Innovative Workflows for Testing and Sampling in Tight Formations Using Wireline and Logging While Drilling Tools
Authors: Ramadan O. , Binghaith A. , Bhat J. , Taher A. , Fouda M. 
Published: November 2024

Wireline (WL) and Logging-While-Drilling (LWD) formation testing & sampling (FTS) tools are commonly utilized in the oil and gas industry for measuring the formation pressure, deriving mobility, and analyzing fluid composition. Their operation depends on achieving a sealed contact with the formation, isolating the tool's flow line from the wellbore fluids and drawing formation fluid (or invaded mud filtrate) from the formation to the tool using drawdown chambers or internal fluid pumps. The successful operation of FTS tools is therefore dependent on the ability to flow the fluid trapped inside the rocks to the tool which can be a real challenge if the rocks are of low permeability. While rock permeabilities in some formations can be inherently low, sometimes the apparent rock permeability is low being affected using lost circulation material (LCM) or bridging materials in the wellbore fluid that could have a plugging effect on the pores reducing the permeability at the rock's "sand face". This paper presents advanced and innovative methodologies to mitigate the challenges of testing and sampling in formations with effectively low permeability rocks using Wireline (probe /packer based) and LWD (probe-based) FTS tools.

Traditionally, FTS tools have struggled to perform successful testing and sampling operations in low permeability formations. In recent years, however, innovative methodologies have been developed to combat some of the challenges of this operation. On the WL side, FTS (probe-based) tools are using multiple pads with higher flow area than traditional pads to help flow in low permeability rocks. For lower permeability rocks where probes don't succeed in drawing fluid to the tool, packer-based FTS tools are being utilized. For ultra-tight rocks, a new methodology has been introduced where packer-based WL FTS tools are deployed with special large volume chambers carrying stimulation fluids. These fluids can be injected into the desired formation to stimulate the rock and hence improve flowing mobility. On the LWD side, other special FTS procedures & workflows have been used to combat the effects of bridging materials and LCM on FTS operations where FTS operations need to start after the shortest possible time from drilling the formation. Taking the tests as soon as possible after drilling has improved the ability of LWD testers in environments where the mud system can have a pore plugging effect.

The customized sampling process has been utilized successfully in low permeability reservoirs where the stimulation fluids pumped into the formation has created the fluid path for acquiring formation pressure and sampling in low quality reservoirs (LQR). Formation pressure has also been measured successfully using LWD formation tester in low permeability reservoirs where there was high uncertainty in formation pressure due to potential reservoir depletion, this enabled optimizing the mud weight while acquiring the data shortly after drilling the low permeability formation. This paper presents novel innovative workflows for testing & sampling in low permeability reservoirs using wireline or LWD tools.