RU2531976C2 - Plant for in-well separation of oil from water - Google Patents

Abstract

FIELD: oil-and-gas industry.

SUBSTANCE: invention can be used for maintenance of seam pressure at water transfer between wells. Proposed plant comprises oil-well tubing with electric rotary pump and flushing check valve lowered in flow string, annulus above said pump for accumulation and reservation of separated oil, separation chamber arranged at well borehole bottom above said pump, flow channel communicating said annulus with said separation chamber, water inlets and outlets. Note here that said pump is equipped with outer sealing jacket to communicated pump inlet with intake device arranged in separation chamber and consisting of shank plugged at its bottom and separated into sections with inlets. Shank is equipped with barrel arranged level with every inlet to intake separated water in said intake device and trap oil drops. Note here that said inlets are arranged in row along said shank and feature diameter decreasing in every next section and upward. Said flow channel is composed by clearance between said jacket and flow string.

EFFECT: simplified design, higher reliability and quality of separation.

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Description

The present invention relates to the oil industry and may find application in a system for maintaining reservoir pressure during cross-hole pumping of water to separate finely divided drip oil from produced products from a water well that has moved from the former oil production category due to flooding of the reservoir.

Known borehole separator, including a separation chamber, an outlet for oil above the separation chamber and an outlet for water under the separation chamber. As the separation chamber, the lower part of the well is used, bounded by a casing string and a separation cuff, which is mounted on a liner attached to a submersible electric motor of an electric centrifugal pump suspended in a well on a tubing string. The shank in the lower part under the separation cuff is equipped with a stopper, and in the upper part above the separation cuff - with an outlet for water. As an outlet for oil, a discharge tube with windows and nozzles was used to communicate the space under the separation sleeve and the space above the reception of the electric centrifugal pump (RF Patent No. 2291291, published on January 10, 2007).

The known device provides the separation of oil and water with small volumes of produced fluid in the wells and has a complex design of downhole equipment.

Closest to the proposed invention in technical essence is a downhole installation for the separation of oil and water, including a separation chamber with a static separator and outlet openings for oil and water. The lower part of the well bounded by a casing string and a separation cuff, which is mounted on a liner attached to a submersible electric motor of a centrifugal pump suspended in a borehole on a tubing string with a flushing and non-return valve above the pump, is used as a separation chamber. The shank is equipped with a casing in the form of a glass, which protects the separation cuff when lowering the installation into the well. The release of the cuff from the casing is carried out when the installation is moving up due to the contact of the spring loaded crackers with the inner surface of the casing wall. The shank in the upper part above the separation cuff is equipped with an outlet for water, and a drain pipe with windows and nozzles is used as an oil outlet for communicating the space under the separation cuff and the space above the reception of the electric centrifugal pump. In the lower part, the shank is equipped with a separator, which is made of external and internal concentrically arranged pipes, closed from below, with an annular space between them, divided by partitions with horizontal holes into sectors. The outer pipe in the upper part in the sectors is equipped with openings for the separated oil to enter the cuff zone and along the entire length has radial openings for fluid to exit into half of the sectors through one. The inner pipe along the entire length in the remaining sectors has radial openings for water to flow into it and gave a shank, as well as a pump intake. In this case, the total area of the outlet as well as the outlet openings is not less than the cross-sectional area of the production casing of the well. (RF patent No. 2290505, publ. December 27, 2006).

The known installation has a complex layout of downhole equipment and when lowering the installation into the well, the cuff opens spontaneously, complicating the process of lowering the equipment. In addition, the tube for diverting the separated oil above the intake of the pump increases the transverse size of the installation, which limits its use. The separator included in the set of downhole equipment has a complex structure.

The proposed invention solves the problem of simplifying the design and improving the reliability of downhole equipment for separating oil from water while ensuring high-quality purification of produced water from oil in the donor well.

The problem is solved in that in an installation for downhole separation of oil from water, including a tubing string with an electric centrifugal pump and a flushing and non-return valve, lowered into the production string of the well, the annulus above the pump for accumulation and reservation of separated oil, a separation chamber, located in the lower part of the well bore under the electric centrifugal pump, a passage channel communicating the annulus above the pump with a separation chamber, inlet According to the invention, the electric and centrifugal pumps are provided with an external sealing casing configured to hydraulically communicate with the electric centrifugal pump with an input device located in the separation chamber, which consists of a shank sealed from the lower end divided into sections with inlet openings. At the same time, at the level of each inlet, the shank is equipped with a glass that performs the functions of inlet of divided water into the inlet device and a water trap for oil drops. Moreover, the inlet openings are arranged in one row along the liner and are made with a decreasing diameter in each subsequent section in an upward direction, and the gap between the casing and the production casing of the well serves as a passage channel for oil drops.

Figure 1 presents the claimed installation for downhole separation of oil from water; figure 2 - the lower part of the input device in figure 1;

Installation for downhole separation of oil from water contains a suspension string tubing 1 with connected to the lower part above the electric centrifugal pump 2 flushing and non-return valve 3, which are lowered into the production casing of the well 4. Submersible motor (PED) 5 and the receiving part (input module) 6 of the electric centrifugal pump 2 from the outside from the annular space 7 (not indicated in the drawing) and the separation chamber 8 are sealed by a casing 9. A shank 11 is connected to the pipe 10 of the casing 9 device located in the separation chamber 8, formed from an annular space enclosed between the production casing 4 and the housing of the input device. The gap between the casing 9 and the production casing 4 provides the inlet of oil droplets and their accumulation in the upper part of the annular space 7 (not shown in the drawing). Muffled with the lower end, the shank 11 is provided along the entire length along the housing with one row of inlets 12 and glasses 13, which perform the function of a water seal for oil droplets. The input device consists of several sections with a decreasing diameter of the inlets 12 in each subsequent section in an upward direction. The annular space 7 (not indicated in the drawing) of the well in the wellhead fittings is connected to the oil pipeline 14, and the flow line is connected to the water supply 15.

The geometric dimensions of the input device for the proposed installation are selected based on the expected flow rate or pump performance. The length of the inlet device is selected based on the number and diameter of the inlet openings to ensure a batch distribution of the produced fluid stream in such a way that the speed of the downward flow of water in each portion entering the glass 13 of the inlet device is less than the rate of ascent of oil droplets in the water. The number and diameter of the inlet 12 is determined as follows:

The number of holes on the shank n≥Q / q,

where Q is the predicted flow rate of the water well or ESP capacity, m ³ / day (m ³ / s); q is the portioned (fractional) water flow through the inlets in m ³ / day (m ³ / s) and is determined as follows:

$$q=U\cdot F;f=\pi \cdot \left(D^2-d^2\right)/\mathrm{four}(\mathrm{one})$$

where, U _nk - the rate of ascent of oil droplets in water, is taken, on average, 0.015 m / s; f is the area of the annular space between the shank 11 and the glass 13, m ² ; D is the inner diameter of the glass; d is the outer diameter of the shank.

The average diameter of the inlets is determined by the formula for the flow of fluid through the small holes.

$$d=\sqrt{\frac{\mathrm{four}q}{\mu \pi \sqrt{2g\Delta H}}}(2)$$

where µ is the flow coefficient for a round hole, at a low value of speed, the outflow is taken 0.65; ΔH is the pressure difference (pressure) in the hole, under the action of which the outflow occurs.

Calculation example.

The expected flow rate of the water well is Q = 80 m ³ / day = 0,000926 m ³ / s. The inner diameter of the cup D = 73 mm = 0.073 m (pipe 3 "), and the outer diameter of the shank d = 48 mm = 0.048 m (pipe 1.5"); DN - the difference in pressure (pressure) in the hole accept 0.01 MPa or 1 m

The fractional flow rate of water entering each inlet through the glass will be:

q = U · π · (0.076 ² -0.048 ² ) / 4 = 0.015 · 3.14 0.003452 / 4 = 0.00004065 m ³ / s = 3.5 m ³ / day.

The number of holes N≥Q / q≥80 / 3,5 = 23 pcs.

The average hole diameter is determined by the formula (2):

$$d=\sqrt{\frac{\mathrm{four}\cdot \mathrm{0,00004065}}{0.65\cdot 3.14\sqrt{2\cdot 9.81\cdot \mathrm{one}}}}=\sqrt{\frac{0.0001626}{\mathrm{2,041}\cdot 4.43}}=0.00424=\mathrm{4,5}mm$$

The obtained values of n and d are rounded up. The total area of the inlets will be determined if it consists only of holes with a diameter of 4.5 mm.

Σf = n · πd ^2/4 = 23 · 3.14 · 4.5 ^2/4 = 366 mm ²

We distribute the location of the diameters of the holes in size and quantity into three sections:

1st section with a diameter of 5 mm in the amount of 12;

2nd section with a diameter of 4 mm in an amount of 8;

3rd section with a diameter of 3 mm in an amount of 5.

Next, we determine the total equivalent hole area of all sections:

$${\displaystyle \sum f=\pi /\mathrm{four}\cdot \left(n_{\mathrm{one}}\cdot d_{\mathrm{one}}^2+n_2+d_2^2+n_3+d_3^2\right)=0.785\left(12\cdot 5^2+8\cdot {\mathrm{four}}^2+5\cdot 3^2\right)}=387m{m}^2>366m{m}^2$$

The final number of holes we accept 25 pieces with a distribution of diameter / number in sections, will be: 5/12 + 4/8 + 3/5. The distance between the holes 12 is chosen 1 m, and the height of the glass 13 is taken 0.2 m. Thus, the length of the input device is 27 m.

Installation for downhole separation of oil from water works as follows.

The operating experience of donor wells with a device for downhole separation of oil from water shows that the most favorable conditions for the gravitational principle of separation of oil from water are in the interval from the top of the formation to the pump. In this interval, due to the laminar regime of fluid movement in the production string, oil droplets emerging from the perforation holes move in separate droplets or, merging (due to the different speeds of the oil droplets in the stream) form large drops of oil. In addition, if there is even slight curvature in the well in this interval, oil droplets merge and move along the upper generatrix of the inner surface of the production string, and depending on the amount of oil in the produced water, it can either be in the form of large drops or a thin stream of oil.

During operation of the electric centrifugal pump 2, an upward flow of water with oil droplets in the annular space of the separation chamber 8, formed between the shank 11 and the production string 4, moves along the inlet device and redistributes along the inlet openings 12. The upward flow of liquid in the separation chamber 8 on the path between the glasses 13 sharply reduces speed due to the large cross-sectional area of the annular space, creating the conditions for gravitational separation of water from oil droplets. In this case, the downward flow of water from the upper open part of the cup 13 and further through the inlet openings 12 enters the liner 11. The speed of each individual portion of the downward flow is less than the rate of ascent of the oil droplets in the water, and the speed of the main one is the upward flow, moving further along the glass 13, it is quite high and provides the removal of oil drops, bypassing the glass 13. This is further facilitated by the coincidence of the direction vectors of the ascent of the oil drops and the upward flow of liquid. In this case, the speed of the upward flow as it rises along the inlet device gradually decreases due to portioned water withdrawal in the previous openings, and inside the shank due to the alternate flow of water it gradually increases, therefore the diameter of the inlet openings 12 of the upper last section of the inlet device is correspondingly smaller than the lower sections. This allows you to have a speed of downward flow of water entering the glasses 13 on the upper section of the inlet device, much less than the speed of ascent of oil droplets in the water, which ensures their further ascent. The produced water purified from oil through the liner 11 enters the intake 6 of the electric centrifugal pump 2, and the oil rises and then accumulates in the annulus 7 (not indicated in the drawing) of the well through the gap between the casing 9 and the production casing 4.

During the operation of the installation, the produced water through the tubing string 1 rises to the surface and is pumped into the injection wells in the wellhead reinforcement of the donor well via flow and water lines 15. At the same time, the process of oil accumulation in the annulus of the borehole 7 (not indicated in the drawing) occurs and the oil-water section eventually approaches the flushing-check valve 3. When filling the annulus 7 (not indicated in the drawing) from the dynamic liquid level to the flushing-reverse valve 3, the installation is turned off. The filling time of the annulus 7 (not indicated in the drawing) of the well with oil is calculated based on the flow rate and water cut of the produced fluid or determined experimentally. When this flush-check valve 3 opens (using the well-known downhole valve device according to the patent of the Russian Federation No. 2150575), the pipe space of the tubing string communicates with the annular space 7 (not shown in the drawing). Next, the secant gate valve is opened on the oil pipeline 14 and oil is displaced from the annulus 7 (not indicated in the drawing) to the oil pipeline 14 by the reverse flow of water from injection wells and the water supply (pressure in the water supply is usually an order of magnitude higher than in the oil pipeline). If the amount of reverse water flow and the pressure in the water supply are insufficient, then the oil is displaced by pumping water from a tanker using the pump unit CA-320. The selected samples in the pipeline 14 determine the end of the oil displacement process, and then start the installation of the donor well.

The proposed installation option significantly simplifies the design of downhole equipment and allows the implementation of the separation of oil from water with almost any amount of produced fluid from water wells due to the possibility of using an input device without limiting its length. The use of the installation allows preserving the injectivity of injection wells due to more high-quality cleaning of injected water from oil products and to extract additional oil from water wells.

Claims (1)

Installation for downhole separation of oil from water, including a tubing string with an electric centrifugal pump and a flushing and non-return valve, lowered into the production string of the well, annulus above the pump for accumulation and reservation of separated oil, a separation chamber located in the lower part of the borehole under by an electric centrifugal pump, a passage channel communicating the annular space above the pump with a separation chamber, inlet openings for production water, characterized in that the electric centrifugal pump is equipped with an external sealing casing, made with the possibility of hydraulic communication receiving the electric centrifugal pump with an input device located in the separation chamber, consisting of a muffled from the lower end of the shank, divided into sections with inlet openings, at the same time each inlet of the shank is equipped with a glass that performs the functions of the inlet of the divided water into the inlet device and a water seal for oil drops, moreover final year at holes arranged in a row along the shank and formed with decreasing diameter in each successive section in an upward direction, and as a passageway for oil droplets is a gap between the casing string and the production well.

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