Abstract The Erskine high-pressure–high-temperature gas condensate field was the first such field developed in the UK Continental Shelf. Since production started in 1997, the field has produced over 350 bcf of gas and 70 MMbbl of condensate. The reservoir pressure has depleted from an initial pressure of 960 bar (13 920 psi) down to 140–400 bar (2030–5800 psi), resulting in some compaction and sand production in some of the wells. Free water production has led to the formation of wellbore scale, which has required interventions to remove. The reservoirs are sandstones of the Jurassic Puffin, Pentland and Heather formations. Estimates of hydrocarbons in place made using production and pressure data compare favourably with the initial estimates made during field development planning, although the Pentland Formation volume is some 20% below the sanction estimate. Several major field outages have occurred, such as a condensate fire in 2010 and a blockage of the multiphase export pipeline in 2007. In addition, the field has experienced flow assurance problems related to scale and wax deposition. A new pipeline section was installed in 2018 to bypass a full pipeline blockage which occurred due to wax deposition.

Abstract Fuzzy c-means clustering (FCM) is an exploratory data-analysis method that identifies groups of samples with similar compositions. In spite of FCM being well established in the field of pattern recognition, to date it has had little application in biostratigraphy. In contrast to the hard clustering methods commonly used in biostratigraphy, FCM has the advantage that it can accommodate mixtures and/or gradations between clusters. This is an important feature for biostratigraphical data analysis because such data sets often include samples that are transitional between two or more “pure” faunal or floral assemblages. As an evaluation of FCM we used it to resolve Jurassic miospore and pollen biofacies from the Pentland, Fulmar, and Heather formations from two closely spaced wells in the Hawkins Field, Central North Sea, UK. These data were chosen because they contain a flora for which there is substantial paleoecological literature and, as such, would provide a suitable evaluation of the application of the FCM method to industrial biostratigraphical data. The results demonstrated that FCM could extract floral associations that were relatable to stratigraphy and sea-level changes. Fuzzy c-means produced a five-cluster (i.e., five assemblages) solution. We named each assemblage after the taxon that was dominant in the assemblage. The Cyathidites assemblage is stratigraphically distinct and restricted entirely to the nonmarine Pentland Formation. The remaining four assemblages (Perinopollenites elatoides, Lycopodiumsporites, Cerebropollenites mesozoicus , and Callialasporites) are ecologically distinct and occur primarily in the Fulmar and Heather formations. The P. elatoides assemblage is representative of lowstand regression. The C. mesozoicus assemblage is indicative of warmer, drier, possibly semiarid or seasonally arid climatic conditions. The Lycopodiumsporites assemblage is transitional between cooler, wetter to warmer, drier climatic conditions with the floral dominance of P. elatoides being replaced by C. mesozoicus . The Callialasporites assemblage is interpreted as representing warm, wet seasonal climatic conditions, possibly a back-mangrove biotope, with its maximum development occurring slightly above the maximum flooding surface. Ultimately, this succession of curves was used as a proxy for sea-level changes in the study area, enabling the recognition of maximum flooding surfaces, genetic sequences, and parasequences that improved inter-well correlation. Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones SEPM Special Publication No. 93, Copyright © 2009 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 9–20.

Abstract The Shearwater Field is a high-pressure–high-temperature (HPHT) gas condensate field located 180 km east of Aberdeen in UKCS Blocks 22/30b and 22/30e within the East Central Graben. Shell UK Limited operates the field on behalf of co-venturers Esso Exploration and Production UK Limited and Arco British Limited, via a fixed steel jacket production platform and bridge-linked wellhead jacket in a water depth of 295 ft. Sandstones of the Upper Jurassic Fulmar Formation constitute the primary reservoir upon which the initial field development was sanctioned; however, additional production has been achieved from intra-Heather Formation sandstones, as well as from the Middle Jurassic Pentland Formation. Following first gas in 2000, a series of well failures occurred such that by 2008 production from the main field Fulmar reservoir had ceased. This resulted in a shut-in period for the main field from 2010 before a platform well slot recovery and redevelopment drilling campaign reinstated production from the Fulmar reservoir in 2015. In addition to replacement wells, the redevelopment drilling also included the design and execution of additional wells targeting undeveloped reservoirs and near-field exploration targets, based on the lessons learned during the initial development campaign, resulting in concurrent production from all discovered reservoirs via six active production wells by 2018.

Abstract The Culzean Field is situated 240 km east of Aberdeen in Block 22/25a. The field was discovered in 2008 by well 22/25a-9Z targeting a tilted fault block, encountering lean-gas condensate in the fluvial Triassic Skagerrak (Joanne Sandstone Member) and the Jurassic Pentland formations. The field is high-pressure–high-temperature (HPHT) with initial conditions of 936 Bar (13 575 psi), 176°C (348°F) and charged with a lean-gas condensate. Development of the field was sanctioned in 2015 and is the latest UK HPHT field to be developed with start-up in mid-2019. The field development plan comprises production from six development wells drilled from a wellhead platform with bridge connections to a central process platform with accommodation on an additional bridge-linked utilities and living quarters platform. Gas is exported to shore via the Central Area Transmission System pipeline and produced condensate is exported via the floating storage and offloading vessel ‘Ailsa’. Production is expected to reach a plateau production rate in the order of 100 000 boepd with an overall recovery of up to 300 MMboe.

Abstract The Maria oilfield is located on a fault-bounded terrace in Block 16/29a of the UK sector of the North Sea, at the intersection of the South Viking Graben and the eastern Witch Ground Graben. The field was discovered in December 1993 by the 16/29a-11Y well and was confirmed by two further appraisal wells. The reservoir consists of shoreface sandstones of the Jurassic Fulmar Formation. The Jurassic sandstones, ranging from 100 to 180 ft in thickness, have variable reservoir properties, with porosities ranging from 10 to 18% and permeabilities from 1 to 300 mD. Hydrocarbons are trapped in a truncated rotated fault block, striking NW–SE. The reservoir sequence is sealed by Kimmeridge Clay Formation and Heather Formation claystones. Geochemical analysis suggests that Middle Jurassic Pentland Formation and Upper Jurassic Kimmeridge Clay Formation mudstones have been the source of the Maria hydrocarbons. Estimated recoverable reserves are 10.6 MMbbl and 67 bcf (21.8 MMboe). Two further production wells were drilled in 2018 to access unexploited areas.

Abstract The Howe and Bardolino fields lie in UK Blocks 22/12a and 22/13a, respectively, on the eastern flank of the Forties–Montrose High. The Howe Field was discovered in 1987 by well 22/12a-1, and Bardolino in 1988 with well 22/13a-1ST. Both share common Jurassic reservoirs, have Upper Jurassic Kimmeridge Clay Formation top seals, require some form of lateral seal and have similar fluids. Howe has been producing relatively dry oil throughout its production life, indicating relatively good connectivity across the field area. In contrast, the Bardolino accumulation is proven to be compartmentalized. Bardolino is likely to be segmented through some fault-related mechanism. In place volumes at the Howe Field are 46.8 MMbbl, with 17 MMbbl produced thus far through a combination of natural aquifer and solution gas cap drive by subsea development well 22/12a-9Z. In place volumes at the Bardolino Field are 11.2 MMbbl, with 1.1 MMbbl produced to date through depletion drive by a subsea development well 22/13a-8. This represents recovery rates of 35% for Howe and 10% for Bardolino to date. In place volumes for the undeveloped Pentland Formation at Howe are 5 MMbbl. In place estimates for the undeveloped Kimmeridge Clay Formation sandstones at Bardolino are 8 MMbbl.

Abstract The Armada development comprises three gas-condensate fields in the Central North Sea: Fleming (Paleocene Maureen Formation reservoir), Drake and Hawkins (Upper Jurassic Fulmar Formation reservoirs). Armada came on stream in 1997, with seven PhaseI wells producing at a plateau rate of 450 × 10 6 SCFD. APhase II drilling campaign, comprising three Armada wells, was implemented in 2002 with the aim of extending the duration of the Armada production plateau and, where possible, accessing new reserves. The first well was a relatively straightforward Paleocene Maureen Formation producer, although the target was revised based on a new seismic attribute study, which revealed important heterogeneities in this deep-marine reservoir. The second well targeted the undrilled western compartment of the Hawkins discovery. Unfortunately, the Fulmar Formation was water-wet with no evidence for any hydrocarbon charge, despite the fact that gas had been proved by an earlier exploration well in a downdip compartment. Fortunately, to mitigate the risks, which had been recognized pre-drill, the well had been designed with a secondary Paleocene Maureen Formation target which came in better than prognosed. A significant aspect of the Armada Phase II programme was the extensive integration across a number of disciplines. The combined team was soon able to propose a convincing explanation for the failure of West Hawkins, giving comfort that East Hawkins should be fully charged and was worth drilling. The final Phase II well was therefore targeted on East Hawkins, although it was a difficult well to plan as the key reservoir horizon had only minor stand-off from the gas-water contact. A number of different well trajectories were considered and 3D visualization proved invaluable in ensuring the final well path was optimized. In addition, a major benefit was derived from a recently installed onsite 3D visualization centre that enabled the multidisciplinary Armada team to work together very effectively. For example, the drilling engineers were truly able to appreciate what was driving the geotechnical requirements for the well and vice versa. The well came in very close to prognosis, adding valuable reserves and further extending the Armada plateau. With a rig on the Armada platform the opportunity was taken to drill the South West Seymour prospect, whose chance of success had increased dramatically after a possible direct hydrocarbon indicator was recognized on an inverted seismic volume. The well discovered hydrocarbons in the primary target, the Fulmar Formation and also in the Pentland Formation and was immediately side-tracked to a previously planned updip Fulmar development location.