This paper presents a novel methodology to successfully maximize sampling and scanning of formation fluids using formation mapping-while-drilling (FMWD) technology in real time when drilling poorly consolidated formations. The methodology, based on a solid workflow built on experience garnered and captured in various operations and geomechanical studies performed around the world, can be applied in a wide range of wellbore geometries and formation types.
The methodology is based on four processes: 1. Predict, assess, and confirm potential fines migration and formation collapse during FMWD operations. The analysis is based on processing and interpreting existing geomechanical properties from offset wells and real-time newly acquired sonic and/or density data. 2. Design FMWD operations such that formation sanding is prevented, and formation integrity is maintained. 3. Prevent mobilized fines from entering the FMWD tool if partial formation collapsing occurs. 4. Focus the workflow on reducing the negative impact solids will have on the flowline, pump out, and optical analyzers if fines enter the tool.
The paper contains two case studies in which the methodology workflow resulted in successful sampling and real-time downhole fluid analysis of formations with very limited diagenesis and a history of sanding and collapsing during formation testing-while-drilling operations. These two case studies show how assessing offset wells during the planning phase and applying this workflow while evaluating logging while drilling (LWD) petrophysical data in real-time provide a quick insight into how a formation will respond during pump out. The results define station depth selection, timing of the operation with respect to wellbore exposure time, and pump out rate strategy. The application of fixed-rate pump out or intelligent pump out with a fixed differential can then be applied based on the real-time indicators. Specific screen sizes are selected in advance, which limit ingress of fines into the sampling tool. In both case studies, the operating company's objectives were met. An additional case study is presented in which the risk of sanding was not perceived, and no qualification of un-consolidation had taken place, ultimately resulting in formation breakdown in the sampling phase, mobilization of fines, and plugging of the tool; thus, highlighting the value of the novel methodology.
The innovation of this workflow is its holistic approach to sampling while drilling in unconsolidated formations, extensively covering both job planning and execution phases. Additionally, the workflow allows for optimizing tool configuration, and by risk identification, suggests a variety of measures to eliminate or mitigate the impact of partial formation collapse. This workflow extends the application of fluid mapping and sampling while drilling into operational environments, which were previously considered highly unsuitable for this technology.