Wells – Processes – Placing fluid into the formation
Reexamination Certificate
1999-06-02
2001-03-27
Bagnell, David (Department: 3672)
Wells
Processes
Placing fluid into the formation
C166S295000
Reexamination Certificate
active
06206102
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process for overcoming effects which hinder the continuous gas flow to a water-bearing natural gas production well or natural gas storage well.
DESCRIPTION OF THE RELATED ART
Natural gas fields and natural gas reservoirs are to be encountered in natural underground cavities of the rock and natural gas reservoirs are also to be encountered in artificial cavities. Said rocks are, by their origin, either sedimentary rocks or evaporites. These rocks are never dry, but are generally associated with stratum waters, possibly even with extended aquifers. Water in the form of saline solutions therefore occurs not only on sinking a well, but on cementing the casing and in the production phase of oil and gas fields. The isolation of water-bearing zones during drilling and cementing and blocking the water ingress in production wells is necessary for economic reasons in order to enable the technical implementation of drilling projects and to avoid or decrease the removal of extracted water which is associated with high costs.
Gas fields or gas reservoirs in which the stratum pressure has already sunk markedly below the hydrostatic pressure constitute a special case. Stratum water can only penetrate into a well if the water saturation in the vicinity of the well is high enough to ensure a continuous flow and the water phase has sufficient expansion energy and/or is entrained by the gas. Owing to the higher water saturation in the pore cavity, the pressure losses increase during flow of the gas phase and the flow pressure on the well bottom decreases, with the water column being able to grow in the well. If the well flow pressure is no longer sufficient, a phase of discontinuous gas production with decreased flow rates occurs.
In the various process variants for sealing off water ingress into wells and during cementation, generally, plugging substances are used, such as cements, swellable clays, epoxide resins having fiber additives, in particular in the case of fissured rocks, gels, suspensions with additives and finely divided silicon dioxide. Reducing the water ingress into production wells can be effected by two methods, that is selective blocking and plugging.
To plug water ingresses, these must be delimitable, so that the remaining productive zones of the rock do not also suffer. Gels of polymeric solutions of polyacrylamide, copolymers and biopolymers can exert a plugging action, but silica gels are also mentioned in some applications. The polymer solution is gelled by admixing or after-flooding with crosslinking substances. Another possibility for exerting a plugging action is precipitations of inorganic salts or organic polymers from aqueous or non-aqueous solvents.
For the selective blocking of the water ingresses over the entire thickness of the hydrocarbon-bearing strata, no precautions need to be taken to select the points of water ingress. Selective blocking is achieved by two process variants, namely by adsorption of hydrophilic polymers or by making the rock surfaces hydrophobic.
The hydrophilic absorption strata increase the flow resistance for the water which continues to flow, which flow resistance is frequently increased by swelling of the absorption stratum. In contrast, for the hydrocarbon phase there is no significant decrease in the permeability. When the rock is made hydrophobic, the interfacial tension has a partially blocking action for the incoming water in the form of the capillary counter pressure.
For the selective blocking, high-molecular-weight polymers based on polyacrylamide (also in cationic form), copolymers, terpolymers and biopolymers are generally used. For making the rock surfaces hydrophobic, silanes, inter alia, have also been tested.
For example, in the Derwent Abstract of SU 1315602, the use of a mixture of tetrabutoxytitanium with a relatively small content of tetrabutoxysilane or tetraethoxysilane for plugging wells against water influx is described. Since these active compounds have low flash points, complex safety precautions are necessary. In the Derwent Abstract of SU 1838587, the use of ethyl silicates for sealing oil wells and gas wells against permeating water is described. In both cases, the gas permeability is also greatly reduced.
The flow resistance must be sufficient to hinder the water at the entrance to the production well. However, the flow resistance cannot be increased as desired, since the liquids injected for blocking must be distributed in the rock to develop their blocking action and the gas must subsequently flush clear its flow paths by displacing the excess unabsorbed treatment liquid. In particular, when the rock permeability is low, the flow resistance cannot be too high, because otherwise the treatment liquid is not injectable and the gas is not able to penetrate the treatment ring.
SUMMARY OF THE INVENTION
The object was therefore to provide a composition which adsorbs to rock surfaces, is readily distributed even in rocks of low permeability, builds up a long-lasting flow resistance for water, but does not hinder the entry of gas by discharging the residual treatment liquid and in the most favorable case even decreases the frictional resistance for gas, so that long-lasting stable gas production is the consequence. These and other objects are achieved by injecting into the water bearing rock a dispersion containing an organosilicon compound as the disperse fraction in a hydrophilic, water-miscible dispersion medium.
The invention relates to a process for stabilizing the gas flow in water-bearing natural gas wells and gas storage wells which deliver at least 50 l of water per 1000 m
3
(S.T.P.) of natural gas produced, in which a dispersion comprising the components
A) an organosilicon compound as disperse fraction,
B) hydrophilic water-miscible dispersion medium and, if appropriate,
C) a dispersant,
is injected into the water-bearing rock.
Preferably, the dispersion is injected by means of a well into the water-bearing rock. In this case organosilicon compound (A) adsorbs to the rock surface. Excess dispersion is preferably distributed in the vicinity of the well by subsequently forcing in gas. The gas used for this purpose can be, for example, air, nitrogen or, preferably, natural gas.
The dispersion is readily distributed in the rock of the natural-gas-containing fields and is chemically inert to the rocks present in the gas fields, the natural gas and the production equipment.
Owing to the selective absorption of organosilicon compound (A) and, if appropriate, dispersant (C) to the rock surfaces, the dispersion introduced into the pore cavity changes. The flow resistance in the rock for water is greatly increased, and that for gas is reduced. The water ingress is therefore reduced and natural gas can flow better. Natural gas scarcely dissolves in organosilicon compound (A) and, if appropriate, dispersant (C) and can, if no excess dispersion blocks the flow paths, flow substantially unhindered to the production well. Owing to the surface-smoothing action of the adsorption stratum, the frictional pressures for injected and produced gas are decreased. This causes an increased production rate for natural gas at the well.
Since the excess dispersion, or its decomposition products, are displaced by gas into the surroundings of the well, no problems occur during production from the well owing to high water saturation in the rock of the surroundings.
In particular, the organosilicon compound (A) is thermally stable at temperatures of 70° C. and significantly above which frequently prevail in gas fields. The flow resistance for water in the rock remains high and the water seal is retained for a long period.
If water flows at high velocity in the rock of the gas fields, the natural gas produced contains at least 50 l of water per 1000 m
3
of natural gas produced. The process is particularly suitable for natural gas wells and gas storage wells which deliver at least 100 l of water, in particular at least 500 l of water, per 1000 m
3
of natural gas produced.
Preferably, the
Burger Willibald
Geck Michael
Meyn Rudiger
Pusch Gunter
Bagnell David
Brooks & Kushman P.C.
Dougherty Jennifer R.
Wacker-Chemie GmbH
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