15 Years of Foamed Cementing in Oman: Future Applications and Lessons Learned from 270+ Foamed Cementing Operations

Abstract

For more than 15 years, foamed cementing has been deployed on wells drilled in the Fahud and Natih fields of North Oman. The production section targets the Natih formation, a fractured Mesozoic hydrocarbon-bearing carbonate sealed by the Fiqa above and the Nahr Umr shale below. The Natih carbonate characteristically requires a cementing design to cure losses while providing zonal isolation. Foamed cement is the standardized cement design used to meet this objective. Previous attempts to mitigate lost circulation during cement placement using conventional lost-circulation materials were attempted with little success. Since 2006, the advent of foamed cementing has been prescribed as the standard design for cement placement across the 8 1/2-in. production section. These wells have experienced an evolution of stage tools as well as liner packers to aid isolation. The cementing operation consists of a decision tree design approach based on the tools used on the 9 5/8-in. section as well as the quality of wellbore returns observed during cement delivery. The initial stage consists of nitrified water with a foaming agent intended to reduce the hydrostatic burden observed on the fractured formations. This is followed by a four-stage "filler" of foam cement, each with a specific nitrogen rate necessary to maintain the designed density at the final placement depth. If wellbore returns are stable throughout the "filler" phase, the nitrogen rate is reduced to target an ideal final cement density to help ensure the cement sheath has optimized sealant capabilities across the section objective. If wellbore returns are unstable, the final nitrogen stages are maintained, and emphasis is placed on finalizing displacement and choking the backside, as necessary, to maintain foam expansion. Approximately 270 foamed cement applications were executed in the field using this approach. The acceptance criteria target for this section is for returns to be observed at the surface during cement displacement before packer installation. Continuous lessons learned on design parameters necessary to achieve the objective were captured in the 15-year period discussed. The value added using stage tools versus liner packers was measured and the base slurry designed used for the foam has been modified over time to deliver the highest probability of success for these wells. Designed cement properties were evaluated and optimized over the 15-year period of foamed cement delivery. Improvement to cement hydration analysis (CHA), permeability, transition time, and expansion slurry properties are discussed. Additionally discussed, as losses continue to be challenging across these sections, a variation of 11-kPa/m ultra-lightweight foamed slurry designed for wells in the Fahud and Natih production sections are an alternative option for extreme losses observed at > 5 m3/hr before cementing.

Foamed Cement Applications in Oil Industry Based on Field Experience: A Comprehensive Review

“…Out of these operations, the operators reported improvement in cement hydration transition time and enhancement in the slurry properties. 54 The Chichimene and Castilla fields in Colombia experienced several operational problems, including difficulty in achieving zonal isolation in the net pay, lost circulation, and hole instability caused by the highly fractured and depleted reservoirs. 30% of the wells completed with conventional cement required remediation to achieve effective zonal isolation.…”

“…The jobs were performed across the Natih formation, which is a fractured Mesozoic hydrocarbon-bearing carbonate associated with severe loss of circulation. Out of these operations, the operators reported improvement in cement hydration transition time and enhancement in the slurry properties …”

“…Out of these operations, the operators reported improvement in cement hydration transition time and enhancement in the slurry properties. 59 …”