Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Maintaining environment nondestructive to metal
Reexamination Certificate
1999-07-27
2002-04-30
Warden, Sr., Robert J. (Department: 1744)
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Maintaining environment nondestructive to metal
C422S007000, C422S012000, C422S015000, C166S279000, C166S310000
Reexamination Certificate
active
06379612
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
The present invention relates to compositions comprising oil-soluble scale inhibitors and their use in inhibiting oil field scale formation. More particularly, the present invention relates to compositions comprising an acid form of a known scale inhibitor and a tertiary alkyl primary amine. The compositions of the present invention may be used in inhibiting oil field scale formation. Such methods of use have many advantages over conventional techniques of inhibiting oil field scale, one benefit being a decrease in the period for which production of oil is suspended or reduced during treatment, and reducing the expense of the descaling operation. Furthermore, the compositions may be used in conjunction with other agents such as anti-corrosion agents, wax inhibitors and asphaltene inhibitors.
When a well bore is initially drilled in an oil field, the oil extracted is usually “dry”, being substantially free of aqueous impurities. However, as the oil reserves dwindle, a progressively greater quantity of aqueous impurities becomes mixed with the oil. Changes in formation physical conditions during the production cycle as well as mixing of incompatible waters (i.e. sea water and barium or strontium containing formation waters) can cause scaling in any part of the production system. Scale that occurs in the production system can result in a significant loss in production and associated revenue.
One problem with scale formation in large industrial wells is the formation of scale on the equipment used to extract oil from the field, particularly on the interior surfaces of production tubing and at the perforations in the wall of the casing itself. At the well head, the sub-surface safety valve is also susceptible to damage caused by scale formation.
There are several conventional techniques to counter the problem of oil field scale formation, all of which bear significant disadvantages. The technique of “downhole squeezing” is commonly used, wherein inhibitor chemicals in aqueous solution are injected into the near-wellbore area. A typical squeeze in a vertical well will comprise a preflush, a squeeze pill and an overflush treatment, before the well is returned to normal function. The preflush, typically comprising a mixture of surfactant/demulsifier solution, stops the formation of emulsions that would block the perforation pores and may wet (with water) formation surfaces. The squeeze pill itself typically involves injection of inhibitor as a 1-20% solution in water, causing saturation of the matrix in a radial area around the well. The overflush comprises a displacement of the squeeze pill that propels the chemical front in a wider circumference around the well bore so that a significant surface of rock matrix is exposed to the inhibitor compound.
When the pressure applied down the well is reversed, about 30% of inhibitor chemical is often immediately flushed from the rock. The remaining solution adsorbs to the rock surface and acts to inhibit scale formation by constant treatment as fluid passes through the rock formation into the well conduit. However, over time the inhibitor is gradually washed from the rock surface as oil production continues until a further descaling treatment is required.
Various techniques have been used to try to increase the proportion of chemical that adsorbs to the rock. For example, the chemical can be “shut in” for a period of time with the expectation that the greater period of exposure to the rock surface might increase the degree of absorbency of inhibitor. However, this leads to an increase in the time for which a well is not in production and additionally is not considered to be particularly effective.
A further problem with downhole squeezing is that the aqueous solutions of scale inhibitor tend to change the wettability of the rock; due to its immiscibility with water, oil will not flow through “water-wet” rock. Once wet, the water permeability of the rock has been changed, sometimes permanently, so that a water channel may eventually open up into a water pocket, leading to the so-called “water coning” effect wherein a well is irreversibly damaged. Such a well will never again return to full productivity and new perforations need therefore be sunk in order to economically extract oil from the field.
Another problem with conventional techniques of treatment derives from the fact that aqueous solutions are usually more dense than the crude oil in the field. Consequently, once an aqueous solution of oil scale inhibitor has been used to treat a well, there is insufficient pressure support in the field for the well to flow naturally after treatment has finished. Consequently, the well must often be “gas-lifted” back into production using coil tubing until the natural oil pressure is sufficient to drive the flow once again. However, the gas lift facilities may not always be available and it is expensive and time-consuming to rig up temporary facilities.
If continuous injection facilities are available, the inhibitor compound may be applied continuously to the production stream. However, such facilities are not always feasible and are only available in relatively modern wells.
It is only now, with the advent of more advanced techniques for analyzing the process of oil extraction that the problems set out above have been appreciated. There thus exists a great need for a method of inhibiting oil scale formation that does not suffer from the disadvantages that beset conventional techniques.
Furthermore, in offshore natural gas production systems, alcohols such as methanol or ethylene glycol are often introduced into the well, well head or flow line to prevent formation of hydrates which can cause plugging problems in the same manner as scale deposition. When gas/condensate production occurs remotely from a platform via a sub-sea flow line, conventionally, chemical injection at the wellhead or downhole is supplied by an umbilical connector in which are contained a bundle of lines. It is necessary to supply scale inhibitor in a separate line because traditional scale inhibitors are generally intolerant of alcohols, to the extent that mixing of the two types of chemical causes severe precipitation problems with the scale inhibitor. However, each line is extremely costly. Accordingly, a scale inhibitor composition that is compatible with both traditional oilfield treatment chemicals and other organic solvent packages is particularly useful, since it avoids the necessity to supply the scale inhibitor separately.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a composition containing an oil-soluble scale inhibitor, said oil-soluble inhibitor comprising a scale inhibitor and a tertiary alkyl primary amine. Preferably, the composition is dissolved in a hydrocarbon or other fluid.
By oil-soluble is meant that the composition is infinitely soluble in usual hydrocarbon carriers such as diesel and kerosene. However, since scale formation in oil wells is only associated with the production of water in the well, it is essential that the scale inhibitor must be able to partition between phases so that it is water soluble in the process system or downhole and therein able to act as an inhibitor of scale formation.
Any inhibitor for which an acid form may be easily produced is suitable for use according to the present invention. Preferably, the acid form of scale inhibitor has a pH of typically less than 2.5. Scale inhibitors suitable for use in accordance with the present invention include phosphonates, acrylic co/ter-polymers, polyacrylic acid (PAA), phosphino carboxylic acid (PPCA) or phosphate esters or other traditional water based scale inhibitor chemistries. Suitable scale inhibitors are known to those of skill in the art.
In order to form a composition according to the present invention, the scale inhibitor in acid form is blended with an amine to form an oil-soluble mix. The scale inhibitor should be mixed with a tertiary alkyl primary amine, such as, for example, the tertiary alkyl pri
Montgomerie Harry
Reizer James M.
Rudel Michael G.
Sitz Curtis D.
Wat Rex M. S.
Bracewell & Patterson, L.L.P
Champion Technologies Inc.
Soubra Imad
Warden, Sr. Robert J.
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