Composition Useful in Sulfate Scale Removal

Abstract

The present invention discloses a novel aqueous composition for use in removing mixed sulfate scale from a surface contaminated with such, said composition comprising: a chelating agent and a counterion component selected from the group consisting of: Li₅DTPA; Na₅DTPA; K₅DTPA; Cs₅DTPA; Na₄EDTA; K₄EDTA; TEAH₄DTPA; and TBAH₅DTPA; a dissolution enhancer; optionally a compound such as sodium gluconate or the like and a carboxyl-containing fructan such as carboxymethyl inulin. There is also disclosed methods to use such compositions.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application claims the benefit of and priority to Canadian Application No. 3,049,343, filed Jul. 11, 2019. The entire specification and figures of the above-referenced application are hereby incorporated, in their entirety by reference.FIELD OF THE INVENTION[0002]The present invention is directed to a composition and method for use in oilfield and industrial operations, more specifically to compositions used in the removal of mixed sulfate scale.BACKGROUND OF THE INVENTION[0003]Scaling, or the formation of sulfate mineral deposits can occur on surfaces of metal, rock or other materials. Scale is caused by a precipitation process as a result of thermodynamic and hydrodynamic factors or changes in pressure, velocity rates and temperature and the subsequent change in the composition of a solution (commonly water).[0004]Typical homogenous scales consist of e.g. calcium carbonate, calcium sulfate, barium sulfate, strontium sulfate, iron s...

AI Technical Summary

Benefits of technology

[0075]allowing sufficient time of exposure to remove the mixed sulfate scale from the contaminated surface.

Problems solved by technology

Sulfate scales and in particular the common Barium sulfate scale is a major challenge for industry and in particular the oilfield industry.

In some cases, scale deposits restrict or even shut-off the production conduit if the produced water composition flow dynamics are interrupted by changes in pressure and / or temperature.

The precipitation of sulfate scales can occur at any point in a production, injection or abandonment-disposal well and associate equipment cycle, and can also be caused by incompatibilities of injected water and formation water, in addition to the changes in temperature and pressure dynamics mentioned above, as well as wellbore additives or upsets in the flow equilibrium.

Sulfate scaling on surface equipment, such as heat exchangers and the associated piping, is a major issue for industry as well, as it typically needs to be managed by mechanical means such as disassembling the equipment in question, manually cleaning the scale and reassembling which is very time consuming and expensive.

As the multiple sulfate composition scaling challenges occur offshore-onshore are typically very difficult to manage efficiently as a whole.

Rules of thumb and general formulas may not be adequate, and selection procedures based on broader experience and more in-depth knowledge may be required.

These alkaline earth metal salts have many similar properties and often precipitate together forming problematic sulfate scales.

The deposition of this scale is a serious problem for oil and gas producers globally, causing fouling in the wellbore and surface related processing equipment These scales not only restrict the hydrocarbon flow from the formation resulting in lost production, and since the formation or injection water is saturated with sulfates, the continued deposition causes fouling and potentially failures of critical equipment such as perforations, casing, tubes, valves, and surface equipment, all with the potential to reduce the rate of oil production and result in substantial lost revenue.

Sulfate scales are not soluble in traditional acid scale dissolvers.

Radium sulfate, while not being the most common sulfate scale represents a challenge in its removal as it is often imbedded in barium sulfate scale and is also radioactive and thus can carry an exposure risk and cause very expensive clean-up or disposal costs of tubing and down-hole equipment etc. when brought out of the well for replacement, general service or abandonment.

Once this water / acid insoluble scale has formed, it is extremely difficult to remove with existing chemical options on the market.

Existing methods to remove sulfate scale include mechanical removal and / or low performance scale dissolvers currently on the market, but both have limitations and disadvantages.

Mechanical removal involves the use of milling tools, scraping, or high-pressure jetting and / or disassembly of key production equipment causing substantial down time of production and processing equipment.

These methods have limited efficiency as the scale is extremely hard to remove, often forming in areas beyond the reach of the mechanical equipment as many facilities have welded joints and limited access.

High pressure jetting will typically only remove the surface of the scale.

), is time-consuming, and has limited dissolution capacity.

This is understood to be a multi-step process which would cause longer shutdown in production and is not determined to actually be applicable in the field.

Despite the existing prior art, there are very few commercial compositions available to remove barium sulfate scale, the situation is made even more complex since most barium sulfate scale occurs in wellbores, pipes and other equipment associated with either oil production and / or oil exploration in offshore or highly regulated jurisdictions such as the North Sea.

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