Schlumberger

Performance Report: KLA-STOP System Successfully Introduced in Colombia

Challenge: An operator in Colombia was using an inhibited water‐base drilling fluid and experiencing long tripping operations due to severe bit balling conditions. M‐I SWACO was requested to design a system that would provide the best possible inhibition to minimize such operational problems.

Solution: The use of the KLA‐STOP additive as a primary shale inhibitor in conjunction with the DRILZONE anti‐accretion additive was proposed in conjunction with a highly inhibitive drilling fluid system for drilling the extremely reactive claystone formation.

Result: The use of KLA‐STOP additive in the system provided outstanding inhibition, minimizing dilution rates. A considerable improvement in the rate of penetration (27%) was observed. Instantaneous penetration rates greater than 250 ft/hr (76 m/hr) were recorded, but had to be reduced for directional control. Excellent cuttings integrity was seen throughout the section. System inhibition produced dry cuttings that prevented screen blinding problems and optimized solids removal efficiency. The additive reduced the tendency toward bit balling and achieved excellent wellbore stability Trips were conducted in safer and faster conditions than had been possible with the previous well, and logging operations were successfully carried out.

Well Information
Location Huila, Colombia
Date July - August 2005
Casing Size 7‐in. casing
Intervals Drilled 1,014 ft to 4,051 ft (309 m to 1,236 m)
Inclination 30°

The composition of the formations drilled is as follows:

Depth (ft) Composition
996 (304 m) 80% Claystone, 20% Sandstone, 30% Smectite
1,145 (349 m) 50% Shaly claystone, 50% Silty claystone, 31% Smectite
2,645 (806 m) 80% Sandstone, clay matrix; 20% Claystone
3,687 (1,124 m) 70% Claystone; 30% Sandstone

The drilling fluid was designed with KLA‐STOP (6‐7 lb/bbl) inhibitor to suppress shale hydration and DRILZONE (7‐8 lb/bbl) additive to prevent accretion and enhance the rate of penetration (ROP). The inhibition properties of the fluid and the depletion rates were such that the MBT value never exceeded 7.5 lb/bbl. Measured properties are described below:

Mud Weight Lb/gal 9.0 (1.08 sg)
PV cP 17
YP lb/100 ft2 28 (14 Pa)
YS 9 (4.5 Pa)
Gel Strength 10ʺ/10ʹ/30’ lb/100 ft2 9/15/17 (4.5/7/5/8/5 Pa)
pH Meter @ 120°F 9.7
Chlorides mg/L 200
Hardness (Ca++) mg/L 40
API Fluid Loss mL/30 min 5
API Filter cake 1/32 in. 1
Retort Solids % vol 5
MBT (equivalent) ppb 5

Tripping operations were efficient and total time per trip was considerably reduced. ROP also increased. These improvements contributed to an overall reduction in total well costs for the operator compared to a previous well drilled without the benefit of the additives.


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