Conclusive Proof of Weak Bedding Planes in the Marcellus Shale and Proposed Mitigation Strategies

Wellbore instability has been experienced in areas of the Marcellus Shale and can become particularly troublesome in the superlaterals that are becoming more prevalent in that play. Often, the instability while drilling these very long lateral wells is minimal; problems are more likely to occur while tripping out after reaching total depth (TD). The most common instability events when pulling out of the hole are tight hole, packoff, and stuck pipe and are often accompanied by excessive cavings. These problems often worsen with time, indicating there is some time dependence to the failure mechanism. In order to develop effective mitigation strategies to combat the instability, it is imperative that the failure mechanism be correctly identified. Previous publications (Riley et al., 2012; Addis et al., 2016; Kowan and Ong, 2016) have suggested that bedding planes may play a role in some of the drilling problems experienced in the Marcellus Shale. This case study provides conclusive proof of weak bedding plane failure along a lateral well in the Marcellus Shale, where over 1,000 feet of anisotropic failure was captured with a logging-while-drilling (LWD) image tool. This image not only provided confirmation of the presence and failure of weak bedding planes in the Marcellus Shale, but was also used to validate an existing geomechanical model for the area. Validating the model gave the operator more confidence in the mitigation strategies developed from that geomechanical model, which had been based on the assumption that weak bedding was contributing to the difficulty experienced on multiple lateral wells when tripping out of the hole. This case study begins with an overview of the geomechanical model, including the drilling history, stress/pore pressure model, and rock properties. Next, some highlights from the image log, showing anisotropic bedding plane failure, are featured, as well as a comparison of the image to the geomechanical model. This case study concludes with proposed mitigation strategies that could be implemented to limit the risks posed by weak beds and to minimize instability when drilling laterals in the Marcellus Shale in this area or similarly complex areas.

A NOVEL TECHNIQUE OF RYLE’S TUBE FIXATION (PARTHA’S TECHNIQUE) FOR CONVENIENT INTRAOPERATIVE USE

Dear sir, Nasogastric tube (Ryle’s tube) insertion is one of the commonest ward procedures done for different indications. During selected surgical procedures, the insertion of such tubes is done in the preoperative ward. There are lot of reported difficulties during insertion in the intraoperative period.1 The Ryle’s tube is inserted in the classical manner but usually adjusted to enable the surgeon to do the gut surgery. The tube is usually fixed to the nose by a plaster wound round the tube. This technique is usually difficult to unwound if there is a need to reposition. In surgical and medical wards, the necessity for repositioning is not very significant. But during the intraoperative period, the surgeons always prefer to move the tube here and there to make the operative field better. This in turn causes much discomfort to the attending anaesthesiologist if the plaster is stuck in a traditional way. Hence, we propose a novel technique of fixation wherein we get the advantages of avoiding accidental removal but with the ease of frequent positional adjustment. A sixty-five-year-old male came for upper Gastro-intestinal surgery. The Ryle’s tube was inserted in the ward and fixed as given in fig 1. To adjust the position after removal of the plaster becomes a herculean task. Its more difficult to adjust the plaster with gloved hands. The plaster was removed before induction and fixed as described below. The first plaster (P1 in fig 2) was vertical and fixed the tube to the nose in a vertical fashion. The portion of the plaster which sticks to the tube should be around 50 % of the plaster length. Usually there is a small gap between the attachment of the tube and the nose. The next or the second plaster (P2 in fig 2) was transverse which fixed the vertical plaster to the nose. The transverse plaster never touched the Ryle’s tube. (Fig 2) If we need to adjust the position, the plasters can be easily loosened to adjust and fix again. The portion of the plaster in the gap can be lifted to loosen. There is no need for changing the plasters. Many a time, the surgeons may ask for repeated changes of position during the surgery. Hence this Partha’s technique of fixation suits repeated unfastening and regluing. There are reports of lost Ryle’s tubes2 after fixation in the wards. Lorente3 in his study of intensive care patients, found an incidence of accidental removal of Ryle’s tube as 4.48%. A single plaster use may be a cause of malposition. An extensive search of the literature did not reveal fixation techniques with their pros and cons. We have been using this technique for many years so far with minimal problems. This report is limited to the fact that it is not used much with no comparative studies to know its advantages and disadvantages.