What does Ophiomorpha irregulaire really look like?

Ophiomorpha irregulaire is a surprisingly poorly characterised ichnotaxon given its common occurrence in hydrocarbon reservoir facies. Current debate surrounds the ichnotaxobases suitable for ichnospecific-level identification and also the palaeogeographic distribution of the taxon. O. irregulaire is conventionally characterised in core by the presence of “spikey”, fine-grained, wall-lining pellets, since the horizontal “meander maze” that is also part of the ichnospecific diagnosis cannot normally be demonstrated. To resolve ichnotaxonomic issues concerning the validity of pellet morphology as a primary ichnotaxobase, material from the type locality is re-described (Cretaceous Book Cliffs, Utah), with an emphasis on burrow wall morphology. Comparative neoichnological studies using the callianassid crustacean Neotrypaea californiensis were additionally conducted to understand the behaviour of modern taxa that produce burrows closely resembling O. irregulaire. High-resolution, three-dimensional morphological models were created from specimens of Ophiomorpha from the type locality of O. irregulaire in Utah, USA, and from Eocene deep marine turbidites of the Juncal Formation, California. Comparison of the morphological features from these two localities, as well as specimens observed in core from offshore Newfoundland, demonstrate conclusively that O. irregulaire is not restricted to the Cretaceous Western Interior Seaway. O. irregulaire may have a stratigraphic range from Jurassic to Recent, and occur in palaeoenvironmental settings ranging from shallow marine to continental slope settings. The flame-like pellet morphology is considered characteristic of the type material, and is a valid criterion for identifying O. irregulaire in core

Oil and gas wells and their integrity: Implications for shale and unconventional resource exploitation

Data from around the world (Australia, Austria, Bahrain, Brazil, Canada, the Netherlands, Poland, the UK and the USA) show that more than four million onshore hydrocarbon wells have been drilled globally. Here we assess all the reliable datasets (25) on well barrier and integrity failure in the published literature and online. These datasets include production, injection, idle and abandoned wells, both onshore and offshore, exploiting both conventional and unconventional reservoirs. The datasets vary considerably in terms of the number of wells examined, their age and their designs. Therefore the percentage of wells that have had some form of well barrier or integrity failure is highly variable (1.9%e75%). Of the 8030 wells targeting the Marcellus shale inspected in Pennsylvania between 2005 and 2013, 6.3% of these have been reported to the authorities for infringements related to well barrier or integrity failure. In a separate study of 3533 Pennsylvanian wells monitored between 2008 and 2011, there were 85 examples of cement or casing failures, 4 blowouts and 2 examples of gas venting. In the UK, 2152 hydrocarbon wells were drilled onshore between 1902 and 2013 mainly targeting conventional reservoirs. UK regulations, like those of other jurisdictions, include reclamation of the well site after well abandonment. As such, there is no visible evidence of 65.2% of these well sites on the land surface today and monitoring is not carried out. The ownership of up to 53% of wells in the UK is unclear; we estimate that between 50 and 100 are orphaned. Of 143 active UK wells that were producing at the end of 2000, one has evidence of a well integrity failure