FIELD OF THE INVENTION

The field of this invention is a method for inhibiting scale formation.

BACKGROUND

The accumulation of unwanted deposits (mineral scales, corrosive products, etc.) occurs in the majority of industrial processes where equipment surfaces are in contact with untreated water. These deposit build-ups can cause operational problems, such as blocking of pipes and pumps, increased running costs, and ultimately equipment failure.

For example, in oilfield applications, precipitation of inorganic salts, such as calcium carbonate, calcium sulfate, barium sulfate or strontium sulfate, from aqueous fluids to form scale is a persistent and common problem during operations to recover hydrocarbons from subterranean formations. Water flooding is the most widely used technique to recover oil from oil-bearing subterranean formations. The technique involves injecting water into the formation to drive oil therein toward a production system composed of one or more wells through which the oil is recovered. The injection water may be produced water or seawater. Seawater, which is readily available in offshore operations, is typically used for the injection water in the water flooding operation. Seawater contains large amounts of dissolved salts such as sulfate. Therefore, sulfate scales are formed when seawater is mixed with formation water. The carbonate scales are primarily generated in the near wellbore/wellbore region due to the pressure drop. Carbon dioxide is frequently introduced into the formations during enhanced oil recovery operations, resulting in absorption of carbon dioxide into aqueous fluids. As aqueous fluids enter the wellbore during production, a reduction in pressure causes the absorbed carbon dioxide to flash out of the aqueous fluids to gas phase. This increases the pH of aqueous fluids and causes growth of carbonate scales in the near wellbore/wellbore region. Furthermore, water encountered in oilfield operations contains low solubility salts. Under certain conditions, these sparingly soluble salts may precipitate out of water resulting in scale formation on various surfaces of the oil recovery system such as walls of pipework, heat exchanger surfaces, valves, and vessels. The scale can block the perforations in the casing, production tubing, downhole pumps and the formation in either the production well or injection wells. Additionally, scale can block the near wellbore region matrix permeability and micro fissures. Scale formation affects heat transfer, interferes with fluid flow, facilitates corrosion and harbors bacteria. In oilfield piping and tubing, scale can cause restriction to flow and high friction loss. Furthermore, the oil production rate declines steadily as the scale forms. To restore the oil production rate, various methods have been used.

In other industrial applications, the emphasis placed on water conservation has made it necessary for industrial water systems to operate at higher concentrations and for extended periods, increasing the potential for deposit accumulation. As a result of this, there is still a significant commercial demand for new and improved additives to control scaling, corrosion, and biofouling.

Polymers derived from carboxylic acids (e.g polyacrylic acids) are one class of scale inhibitors that are used in industrial applications, including oilfield applications, where equipment is subject to fouling from scale growth. See e.g. U.S. Pat. No. 5,032,646A disclosing copolymers of methacrylic acid and itaconic acid for scale inhibition.

There remains a desire for new scale inhibitors, particularly those that are effective at lower application levels.

SUMMARY OF THE INVENTION

The present inventors have found that use of a branched structure polycarboxylic acid having a polymeric backbone and a plurality of relatively short chain polymeric branches from that backbone provides remarkably enhanced scale inhibition as compared to linear polymers of the same polycarboxylic acid.

Thus, disclosed herein is a method for inhibiting scale comprising adding to a fluid that causes scale formation an antiscale agent which is selected from a polycarboxylic acid, a salt thereof, an ester thereof, a combination of two of the acid, the salt and the ester, or a combination of the salt, acid and the ester and which is characterized by having a polymer backbone and a plurality of branches from the polymer backbone.

