Complex fractured basement reservoir
Hurricane Energy plc, is a leading oil and gas company focused on
fractured basement discovery and development in the UK. It holds six licenses
within UK Continental Shelf (UKCS) basement plays and, while having other
exploration and appraisal opportunities, the company is focused on bringing its
UKCS Lancaster field into development.
Lancaster field, located in 160-m water depth in the West of Shetlands
area of the UK Atlantic Margin, was the first basement prospect drilled by
Hurricane and the first exploration well in the UKCS to specifically target the
basement. It proved to be a significant discovery, with well tests flowing
light (38 API) oil. An independent report in 2013 assigned 207 million bbl of
oil equivalent at 2C best-estimate of contingent resources.
The field comprises a highly fractured granitic basement reservoir,
primarily tonalite, featuring fractures at a number of scales. As a Type 1
naturally fractured reservoir, fluid distribution and flow characteristics are
entirely dominated by the fracture network—there is no intergranular
matrix. Fracturing within the reservoir is related to a combination of the
original cooling joints inherent to all igneous rocks and numerous episodes of
tectonic activity throughout the rocks' 2.4 billion year history, which has led
to reactivation of the joints as well as the introduction of seismic-scale
faults and associated damage zones. Extended periods of subaerial exposure and
fluid flow through the reservoir have further enhanced the fracture network.
High-resolution dynamic modeling
The geological complexity of Lancaster field demands high-resolution
modeling to capture the main geological features and consider their impact on
dynamic behavior. Traditional reservoir simulators have difficulty solving the
challenges presented by the field's strong contrasts in permeability and the
extensive presence of faults and fractures. Previous simulation models
exhibited poor performance, required coarsening to complete in a reasonable
time frame, and did not allow investigation of key uncertainty parameters such
as aquifer presence and strength, depth of the free-water level (FWL), and
their impact on production forecasting profiles.
A joint work plan involving resources from Hurricane and Schlumberger
was established to produce an operational full-field reservoir simulation model
at the required geological resolution. A domain-driven workflow was established
using the Petrel E&P software platform to set up the model and leverage the
power of the INTERSECT high-resolution reservoir simulator for field
development planning. The main technical requirement was to match the latest
geological and dynamic data acquired in a recent horizontal drilling campaign.
The ultimate goal was to enable Hurricane's staff to reliably and accurately
model and simulate the subsurface complexity of the field within practical
simulation runtimes using the company's in-house workstations.
Multiple simulation runs would be required to perform sensitivity
analysis and increase confidence in the results. The results of the simulation
would enable better field development decisions, such as future well placement,
through an improved understanding of reservoir behavior—specifically the
potential for water breakthrough, pressure support over time, and permeability