Patent Application
20110247813
In many gas wells, inflowing fluid passes through a sand screen which filters out particulates from the inflowing gas. Generally, the flow rate of the inflowing gas is very high such that any sand production can cause substantial erosion of components in a gas well completion. The sand production is controlled with sand screens employed either as stand-alone screens or in combination with a surrounding gravel pack. However, the velocity of the inflowing gas often can exceed an erosion velocity which causes erosion of the sand screen and ultimate failure of the sand screen. Once the sand screen fails, the risk of erosion arises with respect to other elements of the completion. Use of gravel packing may limit the velocity of particulates; however gravel packs are not necessarily uniform along the entire sand screen, resulting in high, erosive flow rates through poorly packed regions.
In general, the present invention provides a technique for filtering sand; distributing a flow of fluid; e.g. distributing an inflow of gas or condensate; and limiting the potential for erosion of completion components in a wellbore. By way of example, the technique is useful in production applications, but the technique also can be used in fluid injection applications, e.g. gas injection applications. The technique employs a base pipe and a sand screen surrounding the base pipe. The base pipe comprises a plurality of flow restriction elements deployed in a selected pattern along the base pipe to provide a desired distribution of flowing fluid. The pattern of flow restriction elements also maintains a flow rate of the flowing fluid below an erosive flow rate across the entire sand screen.
Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and:
In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible.
The present invention generally relates to a system and methodology for filtering sand from flowing fluid, such as from inflowing gas in a gas production well. As explained in greater detail below, the system and methodology also enable a desired distribution of the flowing fluid across the sand screen while keeping the flow rate of the flowing fluid below an erosion flow rate to protect the sand screen from degradation.
According to one embodiment, a well system is provided with one or more sand screen assemblies coupled into a completion and deployed downhole into a gas well. Each sand screen assembly comprises a base pipe surrounded by a sand screen which filters particulates from an inflowing stream of gas during gas production. The base pipe beneath the sand screen is equipped with a plurality of flow restriction elements through which the inflowing gas moves to an interior of the base pipe after passing through the sand screen.
The flow restriction elements are sized and distributed to provide a controlled pressure drop and to eliminate regions of high flow velocity along the sand screen. The flow velocity is restricted to a rate below an erosion rate of the sand screen to prevent degradation and failure of the sand screen during gas production. The flow restriction elements may be arranged in a variety of patterns to provide the controlled pressure drop and thus the controlled flow rate through the sand screen. For example, multiple flow restriction elements may be evenly distributed along the base pipe to provide an evenly distributed inflow of gas and a consistent pressure drop along the sand screen. However, other patterns of the flow restriction elements also may be selected to create a desired flow control, e.g. a desired variation in pressure drop and/or flow rate along the sand screen.
Referring generally to
Well completion 24 potentially includes many types of devices, components and systems. For example, the well equipment may comprise a variety of artificial lift systems, sensor systems, monitoring systems, and other components designed to facilitate production operations, servicing operations, and/or other well related operations. In the example illustrated, well completion 24 further comprises a sand screen assembly 36.
The sand screen assembly 36 has a sand screen 38 designed to filter sand from gas or other fluid flowing across the sand screen 38. During gas production, for example, gas flows into wellbore 28 from formation 34 and passes through sand screen 38 which filters out sand while allowing the remaining gas to pass into completion 24. The sand screen 38 may be used in cooperation with and/or be positioned between other components of the well completion 24. Additionally, the sand screen assembly 36 may comprise a base pipe 40 positioned such that the sand screen 38 is mounted to surround the base pipe 40.
Completion 24 also may comprise one or more isolation devices 42, e.g. packers, positioned to enable selective isolation of a specific well zone associated with the sand screen assembly 36. It should be noted that well completion 24 may further comprise additional sand control assemblies 36 and isolation devices 42 to isolate and control fluid flow, e.g. gas flow, from (or to) other well zones of the reservoir/formation 34.
In
Referring generally to
Various sizes, densities and patterns of flow restriction elements 48 may be located along the base pipe 40 which is positioned radially beneath the surrounding sand screen 38. The sizes, densities and patterns of flow restriction elements 48 are selected according to the environment, downhole pressures, quality of the formation, presence of a surrounding gravel pack, and other environmental parameters. The size, density and arrangement of the flow restriction elements 48 establish the desired pressure drop along the base pipe 40 and also serve to sufficiently reduce the flow velocity of the gas or other fluid below an erosion flow rate. In specific applications, the arrangement of flow restriction elements 48 is selected to reduce the flow rate of inflowing gas (and particulates carried with the inflowing gas) to a rate which does not cause erosion along any region of the surrounding sand screen 38. In many applications, the flow restriction elements 48 are evenly distributed along the base pipe 40 to provide a constant pressure drop along the base pipe 40 and an evenly distributed inflow of gas. However, the size, density and pattern of the restriction elements 48 also may be varied along the base pipe 40 in a predetermined manner to provide a controlled variation of pressure drop and/or flow rate of, for example, inflowing gas.
In
The inflow area provided by flow restriction elements 48 is a function of perforation/orifice diameter and the number of orifices 54. To achieve an even distribution of the flowing fluid, e.g. inflowing gas, as desired in some embodiments, many small holes may be created through sidewall 50 of base pipe 40 in a consistent or even pattern. This type of pattern through the base pipe 40 creates an even gas inflow pattern toward and through the sand screen 38.
In the embodiment illustrated, sand screen 38 comprises a plurality of layers 56 designed to facilitate both filtering and flow through the sand screen 38. Depending on the well environment and other downhole factors, the actual type and number of layers can vary substantially. However, several types of sand screens 38 comprise an internal drainage layer 58 surrounded by a filter media layer 60. Alternate and/or additional layers also may be provided.
In
In the embodiment illustrated, each nozzle insert 62 comprises a passage 66 through which inflowing gas is routed through sidewall 50 and into the interior 52 of base pipe 40. As described with respect to the previous embodiment, the size of each passage 66 as well as the number and pattern of inserts 62 may be calculated to achieve the desired pressure drop across the base pipe 40 and also the desired reduction in velocity of flowing fluid, e.g. inflowing or outflowing gas, to a flow rate below an erosion rate of the sand screen 38. The nozzle inserts 62 also may be formed from an erosion resistant material, such as a hardened material, carbide material, or other suitable material.
Referring generally to
By choosing nozzles 62 having passages equal to or slightly larger than screen openings 72 of the sand screen 38, a self-healing effect is achieved. If the sand screen 38 undergoes any erosion, as illustrated by the widened screen opening 72 on the right side of
To further improve this self-healing effect, the drainage layer 58 of the sand screen 38 may be separated into several compartments. The compartmentalization may be achieved by placing inserts or other types of flow blocking members in the axial flow channels of the drainage layer 58 to prevent movement of particles 74 in an axial direction along an exterior of the base pipe 40. Preventing particles 74 from flowing axially or tangentially along an outer surface of the base pipe 40 ensures that a significant portion of the sand screen will not fill with sand even if a small part of the sand screen 38 is eroded. By way of example, the inserts or flow blocking members may comprise a ring in the drainage layer, a segment between structural members, e.g. between axial rods, of the sand screen, a shim placed between wrappings of the screen, or other suitable members designed to compartmentalize the screen and thus prevent any substantial transverse flow of fluid and particulates.
Referring generally to
With respect to embodiments of the present erosion prevention system, such as those embodiments discussed above, the size of the passages/flow areas through the flow restriction elements is designed for optimal flow performance. However, various embodiments also may be constructed to provide the self-healing effects discussed above. Generally, each flow restriction element 48 provides a flow connection to the interior 52 of base pipe 40 and acts as a drain for inflowing fluid, e.g. gas, entering the sand screen 38. As a result, the gas flow approaching sand screen assembly 36 tends to converge towards these drainage points.
The focusing effect of the flow may be controlled, at least somewhat, by the slot/opening density of the sand screen 38 and/or by the cross-sectional configuration of the drainage layer 58, as illustrated schematically in
Desired patterns of flow restriction elements 48 may be selected and designed based on optimization of peak flow velocity versus average flow velocity. Knowledge of the peak flow velocity and the average flow velocity is used to design flow restriction element density and flow area to ensure the velocity approaching sand screen 38 stays below an erosion velocity, thereby reducing or preventing erosion of the sand screen 38.
The overall well system 20 may be constructed to accommodate a variety of flow filtering applications in a variety of well environments while limiting or preventing erosion of the screen and other completion components. Accordingly, the number, type and configuration of components and systems within the overall system may be adjusted to accommodate different applications. For example, the size, number and configuration of the sand screen assemblies may vary from one application to another along the completion equipment. Additionally, many types of flow restriction elements and arrangements of those elements may be employed as dictated by the overall design of gas production equipment and by downhole environmental conditions. The base pipe configuration and the sand screen configuration also may be adjusted according to the specific application and environment. The sand screen assemblies and their erosion control elements may be combined into many types of well completions utilized in production and/or servicing operations. Also, the types and arrangements of other downhole equipment used in conjunction with the one or more sand screen assemblies may be selected according to the specific well related application in which the sand screen assemblies are employed.
Although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Accordingly, such modifications are intended to be included within the scope of this invention as defined in the claims.
