GB2248830A

GB2248830A - Method for inhibiting scale formation

Info

Publication number: GB2248830A
Application number: GB9120256A
Authority: GB
Inventors: Peyman Ostovar
Original assignee: Britoil Ltd
Current assignee: Britoil Ltd
Priority date: 1990-10-04
Filing date: 1991-09-23
Publication date: 1992-04-22
Also published as: GB9120256D0

Abstract

A method for inhibiting the formation of scale in water having a high barium content and low pH comprises the addition of an aqueous solution of a phosphonate of formula: <IMAGE> and R = H, CH3 C2H5 or M R<1> = H, CH3, CR3, @C6H5, @SO3H2 y = 1 - 10 n = 10 - 1000 m = 0 - 2 p = 1 - 1000 q = 1 - 1000 M = alkali metal or ammonium ion wherein the molecular weight is in the range 1000-100,000. The scale inhibitors may be present in the form of a fully or partially neutralised salt and may be injected into production fluids obtained from and underground reservoir or injected into the reservoir via a wellbore as part of a squeeze technique.

Description

METHOD FOR INHIBITING SCALE FORMATION This invention relates to a method for inhibiting the formation of scale, in particular to a method for inhibiting the formation of scale in waters having a high barium content and low pH.

A scale inhibitor is a compound or mixture of compounds which inhibits crystal growth and thereby reduces the tendency of scale to form.

Scale inhibitors are used in the oil industry. Water flooding is one of the most successful and extensively used secondary recovery methods. Water is injected under pressure into the reservoir via injection wells and drives the oil through the rock into nearby producing wells. In this type of operation it is most important to ensure that the injection water is free from suspended particles or any chemicals or biological substance which might cause blockage of the pore channels in the reservoir rock. The oil in the reservoir is frequently associated with connate water which contains various cations, sometimes including barium, calcium and strontium.

Many oil fields are situated in offshore locations and for them the only source of injection water is the sea. Sea water contains sulphate and carbonate ions which, in the absence of treatment, would react with alkaline earth metal ions in the connate water to precipitate scale.

In order to prevent this, scale inhibitors are used.

Typical scale inhibitors include sulphonated ethoxylated hydrocarbons, polyacrylates, amine phosphonates and organic polyphosphonic acids.

The main types of scale occurring in oil production operations are calcium carbonate and barium, calcium and strontium sulphates.

Conventional scale inhibitors have proved effective in combating these types of scale. However scale formation encountered in reservoirs which have a high barium content in the formation waters coupled with a low pH is difficult to control with these conventional scale inhibitors.

We have now found that certain polyaminomethylene phosphonates may be used as effective scale inhibitors for waters having a high barium content and low pH.

Thus according to the present invention there is provided a method for inhibiting scale formation in waters having a high barium content and low pH which method comprises adding an aqueous solution of a compound of formula:

wherein X = -NCHR1PO3R2 or CHRlP03R2 -CH(CH2 )y#N or CHR1PO3R2

-CH-(CH2)m-Po3R2 and R = H, CH3 C2H5 or M R1 = H, CH3, CR3, C6H5, S 3H2 y = 1 - 10 n = 10 - 1000 m=0-2 p = 1 - 1000 q = 1 - 1000 M = alkali metal or ammonium ion wherein the molecular weight is in the range 1000-100,000 to an aqueous medium containing potential scale forming constituents.

Preferred compounds are those wherein R and R1 are hydrogen.

By high barium content we mean a content in the range 700 3000 ppm of the original formation water.

By low pH we mean a pH in the range 4 - 6 The scale inhibitors according to the present invention may be suitably employed in either partially or fully neutralised form.

The neutralised scale inhibitors may be in the form of the alkali metal salt or ammonium salt, preferably in the form of the sodium salt.

The scale inhibitors of the present invention may be used either downhole as part of a squeeze technique or they may be injected on an offshore platform.

The scale inhibitors are suitably employed in concentrations in the range 5 - 200 ppm or in aqueous solutions with concentrations in the range 10 - 50% by weight.

The scale inhibitors of the present invention remain active and are thermally stable.

Scale inhibitors according to the present invention may be prepared by conventional methods. For example, by treatment of the appropriate polyamino compound with formaldehyde and phosphorous acid.

Suitable scale inhibitors include compounds of the following formulae:

Claims

Claims: 1. A method for inhibiting scale formation in waters having a high barium content and low pH which method comprises adding an aqueous solution of a compound of formula:

wherein X = -NCHR1PO3R2 or CHR1PO3R2 -CH(CH2 )y#N or CHR1PO3R2

-CH-(CH2)m-PO3R2 and R = H, CH3 C2H5 or M R1 = H, CH3, CR3, C6H5, SO3H2 y = 1 - 10 n = 10 - 1000 m=0-2 p = 1 - 1000 q = 1 - 1000 M = alkali metal or ammonium ion wherein the molecular weight is in the range 1000-100,000 to an aqueous medium containing potential scale forming constituents.
2. A method according to claim 1 wherein R and R1 are hydrogen.
3. A method according to claim 1 wherein the scale inhibitor compound is present in the form of the partial or fully neutralised salt.
4. A method according to claim 3 wherein the salt is the sodium salt.
5. A method according to any of the preceding claims wherein the scale inhibitor is present in a concentration in the range 5-200 mg/l in the aqueous solution.
6. A method according to any of claims 1 to 4 wherein the scale inhibitor is present in a concentration in the range 10-50Z by weight in the aqueous solution.