ABSTRACT This field guide presents a one-day excursion in Prince George’s County, Maryland, USA, and documents the transition across the Cretaceous-Paleogene boundary by examining sediments from the upper Maastrichtian of the Severn Formation to the Paleocene sediments of the Brightseat and Aquia formations. Emphasis is placed on understanding how differences in depositional character and lithostratigraphy are related to changes in both microfossil and macrofossil assemblages. Particular attention is given to the difficulty in distinguishing Upper Cretaceous sediments from lower Paleocene sediments in the field, a problem that has traditionally led to misrepresentation of the distribution and thickness of these units and their correlation on a regional scale. Regarding the Late Cretaceous geology, the guide presents information on the lithology and microfossil biostratigraphy of the Severn Formation, which consists predominantly of silty quartz sand, with less than 5% clay. These sediments are placed in calcareous nannofossil Zone CC25a, suggesting an early late Maastrichtian age. Low abundances of planktic foraminifera combined with sedimentological evidence suggest deposition most likely occurred in a middle neritic environment. Macrofossils in the outcrops along the field trip consist primarily of fragmented bivalve mollusk and cephalopod shell material. A hiatus of ~5 m.y. separates the Cretaceous sediments from the overlying Paleocene deposits. As for the Paleocene geology, the guide presents information on the Brightseat and Aquia formations. The Brightseat represents early Danian age deposition and consists of clayey, silty sand at the base that grades upward into a silty sand. Glauconite is present at <5% throughout the formation in outcrop. Sediments of the Brightseat Formation are placed in calcareous nannofossil Zone NP3. Macrofossils are limited to small bivalve fragments that are scattered throughout. A hiatus representing ~3 m.y. separates the Brightseat from the overlying Aquia Formation, which is Selandian to Thanetian in age and consists of a glauconite-rich (~10%–20%), silty sand with common to abundant macrofossils, including both fragmented and complete gastropods and bivalves.

Abstract Machar is one of several diapir fields located in the Eastern Trough of the UK Central North Sea. It contains light oil in fractured Cretaceous–Danian chalk and Paleocene sandstones draped over and around a tall, steeply-dipping salt diapir that had expressed seafloor relief during chalk deposition. The reservoir geology represents a complex interplay of sedimentology and evolving structure, with slope-related redeposition of both the chalk and sandstone reservoirs affecting distribution and reservoir quality. The best reservoir quality occurs in resedimented chalk (debris flows) and high-density turbidite sandstones. Mapping and characterizing the different facies present has been key to reservoir understanding. The field has been developed by water injection, with conventional sweep in the sandstones and imbibition drive in the chalk. Although the chalk has high matrix microporosity, permeability is typically less than 2 mD, and fractures are essential for achieving high flow rates; test permeabilities can be up to 1500 mD. The next phase of development is blowdown, where water injection is stopped and the field allowed to depressurize. This commenced in February 2018.

Abstract The Stella Field is located in UKCS Block 30/6a, c. 230 km SE of Aberdeen. Stella Field is a four-way, dip-closed and salt-cored dome with a 600 ft gas-condensate column underlain by a 250 ft oil column within the 5–30 ft thick Paleocene Andrew Sandstone Member. Oil is also present in the underlying chalk reservoirs of the Danian Ekofisk and Maastrichtian Tor formations. Following the discovery of the field in 1979 there have been three phases of appraisal followed by the recent development, with first oil in February 2017. The field development has been challenging as the 38-year gap between discovery and first oil illustrates. Principal challenges have included structural undulations and radial faulting combined with a thin primary reservoir, variation in hydrocarbon, compartmentalization and depletion relating to producing fields. These issues have been reviewed following the latest drilling results and ideas on the petroleum geology updated. Block 30/6a, containing the Stella Field, was originally awarded to Shell/Esso in the first Licensing Round in 1964 as part of multi-block licence P011. The current Stella P.011 licence holders are Ithaca Energy (UK) Limited (operator) with 54.66%, Dyas UK Limited with 25.34% and Petrofac GSA Limited with 20%.

Abstract The Burghley Field is a Paleocene oil field located in Block 16/22 on the UK Continental Shelf about 8.5 km NE of the Balmoral Field, in a water depth of c. 143 m. Burghley produces undersaturated oil from sandstones of the Maureen Formation. It comprises a low relief four-way dip-closed structure located on the SE end of the Fladen Ground Spur. The field was discovered in 2005 by well 16/22-7. Overall nine well penetrations were drilled prior to the commitment to develop the field. The Burghley Field was brought on-stream in October 2010 as a single subsea horizontal well development tied back to the Balmoral floating production vessel. The current estimate for oil in place is c. 20 MMbbl for the entire field, with approximately 12 MMbbl in the core area where the development well is located. The expected ultimate recovery is approximately 5.65 MMbbl.