Earth boring – well treating – and oil field chemistry – Well treating – Contains organic component
Reexamination Certificate
1999-04-05
2001-05-08
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Well treating
Contains organic component
C507S225000, C507S226000, C166S305100, C166S295000
Reexamination Certificate
active
06228812
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to methods and compositions for modifying the permeability of subterranean formations. In particular, this invention relates to methods and compositions for selectively reducing the production of water from subterranean formations by modifying formation permeability using a water control treatment fluid containing a terpolymer in an aqueous-based fluid.
2. Description of Related Art
Production of water and aqueous fluids from oil and gas wells is a common phenomenon which may pose a variety of problems. As hydrocarbons are removed from a producing well, water may begin to move through the formation toward the wellbore where it is produced along with the hydrocarbons. Examples of mechanisms responsible for water production include “coning” into the wellbore from an adjacent water column, and/or movement of water through one or more individual strata completed in the wellbore. Other water production mechanisms, as well as combination of such mechanisms are also possible.
Water production is a phenomenon that typically acts to reduce the amount of oil and/or gas that may be ultimately recovered from a well. In this regard, increasing volumes of water take the place of other fluids that may flow or be lifted from a well, and increase the cost and size of equipment required to separate water from the produced hydrocarbons. Furthermore, operating costs associated with disposal of produced water in an environmentally safe manner typically increase with the volume of produced water, thus increasing the threshold amount of hydrocarbons that must be produced in order to continue economical production of the well. Water production also tends to cause other problems such as scaling of tubulars and surface equipment.
In the past, methods that have been used to control or restrict water production include the gellation of polyvinyl alcohol (“PVA”), polyacrylic acid and the condensation polymerization of phenyl and formaldehyde within formation pore channels. These processes are designed to damage pore channels within the formation matrix and restrict fluid movement through the channels. Another technique involves loading a subterranean area adjacent to the wellbore with a barrier, such as concrete resin or particulate matter, so that the loaded areas are effectively plugged. The area above the loaded area is then perforated to begin production.
In another method, polyacrylamide gels crosslinked with chromium (+3) ions have also been employed. In this case, polyacrylamide may be either a homopolymer or terpolymer. The crosslinking reactions are designed to be slow enough that the fluid may be placed in the reservoir before gellation occurs. The resulting viscous gel is designed to function by blocking or preventing further fluid flow through highly permeable portions of reservoir.
Unfortunately, the above-described conventional water control methods are not selective and may damage both hydrocarbon and water producing pathways. Damage to hydrocarbon-producing pathways is undesirable since it may reduce the well's productivity and profitability.
Other conventional methods have employed high molecular weight polymers in an attempt to achieve selective water control without the necessity of zone isolation methods. Such methods include terpolymers based on polyacrylamide, for example, hydrophillic monomers such as ammonium or alkali metal salts of acrylamidomethylpropane sulfonic acid (“AMPS”). In many cases, these polymers have provided poor performance due to inadequate retention within the formation. Addition of anchoring groups, such as dimethyldiallylammonium chloride, have been used to achieve some improvement in performance, but the resulting polymers may still not be adequately retained.
A further disadvantage to many conventional water control compounds is that they are unstable in acids and heavy brines which are frequently found within oil and gas wells, and/or they may degrade with increased temperature. These characteristics may render the compounds useless in many downhole applications.
SUMMARY OF THE INVENTION
Disclosed are compositions that may be used for selective permeability modification of subterranean formations to reduce or substantially eliminate the amount of water produced from oil and/or gas wells, without substantially affecting the production of hydrocarbons. The disclosed compositions include co-polymers having at least one of N-vinylformamide, N-methylacetamide, and/or N,N-diallylacetamide anchoring groups in combination with at least one hydrophillic monomer, such as a monomer based on AMPS. Other optional anchoring groups, such as sodium acrylate, may also be present in the co-polymers. Optional filler monomeric units may also be present.
In practice, one or more of the disclosed polymers may be introduced into a well as part of an aqueous-based water control treatment fluid to achieve selective permeability modification of a subterranean formation. In this regard, the compositions may be used to substantially reduce the production of water in oil and/or gas wells without substantially effecting the production of associated hydrocarbons. While not wishing to be bound by theory, it is believed that the disclosed polymer compositions interact with hydrocarbon and aqueous formation fluids in different ways, to achieve this advantageous and surprising result without the need for mechanical or other forms of zonal isolation. For example, it is believed that the disclosed polymer compositions containing hydrophillic monomer groups are compatible with areas of the formation in which water is the primary constituent, and are anchored in these areas by the anchoring groups of the polymer. However, it is believed that the disclosed compositions are substantially incompatible with high concentrations of hydrocarbons, and thus tend to degrade, release, or are otherwise ineffective in areas of the formation having relatively large concentrations, or saturation, of hydrocarbons.
Advantageously, the disclosed method and compositions are relatively non-damaging to oil permeability, for example, in oil saturated sandstone while exhibiting the ability to decrease water permeability substantially in water saturated zones. Therefore, the disclosed compositions may be applied successfully to a productive zone without the necessity of mechanical isolation in the wellbore. It will be understood with benefit of this disclosure that mechanical isolation, such as isolation of a water producing section or perforations may be employed if so desired, however, such measures typically add significant costs to a water control treatment. Consequently, treatments utilizing the disclosed method and compositions without mechanical isolation are considerably less expensive than conventional methods which require such measures.
In one respect, disclosed is a method for treating a subterranean formation, including introducing a water control treatment fluid into the formation, the water control treatment fluid including a copolymer and an aqueous base fluid; wherein the copolymer may include a hydrophillic monomeric unit and a first anchoring monomeric unit and wherein the first anchoring monomeric unit may be based on at least one of N-vinylformamide, N-methylacetamide, N,N-diallylacetamide, or a mixture thereof. In one particular embodiment, the first anchoring monomeric unit may be based on N-vinylformamide. The copolymer further may also include a second anchoring monomeric unit based on at least one of dimethyldiallyl ammonium chloride, acrylic acid (such as ammonium or alkali metal salts of acrylic acid), or a mixture thereof. The copolymer further may also include a filler monomeric unit based on acrylamide, methylacrylamide, or a mixture thereof. The hydrophillic monomeric unit may be based on at least one of acrylamidomethylpropanesulfonic acid, acrylic acid, acrylate salt, or a mixture thereof. The hydrophillic monomeric unit may be based on ammonium or alkali metal salts of acrylamidomethylprop
Dawson Jeffrey C.
Kesavan Subramanian
Le Hoang V.
BJ Services Company
O'Keefe Egan & Peterman, LLP
Tucker Philip
LandOfFree
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