Patent Application
20110105292
1. Field of the Disclosure
Embodiments disclosed herein relate generally to a centrifuge system for processing a fluid including solids and liquids. In another aspect, embodiments disclosed herein relate to a dual feed centrifuge system for removing solids from a fluid material. In another aspect, embodiments disclosed herein relate to a dual feed centrifuge system for removing solids from a drilling fluid material. In yet another aspect, embodiments disclosed herein relate to a method of separating solids from liquids in a fluid material using a dual feed centrifuge.
2. Background
Oilfield drilling fluid, often called “mud,” is typically a liquid having solids suspended therein. In general, the solids function to impart desired density and rheological properties to the drilling mud. The drilling mud can also contain undesired solids in form of drill cuttings from the downhole drilling operation that require separation.
Drilling muds may contain polymers, biopolymers, clays and organic colloids added to an oil-based or a water-based fluid to obtain the required viscosity and filtration properties. Heavy minerals, such as barite or calcium carbonate, may be added to increase density.
The drilling mud serves multiple purposes in the industry. Among its many functions, the drilling mud acts as a lubricant to cool rotary drill bits and facilitate faster cutting rates. Typically, the mud is mixed at the surface and pumped downhole at high pressure to the drill bit through a bore of the drillstring. Once the mud reaches the drill bit, it exits through various nozzles and ports where it lubricates and cools the drill bit. After exiting through the nozzles, the “spent” fluid returns to the surface through an annulus formed between the drillstring and the drilled wellbore.
Furthermore, drilling mud provides a column of hydrostatic pressure, or head, to prevent “blow out” of the well being drilled. This hydrostatic pressure offsets formation pressures, thereby preventing fluids from blowing out if pressurized deposits in the formation are breached. Two factors contributing to the hydrostatic pressure of the drilling mud column are the height (or depth) of the column (i.e., the vertical distance from the surface to the bottom of the wellbore) itself and the density (or its inverse, specific gravity) of the fluid used. Depending on the type and construction of the formation to be drilled, various weighting and lubrication agents, as mentioned above, are mixed into the drilling mud to obtain the right mixture. Typically, drilling mud weight is reported in “pounds,” short for pounds per gallon. Increasing the amount of weighting agent solute dissolved in the mud base will generally create a heavier drilling mud. Drilling mud that is too light may not protect the formation from blow outs, and drilling mud that is too heavy may over-invade the formation. Thus, a drilling mud can be referred to as weighted or un-weighted, depending upon the amount of weighting agent and other additives contained therein.
Another significant purpose of the drilling mud is to carry the cuttings away from the drill bit at the bottom of the borehole to the surface. As a drill bit pulverizes or scrapes the rock formation at the bottom of the borehole, small pieces of solid material are left behind. The drilling mud exiting the nozzles at the bit acts to stir-up and carries the solid particles of rock and formation to the surface. Therefore, the drilling mud exiting the borehole from the annulus is a slurry containing formation cuttings.
Before the drilling mud can be recycled and re-pumped down through nozzles of the drill bit, certain solids, for example, the drill cuttings, must be removed. In general, the drilling solids can be separated from the drilling mud using various combinations of shale shakers, centrifuges and mud tanks.
One type of apparatus used to remove cuttings and other solid particulates from drilling mud is commonly referred to in the industry as a “shale shaker.” A shale shaker, also known as a vibratory separator, is a vibrating sieve-like table upon which returning used drilling mud is deposited and through which substantially cleaner drilling mud emerges.
In some cases, the drilling mud fluid recovered from the shale shaker may be free from large drill cuttings and can be sent to a mud tank for further separation and processing. For example, the residual fluid can be further processed to form drilling mud for downhole reinjection. However, in other cases, the fluid effluent from the shale shaker may require further solids separation, such as to adjust the levels of or recover various additives from the drilling mud. Such further separation can be accomplished using a centrifuge.
The principle of the centrifuge operation relies upon the density difference between the solids and the liquids within the drilling mud. As a rotational torque is applied to a centrifuge generating a centrifugal force (hereinafter, “G force”), the higher-density solids preferentially accumulate on the outer periphery inside the centrifuge, whereas the lower-density liquids preferentially accumulate closer to the axis of the centrifuge rotation. Upon the initial separation by the G force, the solids and the liquids can be removed from opposite sides of the centrifuge using a ribbon-type screw conveyor, sometimes referred to as a scroll.
Referring to
The wall of the screw conveyor 18 has a feed port 18a near the outlet end of the feed pipe 16 so that the centrifugal forces generated by the rotating bowl 12 move the drilling mud radially outward through the feed port 18a into the annular space between the screw conveyor 18 and the bowl 12. The annular space can be located anywhere along the large bowl section 12d or the conical section 12e of bowl 12. The fluid portion of the drilling mud is displaced toward the end 12b of the bowl 12 and recovered through one or more fluid discharge ports 19c. The entrained solids in the drilling mud slurry settle toward the inner surface of the bowl 12 due to the G forces generated, and are scraped and displaced by the screw conveyor 18 toward the end 12a of the bowl for discharge through a plurality of solids discharge ports 12c formed through the wall of the bowl 12 near its end 12a. The centrifuge 10 is enclosed in a housing or casing (not shown) in a conventional manner.
The main challenges facing the operation of a centrifuge include high feed rates and varying solids content in the feed. As the feed rates increase, high torque is typically required to accomplish the solids separation, thus resulting in increased costs due to equipment size, duplication, and increased energy costs. Additionally, feed inconsistencies due to variations in the solids content require constant torque adjustment, thus resulting in accelerated equipment wear and tear.
There is still a significant need in the art for improved centrifuge devices and methods for more cost-efficient solids separation from drilling muds that can handle high feed rates and varying solids content in the feed.
In one aspect, embodiments disclosed herein relate to a dual feed centrifuge system for separating solids from fluids in a drilling mud, the centrifuge system including: a bowl; a screw conveyor rotatably mounted within the bowl; a first feed pipe mounted within the screw conveyor for feeding a drilling mud through a first feed port in a wall of the screw conveyor to a first annular space between the bowl and the wall of the screw conveyor; and a second feed pipe mounted within the screw conveyor for feeding a drilling mud through a second feed port in the wall of the screw conveyor to a second annular space between the bowl and the wall of the screw conveyor.
In another aspect, embodiments disclosed herein relate to a process for separating solids from fluids in a drilling mud including: feeding a drilling mud through at least one of a first feed pipe and a second feed pipe to a centrifuge, the centrifuge having: a bowl; a screw conveyor rotatably mounted within the bowl; the first feed pipe mounted within the screw conveyor for feeding the drilling mud through a first feed port in a wall of the screw conveyor to a first annular space between the bowl and the wall of the screw conveyor; and the second feed pipe mounted within the screw conveyor for feeding the drilling mud through a second feed port in the wall of the screw conveyor to a second annular space between the bowl and the wall of the screw conveyor; separating the drilling mud into a solid and a fluid, the separating comprising: rotating the bowl with a speed A using a rotation device, wherein the solid accumulates along the bowl; rotating the screw conveyor with a speed B using a rotating device, wherein the fluid moves along the screw conveyor; moving the solid along the bowl using the screw conveyor; recovering the solid through a solid discharge port; and recovering the fluid through a fluid discharge port.
In another aspect, embodiments disclosed herein relate to a method for separating solids from fluids, the method including: feeding a first drilling mud via a first feed pipe to a centrifuge, the centrifuge having: a bowl; a screw conveyor rotatably mounted within the bowl; a first feed port in a wall of the screw conveyor; and a second feed port in the wall of the screw conveyor; wherein the first feed pipe is mounted within the screw conveyor for feeding the drilling mud through the first feed port to an annular space between the bowl and the wall of the screw conveyor; and feeding a second drilling mud via a second feed pipe to the centrifuge, wherein the second feed pipe is mounted within the screw conveyor for feeding the drilling mud through the second feed port to the annular space between the bowl and the wall of the screw conveyor.
In another aspect, embodiments disclosed herein relate to a dual feed centrifuge system for separating solids from fluids in a drilling mud, the centrifuge system including: a bowl; a screw conveyor rotatably mounted within the bowl; a first feed pipe mountable within the screw conveyor for feeding a drilling mud through a first feed port in a wall of the screw conveyor to a first annular space between the bowl and the wall of the screw conveyor; and a second feed pipe mountable within the screw conveyor for feeding a drilling mud through a second feed port in the wall of the screw conveyor to a second annular space between the bowl and the wall of the screw conveyor.
Other aspects and advantages will be apparent from the following description and the appended claims.
In one aspect, embodiments disclosed herein relate to a centrifuge system for processing a fluid including solids and liquids. In another aspect, embodiments disclosed herein relate to a dual feed centrifuge system for separating and removing solids from a fluid material. In another aspect, embodiments disclosed herein relate to a dual feed centrifuge system for separating and removing solids from a drilling fluid material. In yet another aspect, embodiments disclosed herein relate to a method of separating and removing solids from liquids in a fluid material using a dual feed centrifuge. In yet another aspect, embodiments herein relate to a system and a method of controlling the flow to a dual feed centrifuge system based on a fluid property.
As used in embodiments disclosed herein, “drilling mud” refers to a mixture having a fluid and a solid suspended therein. The fluid may be either oil-based or water-based. Solids may include one or more of drill cuttings, additives, or weighting agents. For example, the drilling mud may contain polymers, biopolymers, clays and organic colloids added to oil-based or water-based fluids in order to obtain the required density, viscosity and filtration properties. In other embodiments, the drilling mud may contain heavy minerals, for example, barite or calcium carbonate that may be added to increase density. In yet other embodiments, the drilling mud may contain solids from the drilling formation that become dispersed in the mud as a consequence of drilling.
As used in embodiments disclosed herein, “weighted” and “un-weighted” refer to the relative amount of additives and weighting agents that are dissolved, suspended, or otherwise contained in the drilling mud. Typically, drilling mud weight is reported in “pounds,” short for pounds per gallon. Thus, increasing the weighting of the drilling mud creates a heavier drilling mud.
As used in embodiments disclosed herein, “torque” refers to a force required to rotate the centrifuge for separating solids from fluids in the drilling mud. The torque is supplied to the driving shaft of the centrifuge by a driver, for example, an electrical motor, a gas turbine, or a combustion engine. Where a variable torque is required due to changes in the throughput or the feed weighting characteristics, a torque adjustment device, for example, a gearbox, can be provided.
As used in embodiments disclosed herein, “G force” refers to centrifugal force generated by the rotation of the centrifuge and/or the screw conveyor in response the applied torque. The G force is used in a centrifuge to separate components, such as solids and fluids, based on the relative densities. For example, the heavier solids will accumulate on the outside periphery of the centrifuge chamber, whereas the lighter fluids will accumulate closer to the axis of the centrifuge rotation.
Weighted and un-weighted drilling muds may be efficiently separated using a dual-feed centrifuge according to embodiments disclosed herein. Furthermore, the separation of a drilling mud having a weighting intermediate of a weighted and an un-weighted drilling mud can be optimized using a dual-feed centrifuge according to embodiments disclosed herein.
A dual feed centrifuge according to embodiments disclosed herein may have two separate feed pipes for feeding the drilling mud into the centrifuge. A screw conveyor has a feed port in the form of an opening in its wall located near the outlet end of each feed pipe. As a rotational torque generates G forces inside the centrifuge, the drilling mud in the feed pipe is forced through the feed port into an annular space between the screw conveyor and a bowl for solids separation and recovery.
In one set of embodiments, the entire drilling mud feed may be injected either through the first feed pipe or the second feed pipe, depending on the mud weighting. For example, an un-weighted drilling mud feed may be injected through the first feed pipe into the large bowl section of the centrifuge, where it can undergo premium separation at a low torque. A weighted drilling mud feed may be injected though the second feed pipe into the conical section of the centrifuge, where it can be separated at high throughput rates and a low torque.
In another set of embodiments, the drilling mud feed flow may be allocated between the first feed pipe and the second feed pipe based on the fluid properties. For example, where the solids content of a drilling mud is intermediate that of a weighted mud and an un-weighted mud, the relative flow allocation of the drilling mud between the first and the second feed pipes can be adjusted based on the weighting (density) of the drilling fluid.
Advantageously, one or more embodiments disclosed herein may provide a system and a method for handling high centrifuge feed rates and a varying solids content in the feed.
One or more embodiments disclosed herein may also provide a system and a method to achieve high separation efficiency of the un-weighted drilling muds and high throughput of the weighted drilling muds. Further, embodiments disclosed herein provide a system and a method for processing both weighted and un-weighted drilling muds, thus resulting in equipment costs savings.
One or more embodiments disclosed herein may also provide a system and a method to both achieve the required separation efficiency and to maintain a high feed throughput of a drilling mud having an intermediate weighting.
One or more embodiments disclosed herein may also provide a system and a method to pro-actively adjust the torque loading on the centrifuge and thus reduce the amount of equipment wear and tear.
One or more embodiments disclosed herein may also provide a system and a method to reduce the susceptibility of the centrifuge to solids plugging by adjusting the drilling mud flow between the two feed ports without diminishing the total throughput.
One or more embodiments disclosed herein may also provide a system and a method to increase flexibility of the centrifuge operation by optimizing the profit margin based on the required separation efficiency, throughput, and the costs related to energy consumption, equipment maintenance, and repair based on the centrifuge torque.
For the purpose of illustration and not limitation, various embodiments of the dual-feed centrifuge and the process for separating solids from fluids according to the present disclosure are described below.
Referring to
The wall of the screw conveyor 28 has a first feed port 28a proximate the outlet end of the first feed pipe 26a and a second feed port 28b proximate the outlet of the second feed pipe 26b. The centrifugal forces generated by the rotating bowl 22 move the drilling mud in the first feed pipe 26a radially outward through the first feed port 28a into a first annular space 25a between the screw conveyor 28 and the bowl 22 along the large bowl section 22d of the centrifuge 20. The centrifugal forces generated by the rotating bowl 22 move the drilling mud in the second feed pipe 26b radially outward through the second feed port 28b into a second annular space 25b between the screw conveyor 28 and the bowl 22 along the conical section 22e of the centrifuge 20.
The fluid portion of the drilling mud in both the first annular space 25a and the second annular space 25b is displaced toward the end 22b of the bowl 22 and recovered through one or more fluid discharge ports 29c. The entrained solids in the drilling mud accumulate toward the inner surface of the bowl 22 due to the G forces generated, and are scraped and displaced by the screw conveyor 28 toward the end 22a of the bowl for discharge through a plurality of solids discharge ports 22c formed through the wall of the bowl 22 near its end 22a. The centrifuge 20 is enclosed in a housing or casing (not shown) in a conventional manner.
In some embodiments, the first feed pipe 26a may be mounted within the second feed pipe 26b, commonly referred to as a “double-pipe” arrangement. In other embodiments, the first feed pipe 26a and the second feed pipe 26b may be mounted side-by-side within the centrifuge. In yet other embodiments, the first feed pipe 26a may be an extension of the second feed pipe 26b. A person of ordinary skill in the art would recognize that feed pipes of various other shapes and mounting arrangements can also be used.
In some embodiments, the bowl 22 may be of concentric shape. In other embodiments, only a portion of the bowl 22 may have a concentric shape. In yet other embodiments, the large bowl section 22d of the bowl 22 may be of concentric shape, whereas the conical section 22e of the bowl 22 may be of conical shape. In other embodiments, the diameter of the large bowl section 22d is greater than the average diameter of the conical section 22e. In other embodiments, the large bowl section 22d and the conical section 22e may be located proximately along the axial length of the bowl 22.
In some embodiments, the first feed pipe 26a may terminate proximate a single feed port, the first feed port 28a. In other embodiments, the first feed pipe 26a may terminate proximate multiple first feed ports 28a. For example, multiple first feed ports 28a may be radially spaced along the wall of the screw conveyor 28 with respect the first feed pipe 26a. In some embodiments, the axial location of the first feed port 28a along the bowl 22 may be approximately in the middle of the large bowl section 22d. In other embodiments, the axial location of the first feed port 28a along the bowl 22 may be anywhere along the large bowl section 22d. In yet other embodiments, the axial location of the first feed port 28a along the bowl 22 may be anywhere along the conical section 22e.
In some embodiments, the second feed pipe 26b may terminate proximate a single feed port, the second feed port 28b. In other embodiments, the second feed pipe 26b may terminate proximate multiple second feed ports 28b. For example, the multiple second feed ports 28b may be radially spaced along the wall of the screw conveyor 28 with respect to the second feed pipe 26b. In some embodiments, the axial location of the second feed port 28b along the bowl 22 may be approximately in the middle of the conical section 22e. In other embodiments, the axial location of the second feed port 28b along the bowl 22 may be anywhere along the conical section 22e. In yet other embodiments, the axial location of the second feed port 28b along the bowl 22 may be anywhere along the large bowl section 22d.
Referring to
A density instrument 31, for example, a nuclear, an optical, or a gravity-based density instrument, may be used to measure the density or weighting of the drilling mud upstream of the first valve 33a and the second valve 33b and produce a density signal 31a. The density signal 31a may be communicated to a controller 35 that produces a first valve position signal 35a and a second valve position signal 35b. The first valve position signal 35a and the second valve position signal 35b are communicated by the controller 35 to the first valve 33a and the second valve 33b, respectively. Positions of the first valve 33a and the second valve 33b may be adjusted in response to the first valve position signal 35a and the second valve position signal 35b, respectively, thus adjusting the flow to at least one of the first feed pipe 36a and the second feed pipe 36b.
In some embodiments, the first valve 33a and the second valve 33b may be butterfly control valves. In other embodiments, the first valve 33a and the second valve 33b may be tight-shut-off ball or globe valves. A person of ordinary skill in the art would recognize that other types of valves or other flow control mechanisms can also be used.
In some embodiments, the controller 35 may be a part of a distributed control system (DCS). In other embodiments, the controller 35 may be a stand-alone field controller, such as a programmable logic controller (PLC). A person of ordinary skill in the art would recognize that other types of flow controllers can also be used.
Referring now to
In operation, the first feed pipe 56a may be disposed within the centrifuge, such as for separation of a weighted drilling mud. As first feed port 58a is located closer to the solid outlets 60 than second feed port 58b, the centrifuge will experience less torque than if the weighted drilling mud were fed through second feed port 58b. When it is desired to separate an un-weighted drilling mud, first feed pipe 56a may be withdrawn from centrifuge 50 and second feed pipe 56b may be inserted. In this manner, the benefits of decreased torque may be realized without the need for multiple centrifuges.
First feed pipe 56a, in some embodiments, may include a closed or capped end 62 with feed slots 64 proximate capped end 62 for feeding drilling mud radially into feed chamber 66. The capped end 62 may close the opening to feed chamber 68 and the centrifugal forces generated move the drilling mud fed via first feed pipe 56a radially outward through first feed port 58a into the annular space 70 between the screw conveyor 58 and the bowl 52. When second feed pipe 56b is inserted, the centrifugal forces generated by rotating bowl 52 move the drilling mud fed via second feed pipe 56b radially outward through second feed port 58b into a second annular space 72 between screw conveyor 58 and bowl 52.
As illustrated in
Additional feed ports and feed pipes may also be used, such as three, four, or more feed ports and pipes to allow greater flexibility with respect to the separations and the resulting torque requirements. Intermediate feed zones may be fed using different length feed pipes having closed or capped ends and radial feed. In this manner, carryover between feed chambers is minimized, thus producing the desired improvements in centrifuge performance.
As described above, embodiments disclosed herein relate to a dual feed centrifuge system and a method for separating and removing solids from liquids in a drilling mud.
Advantageously, a dual feed centrifuge according to one or more embodiments disclosed herein may provide a system and a method for handling high centrifuge feed rates and a varying solids content in the feed.
Advantageously, a dual feed centrifuge according to one or more embodiments disclosed herein can be used to achieve high separation efficiency of the un-weighted drilling muds and high throughput of the weighted drilling muds. Further, a dual-feed centrifuge according the embodiments herein can efficiently process both the weighted and the un-weighted drilling muds, thus resulting in equipment cost savings.
Advantageously, a dual feed centrifuge according to one or more embodiments disclosed herein can also be used to both achieve the required separation efficiency and to maintain a high feed throughput of a drilling mud having an intermediate weighting.
Another advantage of a dual-feed centrifuge according to one or more embodiments disclosed herein over a conventional centrifuge is the ability to pro-actively adjust the torque loading on the centrifuge by allocating the drilling mud flow between the first and the second feed pipes, thus compensating for feed quality-related upsets and reducing the amount of wear and tear on the centrifuge driver and gearbox due to torque adjustments.
Yet another advantage of a dual-feed centrifuge according to one or more embodiments disclosed herein over a conventional centrifuge is the reduced susceptibility to solids plugging. The solids plugging is less likely to occur during a continuous, steady-state operation, and thus by pro-actively adjusting to compensate for feed quality-related upsets or changes in mud weighting, the susceptibility to plugging can be reduced. Further, the solids plugging typically takes place near the narrower, conical section, between the feed port and the solids discharge port. Thus, whereas a conventional centrifuge lacks the ability to reduce the feed flow to the conical section without reducing the total throughput, a dual-feed centrifuge can re-allocate a portion of the feed to the large bowl section in order to avoiding the plugging, without diminishing the total throughput.
A centrifuge experiences the highest conveying resistance, which relates to torque, at the transition from the cylindrical to the conical section due to increased G forces to the solids particles. For recovery of weighting materials, the volume of separated solids is relatively high and causes high torque, restricting the capacity of the centrifuge. By using the first feed port/chamber, which discharges to the conical section, the transition area is avoided and therefore reduced torque is encountered, allowing higher feed rate capacities than typical centrifuges.
Yet another advantage of a dual-feed centrifuge according to one or more embodiments disclosed herein over a conventional centrifuge is the increased flexibility of operation. For example, the centrifuge operation can be optimized by taking into account the profit margins based on the required separation efficiency, throughput, and the costs related to energy consumption, equipment maintenance, and repair based on the centrifuge torque.
While the disclosure includes a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the present disclosure. Accordingly, the scope should be limited only by the attached claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 61059532 | Jun 2008 | US | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US09/46445 | 6/5/2009 | WO | 00 | 12/2/2010 |
