Wells – Processes – Distinct – separate injection and producing wells
Reexamination Certificate
2000-12-05
2002-08-27
Suchfield, George (Department: 3672)
Wells
Processes
Distinct, separate injection and producing wells
C166S270100, C166S275000, C166S309000, C166S401000, C166S402000, C166S403000, C507S202000
Reexamination Certificate
active
06439308
ABSTRACT:
The present invention relates to a method for enhancing oil recovery efficiency, and more particularly, to a foam drive method.
BACKGROUND OF THE INVENTION
At present, water flooding is extensively used to produce crude oil in many oil fields worldwide, but because of the heterogeneity of the reservoir and disadvantageous oil-water mobility ratio there still is plenty of residual oil remaining in the subterranean formation after a water-drive. In order to produce such residual oil, besides dense drilling, a variety of new processes of enhanced oil recovery have been gradually converted from experimental research to the industrial practice in the field and have already been widely used in many oil regions in the world. In tertiary recovery techniques, chemical flooding is still one of the promising methods. Of chemical flooding processes, combined drive has been more widely adopted and its application has extended from sandstone reservoir to carbonate reservoir. Operation procedures and effectiveness for the chemical flooding processes are continually being improved. In addition, various combined chemical drive processes have been researched and developed, for example, combined two-components drive process such as an alkali-polymer drive, a surfactant-alkali drive, a surfactant-polymer drive, and combined three-components drive process such as alkali-surfactant-polymer, in order to improve the oil recovery efficiency of the chemical drive and reduce the production cost. Combined chemical agents can produce synergetic action, which not only reduces the used amount of the chemical agents but also results in higher oil recovery than that obtained by a single chemical drive or two-components combined drive. With regard to three-components drive process, not only has mechanism research in laboratory tests been extensively done, but also pilot tests of its application have been made in the recovery practices and a relatively significant effect has been attained. The mechanism of three-components drive process mainly is such: on the one hand, in three-components system the presence of the polymer may increase the viscosity of the displacing phase, thus reducing the oil-water mobility ratio and resulting in an increase in sweep area; on the other hand, the synergetic action of an alkali and a surfactant may bring about the super-low interfacial tension between the water and the oil, which makes crude oil more easily separate from the surface of reservoir rock thereby increasing the driving index, and at last enhancing the recovery by a big margin. In this regard, reference is made to SPE 24144, SPE 21028, SPE 17538.
To improve the ability of plugging high permeability zone or thief zone, through intensive studies, researchers found a foam which can more fully enter and decrease the permeability than a polymer or a gel, wherein the foam is typically divided into a normal foam and an enhanced foam. The normal foam is formed above or under ground generally by adding the surfactant to an injected gas. For example, U.S. Pat. No. 5,363,915 discloses a technique for enhancing oil recovery using the foam produced by a non-ionic surfactant, a non-condensible gas and water, wherein the foam is stable and can be formed under ground or can be formed above ground prior to injection in a well, and it is preferably employed within light oil-bearing carbonate formation. In addition, U.S. Pat. No. 5,074,358 described some other stable foam. In the enhanced foam, as the other foam, there is a chemical agent component that can enhance viscosity besides a surfactant. For example, U.S. Pat. No. 5,307,878 discloses a polymer enhanced foam used to increase foam stability and to reduce gas coning (fingering) problem, and the polymer enhanced foam comprises a polymer, an aqueous solvent and a gas. U.S. Pat. No. 5,129,457 discloses polymer-enhanced foam to treat a fractured subterranean formation thereby enhancing liquid hydrocarbon recovery. Said foam also comprises a polymer, a surfactant, an aqueous solvent and a gas, and the foam preferentially enters fractures present in the subterranean formation. However, the above mentioned processes for enhancing the recovery are directed to improve the sweep efficiency of the displacing agent, and the chemical agent component in the foam can not bring about super-low interfacial tension with the oil as they do in the three-components drive system. Therefore, final oil recovery generally falls within the range of 50 to 60 percent; while in the three-components drive process the profile control ability of a polymer is much less than that of the foam so that the increase of sweep efficiency is limited, and displacement fluid still easily breaks through and channels in high permeability zone. As a result, final oil recovery still is about 60% generally. Consequently, it is necessary to develop a driving process which can make full use of the synergetic advantages of the foam-drive and three-components drive process, as to further enhance the oil recovery in a subterranean oil-bearing formation and allow recovery of the residual oil in low permeability zone of relatively high oil saturation and the oil which is swept by a water flooding but fails to be recovered by the water flooding.
OBJECT OF THE INVENTION
It is the object of the present invention to make full use of the advantages of high flushing efficiency of three-components drive process and high sweep efficiency of foam-drive process and thereby to enhance the oil recovery by injecting a gas and three-components system simultaneously or alternately to form a foam above or under ground, thereby to avoid either the defect of the lower sweep efficiency in three-components drive process or lower flushing efficiency in the foam-drive process alone.
SUMMARY OF THE INVENTION
The present invention relates to a process for enhancing oil recovery from a subterranean oil-bearing formation, and more particularly, to a foam drive process, which comprises the following steps:
(1) injecting into the formation an aqueous polymer solution as a preceding-slug, in an amount of 2-8% pore volume of the formation;
(2) periodically injecting simultaneously or alternately a non-condensible gas and an aqueous solution of foaming composition to form a combined foam under ground or periodically injecting the combined foam formed beforehand by the gas and said aqueous solution above ground, said aqueous solution of foaming composition comprises an alkali, a surfactant and a polymer and its injection amount is 10-50% pore volume of the formation; said aqueous solution of the foaming composition is a super-low interfacial tension system, and the interfacial tension value between the foaming composition and the displaced subterranean oil may reach to 10
−3
mN/m order of magnitude;
(3) injecting an aqueous polymer solution used as protecting-slug, in an amount of 10-45% pore volume of the formation.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a process for enhancing oil recovery from a subterranean oil-bearing formation, and more particularly, to a foam drive process, which comprises the following steps:
(1) injecting into the formation an aqueous polymer solution as a preceding-slug;
(2) periodically injecting simultaneously or alternately a non-condensible gas and an aqueous solution of foaming composition to form a combined foam under ground or periodically injecting the combined foam formed beforehand by the gas and said aqueous solution above ground, said aqueous solution of foaming composition comprises an alkali, a surfactant and a polymer;
(3) injecting an aqueous polymer solution used as protecting-slug.
In prior art, due to the presence of high permeability zone or thief zone in an oil-bearing formation, both the two-components drive and three-components drive lead to coning (fingering) to some extent. After extensive research, it is found that an aqueous polymer solution can be used as preceding-slug before the combined drive system is injected into an oil-bearing formation. Thus, on the one hand, the
Da Qing Petroleum Administration Bureau
Heslin Rothenberg Farley & & Mesiti P.C.
Suchfield George
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