Completion - Drilling Formulas

1) Multiple Zone Completion By DrillingFormulas.Com | May 8, 2016 - 4:59 am | Completion Post Views: 172

Multiple zone completion is one type of completion which allows operators to selectively produce or comingle reservoir fluid from different zones into one well. It is also possible to workover the upper part of completion string without removing the next interval completion. Additionally, through tubing perforation is can performed at the bottom zone. A multiple zone completion can be divided into two parts, which are single string completion and multiple string completion.

Single String Configuration In a single string completion, a packer will be set above each zone in order to isolate fluid from each zone. What’s more, a packer will prevent corrosion in the production casing due to the flow of reservoir fluid. Figure 1 demonstrates an example of a single string configuration

Figure 1 – Completion Equipment Arrangement for a Single String Configuration

Multiple-String Configuration A multiple-string configuration consists of two or more completion strings in one well. This is more expensive and complicated to install than a single-string configuration. However, it has some

advantages such as the ability to simultaneous produce and injec into different zones and has a more accurate production allocation than a single string type.

Figure 2 – Completion Equipment Arrangement for a Dual String Configuration

Nowadays, single string completions are preferred to multiple string completions because of several issues as listed below;    

Less expensive Easier to install and workover Size of a production string in a single string is typically bigger than a multiple string at the same production casing size. Less complications for well control equipment

2) Single Zone Completion By DrillingFormulas.Com | May 8, 2016 - 4:46 am | Completion Post Views: 73

Single zone completion is one of the types of upper completion which allows producing only one zone. Production tubing is a flow path for fluid from a reservoir to flow to the surface so it protects the casing from corrosion and maximizes the efficiency of the flow. In a single tubing string completion, typically a packer is set on top of a reservoir so the reservoir fluid can flow up into the production tubing. Types of packers are based on several factors as temperature, pressure, reservoir fluid, etc. Additionally, complexity of tubing and packer installation is driven by objectives.

Features of a Single String Completion are listed below;    

Through tubing perforation can be performed. Packer can be set with x-mas tree in place. Reservoir can be isolated and workover operation can be done. Downhole measurements can be effectively conducted. Figure 1 and Figure 2 show a simple diagram of a single zone completion. In single zone completion, artificial lift methods as gas lift, ESP, etc. can be deployed.

Figure 1 – Single Zone Completion

Figure 2 – Single Zone Completion with Gas Lift

3) Cased and Perforated Completion By DrillingFormulas.Com | May 8, 2016 - 4:30 am | Completion Post Views: 293

Cased and perforated completion is the most common type of completion which is selected my many companies. For this completion, a production casing or a liner is cemented through reservoir zone(s) and subsequently, a well is perforated in order to provide communication between the formation and wellbore. Perforation should ideally penetrate deeper rather than nearer a wellbore damage zone around a wellbore so fluid from a reservoir can effectively flow into a wellbore. Additionally, several depth control methods help to accurately select which section of reservoir to be perforated. Hence, undesired zones, such as gas, water or weak formation can be avoided and this will improve well production efficiency. Cementing around the wellbore is one of the critical parts for this completion because good cement will effectively isolate all zones and allows a wellbore to produce from several zones without communication between reservoirs. Moreover, packers are run into a wellbore to isolate reservoir fluid when it flows into a wellbore. Another important feature of this completion is the ability to selectively produce or inject into any reservoir. A sliding sleeve on each zone can be opened and closed to allow selective production or injection operation. Figure 1 illustrates the diagram of cased and perforated completion.

Figure 1- Example of Cased and Perforated Schematic

Advantages of cased and perforated completions 

Safer operations

        

Better zonal isolation Facilitation of selective perforation and stimulation Effective way to complete multiple zones in one well Better reservoir management Ability to shut off any undesirable productions such as water, gas, or sand Long term cost effective Ability to work over and recomplete the well Better well integrity Less sand production than open hole completion

Disadvantages of cased and perforated completions  

Extra cost for casing, cementing, perforation and completion equipment. Lower reservoir exposure than open hole completion

4) What is Open Hole Completion? By DrillingFormulas.Com | May 1, 2016 - 10:07 am | Completion Post Views: 815

Open hole completion or bare foot completion is one type of completion where the production casing is set on top of the reservoir, but the open hole section is left without cemented casing. Typically, drilling into a pay zone is drilled with non-damage drilling mud or drilling mud weighted with calcium carbonate, which can be dissolved with acid later if needed.

Open Hole Completion

The pros and cons of this completion are as follows;

Advantages of Open Hole Completion      

Full exposure of reservoir zone No cementing or perforating expense Minimize formation damage Minimize flow path restriction due to cementing and perforating Minimize wellbore skin Improve wellbore performance due to a large inflow area

Disadvantages of Open Hole Completion     

Unable to control excessive water or gas production Unable to isolate hydrocarbon zones Difficult to do reservoir management Has large potential to produce sand Inability to produce at different zones Nowadays, this completion is not very popular due to several limitations as stated earlier. However, some horizontal wells which have competent rock are completed with bare foot completion because the wells can produce at considerable rates compared to cemented casing completion.

5) Basic Sand Control Methods in Oil and Gas Industry By DrillingFormulas.Com | May 16, 2016 - 4:36 am | Completion Post Views: 717

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 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 interparticle 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.

Figure 1 – Slotted Liner

(Ref http://image.ec21.com/image/tjpowerful/oimg_GC02070430_CA07710645/Slotted_Casing_Pipe_Slo tted_Liner_Slotted_Pipes_Tubing.jpg) 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.

Figure 2 – Type of slotted liner

Wire-Wrapped Screen 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.

Figure 3 – Wire-Wrapped Screen

(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 wirewrapped screens are typically used behind a gravel pack because a gravel pack is well-sorted grain size that people can control.

Pre-Packed Screen 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.

Figure 4 – Pre-Packed Screen

(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 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.

Figure 5 – Premium Sand Screen

(Ref- http://www.offshore-mag.com/content/dam/offshore/print-articles/volume74/01/sandfacecompposter_off1401.pdf)

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.

Figure 6 – Open Hole and Cased Hole Gravel Pack

(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 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.