Schlumberger

Case Study: Managed Pressure Drilling Techniques and VIRTUAL HYDRAULICS Modeling are Utilized to Control Abnormal Pressures While Drilling Fractured Production Zone

Challenge:

  • Infield faults contributed to a narrow ECD window, associated loss of circulation and/or well control difficulties
  • Wide mud weight swings due to gas influx control resulted in a heterogeneous fluid column, with an unstable and unpredictable mud weight
  • Excessive days on the well were spent trying to manage the well control and losses of mud contributed to excessive costs and Non Productive Time (NPT)

Solution: Managed Pressure Drilling (MPD) techniques in combination with modeling of the Equivalent Circulation Densities (ECD’s) using VIRTUAL HYDRAULICS (VH) allowed for better well control

Result:

  • By using M-I SWACO LPAC MPD equipment and techniques, constant well bore pressure was maintained, preventing an influx of undesirable quantities of formation gas
  • VH modeling allowed for estimated ECD’s, which enabled proper kill weight mud pills to be calculated and spotted for well control

Stabilized Wellbore Pressure

A South Texas operator was concerned because the previous well ran into abnormal pressures due to gas influx associated with fracture-fed gas. In an attempt to control this gas prior to running and cementing the production liner, excessive mud weights were used and resulted in breaking down the formation. Anticipated infield mud weights were in the range of 10.0-10.5 ppg. Trip pills that were pumped resulted in a system mud weight of 14.0 ppg. Subsequently, large losses of circulation occurred and excessive amounts of NPT were needed to control the well pressure. The operator experienced a well bore column of fluid compromised by gas influx and therefore was trying to maintain the well bore without knowing the mud weight of the downhole fluid column in well kill operations.

Managed Pressure Drilling and VH Modeling

An automated LPAC (Low Pressure Auto Control) managed pressure drilling system was rigged up and wellbore pressures were kept constant using a mud weight of 9.8 ppg. Fluid losses were minimized and wellbore gas influxes were mitigated. Using this method, the fluid column weight was controlled and predictable, and allowed for accurate modeling using VIRTUAL HYDRAULICS. Using MPD, the mud weight was maintained at 9.8 ppg, and kill weight mud pills were constructed to offset the ECD of 12.5 ppg. This equated to a .3 ppg trip margin and allowed safe pipe tripping. During the initial casing run, gas influxes were seen and required shut-in procedures. Well control procedures ensued and the casing was stripped to TD. Successful cementing of this liner then proceeded and good returns were seen throughout the cement job.

Days on Well

Days on the well were reduced from 41 days to 17 days with the associated cost saving attributed to successful implementation of managed pressure drilling.


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