LIGHT WEIGHT AND DUCTILE SLURRY FOR PRODUCTION CASING- REPSOL-YPFBackground

BJ Services de Venezuela provides cementing services in the southeastern area in the Maracaibo Lake called Mene Grande Field, which is located 200 km south from Maracaibo City in Zulia State, Venezuela. This field is being developed by Repsol-YPF since 1997 in a strategic alliance with PDVSA Oil & Gas.

Problem

The field has a very complex geology: faults, unconformities and also natural fractures. Due to low frac gradients at the pay-zones and natural fractures, standard slurries would generate high fluid loss at the

wellbore, inducing damage due to higher hydrostatic pressures against the formation. Also, the fluid loss would not allow the cement to create a proper hydraulic seal all the way up to the liner hanger, but far

away below the intermediate casing shoe. For that reason, a ductile light-weighted slurry with a high early compressive strength was required.

Proposal

The BJ proposal was intended to solve the problem of lowering the hydraulic pressures on bottom, but also to guarantee cement bonding between the casing string and the formation. CM-Vision was used to simulate the environmental features of the wellbore, proving to be an excellent solution for our needs.

Laboratory reports showed good compressive resistance and good tensile strength with moderate amounts of LW-6 and MPA-1. UCA tests also showed compressive strengths over 2,100 psi.

Slurry: Class “H” Cement + 35% S-8 + 15% MPA-1 + 8.5% LW-6 + 1.4% BA-56 + 0.6% CD-33 + 0.05 gps R-21L + 0.8% A-2 + 0.02 gps FP-6L

Density: 13.5 ppg Yield: 2.21 ft³/sk Comp. Str.: 2,100 psi Free Water: ZeroMix-water: 8.27 gals/sk Thick. Time: 250 min. Fluid loss: 40(cc/30min)

Wash: Turbo-solvent @ 9 ppg Production Casing: 7 in O.D.Spacer: MCS III Spacer @ 10 ppg Depth: 10,500 ftMud Weight: 9 ppg (Oil-Based) BHST: 248 °FAverage Caliper: 9.3 in. BHCT: 212 °F

CM-Vision was used to verify tensile, flexural and the height required for zone isolation. The amplitude estimated for CBL in CM-Vision was of 10,5 mV. The acoustic impedance was used for the calibration of CBL instead of compressive strength.

Conclusion

We got cement above the liner hanger and a good isolation casing, checked by a pressure tests up to 1,500 psi. Further workover procedures were performed, and the average CBL amplitude was 12 mV as predicted by CM-Vision that is always used for slurry designs with Repsol. The well was finally put on production that started at 500 barrels/day without stimulation.

Marcos Bertelli and Manuel Navarro, Venezuela