Early Symptom Detection for Downhole Conditions: Principles and Results
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 150422, ’Early Symptom Detection Based on Real-Time Evaluation of Downhole Conditions: Principles and Results From Several North Sea Drilling Operations,’ by Eric Cayeux, SPE, Benoit Daireaux, and Erik Wolden Dvergsnes, SPE, IRIS, and Gunnstein Saelevik, Sekal, prepared for the 2012 SPE Intelligent Energy International, Utrecht, The Netherlands, 27-29 March. The paper has not been peer reviewed.

During drilling operations, downhole conditions may deteriorate and lead to unexpected situations that can result in significant delays. In most cases, warning signs of the deterioration can be observed in advance, and proactive actions can avoid serious incidents such as packoffs or stuck pipe. A new analysis methodology that relies on an automatic real-time computer system has been developed to detect the early indicators.

Introduction

Many drilling operations are confronted with increasing nonproductive time caused by drilling incidents (e.g., pack-off, overpull, high torque, mud loss, or kick). Many of those problems could have been avoided, or at least their effects on the drilling operation could have been reduced, if pre-emptive actions had been taken as soon as the downhole conditions started to deteriorate. A proactive method was developed that consists of recording pick-up weight (PUW), slackoff weight (SOW), and free-rotating torque while drilling, and comparing the evolution of those measurements with precalculated torque-and-drag charts from the well plan. When deviations are observed, the rate of penetration (ROP) can be reduced or hole-cleaning procedures started, to improve the downhole conditions. This work process does not require advanced computer systems to be used in real-time, but requires special friction tests to be performed at regular intervals (e.g., at each connection). 

Circulation influences the drag forces and momentum because of the pressure difference between the interior and exterior of the drillstring. To obtain comparable results, it is necessary to perform the friction tests with no circulation or low circulation rates. Unfortunately, reducing the pump rate, while taking PUW and SOW, is not always performed and, therefore, many valuable data are lost and cannot be used to determine downhole conditions. It also is of interest to monitor the mechanical friction in conditions other than drilling, such as while pulling out of hole (POOH), running in hole, or while backreaming to the casing shoe. To deal with these considerations, it is possible to perform a systematic analysis of all possible off-bottom weights and torques and with any flow rate by implementing a continuous monitoring system that uses an embedded torque/drag model coupled with hydraulic calculations.

With real-time enabled software to monitor hook-load and torque measurements for a drilling operation, it is possible to extend its use for analysis of many other real-time parameters, providing the opportunity to detect changes in downhole drilling conditions besides poor cuttings transport while drilling. The real-time-monitoring system incorporates other types of symptom detection to provide a broader range of real-time analysis of the downhole conditions. The complete paper details results obtained with this system while monitoring 15 drilling operations in five North Sea fields.