Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
  • E21B43/34—Arrangements for separating materials produced by the well
  • E21B43/38—Arrangements for separating materials produced by the well in the well
  • E21B43/385—Arrangements for separating materials produced by the well in the well by reinjecting the separated materials into an earth formation in the same well
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
  • E21B43/12—Methods or apparatus for controlling the flow of the obtained fluid to or in wells
  • E21B43/121—Lifting well fluids
  • E21B43/13—Lifting well fluids specially adapted to dewatering of wells of gas producing reservoirs, e.g. methane producing coal beds

Definitions

• the present invention relates to a method and system of producing gas, in particular hydrocarbon gas, from an underground formation.
• a production well is arranged to penetrate the gas-bearing formation.
• Reservoir fluid can be received in a production interval, e.g. through perforations in the well casing at a certain depth.
• the reservoir fluid often comprises liquids in addition to the gas, in particular water.
• the liquids can be present in the formation fluid when it enters the production well, for example from a so-called high-permeability streak.
• Liquids can also be formed by condensation on the way to the surface in the event that the reservoir conditions (pressure, temperature) at the production interval depth are such that the formation fluid comprises vapour or liquid that is dissolved in the gas.
• One method is to install production tubing in the well, so-called velocity strings, that serve to limit the effective cross-sectional area for the fluid produced to surface, thereby increasing the flow velocity sufficiently to prevent gas/liquid separation.
• Another method is to use foaming chemicals, which lower the surface tension of separated water so that it can be transported more easily to surface by the gas.
• Yet another known method is to pump water from the water column to surface, which is also referred to as plunger lift.
• a compressor is used to reduce the well head pressure.
• 5 913 363 discloses a method for downhole separation of water from gas received from a production zone in a gas well, using a downhole gas/water separator arranged above the production zone, wherein the separated water is directed via packers and a pressure sensitive valve to a disposal formation.
• US patent specification No. 5 443 120 discloses a method for downhole separation of water from hydrocarbons by gravity, in a portion of an inclined wellbore that is isolated by packers, and wherein separated water is injected into a disposal formation which has a lower pressure than the producing formation.
• US patent specification No. 5 366 011 discloses a gas well wherein a special casing/tubing arrangement is placed. The arrangement forms an annulus communicating with the producing formation and has a sliding sleeve to selectively allow fluid communication between the annulus and the tubing. Water can separate from the gas in the annulus and is allowed to flow into the tubing and from there into a non-productive interval.
• US patent specification No. 6 336 504 discloses a method for downhole separation and injection of water, wherein the reservoir fluid contains at least some oil, water and optionally gas, and wherein a separator is arranged at a variable position in the well so as to produce water at a sufficient pressure for injection into a disposal formation.
• a method of producing gas from an underground formation which underground formation is penetrated by a production well extending to surface, which method comprises the steps of: allowing formation fluid comprising gas and liquid to flow from the underground formation into the production well at a production interval; allowing the formation fluid to separate into a gaseous component and into a liquid component; producing the gaseous component through the production well to the surface; accumulating the liquid component in the production well so as to form a liquid column having, at a drainage interval of the production well, a pressure exceeding the pressure in the surrounding formation; and - allowing liquid from the liquid column at the drainage interval to drain away into the surrounding formation, wherein the step of allowing liquid from the liquid column to drain away comprises treating the wall of the production well at the drainage interval and/or treating the formation surrounding the drainage interval so as to increase the flow rate of liquid into the surrounding formation.
• a production well for producing gas from an underground formation, which well extends downwardly from the earth' s surface and is arranged to penetrate the underground formation, the production well comprising: a production interval for allowing formation fluid comprising gas and liquid to flow from the underground formation into the production well; and a drainage interval, wherein the production well is arranged so that a liquid that separates during normal operation from the formation fluid is accumulated to form a liquid column covering at least partly the drainage interval, and wherein the drainage interval is arranged so as to allow liquid from the liquid column to drain away into the surrounding formation, by treating the wall of the production well at the drainage interval and/or treating the formation surrounding the drainage interval.
• the invention is based on the insight gained by Applicant, that the liquid can be drained away into the formation by virtue of its own weight, i.e. due to the hydrostatic pressure formed in the liquid column, if there is sufficient fluid communication between the drainage interval and the surrounding formation.
• This is advantageous for a number of reasons.
• a first advantage is, that by applying the method a limit can be put on the height that the liquid column achieves during normal operation. Therefore, the barrier to inflowing formation fluid that is formed by the liquid column is also limited.
• a further advantage is, that water which is contained in the reservoir fluid does not need to be produced to the surface, and can simply be disposed underground in a variety of practical situations without the need for special reinjection facilities such as a separate reinjection well and pumps.
• the drainage interval can be arranged separately underneath the production interval.
• the well comprises a long interval that is in direct fluid communication with the surrounding gas bearing formation, and wherein during normal operation a liquid column is formed in the well that partially overlaps this interval, the upper part of the interval represents a production interval and the lower part a drainage interval, the boundaries being defined by the amount of overlap.
• Allowing the liquid from the liquid column to drain away suitably comprises treating of the wall of the well and/or treating the formation surrounding the drainage interval so as to make it easier for liquid to flow into the surrounding formation.
• Treatment of the wellbore wall can be particularly advantageous in the case when the wellbore is not cased.
• perforations are arranged in the wall of the production well at the drainage interval, in particular when the well is provided with casing.
• Figure 1 shows schematically a pressure distribution in a well with a liquid column and a gas column on top;
• Figure 2 shows calculated example curves of liquid drainage rates Q ] _ ⁇ as a function of the permeability- thickness product (kh)j_ n j, for three liquid column heights;
• Figure 3 shows a calculated example curve of the liquid drainage time constant ⁇ as a function of the permeability-thickness product (kh)j_ n j
• Figure 4 shows calculated example curves of the height H as a function of the permeability-thickness product (kh)j_ n j, for three liquid entry rates
• Figure 5 shows schematically a first embodiment of the invention
• Figure 6 shows schematically a second embodiment of the invention.
• FIG. 1 The Figure shows schematically the distribution of the pressure p (units: Pa) along the depth d (units: m) of a vertical well which has a liquid column at the bottom and a gas column on top thereof, in a static situation such as during shut-in of a gas well.
• the well is filled with gas between the surface and the depth of the top of the liquid column, d ] _ .
• the liquid column reference numeral 3 in the liquid column
• the pressure distribution as a function of depth in the gas bearing formation surrounding the well is equal to the pressure distribution of an entirely gas-filled well when the well is closed at the top, i.e. corresponds to the pressure distribution as formed by parts 1 and 5 of the pressure curve in Figure 1.
• the driving force for the drainage of a liquid column is the pressure difference ⁇ p - (p - g )g(dp - dj .
• n j denotes the permeability-thickness product of the formation at the drainage interval (m ⁇ ) ; ⁇ j_ denotes the viscosity of the liquid (Pa.s); r e is the drainage radius of the well (m) ; r w is the well bore radius (m) ; S is the skin factor (numeral) ; and ⁇ p has been defined before.
• FIG. 2 shows liquid drainage rates Q ] _ ⁇ (in m-Vday) as a function of the permeability-thickness product (kh)j_ n j (in millidarcy .meter) .
• the curves have been calculated on the basis of equation (1), using the following parameters of Table 1 which have been selected for a typical gas well.
• the rate at which liquid (water) enters the well Q j _ e during gas production is typically in the order of 1...4 m 3 /day, and is also indicated in Figure 2.
• the Figure indicates that when the well is shut in, the rate with which the water drains away is in the same order of magnitude or larger than the water entry rate.
• Figure 3 shows the time constant ⁇ (in days) of equation 2 as a function of the permeability-thickness product (kh)i n j (in millidarcy.meter) , calculated using the parameter values of Table 1.
• Equations 1 and 2 have been derived for a gas well that is shut-in, i.e. closed at the surface so that no gas is produced.
• the well is shut-in for about 5 times the time constant ⁇ , the liquid column above the drainage perforations will have disappeared.
• the gaseous component can be produced continuously to the surface, while liquid is allowed to drain away simultaneously with producing the gaseous component.
• the value of the critical liquid entry rate Qj_ ⁇ ' crit depends on a number of factors such as the the liquid/gas ratio of the inflowing reservoir fluid, the well geometry, the arrangement of perforations, the drainage characteristics, and the reservoir pressure and temperature. It can in principle be determined using a simulation tool.
• draining may occur naturally once a liquid column of sufficient height is formed.
• Another suitable way is to arrange perforations in the wall of the production well, in particular when the well is provided with casing.
• the drainage rate of liquid into the formation can be increased by treating the wall of the production well at the drainage interval and/or treating the formation surrounding the drainage interval. This treatment makes it easier for liquid to flow into the surrounding formation. Treatment of the wellbore wall can be particularly advantageous in the case when the wellbore is not cased. Such a treatment normally reaches only a limited distance into the formation.
• One suitable treatment of the wellbore wall is a treatment using chemicals.
• an acid such as hydrochloric acid can be used in order to remove mud and fines that have precipitated at the wellbore wall, thereby lowering the barrier ("skin") for liquid to flow into the formation.
• the acid can be pumped downhole and will mix with the water column. Acid does not remain active for long, normally shorter than 24 hours.
• pressure pulses are applied to the liquid column so as to generate micro fractures deeper in the formation surrounding the drainage interval.
• Pressure pulses can be provided using means known in the art via hydraulic pulses, also referred to as acoustic pulses.
• Chemical and pressure treatment can also be applied in combination, so as speed up the chemical reaction, and also in order to edge microfractures that are formed in the formation.
• a typical critical gas flow rate corresponds to a gas velocity of approximately 5-6 m/s.
• the method of the present invention can advantageously be used by arranging a gas/liquid separator, either in the well or on surface.
• This separator is arranged so as to receive formation fluid through an inlet, and has outlets for at least a gaseous stream and a liquid stream. The liquid stream is then used to form the liquid column in the well.
• Suitable separators for this purpose are known in the art, e.g. a cyclone separator, a plate pack separator, a curved guiding vane separator, or a mist mat.
• the separator is preferably arranged above this depth.
• a production well 11 extends vertically downwardly from the surface 15 and penetrates a gas-bearing formation 20.
• the well is provided with casing (not shown) , and perforations are arranged at a production interval 24 and a drainage interval 28 below the production interval.
• a separator 30 In the well, above the drainage interval, there is a separator 30 having an inlet for reservoir fluid 32, an outlet for gas 34, and an outlet for liquid 36.
• a conduit 40 is arranged from the outlet 36 to a position 42 below the production interval, within or above the region wherein during normal operation the liquid column 44 is formed. The conduit 40 serves to prevent the separated liquid from being re-entrained by the gas.
• Production tubing 48 provides fluid communication for the gas between the outlet 34 and the wellhead 50.
• reservoir fluid comprising gas and water flows into the well 11 at the production interval 24.
• the reservoir fluid rises in the well and enters the separator 30 through the inlet 32.
• the separator separates the reservoir fluid into a component consisting mainly of gas, and into a liquid component.
• the gas component is conducted to surface via production tubing 48.
• the liquid is guided to a position below the production interval, where a liquid column 44 is formed.
• the height of the liquid column above the drainage interval perforations 28 exerts a hydrostatic pressure larger than the pressure in the formation 20 at the drainage interval. Thereby the liquid from the water column 44 can drain into the formation through the perforations at the drainage interval.
• liquid entry rate Qj_ e When the liquid entry rate Qj_ e is smaller than the critical liquid entry rate Qj_ e ; crit' t ⁇ e gaseous component can be produced continuously to the surface, while liquid is allowed to drain away simultaneously.
• the drainage interval or the formation surrounding the drainage interval can be treated by one of the methods described hereinbefore, so as to allow continuous operation, in particular so that the flow rate of inflowing water at the production interval 24 substantially equals the rate of water drained into the formation at the drainage interval 28.
• production of gas can be stopped by closing the production tubing 48 at the wellhead 50, so as to allow more time for the liquid to drain away.
• the separator 30 does not need to be present if the rate of inflowing gas is below the critical gas flow rate.
• Figure 6 shows schematically another embodiment of the invention. Like numerals as in Figure 5 are used to refer to the same objects.
• the well 60 is cased only at the top and uncased at and below the region 62.
• formation fluid comprising gas and water enters the well 60 in the uncased part and rises.
• the total gas flow rate is low enough so as to allow separation of water droplets 63 which sink to the bottom of the well where they accumulate to form a liquid column 44.
• the liquid column extends to a level which defines the lower end of region 62.
• reservoir fluid can enter the well without hindrance.
• the pressure in the well due to the hydrostatic pressure of the water column is still smaller than the pressure in the formation, so that in region 64 also formation fluid can enter the well as indicated by the arrows, be it somewhat hindered as compared to region 62.
• Regions 62 and 64 form the production interval .
• the hydrostatic pressure in the liquid column is such that the well pressure about equals the pressure in the surrounding formation, so that virtually no fluid is exchanged between well and formation there.
• the hydrostatic pressure is large enough so that the water can drain into the formation. Region 68 forms the drainage interval.

Landscapes

• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Mining & Mineral Resources (AREA)
• Geology (AREA)
• Geochemistry & Mineralogy (AREA)
• Physics & Mathematics (AREA)
• Environmental & Geological Engineering (AREA)
• Fluid Mechanics (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Chemical & Material Sciences (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
• Drilling And Exploitation, And Mining Machines And Methods (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Priority Applications (1)

Applications Claiming Priority (4)

Publications (1)

Family

ID=29266003

Family Applications (1)

Country Status (8)

Families Citing this family (2)

Family Cites Families (31)

• 2003
  • 2003-04-24 EP EP03720532A patent/EP1497531A1/de not_active Withdrawn
  • 2003-04-24 RU RU2004134212/03A patent/RU2311527C2/ru active
  • 2003-04-24 US US10/422,293 patent/US20030213592A1/en not_active Abandoned
  • 2003-04-24 CA CA002483202A patent/CA2483202A1/en not_active Abandoned
  • 2003-04-24 WO PCT/EP2003/004360 patent/WO2003091538A1/en not_active Ceased
  • 2003-04-24 AU AU2003224131A patent/AU2003224131A1/en not_active Abandoned
  • 2003-04-24 CN CNB038125501A patent/CN1332121C/zh not_active Expired - Fee Related
• 2004
  • 2004-11-23 NO NO20045092A patent/NO20045092L/no not_active Application Discontinuation

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events