. Temperature sensors were launched into the wells along the entire length of the shafts, which made it possible to control the temperature of the steam chamber. During the production of high-viscosity oil in the initial stage of development, steam is pumped into the injection well, as a result a steam chamber is formed with a temperature of 190 ° C. The selection of oil is carried out through a producing well. No. 232, the average daily oil flow rate of which is 2.5 tons. With the transition to the late stage of field development, after reaching a residual oil saturation of 0.4, steam injection is stopped. The pore volume of the steam chamber at this moment is 24,274 m ³ . After canceling the injection of steam, the temperature in the steam chamber decreased to 150 ° C. The concentration of bicarbonate ions in the produced water, which is equal to 2.7 g / l, is determined. Calculate the amount of CO ₂ that can be released from this water under the action of heat accumulated in the formation. 0.459 m ³ CO ₂ is released from 1 m ^{3 of} water under normal conditions (n.o.) and 0.102 m ³ CO _{2 is} released at reservoir conditions at T = 423K (150 ° C) and P = 709275 Pa (7 at). In order to fill the volume of the steam chamber with gaseous carbon dioxide, it is necessary to pump 21,653.9 m ^{3 of} produced water. Since the concentration of bicarbonate ions in the produced water is less than 3 g / l and the temperature in the steam chamber is 150 ° C, i.e. above 100 ° C, therefore, urea with a working concentration of 40 wt.% is additionally introduced into the produced water. The required volume of the urea solution is 714 m ³ , while the volume of released CO ₂ is 24,340 m ³ , which is sufficient to fill the volume of the steam chamber, given that part of the CO _{2 will} dissolve in oil. As the urea solution is pumped in, the steam chamber will gradually cool. After reducing the temperature in the steam chamber to 80 ° C, i.e. below 100 ° C, they transfer to the injection of 8.3% potassium hydrogen carbonate solution, the volume of which is 1427 m ³ and, accordingly, 24259 m ³ - the volume of CO ₂ released from it. The average daily oil production rate per well. No. 232, despite the cessation of steam injection and the transition to the injection of produced water, decreased slightly and amounted to 2.3 tons

Maintaining the pressure in the steam chamber by injecting produced water with salts dissolved therein, decomposing with the release of carbon dioxide due to the heat accumulated in the steam chamber, allows to maintain the oil flow rate almost at the same level after the cessation of steam injection and extends the period of cost-effective development of a highly viscous oil field .

Therefore, the proposed method for the development of a highly viscous oil field increases the efficiency of the steam-thermal effect when extracting residual oil due to the use of heat accumulated in the steam chamber after the termination of steam injection.

Claims (1)

A method of developing a highly viscous oil field, including injecting steam into the injection well, heating the producing formation with the creation of a steam chamber, taking oil through the producing well, injecting produced water in the injection well after reaching the design value of the residual oil saturation and canceling the steam injection, characterized in that it is determined the concentration of bicarbonate ions in the produced water, the produced water is pumped with the concentration of bicarbonate ions of at least 3 g / l, and at a concentration of urea carbonate ions in the produced water less than 3 g / l at a temperature in the steam chamber above 100 ° C are additionally injected with urea, after the temperature in the steam chamber is lower than 100 ° C, sodium or ammonium carbonate is introduced into the produced water or sodium or potassium bicarbonate, decomposing with the release of carbon dioxide under the action of heat accumulated in the steam chamber.