DE2123385C3 - Process for oil extraction by means of gas release and water flooding - Google Patents

Description

The extraction of oil from underground oil-bearing reservoirs is normally carried out by exploitation the natural reservoir energy with the help of the water drive, the gas cap drive, the gas release drive or combinations of such methods.

These different forms of energy provide the driving force necessary for oil production from the reservoir is necessary without an external energy source having to be used.

A gas-powered reservoir draws its energy mainly from gas dissolved in oil or from gas the existing free gas zone of the deposit. The reservoir contains gas dissolved in the oil and is initial If there is no gas cap, the oil is pumped through gas release. As long as the reservoir pressure is sufficiently high, the gas will initially remain dissolved in the oil. If the oil extraction is continued, a controlled decrease in reservoir pressure occur. If the reservoir pressure has dropped sufficiently, The released gas forms gas bubbles. The release pressure is understood to mean the gas pressure, in which the gas development in the relevant state of free gas saturation, which is caused by the Occurrence of free gas in the larger and smaller channels or pores is characterized. Which The amount of gas that forms initially exists as a discontinuous and immobile phase. The grows Concentration of the free gas, the gas bubbles combine to form a continuous phase. At this point, known as critical gas saturation, gas permeability occurs and the free gas flows through with little or no displacement of oil the deposit.

The time has come to introduce Zusatzene.gie when the reservoir pressure is exhausted. In order to introduce additional energy, the water is then usually flooded with water or several injection bores and acts in such a way that additional reservoir oil is promoted will.

If the water is flooded in the conventional manner, not all of the oil is displaced and conveyed as a result of the capillary and viscosity forces. Basically that flows Water through the larger channels of the reservoir structure, whereby oil is displaced into smaller pores. the Due to capillary forces, water can no longer flow through pores.

Processes that enable oil extraction beyond water flooding relate to injection of gas, with the reservoir pressure subsequently decreasing and the reservoir without further injection of liquid promotes.

Other proposals for additional oil recovery involve increasing the reservoir pressure Forcing water into the reservoir. This increase in reservoir pressure by indenting however, in many cases, water essentially eliminates the free gas saturation which occurs has set during the gas release drive, with the result that the oil production is less than when Water flooding with free gas saturation. In other cases, the gas release instinct was used until training a continuous gas phase promoted. This results in an undesirable increase in Gas saturation and only low oil production due to subsequent water flooding.

From Frick / Taylor, Petroleum Production Handbook; McGraw Hill Book Company, Inc., New York-Toronto-London, 1962; Volume IL; particularly 34-22 to 34-31 is a process for producing oil known from an oil-bearing reservoir by gas release, the oil-bearing reservoir through the Gas release drive promotes until the reservoir pressure has reached a value below the However, the release pressure is still in the range of the critical gas saturation.

According to DE-AS 12 00 771 and US-PS 31 21 461, the deposit is mediated following the promotion of the gas release drive with the addition of miscible with the reservoir oil under reservoir conditions gaseous or liquid hydrocarbons to build up a miscible phase with an additional at least flooded a gas miscible with the added hydrocarbons and pumped oil.

A method is also known from journal of Petroleum Technology, August 1963, pages 877 to 884, after which water is repeatedly injected into the reservoir to restore the reservoir pressure and then the promotion without further water injection

Deposit occurs. Develops in the deposit is resumed.

The object of the invention was to provide an improved method by combining conventional funding methods To achieve oil production.

The present invention relates to a method for oil extraction according to the preamble of the main claim. The task at hand is solved by the im Characteristics of claim 1 specified measures.

There is an optimal value for the reservoir pressure, which is set by the gas release and indicates the formation of free gas saturation When the value is reached, the water flooding begins. Through this Improved Oil Recovery Is Achieved Accordingly, the present invention provides an improved one Process for the extraction of oil from an oil-bearing deposit through the appropriate use the optimal pressure value in the combination process gas venting / water flooding.

In a preferred embodiment of the method according to the invention, gas release and subsequent water flooding applied in such a way that an optimal value of a single pressure drop for oil extraction is exploited. This optimum value appears below the release pressure, but within the Limits of the critical gas saturation of the reservoir. In general, the critical gas saturation is in Range from about 2 to about 10% of the reservoir void volume.

The proposed improved method for extracting oil from a deposit that is dissolved in the oil Contains gas is realized by the following process steps:

The oil production is driven by the gas release in such a way that the reservoir pressure up to one Pressure level, which is just below the release pressure, but in the area of the critical gas saturation the deposit is located, is lowered in a controlled manner. The lowering of the pressure causes a release of the dissolved Gas, whereby a certain amount of oil from the small capillaries or pores in the larger flow channels is expelled. If the critical gas saturation is reached, the gas release is ended and that Water flooding started at the present lower reservoir pressure. This is a more effective one Displacement of the reservoir oil due to the limited gas saturation in the flow channels of the Deposit possible.

If the oil production rate reaches a predetermined minimum level, at which the continuous water flooding does not occur ■ -> more is feasible, the water injection is ended. The specified minimum height results principally from the oil production rate of the respective production and the knowledge acquired in practice. at The minimum height depends on the given water flood

ίο of the individual deposit and the used Funding conditions. In general, the minimum level is determined by a sharp decrease in the oil production rate in the Compared to the water delivery rate or through the increase in the water / oil ratio of the

i-, th liquids displayed For example, can under given funding conditions, the minimum amount to be specified must be reached when this ratio is up 100: 1 has increased. Then the water injection must be stopped.

2 <i The following step includes another gas release, with the reservoir pressure dropping again in a controlled manner while oil is being pumped away through the production well. The gas is released again up to critical gas saturation (lower reservoir pressure)

2-> driven. Subsequently, after completion of the Gas release, renewed flooding of the water. The alternating process steps are up to a print led, which forces the cessation of production because the reservoir energy is essentially exhausted.

in A series of laboratory tests was carried out for An illustration of the invention carried out by using drill cores from the Pembina field, Alberta, Canada Provided measuring devices, appropriately built into high pressure flow devices. In

γ, each nucleus became an initial saturation of water and oil of 11.6 and 88.4% respectively. The initial pressure was 169 bar. The trials were, as in the Tables compiled, carried out.

The experiments show that with an alternating

4 (i gas release and water flooding an oil production of 63.1% is achieved during the use of water flooding with a subsequent individual Printer exhaustion yields 57.8% oil yield. The inventive method brings about an improvement

A-, ration by 8.3%.

Table 1
Test series 1

Depressurization and flooding in alternating procedures

Pressure in bar oil Saturations of the funded ü step at the end of one extraction Media on End one; one step in% by volume gas % water oil 12.2 Gas release 84.4 12th 11.6 76.2 11.5 Floods 84.4 40.1 36.6 51.9 16.2 Gas release 63.3 45.0 36.6 47.2 14.4 Floods 63.3 58.6 50.1 35.5 18.4 Gas release 42.2 59.6 47.2 34.4 16.3 Floods 42.2 61.1 50.6 33.1 23.2 Gas release 21.1 61.9 44.7 32.1 18.5 Floods 21.1 62.5 49.9 31.6 26.6 Gas release by 0 63.1 42.7 30.7 possible final pressure

5
Table 2
Test series 2
Conventional Water; flood 21 23 385 Oil-
i extraction
% Saturations
Media on
in% by volume
water 6th 0.0
24.6 Pressure in bar
at the end one;
Step 54.2
57.8 59.4
40.2 Floods (1
Gas release p.v.) 0 of the funded
End of a step
Oil gas 40.6
35.2

The resulting application of the invention to one with gas. saturated deposit for a given r, Reservoir pressure should include the following steps:

a) Production from the oil-bearing liquor facility Gas release until the pressure is below the release pressure but within the critical one Gas saturation.

b) End the gas release and start the water flooding by injecting water.

c) Flooding of the deposit to a final 2 ". point caused by the sharp increase in the water production rate compared to the oil production rate is marked.

d) Ending the water flooding and renewed production from the oil-producing deposit by means of gas release, whereby the deposit pressure is again reduced below the release pressure, but remains within the critical gas saturation,
e) Repeat the previous steps until the reservoir pressure has been reached, which excludes further oil production.

The application to undersaturated deposits belongs to the scope of the method according to the invention and is carried out in such a way that the initial step of degassing the injection of Gas in the deposit formation is connected upstream to a gas-saturated deposit before the start of the To produce gas release.

The invention also encompasses the use of viscous liquid in water flooding. Through the Use of a thickener in the injected water can result in an improved mobility ratio during the water flooding can be achieved.

Claims (4)

Patent claims: 1. Process for extracting oil from underground reservoirs by means of at least one injection and a production probe, in which the oil production is initially carried out in a first stage by gas release with pressure drop to below the gas release pressure, but still in the critical range Gas saturation of the oil takes place under reservoir conditions and the reservoir thereafter under Maintenance of oil production and the existing reservoir pressure in a second stage It is flooded until the ratio of the oil produced to the flooding agent produced one falls below predetermined minimum value, characterized in that in the second Stage is flooded with water and the oil production after its completion, initially again with the first Starting level and continuing the second level, alternating with the two funding levels is operated until the reservoir pressure falls below a limit value that precludes oil production has sunk. * 2. The method according to claim 1, characterized in that a before the first gas release Pressure is built up in the deposit until the gas release pressure is reached. 3. The method according to claim 1, characterized in that the pressed into the deposit Water a thickener to improve the mobility ratio when water is injected contains. 4. Application of the method according to claims 1 to 3 on deposits in which the critical Gas saturation at the end of the gas release drive under the existing reservoir pressure is about 2 to 10% of the reservoir pore volume.