In the Huntington field in the North Sea, bilinear flow with a clear one-quarter slope in the pressure derivative has been observed during intermediate times in horizontal-well tests, instead of the usual linear flow with a one-half slope expected in a homogeneous reservoir. This paper offers insight into an integrated effort at combining analytical information, numerical well-test models, and geological evidence to explain the reservoir behavior observed in the Huntington field.
Reservoir Description
The Huntington field is a sandstone reservoir with a maximum oil-column thickness of 120 ft, located within a sand-rich turbidite system in the central North Sea. Vertical appraisal wells show a largely homogeneous reservoir with average porosities of 20%, net/gross ratio of 80–90%, and average permeabilities of 30–60 md. Core samples do not indicate any inherent natural fractures.
The reservoir contains undersaturated light oil with gravity of 43 °API, viscosity of 0.3 cp, and bubblepoint pressure of 2,200 psig at reservoir pressure of 4,000 psig and temperature of 250°F. Well tests of two vertical wells match a homogeneous-reservoir model, but four horizontal producers drilled in this reservoir exhibited a one-quarter-slope straight line in the pressure derivative, stretching up to two log cycles during intermediate time.
Reservoir Connectivity and Areal Anisotropy. Reservoir-connectivity investigations indicate no obvious barriers between the wells and good reservoir connectivity between all the wells.
