Sand control is a method to control sand production into a wellbore. This is common requirement for several oil and gas producing wells around the world. There are two situations which cause sand production. The first cause is rock mechanical failure near wellbore and the second one is dragging force from producing or injection fluid. Sand production can lead to several issues such as production impairment due to sand plugging, erosion to completion string and down hole tool, damage surface facilities as separator, piping, etc.
In order to avoid sand production, there are two main methods as listed below;
Passive sand control
This method uses non-intrusive measures to control, mitigate or avoid sand production from the reservoir. The following techniques are passive sand control methods.
- Oriented perforation
- Selective perforation
- Sand management
Active sand control
This method relies on the use of filters to control sand production and it is known as intrusive measure. The following techniques are active sand control methods.
- Stand alone screens (slotted liner, wire-wrapped screen, prepacked screen and premium screen)
- Expandable sand screen
- Gravel pack & Frack Pack
- Chemical consolidation
Stand alone screens
This type of sand control is to put a screen to stop sand production into a wellbore. Initially, fine sand and silts will pass through the screen. Once sand packs are developed around the screen, they will be like a filtration media which prevents sand to flowing into a wellbore. There are several types of screens used in oil and gas industry, such as slotted liner, wire-wrapped screen, prepacked screen and premium screen. This is suitable for well-sorted, clean with large grain size formation.
Slotted liner, which is one of the oldest sand control methods, is tubing with series of slots cut through a wall of tubular in an axial orientation (Figure 1). Width of slots is design to create inter-particle bridging across the slots. This is the least expensive way of making a standalone screen and it is very simple. The flow area is average about 3%, but it can go up to 6% of total area of pipe. However, flow areas over 6% will be detrimental to pipe tensile strength.
There are two types of slots which are straight and keystone slots (Figure 2). Keystone slots are considered to be a better choice than straight slots because of their self-flush ability. However, keystone slots are generally more expensive than straight slots. In general, slots are 1.5 to 2.5 inches long and width varies from 0.012 to 0.250 inches.
Wire wrapped screen is a perforated pipe with a wire-wrapped jacket welded around. Wires wrapped around the vertical ribs are keystone shaped, which is designed for decreasing the chances of sand plugging the screen because it has a self-cleaning action. It has a bigger flow area in comparison to a slotted liner and it provides good strength and accurate slot opening area.
There are three main types of wire-wrap screens as listed below;
- Rod-based screens
- Pipe-based slip-on
- Pipe-based direct build screens.
Figure 3 shows a drawing of wire-wrapped screen configuration.
(Ref – http://www.sand-screen.com/img/wire-wrapped-screen-structure.jpg)
The wire-wrapped screen can be used as a standalone screen or used with a gravel pack. The critical part of having successful sand control with wire-wrapped screen is to have well-sorted formations. Poorly sorted formation will not be effective because fine particles will pass through the screen, whereas the big particles are blocked. Fine particles in a wellbore will flow with producing fluid and cause damage to downhole and surface equipment. In a poorly sorted reservoir, the wire-wrapped screens are typically used behind a gravel pack because a gravel pack is well-sorted grain size that people can control.
Pre-packed screen is similar to a wire-wrapped screen but it has different filtering media. A media gravel layer with or without resin coating is placed around the internal screen component and is supported by an external screen (Figure 4). Thickness and size of medium layer depends on well requirements, such as formation size, flow rate, hole size, etc.
(Ref Image- http://www.variperm.com/themes/variperm/img/landing-page/pre-pack-screen.jpg)
The main concern about the pre-packed screen is a chance of plugging it with completion fluid, drilling mud, etc. Therefore, in order to mitigate this issue, Carbolite proppant can be utilized as the main pack media rather than re-sieved gravel. There are several advantageous about Carbolite such as bigger pore throats, precise sorting grain size, and better permeability than normal re-sieved sand.
Premium screens are an all metal design with a protective outer metal shroud and a metal mesh filtration. The main advantages of premium screens over other screens are screen plugging resistance and ability to flow back drilling fluid through the screens. The metal mesh can be specially designed depending on each service providers or customer requirements. Pore throat can vary from 60 micron to 300 micron and the ideas it that the mesh will prevent large particles and allow fine particles to flow through at the initial stage. Then large particles will form a permeable sand filter cake layer on the surface of screen, which will prevent fine and large particle from flowing though. Premium screens are normally run behind gravel pack and they are famous for running in long horizontal wells.
Expandable Sand Screen
Expandable screen is the latest screen technology. It includes perforated pip, a filter media and an outer shroud. The screen is run in to a wellbore and the expansion insert is used to expand the screen to the production hole diameter.
The advantages of setting expandable screens against formation are as follows;
- Effective sand control
- Provides wellbore support
- Gives maximum hole diameter
- Gives a high inflow area
Typical expandable screen is consisted of four main parts:
- Base pipe
- Filtration media
- Outer protection shroud
- Integral expandable connector
The video below shows the Weatherford expandable sand screen system.
There are several systems on the market so you may need to do technical and operational comparison among service provides to find the best solution to match with requirements.
Gravel Pack (Cased Hole and Open Hole) and Frack Pack
Gravel pack is one of sand control methods and it uses sized sands as a filter media to prevent sand production. Annulus between wellbore and a sand control screen (wire wrapped or premium screen) is filled with sized gravels which prevent formation sand to flow into a wellbore.
Open hole gravel pack (external gravel pack) is useful for controlling sand in heterogeneous formations. However, cased hole gravel pack (internal gravel pack) is utilized for controlling sand and protecting sand screens from erosion flow. Frack pack is a combined gravel pack with fracturing technique which creates wide and long conductive fractures. This technique will control sand production and improve productivity of wellbore.
(Ref Image – http://www.dunefront.com/images/Open_and_Cased_Hole_Gravel_Packs.png)
Advantages of gravel pack are as follows;
- Productivity impairment can be minimized by proper design
- It can be used in heterogeneous sands.
Disadvantages of gravel pack are as follows;
- Complex operation to install equipment and place gravel in place
- Risk of incomplete gravel pack
- Chemical compatibility of drilling fluid
- Difficult to use in deviated and horizontal wells
- Complex flow control and isolation
Chemical consolidation is an alternative way to the mechanical method to control sand production in unconsolidated formation by injecting chemical into formation in order to strengthen or consolidate sands. The main goal is to cement sand grains together to provide stable compressive strength while maintaining initial permeability as much as possible. This is the most complex sand control method which involves significant risks of damaging reservoirs and/or ineffective chemical placement. This technique involves muti-stage injection of several chemicals into a reservoir.
Jonathan Bellarby, 2009. Well Completion Design, Volume 56 (Developments in Petroleum Science). 1 Edition. Elsevier Science.
Wan Renpu, 2011. Advanced Well Completion Engineering, Third Edition. 3 Edition. Gulf Professional Publishing.
Ted G. Byrom, 2014. Casing and Liners for Drilling and Completion, Second Edition: Design and Application (Gulf Drilling Guides). 2 Edition. Gulf Professional Publishing.