No abstract

The Pierce Field in the Central UK North Sea is a twin diapir structure that produces from the Paleocene Forties Sandstone Member (Forties Sandstone). Different hydrocarbon–water contacts encountered in the wells around both diapirs have been variously ascribed to a hydrodynamically tilted oil–water contact or else some form of stepped (compartmentalized) contact. Recent reinterpretation of the structure, sedimentology and fluid geochemistry has indicated that the stratigraphic architecture of the reservoir is the prime control on fluid flow over both geological and production time-scales. These depositional architectures deflect the hydrodynamic flow of aquifer water around the field, resulting in a modified-tilted-contact. The same depositional architectures control the flow of fluids under production. The Forties Sandstone was emplaced by turbidity flows influenced by pre-existing seafloor topography that funneled the flows into discrete sediment corridors and into the Pierce area. The rising twin diapirs further influenced the flows by forming: (a) a small salt withdrawal basin between the diapirs that captured sediment; and (b) enough seafloor topography to prevent the bulk of the flows from depositing significant amounts of sand over the crest of the diapirs. Because the bulk of the high permeability sands were deposited in a rim around the diapirs, the aquifer and injected water does not always flow to structurally higher elevations, but follows the geometry of the channelized sands. While faults are present on both South and North Pierce, they are not extensive and do not appear to play a major role in the compartmentalization of the field. From production data, pressure communication can be inferred around North Pierce and around the majority of South Pierce, the main exception being a block bound by large throw faults in the SE of the southern diapir. Geochemical fingerprinting of the hydrocarbons in Pierce shows families of oils that suggest that the northern and southern parts of the reservoir are separate oil compartments, which is a result of the interaction of the filling history and the stratigraphic and structural architecture of the reservoir.

No abstract

No abstract