Modified Approach Leads to Successful Off-Bottom Cementing Plugs in Highly Deviated Wells in the Caspian Sea

Abstract

Certain abandonment operations require plugs to be set off-bottom in a well. The challenge in setting plugs in highly deviated wellbores lies in obtaining a competent hydraulic seal that can qualify as a barrier to any potential flow zones. Failure to achieve a good cement plug leads to increased nonproductive time (NPT) from cleanout, drillout, and setting additional plugs. Small slurry volumes, unstable fluid interfaces with respect to gravitational forces, and fluid contamination add to the complications. In the Caspian Sea abandonment operations, plug-placement simulation aided in designing cement plugs and setting procedures in inhibited seawater, water-base, or oil-base drilling fluid environments. The advanced cement plug placement simulator was used to design fluid properties and optimize volumes for plug-placement operations in highly deviated Caspian Sea wells.For successful placement, physical fluid properties and fluid mechanics were used in the advanced placement simulator; in addition to the fluid behavior, the simulation took into account well geometries, tubular dimensions, and mechanical separation devices. Various parameters affecting successful plug placement, including but not limited to, length of tailpipe, gel strengths, underdisplacement volumes, and placement procedures were input into the simulations. Balanced cement plug placement is widely practiced by many operators. In the literature, it has been shown that when smaller diameter tubing or tailpipe is run on the bottom of drillpipe, the assumption that all fluids both inside and outside the drillpipe will remain in hydrostatic equilibrium is wrong. In this study, advanced placement modeling illustrated that an initially balanced cement plug may become unbalanced while pulling a cement string with tailpipe out of the hole. Multiple abandonment operations performed in Caspian Sea wells provided key lessons for wellbore preparation, fluid design, and wellsite execution. Design decisions made from the simulation results and improvements made with implementation of industry best practices increased the ability to get plug placement right every time from the first attempt.

A Review of Past, Present, and Future Technologies for Permanent Plugging and Abandonment of Wellbores and Restoration of Subsurface Geologic Barriers

“…Differences in viscosity and densities can cause an unfavorable interplay between cement slurry and drilling fluid, where the more buoyant fluid rises through the less buoyant (Isgenderov et al, 2015). Since drilling fluids are less dense than cement slurries, they might flow through the cement slurry and form pathways or channels leading to interannular gaps allowing fluids to flow through the cement sheath.…”

Fundamentals of Plug Placement

“…In deviated holes, unstable fluid interfaces with regards to gravitational forces, and fluid contamination introduce complications to balance the fluids during plug placement. A properly designed plug can be contaminated during pulling the tailpipe of the work string out of the cement plug, especially in deviated sections [27]. In addition, deviated boreholes intensify challenges related to free fluid and particle segregation [28].…”

Posicionamento De Tampões Em Poços De Petróleo: Uma Investigação De Escoamentos De Inversão Por Gravidade

“…O sucesso da operação de tamponamento de poços de petróleo abrange diversos desafios, tais como maximizar a eficiência de deslocamento dos fluidos envolvidos, otimizar o volume de pasta de cimento e garantir a estabilidade do tampão após o posicionamento (94,101). Alguns desses desafios são discutidos a seguir.…”