Patent Application
20050077636
The present invention relates to an enhanced oil recovery process with injection of gas-liquid mixture into a reservoir. The process according to the invention finds application notably for improving the displacement of petroleum fluids towards producing wells and therefore for increasing the recovery ratio of the usable fluids, oil and gas, initially in-place in the rock.
The Water-Alternating-Gas (WAG) method where water is combined with gas is a well-known Enhanced Oil Recovery (EOR) method. According to the WAG method, water and gas are injected in succession for as long as petroleum fluids are being produced economically. The purpose of the water slugs is to reduce the mobility of the gas and to widen the swept zone. Many improvements have been proposed for this technique, for example in one method surfactants can be added to the water in order to decrease the water-oil interfacial tension and in another method a foaming agent is added to the water, when foam is created in the presence of gas the mobility of the gas is significantly reduced. The latter method is described in U.S. Pat. No. 3,893,511 or Russian Federation Patent No. 2,039,226. However such a technique requires sophisticated equipment as the parameters of injection must be accurately fulfilled which is difficult to achieve under normal oil field conditions.
U.S. Pat. No. 6,546,962 as well as Russian Federation Patent No. 2,046, 931 describe inventions wherein an ejector is used to introduce air or gas into injection water for enhancement of oil recovery. The injection water is supplied to the ejector at a predetermined pressure while at the same time air or associated gas is also being supplied to the ejector. The pressure and velocity of the water passing through the ejector is arranged so as to draw air or gas into the water stream. The amount of gas drawn into the water is preferably capable of being dissolved entirely at the wellhead (or formation) pressure as well as being sufficient to achieve the desired effect in the formation. The ejector uses the energy of the injector pump to accelerate the injection water, thereby reducing the pressure in order to draw in the gas. However, the gas-water mixture stability is low because the size of the gas bubbles cannot be controlled in accordance with these inventions. In addition, a gas/water mixture requires additional compression relative to injection pressure as compared to a water-only system, thus extra energy is needed. The present invention was developed to overcome these and other drawbacks of prior methods and devices by providing an improved method and apparatus for enhanced oil recovery by injection of a gas-liquid mixture into the oil-bearing formation.
Accordingly, a primary object of a first embodiment of the present invention is to provide an apparatus for making a micro-dispersed gas-liquid mixture which includes a gas-liquid ejector unit, a cavitation unit and a jet dispersing unit installed in a sequence. All above referenced units are installed into a cylindrical housing which in turn includes bottom and top covers and also has a first partition having a conical orifice separating a gas-liquid ejector unit from a cavitation unit and a second partition separating a cavitation unit from a jet dispersing unit. The gas-liquid ejector unit has an inlet located at the bottom of the cylindrical housing for liquid and inlet located on the side surface of housing for gas, these being between bottom cover of housing and first partition. In addition, the inlet for liquid is a nozzle the top having both outside and inside parts of which are adapted to the conical orifice of first partition to provide a required flowrate of an ejected gas through the gas inlet. The gas-liquid ejector unit communicates through the conical orifice of the first partition with a cavitation unit comprising a hollow cylindrical cavitation chamber having at least one tangential inlet allowing a gas-liquid mixture from a gas-liquid ejector unit to flow inside the hollow cylindrical cavitation chamber for breaking of gas bubbles and further to a jet dispersing unit through an orifice of second partition for additional dispersing and homogenization. The jet dispersing unit comprises a hollow cylindrical dispersing chamber attached to the second partition and communicates with the injection flowline of the injection well through an outlet located at the top cover of the cylindrical housing. In addition, the hollow cylindrical dispersing chamber has at least one outlet channel and a hollow dip at the bottom of the hollow cylindrical dispersing chamber.
It is another object of the invention to provide an apparatus for making a micro-dispersed gas-liquid mixture in which there is no first partition and the gas is ejected into the hollow cylindrical cavitation chamber provided a gas pressure in the gas injection line exceeds the liquid injection line pressure by 0.1-20 percent.
It is further object of present invention to provide a method for enhanced recovery of a petroleum fluid produced by a reservoir, comprising injection of a sweep fluid into an oil-bearing reservoir through an injection well, the sweep fluid comprising a micro-dispersed gas-liquid mixture having size of gas bubbles not exceeding 30 percent of an average diameter of the pores of said oil-bearing reservoir under the pressure in gas injection line in the range of ±20 percent of the pressure in liquid injection line and gas content accounting for 10-40 percent of a micro-dispersed gas-liquid mixture bulk volume.
It is another object of present invention to provide a method for enhanced recovery of a petroleum fluid produced by a reservoir in which the injection of a micro-dispersed gas-liquid mixture and liquid without gas carries out intermittently.
Other objects and advantages of the invention will become apparent from the study of the following specification when viewed in light of the accompanying drawings, in which:
Referring to
Referring to
The hollow cylindrical dispersing chamber 15 has at least one outlet channel 16 and a hollow dip 17 with the reflection surface 18 at the bottom of the hollow cylindrical dispersing chamber 15.
Operation:
In the case where pressure in the gas injection line is less than the pressure in the liquid injection line by 0-20 percent a device for producing a micro-dispersed gas-liquid mixture operates as following (
In the case where pressure in the gas injection line exceeds that in the liquid injection line by 0.1-20 percent a device for producing a micro-dispersed gas-liquid mixture operates as follows (
In addition, the present invention is a highly efficient process for enhanced recovery of petroleum fluids produced by a reservoir. The process entails injection of a sweep fluid into an oil-bearing reservoir through an injection well wherein the sweep fluid is a micro-dispersed gas-liquid mixture having gas bubble sizes not exceeding 30 percent of the average diameter of the oil-bearing reservoir pores, performed when the pressure in gas injection line is less than 20 percent of the pressure in liquid injection line and the gas content accounts for 10-40 percent of the micro-dispersed gas-liquid mixture's bulk volume. Under these conditions the micro-dispersed gas-liquid mixture effectively sweeps the residual oil from the oil-saturated porous medium. For example the oil-bearing productive layer AB4-5 of the Samotlor oil field (West Siberia, Russia) underwent an injection of the micro-dispersed gas-liquid mixture during a period of 12 months. There were 90 production wells and 28 injection wells wherein the injection of the micro-dispersed gas-liquid mixture was performed. The average production rate prior to stimulation was 9.6 tons/day per well of an oil and 304 tons/day per well of fluid and the average injection rate was 500 tons/day per well. The water cut accounted for 96%. The average permeability of productive layer accounted for 4*10−1 mc2 which corresponds to 150 microns of average size of pores of the fluid saturated porous medium. The average diameter of the gas bubbles in the injected micro-dispersed gas-liquid mixture accounted for 30-50 microns. The gas content in the micro-dispersed gas-liquid mixture had been changing in the range 10-40% depending on the injection pressure in the gas injection line which in turn was accounted for 8-13.2 MPa. The injection pressure in the liquid injection line accounted for 10-11 MPa. Over the previous 12 months 18.4 million standard cubic meters of gas was injected. The additional oil production due to the injection of the micro-dispersed gas-liquid mixture accounted for 21000 tons.
In addition, the present invention is highly efficient in providing a process for enhanced recovery of a petroleum fluid produced by a reservoir wherein occurs the intermittent injection of a micro-dispersed gas-liquid mixture after exiting from outlet 8 and liquid without gas, in cases where the permeability of the oil-bearing productive layer is less than 5-10 mD.
While in accordance with the provisions of the Patent Statutes the preferred forms and the embodiments of the invention have been illustrated and described, it will be apparent to those of ordinary skill in the art various changes and modifications may be made without deviating from the inventive concepts set forth above.
