اسباب فقدان الطفله في الحفر-Causes Of Lost Circulation in Drilling
In general there are two main causes of lost rotation in drilling operations problem which are as following
Invasion or slush loss to conformations similar as cavernous, vugular, shattered conformations or loose conformations.
Fracturing which is slush loss due to hydraulic fracturing operations from inordinate convinced pressures.
As this composition is one of five papers to cover the lost of rotation problems, I recommend visiting this links for better understanding
*Important preface For Lost Rotation Problem
*Remedial Of Lost rotation Problem,
*preventives To be considered to avoid slush loss problems
*Lost Of Rotation Material Used In drilling
causes of lost of circulation in drilling
- Invasion
Coarse, loose conformations
Coarse, loose conformations can have sufficiently high permeability for whole slush to foray the conformation matrix, causing lost rotation in drilling. This high permeability is frequently present in shallow beach and clay beds. conformations that were formerly reefs and oyster beds also have analogous tendencies. One important reason for precluding slush loss in shallow intervals is that it may beget these loose conformations to wash out, forming a large depression that's less stable which could delve in more fluently from overburden and carriage weight.Depleted conformations
Another implicit loss zone is in depleted conformations( generally beach). Producing conformations in the same field, or general vicinity, may beget fine( depleted) conformation pressure due to the birth of the conformation fluids. In such a case, slush weights needed to control other exposed conformation pressures may be too high for the depleted conformation, forcing slush to foray the low pressure depletedformation.However, plans should be formulated to help similar cause of lost rotation in drilling or wedged pipe from being in the depleted zone, If this situation exists. Special bridging agents and sealing accoutrements should be used to form a good seal and sludge cutlet on the depleted zone.
Cavernous or vugular zones
Cavernous or vugular zones are generally associated with low- pressure carbonate( limestone and dolomite) or stormy conformations. In limestone, vugs are created by the former nonstop inflow of water that dissolved part of the gemstone matrix( filtering), creating a void space frequently latterly filled with oil painting. When these vugular conformations are drilled, the Drill String may fall freely through the void zone which will fleetly beget lost of rotation in drilling. The volume and continuity of this kind of loss depends on the degree to which the vugs are connected. analogous vugs and grottoes can develop during the cooling of stormy magma or ash. Cavernous and vugular conformations are frequently fluently traceable from neutralize wells and predictable from slush logs and lithology.crevices Or Fractures
slush loss also occurs to crevices or fractures in wells where no coarsely passable or cavernous conformations live. These crevices or fractures may do naturally, or may be initiated or extended by hydraulically assessed pressures. Natural fractures live in numerous cases, which may be impermeable under balanced pressure conditions. Losses may also do at closed fault boundaries.- Fracturing
Hydraulic Fracturing
Hydraulic fracturing is initiated and may beget a lost of rotation occurs when some critical fracture pressure is reached or exceeded. Once a fracture is created or opened by an assessed pressure, it may be delicate to repair( heal) and it may noway recapture the original conformation strength, as shown latterly in Figure 5. Lost rotation may persist indeed though the pressure is latterly reduced. This is the cause why it's better to pretreat for, and help, lost rotation in drilling than to permit it to do. Lost rotation performing from convinced pressure is generally caused by one of two situations Setting intermediate covering in the wrongplace.However, the pressures wielded by the heavier slush( needed to balance the adding pressures) will frequently induce fracturing at the weak covering seat, If covering is set above the transition zone crossing from normal to abnormal pressures. Losses due to fracturing are most generally near the former covering seat, not at bit depth, indeed if covering is duly set.excessive e downhole pressures.
These pressures are the result of numerous conditions including1) Mechanical forces.
indecorous hydraulics. inordinate pump rates and rapidity causing high fellow Circulating viscosity* ECD) pressures which may beget a lost of rotation problem especially while drilling operations.*adding pump rates too fleetly after connections and passages. This can be extremely important when dealing with drilling oil painting- base fluids. Failure to bring the pumps over to speed sluggishly can put much advanced circulating pressures on the conformation due to the tendency of drilling oilbase guck to thin at advanced temperatures generated while circulating and to cake at lower temperatures during passages. It's common for circulating pressures to drop 100 psi as the slush heats to circulating temperature.
*Raising or lowering the pipe too presto( swell/ tar).
*Spudding islands.
*inordinate Penetration Rate( ROP) for a given inflow rate will affect in high slices attention in the annular fluid causing a high ECD.
*Pipe whipping.
2) Bad Hole conditions.
*Sloughing shale or increased solids loading in the annulus and high original circulating viscosity.*Accumulation of drilled slices in a washed- out portion of the hole or in the drilling slush.
*slices beds or Barite slack forming on the low side of a directional well, or possible rising.
*Bridges.
*Kick and well- control procedures.
3) slush parcels.
*inordinate density and gel strengths.*Buildup of drilled solids.
*Thick sludge galettes that reduce the hydraulic periphery of the wellbore.
*Inordinate slush viscosity or adding slush viscosity too presto.
*Unstable drilling slush columns.
*Barite slack.
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