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Tullich Field (9/23a-29U) core displays

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journal contribution
posted on 30.04.2020 by J. M. RODRIGUEZ, H. SCHOLEY, K. P. FLANAGAN
Tullich Field, operated 100% by Kerr-McGee North Sea (UK) Limited, lies in block 9/23a. Well 9/23a-29U was drilled 40 feet north east of the original 9/23a-29A vertical well. Two 60 feet cores, cut with 100% recovery from 5576 to 5691.3 feet md in the Lower Eocene, Balder B2 unit, contain the complete sequence of hydrocarbon bearing sands penetrated in the vertical hole. Although no wire line or LWD data were acquired over the cored section, geophysical and image log data obtained from 9/23a-29A correlate closely with the sequence cored. The cores comprise high quality thick bedded structureless reservoir sandstones within an interbedded sequence of argillaceous sandstones, clay clast conglomerates, sandy and muddy debris flows, laminated siltstones and thin tuffaceous claystone beds. The non-reservoir rock represents the high impedance unit observed in the inverted shear wave seismic data. The reservoir sandstones are dusky yellowish-brown, medium-fine grained and well sorted. Six reservoir units were cored giving a total net thickness of 46.5 feet. The main unit is 34.5 feet thick and is represented by several stacked units - at the base lies a thin teredo bored wood mass and towards the top common pyrite is observed. The remaining sandstones are significantly thinner and represent single beds. Porosities vary from 29-36% with permeabilities up to 5 Darcies. Although predominantly massive, some minor dewatering structures and bedding planes are observed as well as a general fining up from base to top. These reservoir sandstones are interpreted as the stacked 'a' division of the Bouma cycle, deposited from a series of concentrated density flows in a deep water marine setting. The non-reservoir sequences by constrast show overturned bedding, rip up clasts and injection structures as well as laminated sediments. These are interpreted as being derived from various sources ranging from background suspension and air born fall out to gravity driven flows in a basinal marine environment. Open and cemented fractures and faults occur throughout the core.

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