Lost Circulation Simulated Accurately in Primary Cementing-Job Design

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 223263, “Simulating Lost Circulation in a Primary Cementing-Job Design,” by Martijn Bogaerts, SPE, Nicolas Flamant, SPE, and Ahmed Abdulaal, SPE, SLB, et al. The paper has not been peer reviewed. _ A proprietary cementing-job simulation software has been upgraded with a losses model. Using the losses model will enable the design engineer to define loss zones in the wellbore. For each identified loss zone, a percentage of losses can be provided. Loss-input and other well and fluid data allow a detailed dynamic simulation. Use of novel loss-zone simulation during cementing-job simulations enables the design team to discuss potential outcomes of cementing operations while experiencing losses. Lost Circulation While Cementing Although losses can occur during all phases of the life of the well, losses during primary cementing can have a major effect on well safety and economics. If losses cannot be cured ahead of the cementing job or occur unexpectedly during it, they can potentially jeopardize the outcome of the job, require remedial work, and lead to the loss of the interval or, in the worst case, the entire well. The eventual outcome of the cementing job will depend on several factors: loss rate or severity, the depth of the loss zone compared with the proposed tops of fluids, when the losses occur during the cement job, and prevention and mitigation measures taken during the cement job. The most obvious result of losses during the cement job is lower top of cement (TOC) in the annulus. Experiencing partial to severe losses can reduce the TOC from reaching potential regulatory requirements. It can also result in partial or no isolation across planned production zones or potential flow zones. Losses also affect mud removal in the annulus and the zonal isolation of the cement sheath. If losses occur, the spacer designed to remove the drilling fluid can be lost to the formation, resulting in increased contamination of the cement slurry. Additionally, fluid velocities will be affected by losses and can result in poor mud-removal isolation across zones of interest. Poor zonal isolation can result in lower production rates, unwanted water production, and casing exposure to corrosive formation fluids. Loss Mitigation and Prevention The ability to simulate losses and predict results by considering the fluid contamination and TOC can be used in the decision-making process to either cure the losses before the cementing job or implement other mitigation measures, such as adding lost-circulation material to the spacer or slurry, adjusting planned volumes, or adjusting pump rates. Alternatively, if the predicted outcome is acceptable for the well design, the decision can be made to proceed with the cementing job with caution. Even if losses are not present before the job and are not expected based on offset wells, they sometimes can appear during job execution. In case of unexpected losses during the cementing job, the ability to simulate the effect using actual cementing-job data immediately afterward can assist with decision-making after the job is complete. For example, it can warrant that an additional cement-evaluation log be run to confirm that cementing-job objectives have been achieved or if a remedial job is required to proceed safely with drilling operations.