TITLE:
Wellbore Shielding Spacer Improves Cement Bond While Preventing Cement Losses
ABSTRACT:
Cement bond integrity and zonal isolation can be compromised when severe losses are encountered during cementing operations. When casing mechanically weak and/or depleted reservoirs, resultant narrow fracture gradient windows and higher cementing equivalent circulating densities (ECDs) can break down the formation. The combination of existing and induced losses invariably requires costly remedial cementing.
Generally, cement spacers are used to create full placement of uncontaminated cement and deliver effective cement bond. However, in loss-prone reservoirs, conventional spacers optimized for hole cleaning are not normally capable of controlling losses. The losses-while-cementing issue has recently been addressed with the development of a spacer suitable for temperatures up to 350 deg F (177 deg C) with loss prevention capabilities, incorporating proprietary Wellbore Shielding (WBS) technology.
Discussion of the role of spacer fluid technology in cleaning the hole of immobile drilling fluid to then creating efficient cement bonds while improving the overall cement job quality will be covered. A sampling of recent field results demonstrating the efficacy of the WBS spacer in delivering high-quality cement jobs in troublesome environments will be shared. Finally, it will be demonstrated in both the laboratory and field, how the new spacer technology supports a high-pressure differential, allowing cementing operations at increased ECD that otherwise would exceed the formation’s fracture gradient. The capacity to safely operate above the fracture gradient under downhole conditions minimizes the cement density limitations posed by low fracture gradients. In addition, by reducing post-placement slurry fallback, the spacer eliminates induced losses and resulting top jobs or liner top squeezes.
