RU2403383C1 - Oil deposit development method - Google Patents

Abstract

FIELD: oil and gas industry. ^ SUBSTANCE: as per the method, injection and production wells are arranged, air, water, combustion gases from products of production well are pumped to injection wells, and oil, combustion gases and associated gases are extracted from production wells. Heat carrier is pumped to injection wells till formation is heated to temperature of not less than 65C to environment of well with radius of 20 m. Portion of hot water alternating with oil solvent with weight of 5-150 tonnes per 1 metre of power of producing interval is pumped. Air with weight of 0.01-0.2 of total weight of pumped water is pumped and heated water-air mixture is pumped, and water-air ratio is determined as per analytical expression. ^ EFFECT: increasing oil recovery of deposit. ^ 1 ex, 1 tbl

Description

The invention relates to the oil industry and can be used in the development of oil deposits.

A known method of developing an oil field, which includes injecting an oxygen-containing mixture through an injection well and creating a zone of oil oxidation in the formation. At a temperature of the formation above 65 ° C, an oxidation zone is created in it with a radius of at least the radius of the zone of complete oxygen consumption in the formation when the oxidation zone is moved toward the producing well. Select the distance between the injection and production wells and the radius of the zone of total oxygen consumption. The injection of an oxygen-containing mixture is stopped when the oxidation zone approaches the production well (RF Patent No. 2139421, publ. 1999.10.10).

The known method has a low coverage by the impact of the reservoir due to breakthroughs in the highly permeable zones of the easily moving expelling agent gas and the burial of significant oil reserves in the reservoir.

Closest to the proposed invention in technical essence is a method for developing deposits with hard-to-recover oil reserves, according to which injection and production wells are placed on deposits, air and water rims are pumped into injection wells to create in-situ combustion in the formation. At the same time, when developing deposits with normal viscosity oil reserves, associated petroleum gases and combustion gases are extracted from the production of production wells. These gases are separately or together with associated petroleum gases injected into injection wells. The injection of air rims alternates with the injection of the above gases and they are separated by the injection of water rims. The ratio of the volumes of injection of the rims of air and water is selected from the condition of maintaining at the combustion front a temperature of 300-400 ° C (RF Patent No. 2109133, publ. 1998.04.20 - prototype).

The known method has increased coverage by the impact of the reservoir due to the use of a displacing agent of increased viscosity - water. However, oil recovery remains low due to the low temperature and, consequently, low mobility, as well as low pressure of the displacing agent on the displaced oil.

The proposed invention solves the problem of increasing oil recovery deposits.

The problem is solved in that in the method of developing an oil deposit by placing injection and production wells, injecting into the injection wells air, water, combustion gases extracted from the production of production wells, and selecting oil, combustion gases and associated oil gases from the production wells, according to the invention , previously, coolant is pumped into injection wells until the formation is heated to a temperature of at least 65 ° C in the vicinity of the well with a radius of 5-20 m, a portion of hot water is pumped in alternating with oil solvent 5-150 tons weight per 1 meter power production interval, pump air 0.01-0.2 mass of the total mass of injected water and pumped into the heated water-air mixture, and the water-air ratio of the reservoir pressure is less than 22,064 MPa is determined from the relationship:

where B is the water-air ratio of the injected components into the reservoir,

R _in - the need for injection of atmospheric air;

C _in - specific heat of water, at a temperature T _Zak ≤T <T _n ,

r _p is the heat of vaporization;

r _to - heat during the combustion of one kilogram of oxygen;

x - dry steam;

T _n - temperature of saturated steam;

T _Zack - the temperature of the injected water,

and the water-air ratio at reservoir pressure greater than 22.064 MPa is determined from the ratio:

where C _in - specific heat of water at a temperature T _Zak ≤T <T _max;

T _max - temperature in the combustion zone (oxidation).

SUMMARY OF THE INVENTION

When developing an oil reservoir using in-situ oxidation and / or combustion, injecting steam from the surface through injection wells is practically useless due to the conversion of steam into water when passing through the pipe string from the mouth of the injection well to the bottom, and when the combustion front is distant from the injection well, bringing steam to the front Combustion and the use of steam as a displacing agent becomes impossible due to the complete conversion of steam under formation conditions into water. The generation of steam or the transfer of water to a supercritical state in reservoir conditions at the combustion front is a complex engineering problem, the solution of which is the subject of the invention. The solution to this problem allows the use of steam or supercritical water as a working (displacing) agent at the combustion front and, due to this, solves the problem of increasing oil recovery of the reservoir. The problem is solved as follows.

When developing an oil deposit, injection and production wells are located. The coolant is pumped into the injection wells until the formation is heated to a temperature of 65 ° C in the vicinity of the well with a radius of 5-20 m. This heating ensures the in-situ combustion and / or oxidation of oil in the near-wellbore zone. Several portions of hot water are pumped in alternation with an oil solvent with a total mass of 5-150 tons per 1 m of productive interval capacity. Most preferably, alternating equal in volume portions of hot water with a bottom hole temperature of 65-100 ° C and an oil solvent. Associated gas, oil distillate, a wide fraction of light hydrocarbons, diesel fuel, desalted and dehydrated low-viscosity oil, etc. can be used as an oil solvent. The number of alternating portions of water and solvent can be from 1 to 10. The use of alternating injections of hot water and solvent allows you to flush the near-wellbore zone to move the future combustion front from the well. Air injection leads to the formation of in-situ combustion in the heated zone at a distance from the well and heating the formation to 200-400 ° C. After creating a stable combustion front, the heated water-air mixture is pumped with a temperature from 65 ° C to 200 ° C, and the water-air ratio is determined from the ratio:

;where is the water-air ratio of the injected components into the reservoir,

;

R _in - the need for injection of atmospheric air, nm ³ ;

C _in - specific heat of water, kJ / (kg · ° C), at a temperature T _Zak ≤T <T _n;

r _p - heat of vaporization, kJ / kg;

r _to heat during the combustion of one kilogram of oxygen, kJ / kg;

x - dry steam, fraction of a unit;

T _n - temperature of saturated steam, ° C;

T _Zack - the temperature of the injected water, ° C.

This ratio is obtained from the following considerations. The heat demand for transferring the injected water to saturated steam per unit mass is determined by the following balance ratio:

where Q is the heat demand, kJ / kg.

Based on a stoichiometric analysis of oxidative reactions, it is known that when one kilogram of oxygen is consumed, heat generation is r _k = 10500-12600 kJ / kg. Then, for heating and transferring 1 kg of hot water into steam, the oxygen demand R _k with its complete combustion will be:

where R _to - the need for oxygen, kg / kg.

If atmospheric air is used as an oxidizing agent, then the demand for R _{in it} will be:

where R _in - the need for air, kg / kg

Usually the water-air ratio is determined by volumetric quantities. In this regard, relation (3) can be represented as follows:

A certain value of the water-air ratio can ensure the transfer of injected water into steam (this is possible only at reservoir pressure less than the critical 22.064 MPa). In this case, the water-air ratio will be:

.where In is the water-air ratio of the injected components into the reservoir,

.

At a reservoir pressure greater than critical (> 22.064 MPa), the water will not boil, but will smoothly transition to the supercritical state, therefore, formula (5) will take the form:

Where

C _in - heat capacity of water, kJ / (kg ° C), at a temperature T _Zak ≤T <T _max ;

T _max - temperature in the combustion zone (oxidation), ° C.

The temperature in the oxidation zone depends on many factors and can be estimated by laboratory methods or by computer simulation on a thermal simulator.

Concrete example

An oil reservoir is developed with the following characteristics: depth 2450 m, effective oil saturated thickness 7 m, porosity 19%, horizontal permeability 0.2 μm ² , vertical permeability 0.02 μm ² , oil saturation 54%, gas solubility in oil 50.7 m ³ / m ³ , viscosity in reservoir conditions: oil 7 MPa · s, water 0.92 MPa · s, air and combustion gases 0.2 MPa · s, density in reservoir conditions: oil 756 kg / m ³ , water 1012 kg / m ³ , air 218 kg / m ³ , gases 296 kg / m ³ , initial reservoir: pressure 25 MPa, temperature 40 ° C, injection pressure of water 37 MPa, air and gas 35 MPa, pressure at the bottom of producing wells 20 MPa. The average temperature in the oxidation zone is 300 ° C. The deposit is developed according to a reversed seven-point pattern with a central injection well.

A coolant is pumped into injection wells - hot water with a temperature of 100 ° C until the formation is heated to a temperature of 74 ° C in the vicinity of a well with a radius of 18.7 m. The total mass of steam is 1080 tons. Then four portions of hot water with a bottom temperature of 80 ° C and a mass of 120 tons each, alternating with the injection of solvent - oil distillate in portions of 95 tons each. Injected air weighing 145 tons (121 thousand nm ³ ), which is 0.093 of the total mass of water injection (1080 + 120 × 4). This produces in situ combustion outside the washed bottomhole zone. After creating a stable combustion front, a water-air mixture heated to 100 ° C is pumped, and the water-air ratio, which ensures the complete transfer of the injected water to a supercritical state, is determined from relation (6).

The heat demand for heating a kilogram of injected water at P _PL = 25 MPa, T _media = (T _max + T _Zak ) / 2 = (300 + 100) = 200 ° C, is C _in (25,200) = 4.38 kJ / kg / ° C. The heat generation during the combustion of 1 kilogram of oxygen under reservoir conditions is r _k = 10500 kJ / kg.

Substituting in (6), we obtain the value of the water-air ratio:

The development is carried out in the following mode: 60 thousand normal cubic meters / day of air are pumped into each injection well, and water is added to provide a given value of the air-to-water ratio. In total, 8 calculations were performed using the CMG STARS simulator. The first two calculations are for comparison purposes only. The first calculation involved the injection of only water, the second - only air. The remaining 6 calculations differed in the temperature of the water-air mixture and the water-air ratio. The results of calculations of the oil recovery coefficient (CIM) after 50 years of development are presented in table 1.

Table 1 Agent Injection Temperature No. Water ratio CIN,% Options 20 ° C one > 1000 19.41 comparative 2 0 26.00 3 0.001 29.92 prototype four 0.003 30.41 5 0.005 18.84 100 ° C 6 0.001 09/30 comparative 7 0.003 31.84 proposed 8 0.005 05/29 comparative

Thus, at the development site using the proposed method, oil recovery of 31.8% is achieved, while the prototype oil recovery is 29.9, 30.4 and 18.8%, depending on the water-air ratio, that is, an average of 26.4%. The increase in CIN amounted to an average of 5.5%.

Note that the value of the water-air ratio calculated by the formula (6), and made it possible to obtain the highest CIN.

The application of the proposed method will solve the problem of increasing oil recovery deposits.

Claims (1)

A method of developing an oil deposit by placing injection and production wells, injecting air, water, combustion gases extracted from production of production wells into injection wells, and selecting oil, combustion gases and associated oil gases from production wells, characterized in that it is preliminarily injected into wells the coolant is pumped to warm the formation to a temperature of at least 65 ° C in the vicinity of the well with a radius of 5-20 m, a portion of hot water is pumped in alternation with an oil solvent weighing 5-150 tons per 1 m of power of the productive interval, they pump air with a mass of 0.01-0.2 of the total weight of the pumped water and pump the heated water-air mixture, and the water-air ratio at reservoir pressure less than 22.064 MPa is determined from the ratio:

where In - water-air ratio of the injected components into the reservoir;
R _in - the need for injection of atmospheric air;
C _in - specific heat of water at a temperature T _Zak ≤T <T _n ;
r _p is the heat of vaporization;
r _to - heat during the combustion of one kilogram of oxygen;
x - dry steam;
T _n - temperature of saturated steam;
T _Zack - the temperature of the injected water,
and the water-air ratio at reservoir pressure greater than 22.064 MPa is determined from the ratio:

,
where C _in - specific heat of water at a temperature T _Zak ≤T <T _max ;
T _max - temperature in the combustion-oxidation zone.