Outcrop Studies of Lower Cretaceous Tidal Sandstone Bodies for Reservoir Characterization of the Tilje Formation (Lower Jurassic), Offshore Mid-Norway

Abstract

The Vectis Formation (Lower Cretaceous) in the Isle of Wight, south England, serves as an excellent outcrop analog for tidal sandstone reservoirs, including parts of the Lower Jurassic Tilje Formation, Norway. It consists of at least two juxtaposed marginal-marine depositional systems separated by a regionally extensive erosional sequence boundary. The lower mud-dominated system is characterized by a muddy succession with few lateral facies variations that transgressively overlies fluvial strata and is interpreted as a broad lagoonal complex. The upper system exhibits considerable lateral facies variations over a short distance with abundant tidal sedimentary structures and is interpreted as a channel and bar complex within a broad macro-tidal estuary. It contains a complex array of sedimentary structures and heterogeneities ranging from regional scale (tens of kilometers wide, tens to hundreds of meters thick) down to the scale of individual laminae (millimeter thick). The large-scale heterogeneities and facies variations are best explained within a sequence stratigraphic framework. Intermediate- and small-scale heterogeneities (centimeter to meter thick, a scale of individual bedforms and laminae) were examined (1) by photographing and digitizing small areas (about 1 m × 1 m) of 2-D outcrops with a resolution of 1 mm or greater and (2) by using serial sectioning techniques (cut at 1-2 cm intervals) to reconstruct the 3-D geometry of tidal sedimentary structures directly from rock samples taken from different facies types (see Jackson and others in this volume).

The Tilje 1 stratigraphic interval in Heidrun field, offshore mid-Norway, is also interpreted, in part, to have formed in a comparable depositional setting. This interval is characterized by a heterolithic and overall upward- coarsening unit interpreted as tidal bar deposits that is erosionally overlain by blocky to upward-fining units interpreted as tidal channel deposits. These deposits were interpreted to have been formed in an estuary or embayment (see Martinius and others in this volume).

Reservoir models of Heidrun field have used geometrical data on small- and intermediate-scale heterogeneities obtained from the outcrops to populate stochastic models of heterolithic tidal facies (flaser and wavy bedding) and to assist in developing object-based stochastic models.