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Knowledge of actual frac and pore pressure gradients are critical during the cement design phase of well planning. Unfortunately, in exploration wells, engineers may be forced to estimate the frac and pore pressure gradients’ values. Considering this, cement circulation can fail due to uncertainties in the engineering estimates. If errors in the engineering estimates cause partial to total lost circulation, at minimum the casing will not be supported. Some of these situations will require costly remedial work and in the worst case, the well must be skidded and re-drilled.
This paper will explain how a Wellbore Shielding (WBS) spacer incorporates technology that deposits a micron-thin barrier on the inside face of the wellbore. This deposited barrier, to an extent, isolates the formation from the full wellbore equivalent circulating density (ECD). Typically, in situations where lost circulation events occur due to an increase in cement-related ECD, WBS technology contributes to maintaining or regaining full circulation. Full circulation can be maintained even when the over-estimated frac gradient would normally result in a failure to achieve the required and/or desired Top-of-Cement (TOC). Without WBS technology, the design engineer would be forced to choose to use lighter, less capable cement and/or a slower than ideal displacement rate in an effort to minimize ECD. However, slowing the displacement rate adversely affects displacement efficiency.