Flow Back Optimization in Deep Water in Presence of Solids - Contingency Management and Flaring Abatement
Authors: Theuveny B. C. , Rashid K. , Kotlyar L. , Gemmel D. , Hay G. , Bailey W. , Ling D. , Mei K. 
Published: September 2024

Abstract
Considering the need to reduce emissions, it is imperative to define clean-up and flowback strategies that allow for a minimization of the carbon footprint of these operations while ensuring a proper level of cleanness of the completion.
Maximizing productivity from new wells is crucial, particularly in deep-water environments where subsequent remediation efforts can be prohibitively expensive and logistically challenging due to limited intervention vessel availability. The primary objective of the drilling and completion phases is to establish robust safety barriers, whether mechanical or hydraulic, to prevent the influx of hydrocarbon fluids from the reservoir into the wellbore. Production commencement hinges on effectively clearing the wellbore of residual drilling and completion fluids. This cleanup process typically unfolds in two key stages. Initially, lighter fluids are displaced within the wellbore to achieve the necessary level of underbalance. Subsequently, a gradual unloading of the well occurs, meticulously managed by regulating the choke opening.
A successful clean-up or flowback operation should also result in enhanced well productivity, adherence to the reservoir drainage outlined in the field development plan, and significantly reduced occurrences of production disruptions caused by the delayed mobilization of undesired solids or fluids into surface facilities. A novel optimization algorithm evaluates a series of realizations from a robust transient well bore dynamics flow simulator that has been specially developed for clean-up and flowback operations.
The optimizer reconciles the conflicting requirements for achieving high rates, necessary for effectively displacing drilling fines and filtrate near the wellbore while also facilitating the lifting of filtrate, completion fluid, and denser solids from the well bottom to the surface. Conversely, it serves to restrict drawdown to prevent formation collapse or sand production, as well as the potential collapse of completion equipment like gravel packs and tubing. In the context of stimulated wells, it also mitigates the risk of proppant mobilization from hydraulic fractures. The presence of solids in the completion (perforating debris, residuals from the cementing operations, fines and sand or proppant migration) require sufficient lift performance, which in turns can require higher flowrates. The combination of all these factors is complex, and its optimization leads to non-intuitive solutions.
Field implementations show that this novel process can lead to reduction of emissions up to 60% during flowback operations yet delivering quality wells to the production system. In the specific case of solid removal, we demonstrate that the gains are smaller for oil wells and almost irrelevant for gas wells. The lack of gains for the case of gas wells in the presence of solids is fundamentally due to a combination of two aspects: HSE/Safety/Flow assurance issues of well management when rocking the choke, and the minimum lifting velocity that is necessary to get solids to move up. It is possible for vertical or near-vertical wells to gain some efficiency from a sustainability perspective if one accepts to shut the well in and let solids fall back below the lower interval.