New Interactive Cementing System Improves Zonal Isolation in Horizontal Wells
Authors: Feder Judy 
Published: May 2019

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 191561, “Effective Zonal Isolation in Horizontal Wells: Mitigating Negative Impact of Mud Channels,” by Petr Kolchanov, SPE, Dominic Perroni, SPE, Anatoly Medvedev, SPE, Yan Gao, Randy Tercero, SPE, Larry Todd, SPE, and Bernhard Lungwitz, SPE, Schlumberger, and Kenneth Cowan and William Turner, SPE, Occidental Petroleum, prepared for the 2018 SPE Annual Technical Conference and Exhibition, Dallas, 24–26 September. The paper has not been peer reviewed.
Hydraulic isolation of wells drilled with nonaqueous fluids (NAFs) relies heavily on eliminating mud from the annuli before placing cement. Failure to expel all NAFs results in residual fluid channels that may compromise well integrity and can serve as nonproductive communication pathways during subsequent stimulation treatments. This paper presents an interactive cementing system (ICS) that is designed to mitigate these risks by reducing conductivity of the residual mud channels.
Introduction
Currently, most horizontal wells drilled in the US are completed with multistage stimulation treatments. Isolation between stages is required both inside and outside the production casing string for effective stimulation. Although plugs can be used between stages for effective isolation inside the casing, cement must create external isolation. Lateral cement jobs are pumped according to plan; however, it is difficult to optimize fully all design inputs needed for an optimal cement job. With few operators logging horizontal well sections to understand actual lateral cement quality, mud channels are frequently identified as the root cause of stimulation inefficiency. Because completion effectiveness and well productivity depend upon good zonal isolation, profitability of the well is thought to be compromised.
Mud removal remains an integral part of the cementing process. A cement formulation was developed to improve zonal isolation in the case of poor mud removal. The ICS reacts with the hydrocarbons present in NAFs, reducing channel permeability and mobility to significantly improve the likelihood of hydraulic isolation. Specialized testing protocols were developed to demonstrate the capabilities of this new system. Additionally, American Petroleum Institute (API) testing methods and analytical techniques were used to optimize the slurry.
Historically, zonal isolation was dependent on complete mud removal, which was a function of many parameters. Even after well preparation is completed, mud removal is dependent on adequate centralization. Although most drilling engineers agree that well-centralized casing results in a better cement job, the tradeoff comes with the challenges of getting casing to bottom on long-lateral and extended-reach wells. Rotating and reciprocating casing can improve mud removal and cement quality, but significant cost and safety concerns limit their use. Spacer type and volume also influence mud removal. After decisions have been made on these cement-design parameters, cement placement should be optimized using computer simulation models to maintain adequate rheological parameters and achieve mud removal. The likelihood of a mud channel is much greater if these design parameters are not optimized.