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

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

Using Wireline Standoffs (WLSOs) To Mitigate Cable Sticking

“…For cylindrical objects, such as drill pipe, logging tools, or cable, the pull-to-free force per unit length is proportional to t 0.25 (Underhill, Moore, & Meeten, 1998;Reid, et al, 1996), where t ϭ stationary time of the object from the moment the toolstring stops on station (after which cake compression and extension can compound the sticking forces). The result of this time dependency factor is that "a doubling of the stationary time results in less than a 20% increase in sticking forces.…”

“…It is known that in a sinusoidal borehole the cable contact length will increase in smaller holes, since the inflexion distance between opposing sides will be shorter (Underhill, Moore, & Meeten, 1998). For a qualitative approach on real wells we can consider the variation of cable thrust vectors over the zones of interest.…”

“…A comprehensive study of formation tester sticking modes for the Gulf Coast region determined that about 70% of sticking events from a total of 664 jobs studied involved stuck cable (Underhill, Moore, & Meeten, 1998). In another study of 295 jobs (region unspecified), it was reported that the use of wireline jars drastically reduced the overall fishing rate.…”

Diagnostic Approach to Control and Minimize Wireline Formation Tester (WFT) Sticking Problem

“…There are several ways a cable or tool may get stuck in a well during job execution. Sticking mechanisms of cable deployed WFT can be categorized into three different mechanisms; differential sticking, mechanical sticking and formation driven sticking [2].…”

“…Key seating occurs more often in softer formations and highly deviated wells. This type of sticking encountered in borehole is mechanical sticking [2].…”