Prevention of Water and Condensate Blocks in Wells

Abstract

Compositions and methods are given to prevent, alleviate and remedy water blocks and gas blocks (condensate block or condensate banking). Wettability modifiers are contacted with the formation to change the surfaces from water wet or oil wet to intermediate wet or gas wet. Preferred wettability modifiers include partially or completely fluorinated surfactants or polymers, for example fluorosilanes such as perfluorosilanes, urethane oligomers containing perfluoro alkyl moieties, fluoroacrylates, and fluoroalkyl containing terpolymers or their mixtures. Other examples include surfactants, for example viscoelastic surfactants such as cationic surfactants such as quaternary amines, and zwitterionic surfactants, such as betaines, optionally mixed with co-surfactants.

Description

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 60 / 706238, filed on Aug. 5, 2005.FIELD OF THE INVENTION [0002] The invention relates to the prevention of water blocks and the prevention of condensate banking in oil and gas producing subterranean formations. More particularly, it relates to treating subterranean formations to change the wettability from oil or water wet to intermediate wet or gas wet. BACKGROUND OF THE INVENTION [0003] The accumulation of water near the wellbore in an oil or gas well can decrease the productivity by decreasing the relative permeability of oil or gas. The sources for water accumulation could be filtrate water from drilling mud, cross flow of water from water-bearing zones, water from completion or workover operations, water from matrix / fracture treatments, water from emulsions, etc. The problem of productivity decline because of an increase in near wellbore water saturation is known as water block. [0004] In gas w...

AI Technical Summary

Benefits of technology

[0008] A method has been developed for prevention of water blocks in gas and oil wells and condensate blocks in gas wells using wettability modifiers. This method may be applied to all oil or gas wells with no water or condensate block problems as a preventive solution. It may also be used as a remedial method for clean-up of most or all of existing water or condensate blocks; after these clean-ups it will act to prevent future water block or condensate blocking in the same location. Alternatively, the chemical system may be mixed with fluids used in fracturing, acidizing, drilling and other workover operations to unload the unwanted oil or water based fluids that enter the formation during the operation. The method may also be used to enhance production in oil wells and injection of water in injector wells because of low near well bore pressure drop resulting from the wettability alteration. The wettability alteration is permanent.

[0009] The application of this method to treating a subterranean formation may involve single or multiple stages, separated into pretreatment, main and post treatment stages. The pretreatment stage may involve injection of a preflush of water or brine, one or more alcohols, one or more of other solvents, one or more clay stabilizers, one or more water-solvent mixtures, or one or more treatment fluids used in such oilfield treatments as matrix stimulation, and other treatments, one or more other fluids, or mixtures of such fluids. In the main stage, the wettability modifier may be dispersed or mixed in a carrier fluid that may be a solvent or water and may be injected into the well. Optionally, the formation may be soaked in the fluid that contains a wettability modifier for a period of time (shut-in period). The soaking may not be necessary for some wettability modifiers, some formations, or some conditions. The wettability modifier adheres to the formation by adsorption, chemical bonding, aggregation, electrostatic attraction, precipitation, aggregation, etc. In a typical post treatment stage the fluid injected in the main stage is displaced immediately after the main stage, or after a shut-in period, using a gas such as N2, CO2, etc., or any of the fluids used in the pretreatment stage, or fluids similar to those fluids. This procedure provides better placement of the wettability modifier, and / or enhancement of the flow back of the fluid or fluids injected in the main stage. In this specification, we may occasionally use the term “solvent” or “carrier fluid” for any of the pretreatment main or post treatment fluids. When the well is put into production, or back on production, or used as an injector, the solvent and the left-over wettability modifier flow out of the formation or deeper into the formation, leaving a coating of the wettability modifier in the formation. This alters the wettability of the formation that is initially water or oil wet to an intermediate or gas wetting condition that reduces the capillary pressure of the formation. During the production life cycle of the well, although it generally will not occur, if any water or condensate accumulate in this wettability altered zone, they may easily be cleaned up, thus preventing the formation of water or condensate blocks and enhancing production.

[0012] Since this is a preventive or remediative treatment, the fluids injected into the formation should not create an additional water or condensate block. Thus, the carrier fluid for the chemicals may optionally contain solvents that are volatile (e.g.: alcohol-based solvents) or have low interfacial tension with the gas phase (low capillary pressure) so that, when the well is put on production, the fluid flows out of the formation or deeper into the formation either because of displacement by the gas or evaporation into the gas phase because of high volatility. Since the wettability modifier is adhering to the formation and cannot easily be removed by the flow of fluids or gas, this composition and method provides a long-term solution for the prevention of water / condensate blocks.

Problems solved by technology

The accumulation of water near the wellbore in an oil or gas well can decrease the productivity by decreasing the relative permeability of oil or gas.

In gas wells, in addition to water, liquid hydrocarbons that accumulate near the wellbore can also decrease the productivity of gas.

In addition to such external sources, the liquid hydrocarbons that condense out of the gas phase (called condensates) due to the decline in pressure below the dew point pressure of the gas also hinder the gas production.

When condensates block the production, the problem is called condensate block or condensate banking.

Water blocks and condensate banks can occur together or independently, leading to a decrease in well productivity and in some cases to complete shut down in production.

Condensate banking is a continuing problem, because the condensate accumulates with time even after an initial cleanup.

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