Schlumberger

Performance Report: SILDRIL Gives Top Performance in Nile Delta Well

Challenge:

After drilling of 12.25” hole to the casing point @ 2,580 Meter using KCl/Glycol mud, and while the last conditioning trip prior running the 9⅝” casing, the hole was packed-off. A fish was left in hole. Petrobel decided to run 9⅝” casing to save the shale section of the exposed open hole. After setting 9⅝” casing at 2,135 Meter (top of fish in hole), a window was opened @ 2,020 Meter to side track the well in order to finish the reactive shale section.

The formation to be drilled was highly reactive “Kafr El-Sheikh Formation” shale interbedded with unconsolidated sands.

The off-set wells experienced down-hole losses with mud weight 1.28 Kg/L. On the other hand, the shale won’t be stabilized with mud weight not less than 1.40 Kg/l.

To drill this interval successfully, would require a high degree of inhibition and optimal hole cleaning. The correct mud weight together with the proper rheology profile should be applied to avoid the expected losses within the sand bodies.

Solution:

M-I Overseas, Egypt Branch, offered to use the same mud existed from the previous section (KCL/Glycol) and to be switched to SILDRIL system after treating out the hardness from the mud. We’ve figured the weight of 1.40 Kg/L to start with.

The system was treated out using Soda ash, and the Sodium Silicate was mixed to 12% by volume. The shaker screens were sized down from 110 mesh to 200 mesh which was allowed after observing the cutting on the shakers.

Result:

  • Fast Drilling: The interval was finished in nine days includind five days drilling, two days tripping, one day for logging and one day for running 7” liner.
  • All Targets Met: All targets were achieved as the reactive shale section was cased off together with the first 30 meter of reactive shale of the next formation. Moreover, no losses were experienced within the low pressure sand even with using higher mud weight than what used for the off-set well.
  • Excellent Lubricity: Because of the low angle of the well, no lubricants were used while drilling the interval. But still, the degree of lubricity which illustrated from the tripping and the directional work to kick-off the well, indicated how lubricant is the SILDRIL system.
  • Less Solids Content: Because of the big size of the cuttings drilled, the screens were sized down from 110 mesh to 200 mesh which improved the cleaning of the system from the L.G.S.
  • Less Mud Cost: The whole interval (795 Meter) was drilled without using a single barrel for dilution which resulted in overall reduction in mud cost.
  • No accretion: Neither bit balling nor shale sticking on BHA were observed while tripping.
  • Well Information
    Location Nile Delta, Mansoura, Egypt
    Spud / Completion April, 2002
    Interval Drilled 8½” hole from 2020 Meter to total of 2,815 Meter (795 Meter)
    Deviation

    The Details

    A window was milled in the 9⅝” casing from 2,015 Meter to 2,020 Meter with a flow rate of 378 gal/min. A rat hole was drilled from 2,020 Meter to 2,025 Meter and the hole was circulated clean at 400 gal/min.

    The 8½” hole was drilled with a SILDRIL mud from 2,025 Meter to 2,096 Meter with tool face orientation as necessary through Kafr El Shaikh shale formation. A short trip was made, and the drill-string was run back to bottom without any problems. The hole appeared in good shape.

    The drilling process of 8.5” hole was advanced from 2,025 Meter to 2,096 Meter where the MWD failed to read survey shots. The hole was circulated clean prior tripping out of hole from 2,096 Meter to 2,020 Meterm (9⅝” window). After pulling out of the hole to replace the MWD, the same directional assembly was run in the hole. Drilling 8½” hole was continued from 2,096 Meter to 2,501 Meter with intermittent sliding. After circulating bottoms up with 437 gal/min, a wiper trip was done to check the hole.

    After running in the hole to 2,501 Meter, drilling continued to liner point @ 2,815 Meter (50 Meter inside Abu Madi formation). The hole was then circulated clean many times at 441 gal/min. The string was pulled out of hole from 2,815 Meter to the window for running the 7” liner. No accretion of cuttings on the drill-pipe was observed, which means that the flow rate was enough to clean hole and transport cuttings to the surface and the hole was in good shape.

    The 7” liner was safely run and cemented on bottom.

    The Mud System

    While drilling with the SILDRIL System, the two shale shakers were fitted with 200 mesh layered screens to improve the removal of fine solids. LSRV rheology and fluid loss (<2ml) were easily maintained with the addition of premixed Biopolymer/Drispac SL to the active system.

    12% by volume of SILDRIL was added on the rig to 1,095 bbls of old Kcl/Glycol/ polymer mud remained from previous interval to drill the shale interval of Kafr El Shaikh. The composition of the SILDRIL was as follow:

    Additives PPB
    DUO-VIS (biopolymer) 2.0
    DRISPAC SL 4.0
    SILDRIL 50.0
    KCL (Potassium Chloride) 35.0
    Sodium Bicarbonate & Soda Ash 3.0

    250 bbls of premixed (same concentration) was also mixed before drilling for maintenance during drilling and potential losses.

    During drilling, no biopolymer (Duo-Vis) was added to the active system because the low shear rheology values were optimum from the beginning of the interval and didn’t change a lot. The API fluid loss was less than 2 ml/30 min all the time which eliminated more addition of Drispac-SL. The mud weight was maintained within 1.40 Kg/L and it was decreased while drilling because of the finer screens used.
    The mud weight was frequently adjusted by mixing Barite.

    Fann Reading
    / Depth
    2020 2096 2263 2444
    600 69 67 67 74
    300 45 43 44 48
    200 33 34 32 32
    100 22 23 22 23
    6 9 11 12 12
    3 8 8 11 11
    10 sec Gel Strength 8 8 11 9
    10 min Gel Strength 11 12 14 12
    PV 24 24 23 26
    YP 21 19 21 22
    AV 34.5 33.5 33.5 37
    N 0.4043 0.3047 0.3047 0.3135
    K 4.4139 7.1402 7.1402 7.0387
    Fann Reading
    / Depth
    2528 2600 2785 2815
    600 74 75 75 77
    300 49 50 50 50
    200 33 36 34 35
    100 24 24 23 23
    6 12 12 12 12
    3 11 11 11 11
    10 sec Gel Strength 11 12 12 12
    10 min Gel Strength 14 14 14 14
    PV 25 25 25 27
    YP 24 25 25 23
    AV 37 37.5 37.5 38.5
    N 0.3135 0.322 0.322 0.322
    K 7.0387 6.9416 6.9416 6.9416

    Well-bore Stabilization

    With the proper mud weight used, SILDRIL is the primary wellbore stabilizer additive. KCl was used as a secondary inhibitor. In combination they synergistically provide an effective wellbore stabilization system for swelling and dispersive and the reactive shale.

    Optimum concentration of SILDRIL is 10-12% to ensure optimum chemical stabilization performance. KCl is maintained at 10% by weight.

    The SILDRIL concentration was monitored using a Hach Silicate Test Kit, pH, and the mud and filtrate alkalinities. The alkalinity values were the most sensitive response to the depletion of silicate.

    The following calibration table compares the various parameters for standard reference SILDRIL concentrations from 7% to 15%.

    Solids Control Equipment: (SHALE SHAKERS)

    Prior Displacement with SILDRIL System:
    DERRICK SHAKER #1 SHAKER #2
    HIGH PERFORMANCE FINE SCREEN SHAKER HP110 HP110
    HP110 HP110
    HP110 HP110
    After Displacement with SILDRIL System:
    DERRICK SHAKER #1 SHAKER #2
    HIGH PERFORMANCE FINE SCREEN SHAKER HP200 HP200
    HP200 HP200
    HP200 HP200

    Observations and Recommendations

    • The SILDRIL System is the recommended water base system to provide optimum wellbore stabilization for shale and limestone formations, minimum dilution rate, and minimum environmental impact. The performance of the system was demonstrated while drilling the well Batra-3 Sidetrack.
    • The inhibition of the SILDRIL System was also demonstrated with the improved integrity of the cuttings in the Kafr El Shaikh shale. The well-site geologist commented on the improved condition of the drilled cuttings for identification.
    • After drilling the Kafr El Shaikh shale, a wiper trip was made without any excess torque and drag. Following the wiper trip, the string was run directly to bottom without circulating or washing. 
    • The trip out of the hole to run the liner was also made without any significant problems. 
    • On the trip out of the hole, no accretion of drill cuttings was observed on the drill pipe. 
    • The use of lubricant was not deemed necessary because the torque observed with the SILDRIL System showed no appreciable difference.

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SILDRIL is the Primary Wellbore Stabilizer Additive

Fluid Loss ControlSILDRIL L ConcentrationpH versus Depth
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