Model-Based Sticking Risk Assessment for Wireline Formation Testing Tools in the U.S. Gulf Coast

Abstract

Abstract A model is developed to characterize wireline formation tester sticking from quantitative analyses of the most prevalent sticking modes. An appropriate description of differential pressure sticking mechanics for stationary logging tools and cables forms the foundation of the model, and a supplemental formulation provides a quantitative relationship for key-seat development based on borehole and tool parameters. The results of the analysis are converted into a sticking probability formula that allows quantitative risk assessment at the job planning stage. The primary form of the model uses mud cake parameters derived from a wellsite evaluation device, but an alternative formulation utilizes laboratory and field measurements of mudcake properties and only requires conventionally available parameters for risk assessment. The model is calibrated and tested by application to a database of 664 formation testing jobs in the Gulf Coast area. The resulting strong correlation between calculated sticking probability and actual fishing frequency illustrates the power of a model-based approach to risk assessment. In contrast to most statistically based approaches, it is possible to incorporate a large number of relevant parameters and quantitatively examine risk levels as adjustments are made. Direct measurement of mudcake properties at the wellsite will further enhance the risk assessment accuracy. P. 79