GB2483436A

GB2483436A - Magnetohydrodynamic device for the control of scale in oil well production columns

Info

Publication number: GB2483436A
Application number: GB1014604.1A
Authority: GB
Inventors: Joao Crisosthomo De Queiroz Neto; Marco Antonio Magalha Es De Menezes; Gabriel Menezes Barreto De Oliviera; Jorge Alberto Da Silva; Fernando De Castro Junqueira
Original assignee: Petroleo Brasileiro SA Petrobras
Current assignee: Petroleo Brasileiro SA Petrobras
Priority date: 2010-09-02
Filing date: 2010-09-02
Publication date: 2012-03-14
Anticipated expiration: 2030-09-02
Also published as: GB201014604D0; GB2483436B

Abstract

A magnetohydrodynamic device D for the control of scale in oil well production columns comprises a first flange 1, of the same diameter as a first flange of the production column 2, having continuity with a first length of pipe 3 of the same internal diameter as the production column C with a first termination in the form of a cup 4. A plurality of magnets 5, 6 are positioned as diametrically opposite pairs with a lateral space between each pair. Each end of the magnets are attached to first and second cups 4, 7. The second cup has continuity with a second length of pipe 8 which terminates in a second flange 9 of the same diameter as a second flange of the production column 10. The magnets have a sufficient and preferably constant magnetic field. Also, the magnets are regularly spaced apart such that the flow of fluid (F, Fig. 1) originating from a well (P, Fig. 1) flows through the spaces between the magnets.

Description

MAGNETOHYDRODYNAMIC DEVICE FOR THE PREVENTIVE CONTROL

OF SCALE IN OIL WELL PRODUCTION COLUMNS

FIELD OF THE INVENTION

The field of application of this invention

includes devices and equipment to control the deposition of substances on the internal walls of piping by means of magnetic fields, by changing the morphology of the crystals of these substances. It has particular application in pipelines transporting petroleum, but more specifically where the pipe is a production column in a producer well.

BASIS OF THE INVENTION

The deposition of solid inorganic minerals (barium sulphate, strontium sulphate and calcium carbonate) forming scale has long been a major challenge which has to be overcome by the oil industry. The formation of scale reduces production and the injectivity of oil wells. It can also occur in equipment located at the bottom of a well, such as for example sand-containment screens, valves, connectors, etc. It also occurs in perforators and in surface equipment, such as for example heat exchangers, separators, production line piping, etc. The mechanisms by which a precipitate reduces the permeability of a forthation for a well include: -the deposition of solids on the walls of the pores of the formation caused by attractive forces between the particles and the surfaces of the pores, -individual particles blocking pore openings, and -a number of particles forming bridges across pore openings.

The characteristics of the precipitate affect the extent of the damage in porous rocks.

Conditions such as a high degree of supersaturation, the presence of impurities, temperature change, and mixing rate control the quantity and morphology of the precipitating crystals.

The scale most commonly comprises: -calcium carbonate (calcite) and iron carbonate, -calcium sulphate (gypsum, hemihydrite, anhydrite), barium sulphate (barytes) and strontium sulphate (celestite), -iron sulphide, and -ferrous hydroxide.

In the context of oil and gas extraction, scale originating from solutes in water occurs in primary wells, secondary wells, injector wells and pipes connecting tanks.

Most scale in injector wells, particularly in Brazil, comprises compounds of barium sulphate, strontium sulphate and calcium carbonate, all of which are insoluble in acids.

RELPSTED ART

Dyer & Graham [The effect of temperature and

pressure on oilfield scale formation, Journal of

Petroleum Science and Engineering 35 (2002), 95-107], included here as a reference, have carried out dynamic blocking tests on pipes to determine the effect of increase in temperature and pressure on the formation of barium sulphate and calcium carbonate scale as part of an investigation considering the application of scale inhibitors in high-pressure high-temperature reservoirs.

As the pressure increased it was found that the tendency of the brines tested to form carbonate and sulphate scale decreased, as predicted by the software's scale prediction.

As the temperature increased the brine's tendency to form carbonate scale increased, while the scaling tendency of a brine with a high-sulphate content decreased.

The effect of temperature on the tendency to produce scale was more significant than the effect of pressure.

A brine with a low sulphur content was also tested and this failed to precipitate scale at a time when there was the highest tendency to precipitate scale.

Under these test conditions the kinetics of the precipitation of scale were slow, so the rate of precipitation was more significant than the thermodynamic force driving precipitation.

A. T. Kan et al. [Scale formation and prevention in the presence of hydrate inhibitors, SPE 80255, Society of Petroleum Engineers (2003), 16 pp and Effect of hydrate inhibitors on oilfield scale formation and inhibition, SPE 74657, Society of Petroleum Engineers (2002), 6 pp], included here as a reference, investigated the effect of inhibitors, particularly methanol at a concentration of 5% by volume, together with ethanol, ethylene glycol and triethylene glycol, as hydrate co-solvents on scale formation in oil fields. The effect of hydrate inhibitor in inhibiting scale formation by common inhibitors is still not well known. The cost of this alternative is high, and there are associated environmental problems.

In 1945, Vermeiren in Belgium [as cited in Gehr, R., Zhai, Z.A., Finch, J.A.,, Rao, S.R., Water Res.., 1995, 29(3), 933-940 and Klassen, V.1., Developments in mineral processing, Part B, Mineral Processing, 1981, 1077-1097], included here as a reference, carried out the first magnetic treatment on water to prevent sedimentation and remove accumulated sediments.

This possibility was most clearly demonstrated in the work by Gehr et al., exposing aqueous solutions to

a magnetic field of 4.75 T (at 200 MHz) and

investigating the factors affecting the solubility of calcium sulphate (gypsum)

In his conclusions it was stated that magnetic

treatment inhibits the nucleation and growth of gypsum on receptive solid surfaces and instead promotes direct "homogeneous" crystallisation, avoiding blocking scale in porous rocks through which oil and gas should flow.

The insight that water molecules (which are naturally dipolar) line up in relation to magnetic

field and retain a memory of that alignment for an

appreciable period of time led researchers in other fields of human interest to seize upon this effect for applications of special interest, and mention may be made of the work of Porto on changes in the biological and physical/chemical properties of water brought about

by magnetic fields [Porto, M.E.G., Changes in the

biological and physical/chemical properties of water

induced by magnetic fields. Masters Dissertation,

Institute of Chemistry -Department of Physical Chemistry, UNICAMP, p. 111, 1998] Document US 6,733,668 [Omni-Tech 2000 Inc.], included here as a reference, describes an instrument for the magnetic treatment of liquids produced in a hydrocarbon well which comprises a hydrocarbon section and a reactor section. The hydrocarbon section is designed to treat crude oil and inhibit the deposition of paraffin, asphaltenes and the like. The reactor section is designed to treat aqueous liquids to inhibit the deposition of mineral scale, in particular the deposition of barium sulphate. The two sections are provided with magnets which are arranged in a coaxial linear relationship. Activation of the radial magnets provided to the second reactor distorts the magnetic field and inhibits the formation of scale in production piping. The instrument is effective in preventing the deposition of barium sulphate.

Document US 5,118,415 [Enecon Corporation], included here as a reference, shows an arrangement for removing scale and deposits on the insides of pipes by means of a permanent magnetic unit of high capacity which does not require an external energy source, mounted outside the pipe in such a way as to establish a magnetic field flux in line with most of the flow of fluid flowing within the pipe. The magnetic unit comprises high magnetic density magnets mounted in diametrically-opposite pairs. The unit can modify hard calcite deposits present in the flow of fluid into crystals of aragonite/valerite, which can easily be removed by the liquid medium to dissolve existing scale and also effectively prevent the formation of new scale on the internal walls of the pipe.

Document US 5,238,558 [Rare Earth Technologies], included here as a reference, discloses a magnetohydrodynamic system and a method for treating pipes and the fluid transported by them in such a way as to prevent the occurrence of accumulations of deposits within the pipes. The system comprises a pipe within which a fluid flows and at least one magnetic unit confining an external region of the pipe being treated. The magnetic unit comprises at least four magnets, each having a magnetic field density of around 6,700 gauss, with part of the polarity at the ends of a unit, part of the polarity in the cover of the structure of the unit and another part of the polarity on the side in contact with the pipe being treated.

SUMMARY OF THE INVENTION

The object of this invention is a magnetohydrodynamic device to control the deposition of inorganic solid minerals forming deposits and scale which reduce the internal diameter of pipes transporting oil, interfering with or interrupting the flow, and more specifically the pipes are production columns.

The object of this invention is accomplished through a device fitted between two sections of a production column by welding or using flanges, normally below the equipment sealing the well annulus/column, known by the term "packer", and which will henceforth refer to an oil production well.

The device is of the magnetohydrodynamic type and includes a plurality of magnets having a sufficient and constant magnetic field, which are regularly spaced apart so that fluid coming from the well flows through the space between them within the production column, and for this purpose these magnets have a substantially cylindrical arrangement with a polarity configuration between them such that the direction of the magnetic flux density is tangential to a pair in the arrangement of magnets in the device, resulting in a circular total magnetic flux with respect to the cylindrical configuration of the device acting transversely to the fluid which passes between two adjacent magnets.

The effect of an adequate magnetic field strength

on the crystals of inorganic salts alters the morphology of the crystals, making them soluble and preventing them from depositing and subsequently converting into scale through accumulation.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is an illustration of application of the method according to this invention to a zone of no interest located above a zone of interest.

Figure 2 is an illustration of application of a method according to this invention to a zone of no interest located below a zone of interest.

Figure 3 is an illustration of application of a method according to this invention to a zone of no interest located above and below a zone of interest.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a magnetohydrodynamic device for controlling the deposition of solid inorganic minerals forming deposits and scale which reduce the internal diameter of pipes transporting oil, interfering with or interrupting the flow, more specifically where the pipes are production columns.

A calcium carbonate (Ca003) precipitate is the main component of the scale which can occur in a production column and its particles crystallise out in three polymorphic varieties, these being calcite, valerite and aragonite, although there are also amorphous and hydrated calcium carbonates which are highly unstable and only occur during the initial stages of the formation of calcium carbonate, before it begins to crystallise.

Calcite has a hexagonal crystalline structure and is thermodynamically the most stable phase. It is therefore the most common variety in nature. The accumulation of calcite crystals produces a very hard dense scale.

Valerite has a hexagonal crystalline structure, similar to calcite, but is less stable than the latter.

Aragonite however has an orthorhombic crystalline structure and is metastable at atmospheric pressure and low temperatures. Aragonite forms as a precipitate at temperatures below the range between 60°C and 70°C, in a very narrow range of physical and chemical conditions, producing acicular crystals and soft porous deposits which are more soluble and easier to remove.

Investigations in the prior art have reached the

conclusion that application of a magnetic field

improves the precipitation of aragonite from carbonate-rich solutions, and that the magnetic treatment parameters which influence the quantity of aragonite precipitated and are considered to be the most important are magnetic induction and exposure time.

Curiously the flow rate of the fluid does not have any effect which can be considered significant.

Investigations have also established that when scale forms from a mixture of solutions of CaC12 and Na2CO3 the frequency of nucleation of CaCO3 particles is suppressed, but particle growth is accelerated when the magnetic flow density to which it is exposed is greater than 3000 gauss and the exposure time is greater than minutes. The magnetic effect can mainly be attributed to the exposure of solutions of Na2CO3 and not to the solution of CaC12; the magnetic effect was observed even when solutions of CaC12 and Na2CO3 were mixed at a time of 120 hours after magnetic exposure, and formation of the aragonite structure of CaCO3 crystals is accelerated by magnetic exposure.

"Magnetic memory" phenomena, that is the phenomenon of retaining anti-scaling properties in magnetically-treated water for some time after treatment, have been studied by some researchers and lasts for more than 24 to 36 hours, according to the manufacturer of water conditioners, or up to 200 hours according to other manufacturers, or even 1 month if the treatment is performed on the basis of CEPI (Conditionnement Elect roma gnétique Par Induction -Electromagnetic Conditioning by Induction) With regard to scale and precipitates of barium and strontium sulphates, investigations have been carried out to check the formation of scale by the abovementioned sulphates as a result of mixing incompatible waters. The chemical incompatibility between sea water and ground water in rocks containing oil and gas may promote the deposition of BaSO4 and SrSO4 scale.

On the basis of everything which has been presented hitherto it can be said that the application

of a magnetic field through a device of the

magnetohydrodynamic type such as the object of this invention, when applied to the preventive control of scale in the production column, interferes with the rates of growth and nucleation of the crystal particles of the salts present in the flow of fluid produced. The interference is brought about by altering the morphology of the particles, preventing their adsorption on the metal surface of the production column. Also, and more particularly with regard to this invention, it can be said that the strength of the

magnetic field used does not cause problems to the

health of humans involved in the operations or cause any interference for the environment. The possible technology for applying this invention is complementary to or replaces the chemical treatments currently in use.

Figure 1 shows an illustration of the device CD) according to this invention, installed between two lengths of a production column (C) in an oil-producing well (P) (the latter in longitudinal cross-section) The direction of a flow of fluid (F) through the device CD) is also indicated in Figure 1.

Figure 2 shows an illustration of the device CD) to which this invention relates connected to a S production column (C) by means which may be selected from welding or attachment by flanges. In the case of this invention flange attachment is preferred. It may be seen that this comprises: -a first flange (I), of the same diameter as a first flange in the production column (2), has continuity with a first length of pipe (3) of the same diameter within the production column (C), with a first termination in the form of a cup (4), -a plurality of magnets (5, 6) positioned as diametrically opposite pairs with lateral spaces between each pair are rigidly attached and held in their positions through attachment of the outer regions of one of their extremities to the inside surface of the first termination in the form of a cup (4), -a second termination in the form of a cup (7) attached to the external region of the other extremities of the pairs of magnets (5, 6) has continuity with a second length of pipe (8) which ends in a second flange (9) of the same diameter as a second flange of the production column (10) Magnets (5, 6) are of the permanent type and the material is selected from rare earth elements.

Preferably magnets (5, 6) are of neodymium-iron-boron (NdFeB) Magnets (5, 6) are of the same material, but have different properties determined according to the intended treatment, which for example depend on the production flow from the well.

Magnets (5, 6) have different strengths, but the magnetic field generated by them is constant. Pairs of diametrically opposite magnets of lesser magnetic strength (5) are positioned adjacent to diametrically-opposite pairs of magnets of greater magnetic strength (6).

Contrary to the normal state of the art, instead of the magnetic field generated by the magnets being aligned with the axis of a flow of fluid (F), in this

invention the lines of the magnetic field pass

S transversely through the flow of fluid (F) because it is circular in nature.

With the assistance now of Figure 3, which shows the production column (C), the well (P) and the device (D) in longitudinal cross-section, it will be seen that the flow of fluid (F) can only pass through the space between two adjacent magnets (5, 6) and the magnetic field is in a transverse direction, the entire flow of fluid (F) passing between these adjacent magnets (5, 6) receiving the effect of the magnetic

field at a uniform strength.

As a result of its construction, the device (D) according to this invention offers no restriction to operational processes on the production column (C) or well (P), such as for example fishing, the passage of logs, scale detectors, sand-level detectors, etc. Although this invention has been described in its preferred embodiment, the main concept underlying this invention, which is a magnetohydrodynamic device for controlling the deposition of solid inorganic minerals forming deposits and scale which reduce the internal diameters of pipes transporting oil, interfering with or interrupting the flow, more particularly where the pipes are production columns, will retain its innovative character even when those normally skilled in the art can envisage and make variations, changes, amendments, adaptations and equivalents which are necessary and compatible with the method of working in question without thereby going beyond the scope of the sprit and scope of this invention, which is represented by the following claims.