Lost circulation in a drilling operation is a critical event that can cause anything from downtime (NPT), Significant loss of drilling fluid to weak or fractured formations or if not handled swiftly, can end up in critical well control operations causing severe NPT and worse.
In well construction, the primary well barriers are relying on critical cementing operations. These operations are regularly corrupted by loss of cement to formation during placement, causing uncertainties to the barrier behind the casing. These situations are very difficult to repair after the cement job is completed and undesired flow may occur behind the casing as a result of this.
The lost circulation issue has been with the drilling industry since the start and many recipes and remedies has been used to stop this. As this is still a common situation around the world causing lost time and resources, we have developed a product that answers many of the problems with the existing available technology.
Current options used when experiencing a lost circulation situation is to add various plugging materials to the mud pumped to form a plug in the fractures or pores to control/stop the loss. This situation can go on for days with lost productive time and significant loss of mud material as a result.
Alternatively, cement slurries of various weights and compositions related to the formation and situation are used.
The QuartzPack™ (QP) used as LCM is an application called SandBlock, that allows a lost circulation situation to be effectively cured, both in unconsolidated weak formations, high permeable zones or through fractures.
There will be no fluid loss from QP itself, due to the low permeability and the large particles that cannot move through the lattice.
When the pressure applied to propagate QP into a fracture is bled off, formation closes and traps the material inside a fracture, which then acts as a permanent seal. QP cannot enter the porosity around the fracture.
The only way to get more material into a fracture is by widening the aperture and radius of the fracture. This again creates additional counteracting, so called hoop stress. The hoop stressed ring around the well bore will act as a reinforcement element of the near-well rock volume; therefore, improved well bore stability.
This phenomenon has been observed in building of arches and modelled with the presence of grain sizes, in the range from 2.5 mm to less than 0,0005 mm, as is the case for SandBlock.
Corrective or Preventive solution to drilling problems
The main objective for an efficient Lost Circulation Material (LCM) is to prevent the hydrostatic and generated pressure (ECD) from the wellbore entering adjacent fractures by rapidly building an impermeable barrier at the mouth of the fracture.It is also desirable to strengthen the borehole by introducing “wedges” in the same fractures, allowing higher mud weight and increase the drilling window. This is often described as stress caging or borehole strengthening. The principle is similar to placing wedges in a stone arc or packing snow and ice between ice blocks from the inside of an igloo.
Drilling induced vertical fracture
The illustration shows a drilling-induced vertical fracture developing in the wellbore.
Such fractures can grow tens or hundreds of meters from the well with a large amount of drilling mud needed to regain well control.
Note that we do not recommend pumping SandBlock™ through narrow restrictions; therefore, a circulation sub is recommended placed immediately above the BHA.
SandBlock ™ is here being pumped into the well through the drill string. Conventional LCM is often used as an additive in the mud when drilling through problem zones.
SandBlock ™ on the other hand, is pumped as a continuous pill; either after losses occur or for stress caging prior to entering a weak zone.
Bridge off at the fracture mouth
The Sandblock™ follows the flow to the fracture and bridges off at the fracture mouth, isolates the hydrostatic head from the fracture and stops further growth very rapidly.
Prior to circulating out the excess SandBlock ™, the borehole can now be strengthened by closing the annular BOP and pressuring up the borehole.
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Stig Hetlevik Chief Executive Officer
Mr. Hetlevik is the founder and CEO of Flopetrol Well Barrier AS. He has been working in the oil and gas-industry since 1980. His experience includes 20 years of fieldwork in Drilling and Well operations on/offshore within the service industry (Flopetrol Schlumberger), for Operating companies (Norsk Hydro, Saga Petroleum, BP, ExxonMobil, Statoil), and for Norwegian Authorities (NPD/PSA) as a principal engineer within Drilling, well operations and well integrity. He has been a Chairman, and later a member of NORSOK Expert Group Drilling (EGD) from 1999, which is still ongoing. His experience includes over 19 years in project and management positions, including VP Operations in Prosafe Offshore Drilling, Co-Founder and VP Operations/Projects Offshore Rig Services ( Drilling Contractor) for Design and construction of 3 midwater semi’s. He previously had the position as Director Marine Operations in Eastern Hemisphere for FMC Technologies, with all operations relevant to subsea systems.
Phone: +47 905 90 967