Wells – Processes – Producing the well
Reexamination Certificate
2001-12-11
2004-03-09
Bagnell, David (Department: 3672)
Wells
Processes
Producing the well
C166S068000, C166S105500, C166S250030, C166S250150
Reexamination Certificate
active
06702028
ABSTRACT:
FIELD OF INVENTION
This present invention enhances the production capacity from oil and gas reservoirs by combining a downhole gravitational separation process and submersible downhole pumps. In on of the preferred embodiments the downhole gravitational separating process win be preformed to a such degre of pureness that the oil will remain gas-free throughout the whole transportation of the oil, which especially is important when oil pressure is significantly dropping when transported upwards through production tubings.
BACKGROUND OF THE INVENTION
Most reservoirs contains a mixture of oil and gas, but the ration may vary. It is also usual that oil contains water and other liquids to some extent, so the further use of the term oil is therefor meant to also include water and other liquids.
Production methods of such reservoirs are restricted by the well-head-pressure, that is the reservoir pressure minus the pressure drop towards the surface (pressure drop due to the oil column height). The reservoir pressure is decreasing as production take place. The production of oil, that is the volume-flow of oil, is determined by a sufficiently well-head-pressure to be economical feasible, and as a minimum this requires at least a positive well-head-pressure.
To sustain or increase the reservoir pressure, a common solution is to reinject produced gas, and inject water and chemicals into the reservoir. However, in many cases, it is not physical or economic feasible to create or sustain a sufficiently reservoir pressure by these methods. This cause for a need and a desire for other solutions, such as using submersible pumps to pump the oil up.
An additional reason why one might want to make use of downhole submersible pumps, is that this allows reservoir pressure at borehole to drop, thus a larger pressure difference throughout the reservoir is created. This means a larger flow towards the borehole and larger production.
If there is a very small ration of gas present (approximately less than 10 vol % gas) in the reservoir, regular submersible downhole motor pumps are applicable, and are therefore usually used. This prolongs the production lifetime of the reservoir, and thus increase the total volume produced from the reservoir. However, if there is a large amount of gas present, these kinds of pumps are not applicable. Such pumps only allows a limited amount of gas to be entrained therein, without developing problems which may damage the pump and generally cause unsatisfactory operations.
Creative research has resulted in different kinds of centrifugal separation systems, which separates gas from the oil-gas mixture, thus making downhole pumps applicable. An example of such separating system is patent publication NO 3000515 B1, which has rotating helical bafflers within the production tube, creating larger centrifugal forces on the oil than it does on the lighter gas. A tubing within the production tube collects this separated oil, and it is then pumped upwards. U.S. Pat. No. 5,482,117 is based on the same centrifugal principle, but makes use of stationary helical bafflers in stead of rotating helical bafflers. In addition, these patents suggest to make use of the separated gas, as so called “gas-lift”. Gas due to it has low weight per volume, does not have the same pressure drop in heights as oil, thus when it is injected in the oil column above the pump this will increase the pressure, lifting the oil upwards.
Systems based on centrifugal separation are characterized by requiring complex baffler constructions, and complex tubing arrangements to make space for: bafflers, pumps and the two tubes for the gas and the oil. Further, rotational bafflers are fairly energy (electricity) consuming. At some production sites electricity is not easily or economic available, such as off-shore production sites.
In addition when a very high ratio of gas occur, in the case for rotational bafflers, the baffler motor might overheat due to the reduced heat capacity in oil-gas mixture. In the case for stationary bafflers, a pressure drop will occur proportional with the number of turns the helical baffler has, thus larger pump power will be required. The centrifugal separation does not necessary imply a totally separation, thus an additional separation is needed at ground level. Further problems could be that the helical bafflers may easily be plunged up, even if small object enters into the path.
Due to these problems it is desirable to find new solutions making regular submersible downhole motor pumps applicable for reservoirs containing gas. Until now, centrifugal separation methods seems to be the only solution the industry has come up with to solve this problem.
However, to separate gas to make regular submersible downhole motor pumps applicable in reservoirs containing gas, is only one of the objectives by this present invention. During production of oil, it is transported vertically through production tube, thus the oil pressure will decrease. So, even if gas apparently seems separated from oil down in the tubing, this is not correct since gas will “appear” proportionally with the pressure decrease in height, due to gas is much more compressible than oil. That is, the gas together with oil is so compressed at high pressures (at large depths) that it seems not to be present. When the pressure of this mixture decreases, the gas expand (in volume) relatively much more than oil. This causes many problems. One is that the oil produced is not pure enough to be transported away and therefore needs additional separation. When oil is transported over long distances this requires additional pumping activities, which means no gas can be present. So, another accomplishment of this present invention is performing the downhole separating process to a such degree of pureness that the oil will remain gas-free throughout the whole transportation of the oil production.
SUMMARY OF THE INVENTION
This present invention enhances production capacity from oil and gas reservoirs. This is primary achieved by making regular submersible downhole motor pumps applicable in oil reservoirs containing gas in a more economical and profitable way. This could partly be achieved by making a solution not being depended on centrifugal separation. Further, this invention is understood to be easier and less expensive to make and use, and also be more sustainable. In addition this invention has the opportunity, if desired, to produce totally separated products of oil and gas.
The core idea in this present invention is to place a pump
5
in a <<bath>> of oil
14
, in which oil <<bath>>
14
makes a gas seal assuring the pump only to be imposed to oil without gas. In one of the preferred embodiments (FIG.
1
), oil and gas from the reservoir flows trough perforations
2
, into a ring-space
3
. This creates a significantly pressure drop of the mixture, in which creates turbulence so the gas content will separate from the oil. The pressure drop is regulated by the gas pressure valve
4
.
Mainly due to gravity and to some extent the pumping activity
5
, the mixture flow is directed downwards. During a limited time this mixture will appear in a turbulent flow, then most gas will escape from the oil. The remaining gas content will be grouping together as larger bobbles. Since gas is lighter than oil, the gas contents will increase its buoyancy relative to oil during the grouping process. This increased buoyancy creates a flow of gas in the opposite direction, that is upwards, at a speed relative larger than the oil flow downwards. At some height level
11
, the turbulent flow turns to laminar flow, and it is from this height level and downwards the <<bath>> of oil is present. Then, only an insignificant content of gas is present, this is the height level
11
, which also is referred to as the gas seal
11
.
Viewed isolated, this gravitational separation principle is in its self a technology which from U.S. Pat. No. 2,293,196 was known to the industry already in 1939 (see FIG.
4
). And of course, at that point
Abel Christian D.
Bagnell David
Gay Jennifer H
Onsagers AS
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