Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02407554 2005-04-O1
1 "METHOD AND APF~ARATUS FOR
2 DESANDING WELLHEAD PRODUCTION"
3
4 FIELD OF THE INVENTION
The present invention relates i:o apparatus and methodology for the
6 removal of particulates such as sand from fluid streams produced from a well
while
7 minimizing erosion of the involved equipment.
8
9 BACKGROUND OF THE INVENTION
Production from wells in the oil and gas industry often contains
11 particulates. These particulates could be part of the formation from which
the
12 hydrocarbon is being produced, introduced ~>articulates from hydraulic
fracturing or
13 fluid loss material from drilling mud or fracturing fluids or from a phase
changes of
14 produced hydrocarbons caused by changing conditions at the wellbore
(asphalt or
wax formation). As the particulates are produced, problems occur due to
abrasion,
16 and plugging of production equipment. In a typical startup after
fracturing, a
17 stimulated well may produce sand until the ~Nell has stabilized, sometimes
up to a
18 month.
19 In the case of gas wells, fluid velocities can be high enough that the
erosion of the production equipment is severe enough to cause catastrophic
failure.
21 High velocities are typical and are even designed for elutriating particles
up the well
22 and to the surface. An erosive failure of this nature can become a serious
safety
23 and environmental issue for the well operator. In all cases, particulate
production
CA 02407554 2005-04-O1
1 contaminates surface equipment and produced fluids and impairs the normal
2 operation of the oil and gas gathering system and process facilities.
3 In one prior art system, a pressurized tank ("P Tank") is placed on the
4 wellsite and the well is allowed to produce f'uid and particulates into this
tank until
sand production ceases. The large size of v:he tank usually restricts the
maximum
6 operating pressure of the vessel to somethirn~ in the order of 1,000 - 2,100
kPa. In
7 the case of a gas well, this requires some pressure control to be placed on
the well
8 to protect the P Tank. Further, for a gas ~Nell, the pressure reduction
usually is
9 associated with an increase in gas velocity which in turn makes the sand
laden well
effluent much more abrasive. Other problems associated with this type of
desanding
11 technique are that it is a temporary solution. If the well continues to
make sand, the
12 solution becomes prohibitively expensive. In most situations with this kind
of
13 temporary solution, the gas vapors are not conserved and sold as a
commercial
14 product.
An alternate known prior art system includes employing filters to
16 remove particulates. A common design is ':o have a number of fibre mesh
bags
17 placed inside a pressure vessel. The fibre density is matched to the
anticipated
18 particulate size. Filter bags are generally not effective in the removal of
particulates
19 in a multiphase conditions. Usually multipha:~e flow in the oil and gas
operations is
unstable. Large slugs of fluid followed by a g~~s mist is common. In these
cases, the
21 fibre bags become a pressure drop point and often fail due to the liquid
flow through
22 filter. Due to the high chance of failure, the filter may not be trusted to
remove
23 particulates in critical applications or where the flow parameters of a
well are
2
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1 unknown. An additional problem with filters in most jurisdictions is
associated with
2 cost of disposal. The fibre bags are considered to be contaminated with
3 hydrocarbons and must be disposed of in accordance to local environmental
4 regulations.
Clearly there is a need for more versatile and cost effective system.
6
7 SUMMARY OF THE. INVENTION
8 Apparatus is provided which is placed adjacent to the wellhead for
9 intercepting wellhead fluid flow before and prior to entry to any operators
equipment
including separators, valves, chokes and all other downstream equipment.
11 A pressure vessel is inserted in the flowsteam by connecting it
12 adjacent to the wellhead and to the input high velocity field piping
extending from the
13 wellhead. The vessel contains a freeboard volume having a cross-sectional
area
14 which is greater than that of the field piping i~rom whence the fluids
emanate. As a
result, fluid velocity drops and particulates cannot be maintained in
suspension. The
16 freeboard cross-sectional area is maintained through a downcomer weir or
17 depending nozzle at the vessel's exit which ensures that a minimum
freeboard
18 volume and cross-sectional area is maintained for the collection of
particulates, and
19 promotes maximum use of the freeboard area, thereby reducing the number of
times
maintenance of the system, by cleaning the freeboard area of accumulated
21 particulates, need be conducted.
22
3
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1 BRIEF DESCRIPTION OF THE DRAWINGS
2 Figure 1 is a cross-sectional side view of one embodiment of the
3 invention;
4 Figure 2 is a typical installation for wellsite service, such as that
provided on a portable trailer; and
6 Figure 3 is a performance graph of the achievable gas rates while
7 still achieving particulate removal.
8
9 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in Fig. 1, a desander 10 comprises a substantially
11 horizontal, cylindrical, pressure vessel 11 having an inlet end 23 adapted
for
12 connection to a wellhead piping 9 and fluid stream F, typically gas G and
sand S.
13 As stated in the background and below, the fluid stream F may also contain
liquid
14 L.
A fluid inlet 12 comprises a nozzle 21 extending into an upper
16 freeboard 30 volume adjacent the top of the vessel 11. An eccentric fitting
31
17 shifts the axis A of the vessel 11 downward to form a belly storage portion
32 for
18 receiving and temporarily storing sand S. The nozzle 21 extends beyond the
end
19 of the vessel 11 and into the freeboard 30 which minimizes localized wear.
Gas G containing sand S enters through the fluid inlet 12 and is received by a
21 larger cross-sectional area of the freeboard 30. The velocity slows and
sand falls
22 out of suspension. The freeboard 30 is maintained using means to ensure
that
23 the particulate free fluid is collected by an outlet 13 from mid-vessel.
4
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1 This is achieved using either flow barrier such as a weir 40 as shown or by
inserting
2 the fluid outlet into the vessel 11, away from the vessel wall.
3 As shown in Fig. 1, if a weir 40 is used, it is spaced from the fluid inlet
4 12 and positioned between the fluid inlet 12 and the fluid outlet 13.
As shown in Fig. 1, both a wE:ir 40, and a fluid outlet 13, having a
6 downwardly extending portion which extends into the vessel 11, are used as a
flow
7 barrier in a preferred embodiment.
8 The fluid outlet 13 for the ves,el 11 is preferably perpendicular and
9 upward, drawing from the lower level of the freeboard 30 volume.
A quick release pressure-vessel compatible cleanout 50 is provided for
11 sand removal access. The vessel 11 must be depressurized before opening and
12 cleaning out particulates. Manual cleanout is performed although automated
13 cleanout could be incorporated without diverging from the intent of the
invention.
14 A typical vessel 11 may be a 6" diameter, schedule 160 shell having a
capacity for 8 million cubic feet of gas G per day and a corresponding and
typical
16 collection rate of 1.5 gallons of particulates pE~r day.
17 The advantages of the system include:
18 ~ As the desander is more cost effective than a "P Tank", the
19 desander can be economically placed on a well for long term
(substantially permanent) sand protection;
21 ~ With a pressure rating that allows it to operate at the wells
22 conditions, minimal pressure drop is experienced across the
23 vessel. The desander i > designed to exceed ASME code for
5
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1 pressure vessels. This permits the sand to be removed from
2 the flow stream without becoming erosive.
3 ~ Since the vessel is passive and has no moving parts, plugging
4 caused by particulates is not an issue. Sand is removed
mechanically from the vE;ssel at regular intervals. By removing
6 the sand prior to it entering the producing system, contamination
7 of equipment and produced fluids is avoided.
8 . The vessel is capable of handling multiphase production and
9 has demonstrated the a~~ility to remove sand from both gas and
oil streams. This result: in a wider application than the filter
11 methods.
6
