One of the critical modules in formation testing to get early insight in tight and unconsolidated formation is dual packer. However, it's operational efficiency depends on many factors such as differential pressure due to drawdown, pressure difference above and below packer, gauged hole, and time constraints per station. In this paper, we will discuss how wellbore dynamics and sump volume below the packer affects the dual packer operation and what could be the possible remedy.
Pressure drops below the packer causes the increase in head tension and can damage the packer as well. Therefore, pressure below the packer needs to be equalized frequently. Sensitivities are run for different sump intervals, considering classical static filtration theory and multiple scenarios in wellbore dynamics. The sensitivity analysis will show the effect on frequency of equalization during sampling or pumping. These sensitivities primarily include hole diameter, mud type, filtrate viscosity, thief zone permeability etc. Hole diameter and sump interval affect the sump volume and in turn act on the pressure drop due to filtration loss. Compressibility will be different for different mud type. Filtrate viscosity and thief zone permeability will influence the filtration loss rate.
Feasibility of the dual packer operation will be discussed for certain scenarios; alternate solution and possible remedies will also be highlighted at the end of the study. The most important aspect of the study will be combining filtration loss with sump volume for different well bore dynamics to get frequency of equalization. Information regarding frequency of equalization is important because it affects the cleaning process and sampling operations and causes fatigue in the packer. How tool strings can be optimized to overcome such scenarios well in advance will also be included.
This innovative approach of combining classical filtration theory with wellbore dynamics and sump volume to understand the possible challenges of use of dual packer and its remedy in advance can help industries in planning the operation and reducing cost.
