Modeling Flow along Fault Damage Zones in a Sandstone Reservoir; an Unconventional Modeling Technique Using Conventional Modeling Tools in the Douglas Field, Irish Sea, UK

Abstract

Abstract The Douglas and West Douglas fields are part of the Liverpool Bay development in the East Irish Sea. The reservoir is a high net-to-gross, largely good quality (100-1000mD) Triassic sandstone lying in a series of fault terraces. The fields have been on production for over 10 years and whereas some wells have shown a watercut development typical for a waterflood, other wells recorded anomalous behaviour. This work addressed these anomalies as these directly influence the value of a late-life infill programme. The subsurface team reviewed outcrops of the reservoir in NW England, addressing the possibility of vertical flow up and along damage zones of faults which may be otherwise sealing (‘fault-related fractures') - a feature not previously identified in the field. The presence of fault-related fractures, observed in the outcrops, was tested in simulation models and provided a solution to the anomalous behaviour. A novel technique was employed to pragmatically characterise the fault-related fractures in the simulator. The technique involved installing wells as ‘pipes’ in cells around the faults, allowing flow up and along the fault damage zones without necessarily affecting fault transmissibility across the major zones. The size and location of the pipes representing the fractures was then used as a history matching parameter in the model and resulted in the improved history match of the anomalous wells and the match in general.