Wells – Processes – Placing fluid into the formation
Reexamination Certificate
1998-10-09
2001-02-06
Neuder, William (Department: 3672)
Wells
Processes
Placing fluid into the formation
C166S279000
Reexamination Certificate
active
06182759
ABSTRACT:
TECHNICAL FIELD
The invention relates to a process for treating water-containing natural gas wells and natural gas storage wells in which a homogeneous phase containing a water-repellent, solvolysis-resistant active compound is injected.
DESCRIPTION OF THE RELATED ART
Natural gas fields and natural gas storages are encountered in natural subterranean rock cavities. Natural gas storages are also encountered in artificial cavities. These subterranean rocks are by origin either sedimentary rocks or evaporites. These rocks are never dry, and are usually in communication with stratum waters, in many cases with extensive aquifers. Water, in particular in the form of salt solutions, therefore is often encountered on sinking a well, during the cementing of the casing, and in the production phase of gas fields. Drying out water-containing zones and blocking water influx in production wells is necessary for economic reasons, in order to maintain continuous gas flow and to avoid or decrease the disposal of the transported water, which is associated with high costs.
A special case occurs in gas fields or gas storages in which the stratum pressure has already fallen markedly below the hydrostatic pressure. Stratum water can only penetrate into a well if the water saturation in the vicinity of the well is high enough in order to ensure 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 region, the pressure drops increase on flow of the gas phase, and the flow pressure on the well hole bottom decreases, as a result of which the water column in the well hole can increase. If the well hole flow pressure is no longer sufficient, a phase of discontinuous gas production with decreased flow rates occurs.
The reduction of the influx of water into production wells can be effected by two methods: selected blocking, and plugging. Of the various process variants for sealing off water influxes into wells and in the cementing operation, plugging methods generally are used.
For example, the Derwent Abstract of SU 1315602 describes the use of a mixture of tetrabutoxytitanium having a relatively low content of tetrabutoxysilane or tetraethoxysilane for plugging wells against water ingress. The Derwent Abstract of SU 1838587 describes the use of ethylsilicates for sealing off oil and gas wells from percolating water. In both cases, the gas permeability is also greatly reduced.
Other substances used for plugging are cements, swellable clays, epoxide resins having additives of fiber, and especially useful in the case of fissured rocks, gels, suspensions containing additives and finely divided silicon dioxide.
For plugging water influxes, these must be delimitable, so that the remaining productive zones of the rock do not also suffer. A plugging action can be exerted by gels of polymeric solutions of polyacrylamide, copolymers and biopolymers, and silica gels are also mentioned in some applications. The gellation of the polymer solution is effected by admixing or after flooding crosslinking substances. Another possible method of exerting plugging actions is by precipitation of inorganic salts or organic polymers from aqueous or non-aqueous solvents.
For selective blocking of the water influxes over the entire thickness of the hydrocarbon-bearing strata, no precautions need to be taken for selecting the points of water ingress. The selective blocking is performed by two process variants, that is by adsorption of hydrophilic polymers or by rendering rock surfaces hydrophobic.
The hydrophilic adsorption layers increase the flow resistance for the flowing water, which is frequently increased by swelling of the adsorption layer. For the hydrocarbon phase, in contrast, there is no significant decrease in the permeability. When the rock surface is rendered hydrophobic, the surface tension has a partial blocking action for the penetrating water in the form of the capillary counterpressure.
For selective blocking, use is generally made of high molecular weight polymers based on polyacrylamide (also in cationic form), copolymers, terpolymers and biopolymers. For rendering the rock surfaces hydrophobic, inter alia, silanes have also been tested.
The flow resistance of the blocked rock formation must be sufficient to impede the water at the entry to the production well. However, the flow resistance cannot be increased as desired, since the liquids injected for the blocking must be distributed in the rock to develop their blocking action and the gas must thereafter flush clear its flow paths by displacing the excess non-adsorbed treatment liquid. In particular, in the case of low rock permeability, the flow resistance must not be excessive, because otherwise the treatment liquid is not injectable and the gas is not able to penetrate the treatment ring. Thus plugging instead of blocking takes place.
A further special case is represented by the gas fields in which the water is very salty. There, evaporation of water in the vicinity of the well hole causes the solubility limit to be exceeded; in particular chloride salts crystallize out. Since salt water is continuously drawn into the pore cavities by capillary forces, the salt crystals continue to grow until the flow channels are closed to the point of impermeability to natural gas.
The current process for improving the productivity of natural gas wells is the hydraulic generation and stabilization of fractures in the surrounds of the well hole. The additional drainage areas produced by this means and the high gas flow density in the fractures leads to an increased well production rate. However, this process is very expensive. The fracture formation can be controlled only to a very limited extent.
Salt deposits, in particular chloride salts, can be removed by flushing with fresh water. Since the salt deposits continuously reform, these flushings must be carried out regularly, which causes frequent production outages.
It would be desirable to provide a means which permanently improves gas flow in water-containing natural gas wells and natural gas storage wells.
SUMMARY OF THE INVENTION
The invention relates to a process for treating water-containing natural gas wells and natural gas storage wells in which a homogeneous phase comprising a water-repellent, solvolysis-resistant active compound is injected into the water-bearing rock.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Preferably, the homogeneous phase is injected into the water-bearing rock by means of a well. In this case, the active compound is adsorbed or reacts on the rock surface. Excess homogeneous phase is preferably distributed in the surrounds of the well by recompressing gas. The gas used can be, for this purpose, for example, air, nitrogen or, preferably, natural gas.
The homogeneous phase can be readily distributed in the rock of the natural gas-containing fields and has chemical inertness to the natural gas and the transport devices.
Owing to the selective adsorption of water-repellent active compound, the flow resistance in the rock greatly increases for water, and that for gas falls. The water influx is therefore reduced and natural gas can flow better. Natural gas is virtually insoluble in the active compound and can, if no excess homogeneous phase obstructs the flow paths, flow through virtually unhindered to the production well. The surface-smoothing action of the adsorption layer decreases the friction pressures for injected and transported gas. This causes an increased production rate for natural gas at the well hole.
In addition, in rock zones rendered hydrophobic, into which no water flows, the capillary flow of water is greatly decreased and the treated area gradually dries out by evaporation of the water.
The drying out of the rock in the surrounds of the well avoids the plugging of the capillaries of the rock and salt deposits on equipment for transport, storage and further processing.
Since, at the same capillary pressure, the water saturation in rock of low permeability having narrow capillaries is g
Burger Willibald
Deubzer Bernward
Lautenschlager Hans
Mayer Hans
Schrock Robert
Brooks & Kushman P.C.
Neuder William
Wacker-Chemie GmbH
LandOfFree
Process for treating water-containing natural gas wells and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for treating water-containing natural gas wells and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for treating water-containing natural gas wells and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2612567