Centraflow Introduction Company established in September 2015 ipark, Stavanger Two office locations: Blackburn, Aberdeen Centraflow is focused on the design and development of downhole flow diversion technology
Problem Definition Cementing casing or liner with poor stand off (~below 67 %) can lead to mud channeling and lack of zonal isolation leading to sustained casing pressure, formation X flow or loss of production. Good casing centralization is key, rotation is preferred. BUT: often we can t rotate casing and actual stand off is often less than 50%. If we have an eccentric annulus with greater flow area on the high side, fluid will follow the path of least resistance. This leads to a velocity imbalance velocity on the high side of the wellbore is much greater than the velocity on the low side. If fluid moves too slowly on the low side, residual cuttings and filter cake cannot be removed and effective cement displacement cannot take place.
Downhole Flow Diversion Introducing a restriction into the casing wellbore annulus on the high side of the wellbore creates a velocity inversion effect. Increasing the low side velocity above the critical transportation rate removes residual cuttings and filter cake from underneath the casing. Low side channels are eliminated and full circumferential cement displacement can be achieved.
The theory in practice Please refer to flow loop video on our homepage: http://www.centraflow.com/home
Physical Flow Loop Cement Testing The flow loop represents a scaled 12 1/4" hole (perspex) with 9 5/8" casing (PVC pipe). This setup had a standoff of 51% in both cases with pump rates and cuttings volume matched throughout the testing regime (6.7 mm cuttings bed height). The test clearly showed that with CE Bond, the low side of the well had excellent cement displacement which generated an optimal bond between the Perspex and PVC. In comparison, the run without CE Bond was unable to clear all of the cuttings (as proved in our previous flow loop testing), and was therefore unable to get a good cement coverage. This led to multiple channels on the low side caused by a combination of cuttings beds and poor low side fluid velocities (poor displacement).
What does a downhole flow diverter look like? Design brief: Flow diverter needs to function autonomously and be able to differentiate between low side and high side. Should be simple to install and should should not impact normal casing running & cementing operations. Needs to be suitably robust (axial, torsional, abrasion & impact loadings). Centraflow has designed & built a novel casing accessory to meet this brief: Installed between stop collars in the same way as a regular solid body centralizer. Functions autonomously via an atmospheric buoyancy chamber self orientates the diverter element to face highside when wellbore inclination exceeds ±5.
Computational Fluid Dynamics (CFD) Centraflow uses in house CFD capabilities to model well specific scenarios, taking into account: Average hole diameter (under gauge or over gauge). Wellbore inclination. Centralization scheme and associated stand off. Flow rates. Mud, spacer & cement properties. Distance taken to return to high side steady flow. Turbulence. The effect of downhole fluid diversion can then be assessed: Velocity inversion effects and flow regime. Distance taken downstream to return to high side steady state flow. Turbulence effects. Optimal spacing for fluid diverter tools on the casing.
Velocity Inversion 12.5 ppg OBM, 12 bbl/min 9 5/8ˮ Casing inside 12 1/4ˮ hole Wellbore inclination: 90 Steady state (upstream): High side: 0.95 m/s Low side: 0.55 m/s High side & Low side flow equalized for 3m downstream of the flow diverter pseudo vertical hole. Velocity inversion (downstream): Low side: >3 m/s (peak)
Velocity Inversion different fluid types
Reciprocation
Pressure Drop & ECD Representative pressure drop for a flow diverter on 9 5/8 casing inside 12 1/4 gauge hole: ANSYS Fluent CFD Solver. Scenario #1: 12.5 ppg (1.497 S.G.) OBM, pumped at 12 bbl/min (1,908 L/min). Pressure drop of 3.5 psi (0.241 bar) created by each flow diverter tool. Scenario #2: 15.86 ppg (1.9 S.G.) tail cement slurry, pumped at 8 bbl/min (1,272 L/min). Pressure drop of 1.4 psi (0.097 bar) created by each flow diverter tool. If you were to run 50x flow diverter tools at a frequency of one tool per casing joint, in order to deliver effective cement bond across 600m of wellbore the associated total annular pressure loss would be 70 psi (4.83 bar) while pumping cement at 8 bpm. Potential to deliver a net reduction in ECD if residual cuttings beds are removed during pre circulation prior to cementing.
Applications for downhole flow diversion Well Types: Deviated wellbore + unable to rotate casing/liner + stand off <70%. Key Applications: Long deviated openhole sections (60 plus wellbore inclination). Under reamed hole sections (requires expandable flow diverters). Cemented completions. Unconventionals. ECD critical applications (potential to lower flow rate and still achieve better cement displacement). Functionality: Elimination of cement channelling effects (mitigating against potential influx and Sustained Casing Pressure). Zonal Isolation (hydrocarbon & water bearing zones). Shoe Isolation. Groundwater protection. Fraccing optimisation.
Development Status CE BOND tools built & tested. Upcoming trial wells (9 5/8ˮ casing): NCS shallow TVD reservoir. UAE ERD wells 11,000 ft openhole section of 12 1/4ˮ hole, inclination ranging from 60 90 degrees. KSA need to address cement channeling in deep vertical gas wells (wellbore inclination of up to 20 ) Actively scouting for trial wells with deviated 13 3/8ˮ casing and Operator willing to run an ultrasonic cement bond log to verify results.
FAQ s
FAQ s Is CE-BOND a replacement for casing centralizers? No, not at all. CE Bond is designed to be run in conjunction with casing centralisers. The Operator can choose to run bow spring or solid body centralizers of their choice as normal. CE BOND will be installed using the same "slip on" method and retained between two stop collars. But CE BOND does not centralise a casing string it optimises circumferential fluid displacement by altering the velocity profile in the casing to wellbore annulus.
FAQ s How many CE BOND s are used per joint? Are they used all the way to surface? Each well is different and multiple factors come in to play such as: calliper data, hole angle, geology, etc. This information is used to provide space out requirements on a well by well basis. On average, CE BOND will be spaced one per joint with the shoe track possibly having two per joint. CE BOND is only suggested for use in areas of critical cement requirements such as the shoe, isolating formations, future abandonment zones and structural areas.
FAQ s Does CE BOND increase pack off risk? No. Pack off risk is defined by the size of discrete flow areas in the casing to wellbore annulus, and the fluid velocity within these flow areas. If CE BOND is compared to a conventional solid body casing centralizer, CE BOND represents a lower pack off risk. This is because the flow area on CE BOND is larger than the discrete flow areas between blades on a solid body centralizer, and for identical flow rates the fluid velocity within the CE BOND flow area is significantly higher. Solid Body Centraliser CE BOND
FAQ s Does CE BOND work in wash outs? CE BOND functions also in wash outs, as it has choking effect on the high side flow, leading to better flow distribution. CFD modelling shows that the CE BOND is effective in improving cement displacement for up to a 1 wash out.
FAQ s How can we be sure that CE BOND will self orientate? CE BOND has been designed with a strong upwards buoyancy force (around 10kg equivalent). To put this into perspective, picture a 10 kg weight hanging from a casing joint the force required to rotate this weight is significant. It should be noted that this buoyancy force comes into play as soon as the wellbore builds angle, so CE BOND will self orientate onto the high side as soon as wellbore angle exceeds around 5. This self orientation will therefore normally take place during cased hole. Once CE BOND is orientated onto the high side, the tendency of the casing to lay on the low side (due to gravity) and the elliptical geometry of CE BOND mean that it is almost impossible for CE BOND to be forced onto the low side. It should also be noted that as long as multiple CE BOND tools are run on a casing string, it is not essential for them all to be perfectly orientated onto the high side. A step change in hole cleaning and cement displacement will still be observed if only 80% of the CE BOND tools on the casing string are correctly orientated for example. Due to the unique design, CE-BOND, once orientated, is limited to remain in a zone on the high-side of the well only being able to rotate roughly 70 degrees maximum off top which still ensures effective displacement.
FAQ s Will CE BOND increase the risk of casing becoming stuck? In comparison to a solid body centraliser, the maximum OD on CE Bond is only 1/8" (3mm) larger than the centralizer blade height. In gauge hole, CE BOND is intended to lightly contact the high side of the wellbore only if the casing is 100% centralized. Regardless of the centralizer programme in use, achieving more than 80% casing stand off is effectively impossible to achieve in deviated hole. CE BOND also has the freedom to rotate. It can therefore rotate itself clear of a high side (below gauge) restriction using it's plough shaped nose and then flip back to the high side under buoyancy force to be correctly orientated. CE BOND is extremely robust, and will be physically tested to withstand 100,000 lbs (45 T) overpull force without damage (in case stuck casing is being worked or jarred free).
FAQ s Is there a risk that CE-BOND tools become damaged whilst RIH? CE-BOND uses state of the art composite materials (the space industries material of choice). With a combination of Carbon Fibre and Kevlar, CE-BOND is stronger than steel and has a high resistance to impact and abrasion. CE-BOND was designed using advanced composite Finite Element Analysis (FEA) techniques to ensure the capability to withstand all possible downhole forces and service loads that occur while installing casing. A physical testing programme is also used to categorically demonstrate the ability of CE-BOND to withstand all possible downhole load conditions. CE-Bond will also be tested for impact resistance which simulates the casing string travelling at running speed while coming into contact with a solid restriction.
FAQ s Can the composite material that CE BOND is manufactured from be damaged by H2S, CO2, OBM, or other wellbore fluids or gases? Composite materials are extremely inert and are highly resistant to ph, H2S, CO2 and oil based chemicals. Ironically, since water molecules are so small, designing a composite material to be fully water resistant under high pressure is the big challenge! The finished product will have an almost indefinite shelf life in a cool, dry warehouse. Due to surfaces finishes, it can be completely protected against UV. An extensive physical testing programme has been developed to categorically demonstrate the compatibility of CE BOND with all fluids and gasses that may be encountered downhole.
FAQ s Does CE BOND increase drag while running casing? Typically no; in gauge hole, CE BOND will only come into contact with the wellbore if the casing is 100% centralized. Since no centralizer programme can achieve 100% standoff, this scenario will only occur through areas with high dogleg severity. The composite material that CE BOND is manufactured from has a very low coefficient of friction, so if CE BOND does contact the wellbore, drag is not significantly impacted. The length of each CE BOND is short, so even a scenario where multiple CE BOND tools are contracting the wellbore will not significantly affect the friction factor seen by the casing string.
FAQ s Can Casing be rotated and reciprocated if CE BOND is being used? Casing can be freely reciprocated with CE BOND installed. In fact, reciprocation while circulating prior to cementing operations increases the wellbore cleaning efficiency of CE BOND so is a recommend step in the operational procedures. Casing can also be rotated with CE BOND installed if required.
FAQ s How can we verify the effectiveness of CE BOND? Ultrasonic cement bond logs provide a high resolution 'image' of cement bond quality around the casing circumference, and the ability to identify channels and assess overall cement bond quality. If an ultrasonic cement bond log is performed after installing casing with CE BOND, the log data will normally have sufficient resolution to identify the depth and orientation of the CE BOND tools, as well as qualifying the circumferential cement bond that has been achieved. If relevant offset well data is available from the same field, a direct comparison can be made between ultrasonic cement bond logs from similar wells, with and without CE BOND. If an ultrasonic cement bond log is not planned, the effectiveness of CE BOND can be physically confirmed by the increase in hole cleaning efficiency that is observed while circulating before the cement job (increased cuttings returns at surface). The improvement in well integrity that is associated with full circumferential cement bond will also be observed and recorded throughout the well lifecycle as part of routine well integrity management.
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