The NW Hutton Field lies within the Brent Province of the East Shetland Basin and is located in Block 211/27, 130 km NE of the Shetland Islands. Oil of 37° API, the source of which is the Upper Jurassic Kimmeridge Clay Formation, is reservoired in Brent Group sandstones in a complex, highly faulted and tilted fault-block structure at an average depth of 12000 ft subsea. The Brent Group Reservoir shows a complex diagenetic sequence. Early calcite concretions showing partial replacement by siderite occur in the marine-facies sandstones of the Broom and Rannoch Formations. The fluvio-deltaic and marine-facies sandstones of the Etive, Ness and Tarbert Formations show a different diagenetic sequence (post-dating carbonate cementation) of secondary porosity formation by K-feldspar dissolution, followed by quartz overgrowth cementation and kaolinite and illite authigenesis. Development of kaolinite was concentrated in the crestal areas of the structure while both illite and quartz cements increase with depth in the downflank areas. The marine sandstones of the Broom Formation are the exception, being kaolinite-rich with little illite even below the oil-water contact. An early phase of oil migration into the structure appears to have been concurrent with the later stages of quartz overgrowth and clay mineral cementation, the later main phase of migration causing diagenesis to cease in the crestal part of the field. In the down-flank areas illite cementation appears to have ceased soon after the main migration of hydrocarbon fluids into the structure.