WO2016168626A1

WO2016168626A1 - Method for measuring thickness of the crude oil layer above brine in depleted oil wells

Info

Publication number: WO2016168626A1
Application number: PCT/US2016/027788
Authority: WO
Inventors: Priyank Jaiswal
Original assignee: The Board Of Regents For Oklahoma State University
Priority date: 2015-04-17
Filing date: 2016-04-15
Publication date: 2016-10-20

Abstract

According to an embodiment, there is provided a system and method of determining the oil column thickness in a well. One embodiment utilizes an assembly of mechanical and electrical components that, based on the density difference between the overlying oil and the underlying brine, senses the depth of the oil-brine interface.

Description

METHOD FOR MEASURING THICKNESS OF THE CRUDE OIL LAYER ABOVE BRINE IN DEPLETED OIL WELLS

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application serial number 62/148,840 filed on April 17, 2015, and incorporates said provisional application by reference into this document as if fully set out at this point. TECHNICAL FIELD

This disclosure relates generally to assessing the downhole status of a well and, more particularly, to systems and methods for assisting in secondary and tertiary recovery of hydrocarbons from depleted oilfields.

BACKGROUND

After an oil field stops flowing under its own pressure, fluids have to be lifted from downhole to the surface. There are two main components to the fluids that are typically produced at this stage: brine (a denser phase) and the hydrocarbon (a lighter phase).

There are many options today for pumping oil out of the ground. A key factor in choosing the particular method of pumping is the whether the chosen production methodology is economically sound. This factor is influence greatly by the relative proportions of oil and brine in the fluid that is being pumped out of the wells. Excessive amounts of brine in the produced fluids can make production noneconomic and cause the well to have to be shut in.

As a well nears the end of its economic life, it is conventional to operate the pump for a certain period of time and then let the oil column in the well replenish itself through diffusion, at which time additional oil can be produced.

Obviously, it would be advantageous to know the point in time when the oil that has accumulated in the well is of a volume sufficient to merit resuming pumping. Absent this knowledge, excessive amounts of water will be produced that must subsequently be disposed of. Since this water will be mixed with at least some oil and with other miscellaneous sold and materials in solution (e.g., salt), disposing of the produced water can be problematic environmentally. As such, there is every incentive to lift only oil to the surface leaving the water behind. However, present techniques for estimating the thickness of the oil column in a cased well cannot reliably determine the thickness of the oil column in a cased well.

Heretofore, as is well known in the oil production arts there has been a need for an invention that is designed to overcome the disadvantages of prior art approaches. Accordingly it should now be recognized, as was recognized by the present inventors, that there exists, and has existed for some time, a very real need for a system that would address and solve the above-described and other problems.

Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims.

SUMMARY OF THE INVENTION

According to an embodiment, there is provided and system and method of determining the oil column thickness in a well. One embodiment utilizes an assembly of mechanical and electrical components that, based on the density difference between the overlying oil and the underlying brine, senses the oil-brine interface. A similar device senses the top of oil. The two units in combination can then be used to determine the thickness of the oil column in a well.

There is provided herein a device for determining an oil / brine contact in a well, comprising: an outer chamber, said outer chamber having a perforated top and a perforated bottom; a proximity switch mounted on said outer chamber; a sealed inner chamber within said outer chamber; and, a magnet mounted on said sealed inner chamber, wherein said inner chamber and magnet together have a substantially neutral buoyancy in oil and a positive buoyancy in brine, and, wherein said magnet is mounted on said inner chamber to cause it to become proximate to said proximity switch when a bottom of said sealed inner chamber encounters the oil / brine contact in a well.

According to another embodiment, there is provided a device for determining a top of brine in a well, comprising: an outer chamber, said outer chamber having a perforated top and a perforated bottom; a proximity switch mounted on said outer chamber; a sealed inner chamber within said outer chamber; and, a magnet mounted on said sealed inner chamber, wherein said inner chamber and magnet together have a positive buoyancy in brine and a negative buoyancy in oil, wherein said magnet is mounted on said inner chamber to cause it to become proximate to proximity switch when a bottom of said sealed inner chamber encounters a the top of brine contact in a well.

According to a further embodiment, there is taught herein a device for determining an thickness of an oil layer over brine in a well, comprising: a lower outer chamber, said lower outer chamber having a perforated top and a perforated bottom; a lower proximity switch mounted on said lower outer chamber; a sealed lower inner chamber within said lower outer chamber; and, a lower magnet mounted on said sealed lower inner chamber, wherein said lower inner chamber and lower magnet together have substantially neutral buoyancy in oil and a positive buoyancy in brine, and, wherein said lower magnet is mounted on said lower inner chamber to cause it to become proximate to said proximity switch when a bottom of said sealed inner chamber encounters the oil / brine contact in a well; an upper outer chamber in mechanical communication with said lower outer chamber, said upper outer chamber having a perforated top and a perforated bottom; an upper proximity switch mounted on said upper outer chamber; a sealed upper inner chamber within said upper outer chamber; and, an upper magnet mounted on said sealed upper inner chamber, wherein said upper inner chamber and upper magnet together have positive buoyancy in brine and a negative buoyancy in oil, and wherein said upper magnet is mounted on said upper inner chamber to cause it to become proximate to upper proximity switch when a bottom of said sealed upper inner chamber encounters a top of a brine contact on top of the oil layer in the well.

The foregoing has outlined in broad terms some of the more important features of the invention disclosed herein so that the detailed description that follows may be more clearly understood, and so that the contribution of the instant inventors to the art may be better appreciated. The instant invention is not to be limited in its application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. Rather, the invention is capable of other embodiments and of being practiced and carried out in various other ways not specifically enumerated herein. Finally, it should be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting, unless the specification specifically so limits the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further aspects of the invention are described in detail in the following examples and accompanying drawings.

Figure 1 contains an embodiment of the invention.

Figure 2 contains a schematic illustration of how an embodiment might operate in practice to sense the top of the oil / brine contact.

Figure 3 contains a schematic illustration of how an embodiment might operate in practice to sense the top of oil in a well.

DETAILED DESCRIPTION

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings, and will herein be described hereinafter in detail, some specific embodiments of the instant invention. It should be understood, however, that the present disclosure is to be considered an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments or algorithms so described.

One embodiment 100 comprises two coaxial cylinders (Figure 1) which form an outer fluid chamber 110 and an inner calibration chamber 120. That being said, the shape of the inner 110 and outer 120 cylinders is immaterial to the operation of various embodiments of the invention. Of course, cylindrical shapes are most frequently used in downhole applications but that shape is not a requirement here. Thus, for purposes of the claims that follow, the terms "inner chamber" and "outer chamber" will be used to describe these two components.

The inner, smaller sealed cylinder 120 will be filled a lighter fluid, the density of which will be chosen as described below. In this particular embodiment, the inner calibration cylinder 120 has a magnet 140 attached to its top. The outer, larger cylinder 110 has a perforated top and bottom to allow vertical fluid flow through it as it is raised and lowered in the well and/or as the fluid levels change in the well. Thus, once it is positioned in a well it will be filled with well fluids that are present at its current depth. Although this embodiment utilizes a "perforated" top and bottom, it is not required that actual "perforations" be used. Any arrangement that allows fluid to flow through the outer cylinder 110 and which impedes the vertical progress of the inner cylinder 120 at its top would suffice. That being said, for purposes of the instant application the term "perforate" will be used to indicate any variation of the outer chamber which provides free flow of fluid therethrough.

Continuing with the present example, the outer cylinder 110 has a magnetic switch 130 (e.g., a reed switch) positioned near its top. In this embodiment, the magnetic switch 130 will be in an "on" state when it comes in contact with the magnet or is proximate thereto. Of course, the switch 130 need not be positioned at the top of the outer cylinder 110. It could be placed along its side so long as the magnet 140 was similarly positioned on the side of the inner cylinder 120 and the two were brought into proximity with each other at the point where the inner cylinder 120 reaches the top of the outer cylinder 120. Since the inner cylinder 120 is free to rotate in this embodiment, a side orientation would not be optimal but other configurations / shapes of an inner and outer chamber might be able to utilize a side-mounted arrangement.

In practice and as is generally illustrated in Figures 2a, 2b, and 2c, when the whole assembly 100 is lowered in the well, relative movement of the inner and the outer cylinders take place (Figures 2a - 2c). As the outer cylinder 110 moves through the oil column, the inner cylinder initially sits at its base (Figure 2a). When the outer cylinder encounters the oil-brine interface, the inner cylinder 120 will begin to rise towards the top of the outer cylinder (Figure 2b). Finally, when the outer cylinder 110 is in the brine column by a distance which is equal to the length of the inner cylinder the magnet 140 will come into proximity with the switch 130, which in turn closes or otherwise activates a circuit (Figure 2c, where the light bulb is illustrated as being "on"), which activation can be sensed remotely. This switch closure will indicate the depth in the well where the oil - water interface can be found.

In normal operation, an embodiment of the device 100 will be mechanically lowered in the well until it reaches a point where the magnet activates the reed switch, thereby completing the circuit and signaling to the operator that the oil-water interface has been reached. By way of additional clarification of an embodiment, the density of the fluid in the inner cylinder will be approximately the same the same as the density of the lighter fluid. Volume calculation for the fluid in the inner cylinder is done in the following way:

By way of introduction, let

Vc = volume of the inner cylinder

Mc - mass of the inner cylinder

Mm = mass of the magnet in the inner cylinder

Vi = volume of the fluid in the inner cylinder

Vc - Vi = volume of the air in inner cylinder

Po = density of oil in the inner cylinder

p_a = density of air.

One element of the operation of an embodiment is that the inner cylinder should sink in oil (the lighter fluid) but float in brine (the heavier fluid). In order to be heavy enough to sink, the mass of the displaced oil should be less than the mass of the inner cylinder which includes mass of the cylinder plus the mass of the magnet plus the mass of the oil within it. Given various parameters about the size of the inner cylinder, and the density, fill the oil all the way to the top and the inner cylinder will sink. However to ensure that the inner cylinder floats on brine, other criteria need to be met.

Let:

M_b be the mass of the brine displaced by the inner cylinder.

M₀ be the mass of the oil displaced by the inner cylinder.

In the limiting case, the cylinder will sink in the oil and float in brine under the following condition:

Generally the density of oil will vary between 0.8 g/cc and 0.9g/cc. Similarly the density of brine will vary between 1 g/cc to 1.1 g/cc. This density difference will not normally be enough to balance even a small magnet.

As a result, to keep the inner cylinder and magnet floating on the brine column, some oil from the cylinder will be removed and replaced with a fluid or gas having a lesser density. In one embodiment, the replaced fluid will be air. When the inner cylinder 120 is filled with some amount of air, the following formula applies

M_b > M_c + (V_c - Vj)* p_a + Vi*p₀ + M_m > M₀ Assuming p_a = 1 ,

M_b > M_c + (V_c - Vi) + Vi*p₀ + M_m > Mo

M_b > M_c + V_c + Vi*(p₀ -1) + M_m > M₀

The equation can be intuitively understood in the following manner. If the mass of the magnet placed inside the inner cylinder 120 is increased, the volume of the fluid in the inner cylinder needs to be decreased by replacing such that there is more air in it and the overall system stays buoyant. For an inner cylinder of given dimensions, following parameters can be experimentally measured: Mb, M₀, M_c, V_c, p₀, and M_m.

The range of permissible Vj can thus be computed using the previous formulas. Of course, those of ordinary skill in the art will recognize that although a combination of oil and air within the inner cylinder 120 is preferred, that would not be required. Also that is necessary is to create an object that has an average density

(including the container itself, its contents and an activation device such as a magnet) that is between that of oil and brine so that it sinks in oil and floats in brine. In some embodiments, the average density of the inner cylinder 120 will be chosen to give it near neutral buoyancy within the oil.

Those of ordinary skill in the art will recognize that there could be some amount of inaccuracy in this location information since the cylinder 120 could sink some distance into the top of the brine if the densities don't match up exactly. However, the inventive approach provides a level of accuracy far beyond the typical ad hoc approaches used currently.

In this embodiment a magnet / reed switch is used as a signaling circuit but, of course, other sorts of switches might be used instead. Generally speaking, any sort of proximity switch might be used.

Of course, the forgoing demonstrates how an embodiment can determine the depth of the brine / oil interface. Figure 3 contains a schematic illustration of another embodiment which is substantially similar to the foregoing and which locates the top of oil in a well. The depth of top of oil can then be used together with the depth of the oil/brine interface to determine the thickness of the oil column.

Similar to the variation discussed previously, embodiment 300 comprises two coaxial cylinders (Figure 3) which form an outer fluid chamber 310 and an inner calibration chamber 320. That being said, the shape of the inner 310 and outer 320 cylinders is immaterial to the operation of various embodiments of the invention. Of course, cylindrical shapes are most frequently used in downhole applications but that shape is not a requirement here.

The inner, smaller sealed cylinder 320 will be filled with air or any other fluid that causes the density of the cylinder 320 to be less than that of oil. In the embodiment of Figure 3, it is suggested that this cylinder 320 might be filled with air ("void"). In this particular embodiment, the inner calibration cylinder 320 has a magnet 340 attached to its top. The outer, larger well fluid cylinder 310 has a perforated top and bottom to allow vertical fluid flow through it as it is raised and lowered in the well and/or as the fluid levels change in the well. Thus, once it is positioned in a well it will be filled with well fluids that are present at its current depth.

Continuing with the present example, the outer cylinder 310 has a proximity or, more generally, a magnetic switch 330 (e.g., a reed switch) positioned near its top. In this embodiment, the magnetic switch 330 will be in an "on" state when it comes in contact with the magnet or is proximate thereto.

In practice and as is generally illustrated in Figures 3a, 3b, and 3c, when the whole assembly 300 is lowered in the well, relative movement of the inner 320 and the outer 310 cylinders take place (Figures 3a - 3c) as fluid is encountered. When the outer cylinder 310 encounters the top of oil, the inner cylinder 320 initially sits at its base (Figure 3a). As the outer cylinder descends deeper into the oil layer, the inner cylinder 320 will begin to rise towards the top of the outer cylinder 310 (Figure 3b). Finally, the outer cylinder 310 will descend into the oil until inner cylinder 320 is raised to the point where the magnet 340 comes into proximity or contact with the proximity switch 330. This will, in turn, close or otherwise activate a circuit (Figure 3c, where the light bulb is illustrated as being "on"), which activation can be sensed remotely. This switch closure will indicate the depth in the well where the top of the oil is currently located.

In normal operation, an embodiment of the device 300 will be mechanically lowered in the well until it reaches a point where the magnet activates the reed switch, thereby completing the circuit and signaling to the operator that the top of oil has been reached.

In order to estimate the thickness of the oil layer, a device 100 and a device 300 will be lowered into the well, preferably simultaneously (although sequential lowering could be useful in some applications), with the device 100 being lower in the well if both are in the well at the same time. Preferably, each will be under the control of a different winch or other engine for raising and lowering items of this sort in the well, although that is not a requirement and the devices could certainly be simultaneously lowered until each has registered its target. The lowering of the device 100 will continue until the oil/brine contact is sensed and, similarly, the device 300 will be lowered until the oil contact is sensed, with the difference between the two depths being representative of the thickness of the oil layer in this well. The two devices 100 and 300 could be made as a unit (e.g., part of the same downhole tool) or otherwise in mechanical communication with each other. In such a case, the combined tool could be lowered through the oil at least until the device 100 reaches the oil / brine interface and the device 300 encounters the top of oil.

It is to be understood that the terms "including", "comprising", "consisting" and grammatical variants thereof do not preclude the addition of one or more components, features, steps, or integers or groups thereof and that the terms are to be construed as specifying components, features, steps or integers.

If the specification or claims refer to "an additional" element, that does not preclude there being more than one of the additional element.

It is to be understood that where the claims or specification refer to "a" or "an" element, such reference is not be construed that there is only one of that element.

It is to be understood that where the specification states that a component, feature, structure, or characteristic "may", "might", "can" or "could" be included, that particular component, feature, structure, or characteristic is not required to be included.

Where applicable, although state diagrams, flow diagrams or both may be used to describe embodiments, the invention is not limited to those diagrams or to the corresponding descriptions. For example, flow need not move through each illustrated box or state, or in exactly the same order as illustrated and described.

Methods of the present invention may be implemented by performing or completing manually, automatically, or a combination thereof, selected steps or tasks.

The term "method" may refer to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the art to which the invention belongs.

For purposes of the instant disclosure, the term "at least" followed by a number is used herein to denote the start of a range beginning with that number (which may be a ranger having an upper limit or no upper limit, depending on the variable being defined). For example, "at least 1 " means 1 or more than 1. The term "at most" followed by a number is used herein to denote the end of a range ending with that number (which may be a range having 1 or 0 as its lower limit, or a range having no lower limit, depending upon the variable being defined). For example, "at most 4" means 4 or less than 4, and "at most 40%" means 40% or less than 40%. Terms of approximation (e.g., "about", "substantially", "approximately", etc.) should be interpreted according to their ordinary and customary meanings as used in the associated art unless indicated otherwise. Absent a specific definition and absent ordinary and customary usage in the associated art, such terms should be interpreted to be ± 10% of the base value.

When, in this document, a range is given as "(a first number) to (a second number)" or "(a first number) - (a second number)", this means a range whose lower limit is the first number and whose upper limit is the second number. For example, 25 to 100 should be interpreted to mean a range whose lower limit is 25 and whose upper limit is 100. Additionally, it should be noted that where a range is given, every possible subrange or interval within that range is also specifically intended unless the context indicates to the contrary. For example, if the specification indicates a range of 25 to 100 such range is also intended to include subranges such as 26 -100, 27-100, etc., 25-99, 25- 98, etc., as well as any other possible combination of lower and upper values within the stated range, e.g., 33-47, 60-97, 41 -45, 28-96, etc. Note that integer range values have been used in this paragraph for purposes of illustration only and decimal and fractional values (e.g., 46.7 - 91.3) should also be understood to be intended as possible subrange endpoints unless specifically excluded.

It should be noted that where reference is made herein to a method comprising two or more defined steps, the defined steps can be carried out in any order or simultaneously (except where context excludes that possibility), and the method can also include one or more other steps which are carried out before any of the defined steps, between two of the defined steps, or after all of the defined steps (except where context excludes that possibility).

Further, it should be noted that terms of approximation (e.g., "about", "substantially", "approximately", etc.) are to be interpreted according to their ordinary and customary meanings as used in the associated art unless indicated otherwise herein. Absent a specific definition within this disclosure, and absent ordinary and customary usage in the associated art, such terms should be interpreted to be plus or minus 10% of the base value.

Still further, additional aspects of the instant invention may be found in one or more appendices attached hereto and/or filed herewith, the disclosures of which are incorporated herein by reference as if fully set out at this point.

Thus, the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned above as well as those inherent therein. While the inventive device has been described and illustrated herein by reference to certain preferred embodiments in relation to the drawings attached thereto, various changes and further modifications, apart from those shown or suggested herein, may be made therein by those of ordinary skill in the art, without departing from the spirit of the inventive concept the scope of which is to be determined by the following claims.

Claims

What is claimed is:

A device for determining an oil / brine contact in a well, comprising:

a. an outer chamber, said outer chamber having a perforated top and a

perforated bottom;

b. a proximity switch mounted on said outer chamber;

c. a sealed inner chamber within said outer chamber; and,

d. a magnet mounted on said sealed inner chamber,

wherein said inner chamber and magnet together have a substantially neutral buoyancy in oil and a positive buoyancy in brine, and, wherein said magnet is mounted on said inner chamber to cause it to become proximate to said proximity switch when a bottom of said sealed inner chamber encounters the oil / brine contact in a well.

2. The device for determining an oil / brine contact in a well according to Claim 1, wherein said proximity switch is a reed switch.

3. The device for determining an oil / brine contact in a well according to Claim 1 , wherein said proximity switch is mounted at a top of said outer chamber and said magnet is mounted on a top of said sealed inner chamber.

A device for determining a top of brine in a well, comprising:

a. an outer chamber, said outer chamber having a perforated top and a

perforated bottom;

b. a proximity switch mounted on said outer chamber;

c. a sealed inner chamber within said outer chamber; and,

d. a magnet mounted on said sealed inner chamber, wherein said inner chamber and magnet together have a positive buoyancy in brine and a negative buoyancy in oil,

wherein said magnet is mounted on said inner chamber to cause it to become proximate to proximity switch when a bottom of said sealed inner chamber encounters a the top of brine contact in a well.

5. The device for determining a top of brine in a well according to Claim 4, wherein said proximity switch is a reed switch.

6. The device for determining a top of brine in a well according to Claim 4, wherein said proximity switch is mounted at a top of said outer chamber and said magnet is mounted on a top of said sealed inner chamber.

7. A device for determining an thickness of an oil layer over brine in a well,

comprising:

a. lower outer chamber, said lower outer chamber having a perforated top and a perforated bottom;

b. a lower proximity switch mounted on said lower outer chamber;

c. a sealed lower inner chamber within said lower outer chamber; and, d. a lower magnet mounted on said sealed lower inner chamber,

wherein said lower inner chamber and lower magnet together have substantially neutral buoyancy in oil and a positive buoyancy in brine, and,

wherein said lower magnet is mounted on said lower inner chamber to cause it to become proximate to said proximity switch when a bottom of said sealed inner chamber encounters the oil / brine contact in a well; e. an upper outer chamber in mechanical communication with said lower outer chamber, said upper outer chamber having a perforated top and a perforated bottom; f. an upper proximity switch mounted on said upper outer chamber;

g. a sealed upper inner chamber within said upper outer chamber; and, h. an upper magnet mounted on said sealed upper inner chamber,

wherein said upper inner chamber and upper magnet together have positive buoyancy in brine and a negative buoyancy in oil, and, wherein said upper magnet is mounted on said upper inner chamber to cause it to become proximate to upper proximity switch when a bottom of said sealed upper inner chamber encounters a top of a brine contact on top of the oil layer in the well.

8. The device for determining an thickness of an oil layer over brine in a well

according to Claim 7, wherein said lower proximity switch and said upper proximity switch are both a reed switch.