RE: Seismic31 Jul 2019 00:49
'mapping of porosity using seismic methods is not possible -- mapping of seismic scale faults and attributing Fault Zone widths as statistical ranges'
This might help - cut & pasted from FB references:
'In the case of the Rona play, porosity is almost entirely associated with fissure fills, joints and microfractures that are present within and without zones associated with larger faults identified from seismic interpretation (Belaidi et al., 2016). This distribution is split into two facies: Fault Zones (Fracture System) and Fractured Basement (Host Rocks). As an example, the average porosity for the Lancaster Field is 4% with average Fault Zone (FS) porosity 4.8% and Fractured Basement (HR) porosity 3.2%. Despite the improved porosity associated with Fault Zones, mapping of porosity using seismic methods is not possible and areas of potential high porosity are quantified through the mapping of seismic scale faults and attributing Fault Zone widths as statistical ranges. Fault Zone widths are estimated from the ranges of Fault Zones established through drilling and wireline data (Belaidi et al., 2016). Porosity generation is attributed to a pre existing fracture network that has been enhanced by a combination of fissuring (tensile failure), partial mineralization due to influx of hydrothermal fluids and deep penetration of surface weathering processes down fissures (Trice et al., 2018; Holdsworth et al. 2019).'
So static reservoir modelling biased heavily by statistical methods - know from logs eg Lincoln - that fracture density within structural closure (crestal) >> deeper below structural closure. Problem with seismic is it is shot in time not depth - so hard to pin-point exact position in depth of seismic scale faulting (can easily be >100ft out in depth) - as well as oriented sub-vertical or sub-horizontal from seismic image 'cube'. Also Lancaster & WD seem to have perched water too - not modelled pre-WD. Perched water seems to increase with depth too, while fracture density decrease. But HE has proved connected oil (ie oil column) is present below structural closure.
In WD if they had drilled an exploration slanted hole (more costly) they would have encountered fractures which they could (1) checked if statistics in model ok, & (2) drilled the horizontal well as an appraisal well to hit best encountered in slanted pilot hole - appraising rather than exploring at WD with horizontal. Actual horizontal was drilled deeper than planned so - statistics would be worse still.
So models not 100% accurate as based on interpretation of seismic (+ depth to time issues) & statistics of expected fracture density with depth... Drilling deep in Lancaster below the structural closure could result in same result! HE know the approximate OWCs - so in the future 'hopefully' will not drill this region again while we are investors and instead evaluate this region based on volumes connected to producers through dynamic production modelling.