GB2192809A - Separating water from oil or gas - Google Patents

Abstract

Water is removed from oil or gas as it flows through a bed comprising glass spheres of at least 0.95 cms diameter. Contact with the glass coalesces the water content of an oil-water mixture, enabling separation by gravity downstream. Natural gas is passed upwards through the bed against a descending flow of glycol which takes up the water from the gas.

Description

SPECIFICATION Separation of aqueous phase from fluid media The present invention is concerned with the separation of aqueous phases from fluid media, for example, in the treatment of oil-andwater emulsions or the coalescing of water entrained in a flow of natural gas.

Crude oil emulsions are obtained in many oilfields, such emulsions being a homogenised mixture of oil with 5 to 50% water and solid impurities, such as sand, clay, shale, or salt, typically in an amount of less than 1%.

Oil-and-water emulsions can be broken either physically or chemically; the traditional physical treatment involves the use of wood excelsior (that is, finely shaved wood resembling coarse hay or straw). The wood excelsior is packed tightly in treatment apparatus to a depth of approximately two-thirds the depth of the apparatus, the apparatus is then filled with water and heated for a prolonged period (such as about 24 hours) so as to saturate the wood. An oil-and-water emulsion is then passed through the saturated wood, so that the water is absorbed by the saturated wood, allowing the oil to pass through.

Although this method is relatively effective, it has a number of problems, as follows: 1. The filter is easily plugged with impure produce from the well.

2. Oil and water emulsion tends to find the easiest route through the filter, resulting in channelling, cutting the efficiency by as much as 90%.

3. The filter must be changed at least once a year. This is a very expensive process as the contaminated wood is hazardous waste and must be treated accordingly.

It is also known to use corrugated plastic plates arranged according to the density of the crude oil being treated; such plates are said to coalesce the water as an emulsion travels across their surface. The greatest problem with this system is that the plates tend to distort at about 180 F, resulting in channelling and therefore decreased efficiency.

Ultimately chemical treatment is required to complete the process.

Natural gas generally contains a substantial proportion of water; the most common way for removing such entrained water is by glycol treatment. In this method, the natural gas is flowed upwards through a tower of height typically 10 to 40 feet, and glycol is passed in countercurrent down the tower. The object of this is to cause the glycol to entrain the water; in order to enhance contact of the gas with the water, the tower is generally filled with either trays or shaped bodies.

In trayed apparatus, a series of trays with bubble caps (caps shaped like inverted teacups with notches around their bottom edges) is stacked inside the apparatus; in operation, glycol accumulates in each tray before overflowing into the tray below, while the gas flows up through one tray, down through accumulated glycol, and then up through the next tray. Typically 4 to 12 trays (for example, 6 to 8 trays) are employed.

In apparatus containing a multiplicity of shaped bodies, the latter are typically of metal (for example, small steel cones commercially available under the trade mark Pahal Rings) or ceramic (for example, ceramic bodies of horseshoe configuration commercially available under the trade mark Rashic Rings). Both apparatus containing a multiplicity of shaped bodies and trayed apparatus suffer from the disadvantage that, if the circulating glycol is contaminated in some way (for example, by asphaltenes and bitumens), then the apparatus may be ineradicably contaminated. The trayed apparatus also has the major disadvantage of the inflexibility of the design.

According to the present invention, there is provided a method of treatment of a fluid medium containing entrained water, which comprises providing at least one treatment zone having stacked therein a multiplicity of substantially non-conductive, smooth-surfaced, substantially non-absorbent beads, and passing said fluid medium through said stack so as to cause separation of said entrained water from said fluid medium.

The beads used in the method according to the invention are preferably of hydrophilic ,ma- terial, such as glass, and are preferably spherical in shape.

The glass beads preferably have an average diameter in the range of 3/8 inch to 2 inches.

It is further preferable to avoid more than a small proportion of beads with a diameter of less than 3/8 inch, as beads smaller than this tend to pack too tightly for the purposes of the present invention. In an exemplary embodiment of the invention, approximately one quarter of the beads have a diameter of about 3/8 inch, approximately one quarter have a diameter of about 1/2 inch, and the remainder a diameter of approximately 3/4 inch.

When the method according to the invention is used for treatment of an oil-and-water emulsion, the latter may be passed through the beads at an elevated temperature (for example 120 to 2000F), so as to cause breaking of the emulsion.

The emulsion used in this method is typically of a heavy crude oil and has a water content of 5 to 50%; by this means the water content can be reduced to as little as 0.1%.

The diameter of the beads, the number and the depth of treatment zone are chosen according to the specific gravity of the emulsion, the amount of solid impurities and velocity of flow. Water will follow any smooth hydrophilic surface, and as the emulsion is forced through the stacked beads, it coalesces on the beads; the lighter oil rises through the apparatus leaving the water to sink.

When the method according to the invention is used for dehydrating a gas such as natural gas, the latter is preferably allowed to flow upwards through the stack against a counter-current of glycol. As the contaminated gas flow is forced upward past and across the beads, the latter will cause a coalescing action on any water entrained in the gas, while at the same time the glycol will be forced down and around the beads, thus forcing maximum contact between the glycol and gas flow. As flow past smooth beads is substantially turbulence-free, the problem of foaming is greatly reduced.

By using stacked beads, there are no design restrictions as to the flow rate. By adjusting the glycol rate, the flow could be adjusted from zero, up to the maximum capacity of the apparatus. As the beads are smooth-surfaced and non-absorbent, contamination is not very likely, but if for some reason contamination does occur it is possible to flush the bead stack in the field at an acceptable cost. As the bead stack is not corrosive and is self packing, the integrity of the system is assured.

An exemplary embodiment of the present invention will now be described with reference to the accompanying drawing, which is a schematic view of a method according to the invention of breaking an oil-and-water emuision.

The oil-and-water emulsion is passed through a horizontally disposed treating vessel 1, via inlet 2 into chamber 3. The emulsion, which is generally at a temperature of 120 to 200 F, passes downwards through a first coalescing section comprising a wire mesh box 4 which is filled with closely stacked spherical glass beads 5 (the latter substantially filling the liquid flow path), then beneath baffle 6 and into chamber 7. The liquid flow (which by this point is partially coalesced), is passed upwards over baffle 8 (gas being drawn off at this point through vent 9) into chamber 10, and then downwards beneath baffle 11 into chamber 1#2.

In chamber 12, the partially coalesced emulsion is passed through a wire mesh box 13 which is filled with closely stacked spherical glass beads 14; the box is such that it, and the glass beads, substantially fill the liquid flow path.

After passing through the glass beads, the by now broken emulsion passes over a further baffle 15, and exits from the top 16 of the vessel 1, after passing over a further baffle 17. Water is meanwhile continuously drawn off from the base 18 of the vessel at such a rate that the water level in the vessel is kept substantially -constant.

Claims (8)

1. A method of treatment of a fluid medium containing entrained water, which comprises the steps of: (a) providing at least one treatment zone having stacked therein a multiplicity of substantially non-conductive, smooth-surfaced, substantially non-absorbant beads of regular shape, substantially all of which hava a minimum dimension of at least 3/8 inch; and (b) passing said fluid medium through said zone so as to cause separation of said entrained water from said fluid medium.

2. A method according to claim 1, in which said beads have a surface composition substantially identical to the cores thereof.

3. A method according to claim 2, in which said beads are of a hydrophilic material.

4. A method according to claim 3, in which said beads are of silicate glass.

5. A method according to any of claims 1 to 4, in which said fluid medium is an oil-andwater emulsion.

6. A method according to claim 5, in which said fluid medium is passed at an elevated temperature through said beads.

7. A method according to any of claims 1 to 4, in which said fluid medium comprises natural gas.

8. A method according to claim 7, in which said fluid medium is passed against a countercurrent of glycol.