Effective Mitigation of Tool Sticking Risk in Formation Testing and Fluid Sampling Operations
- Tushar Prasad (Shell) | Homero Cesar Castillo (Baker Hughes Inc.) | Hani Elshahawi (Shell)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 8-10 October, San Antonio, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 7.2.1 Risk, Uncertainty and Risk Assessment, 3.3.1 Production Logging, 1.10 Drilling Equipment, 5.1 Reservoir Characterisation, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.2.2 Geomechanics, 5.2 Reservoir Fluid Dynamics, 1.6 Drilling Operations, 4.3.4 Scale, 1.12.2 Logging While Drilling, 5.6.1 Open hole/cased hole log analysis, 1.11 Drilling Fluids and Materials, 3 Production and Well Operations
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The increased use of deep, highly-deviated and tortuous wells has increased the risk of wireline logging tool strings getting stuck downhole. If this risk is not appropriately managed and effectively mitigated, significant financial exposure can result from the cost of the multi-day fishing operations, the lost-in-hole and replacement charges, and -most importantly- the loss of opportunity to acquire critical subsurface data. This exposure is even higher in environments with large operating costs, such as deep water.
Historically, formation testing and fluid sampling tools have been among the most frequently stuck, fished and lost logging equipment. On the other hand, formation testing continues to provide some of the most essential information for reservoir characterization. Therefore, managing the risks associated with tool deployment is essential.
This paper discusses the sticking mechanisms of formation testing and fluid sampling tool strings, and provides specific recommendations for the planning and execution of such operations. The various factors that lead to differential sticking or keyseating of the tool string and the wireline cable are discussed. A dataset that explores a wide variety of situations is analyzed to provide a pragmatic guideline for effective mitigation of tool and cable sticking. A specific example from highly deviated deep water well is shown to highlight the significance of proactive planning.
Fishing logging tools has become increasingly costly as rig costs have continued to rise (up to USD 1.5 M/day spread rate for some deep water rigs). A 2007 study  estimates that 3% of exploration and production costs were related to sticking of tools in the borehole - over USD 100M out of USD 3.43B of total expenditure was associated with tool sticking. These results came from the analysis of 260 wells. Similar figures were reported by a 2009 study . Compared to other wireline conveyed logging, wireline formation testers have a tendency to stick more often than others mainly because formation testing operations involve longer and heavier tool strings and significantly longer stationary periods.
This paper discusses the effect of various factors that contribute to tool and cable sticking. The accurate prediction of tool or cable sticking risk has remained elusive because the likelihood of sticking is a complex function of multiple parameters which include overpressure, mud properties, well trajectory, borehole quality, length of open-hole, stationary time on station, tool dimensions and weight, number of depleted sands in the open-hole, etc. A dataset that includes the most critical formation testing operations carried out by Shell and various oilfield service providers over the last decade is analyzed. The analysis confirms the combination of conditions under which sticking becomes highly likely: high overbalance, poor mud quality resulting in thick mudcake, long and heavy tool string in a highly deviated well, tight clearance between the tool and the borehole wall, exceptionally long stationary time, etc. Some recommendations to reduce the sticking risk are provided. A case study is presented to illustrate that fundamental understanding and good planning are essential to minimizing the risk of tool and cable sticking during any logging run.
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