Friday, 1 May 2020

SIMPLE TIPS FOR REMEDIAL & CURING LOST OF CIRCULATION PROBLEM WITH CASE STUDIES

Remedial & Curing Lost of Circulation Problem

lost circulation Remedial CuringA lost-circulation incident exacts a heavy cost that goes far beyond the price of products that are used to treat it. Lost circulation always causes nonproductive time that includes the cost of rig time and all the services that support the drilling operation. Losing mud into the oil or gas reservoir can drastically reduce or even eliminate the operator’s ability to produce the zone. Prevention is critical, but because lost circulation is such a common occurrence, effective methods of remediation are also a high priority.

Rock mechanics and hydraulic-fracture theory indicate that it is easier to prevent fracture propagation than it is to plug the fracture later to prevent fluid from re-entering. Because of the high cost of most weighted, treated drilling-fluid systems, LCM routinely is carried in the active system on many operations in which probable lost-circulation zones exist, such as in a “rubble” zone beneath salt or in a known depleted zone. Other conditions that are prone to loss of circulation include natural and induced fractures, formations with high permeability and/or high porosity, and vugular formations (e.g., limestone and chalk). Using an LCM that can be carried in the drilling fluid without significantly affecting its rheology or fluid-loss characteristics facilitates the preventive pretreatment. Pretreatment can mitigate wellbore breathing (ballooning), seepage losses, and/or potential lost circulation when drilling depleted zones.

The best approach to control lost circulation is to make an assessment of the severity of a loss zone and match the remedial material and technique to it in terms of both the size of the material and its function.

Lost Circulation severity classification

Seepage Circulation Losses Remedial 

Seeping losses can occur in any formation type when the bridging agents are not large enough to form a seal, or when there are no fine particles to complete the seal.
  • The pull-up-and-wait technique should be the first technique used to attempt to regain full returns.
    • Pull out to shoe and wait
      In cases of seeping, partial or complete loss, the "Pullout to shoe and Wait" technique is common. At the first indication of loss, circulation is stopped and bit is pulled to the point of safety usually to casing shoe. While tripping the pipe care must be taken to minimize surge and swab pressures that could further break down the formation. The hole is then allowed to remain static for 4 to 8 hours.
      The theory which supports this technique is that the fracture was created by putting excessive, unrequired pressure on the formation. If the pressure is removed the fractures will close and heal during waiting period. Speculating that returns will not be obtained by waiting I mix a pill of lost circulation material in the mud. This type of pill is generally made up of fine to medium grain LCM and rarely exceeds 43 kg/m3 (15 ppb) if it is to be pumped through jets of bit. Higher concentrations and coarser LCM can be used if open end string is placed next to the zone. If circulation is not regained after this pill, a squeezing or cementing technique should be considered.
  • If the hole will not stand full while waiting, the technique of mixing an LCM slurry containing fine to medium bridging agents or utilizing a high-filter-loss slurry squeeze should be considered.
  • Reduce mud weight if possible.

Partial Circulation Losses Remedial 

Partial circulation losses occur in gravel, small natural fractures and barely opened induced fractures . The same techniques used in seeping losses should be used in partial losses.
  • The pull-up-and-wait technique should be the first technique used to attempt to regain full returns.
  • If the hole will not stand full while waiting, the technique of mixing an LCM slurry containing a blend of medium to large bridging agents or utilizing a high-filter loss slurry squeeze should be considered.
  • Reduce mud weight if possible.

Complete Circulation Losses Remedial

Complete losses occur to long, open sections of gravel, long intervals of small natural fractures, large natural fractures or open induced fractures
  • The pull-up-and-wait technique should be the first technique used to attempt to regain full returns.
  • Use high-filter-loss slurry squeeze technique.
    • Once the thief zone has been located, one of the following squeezing techniques may be tried to seal it off .All applications are similar, the main difference being in the size and type of LCM to be used. Once the materials are selected the pipe should be placed
      at or just above thief zone, preferably open ended.
      The pipe rams are then closed and the slurry is squeezed into the zone by pumping slowly.
      (1) Bridging agents in mud either in water or oil base mud
      (2) High filter loss slurry
      (3) Down hole mixed soft plugs
      (4) DOB plugs.(diesel oil + bentonite)
  • If returns are not regained with this technique, a hard plug such as a cement, cement-bentonite, cementgilsonite or diesel-oil-bentonitecement is recommended.
  • Reduce mud weight if possible.

Partial Or Complete Circulation Loss To Deep, Induced Fractures Remedial.

  • The pull-up-and-wait technique (4 to 8 hr) should be the first technique used to attempt to regain full returns.
  • Apply soft plug squeeze .
  • If the hole will not stand full while waiting, the technique of mixing an LCM slurry containing a blend of large bridging agents or utilizing a high-filter-loss slurry squeeze should be considered.
  • Reduce mud weight if possible.

Severe Complete Losses Remedial

Severe complete losses occur to large, open natural fractures, caverns and open induced fractures.
  • Squeeze with either a high-filter loss slurry squeeze or large amounts of diesel-oil bentonite-cement slurries.
  • If the severe, complete losses continue to occur as more open, natural fractures or caverns are penetrated, the technique of drilling blind or with aerated mud and setting casing should be considered.
  • Reduce mud weight if possible.

Remedial For Circulation Losses Problem Case Studies

Preventing, Mitigating, or Stopping Lost Circulation in Dammam Formation, South Rumaila Field, Iraq; Requires Engineering Solutions, the Best Treatments Strategies, and Economic Evaluation Analysis

Real field data (e.g. MW, ECD, Yp, RPM, SPM, and ROP) at the time of each event are recordedalong with the lost circulation remedies attempted, and the outcome of those remedies. Practical fieldinformation from South Rumaila field and range of sources are reviewed and summarized to develop anintegrated methodology and flowchart for handling lost circulation events in this zone. This paper will beextended work along with previous comprehensive statistical study and sensitivity analysis models aboutthe Dammam formation. In addition, economic evaluation analysis is conducted for partial, severe, andcomplete losses to obtain the best field procedures.

Drilling Strategies to Control Lost Circulation in Basra Oil Fields, Iraq

This paper is a combination of several case histories and an analysis of the successfulness of the various techniques used to combat continuing lost circulation events in the Basra area. Data was gathered from drilling reports and analyzed to better understand what works for which formations – focusing on mechanical drilling strategies rather than particulate solutions such as pills.


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