We have developed a 1D stochastic algorithm for estimating reservoir properties, based on matching large numbers of pseudo-wells to seismic angle stacks. The pseudo-wells are part deterministic and part stochastic 1D stratigraphic profiles with consistent elastic and reservoir properties. Pseudo-wells are sampled from a prior distribution defined by the geological interpretation, a rock physics model and a model for the vertical statistics that provides close control of the lithofacies proportions. A new set of pseudo-wells, typically [Formula: see text] tied to the local stratigraphy, is constructed for each seismic trace. Synthetics, derived from the pseudo-wells using extended elastic impedance, are matched to either one or two seismic angle stacks, and the best matches are selected and averaged to provide a joint estimate of reservoir properties and impedances and the associated uncertainties. The algorithm has been tested on a number of data sets and validated by blind well ties. The algorithm is 1D with no additional constraints on spatial correlation beyond that provided by the seismic data. This restricts the maximum frequency to that of the seismic; however, it makes the algorithm highly parallelizable, allowing for large data sets to be inverted in a few hours given adequate computing resources. We envisage that this inversion algorithm could form the first part of a two-step process with the output used to constrain subsequent geostatistical modeling.
Seismic coherency is a measure of the similarity between seismic traces. Coherency data play an important role in the delineation of structural and stratigraphic features by enhancing the images seen on conventional 3D seismic data. Through integration of coherency data with other technologies and calibration to well data, new applications are emerging. This paper discusses three examples from the UKCS.Partial permeability barriers in the Leman Field were known to exist from well pressure data. A coherency cube revealed several lineations that separated the wells. These lineations can be correlated to a previously unmapped fault trend with very small throws on the vertical seismic lines. The coherency cube therefore provided additional information to improve confidence in the interpretation and enabled significant time-savings in the fault pattern interpretation.Coherency data were used to assist in the well planning for the Arkwright Field development programme. Coherency slices through high pressure zones were characterized by polygonal faulting, whilst less faulting was observed in areas of lower pore pressure. These pressure zones were calibrated to pore pressures predicted from the original discovery well. The development trajectories were optimized with respect to the fault patterns interpreted from the coherency data. Model predictions were confirmed by drilling results.A coherency cube was utilized to enable a quick interpretation of the structural framework of an area of the Central Graben. In particular the distribution of faulted Triassic rafts and Jurassic rifts is easily observed because the relatively coherent Jurassic reflectors contrast well with the relatively incoherent Triassic seismic reflectivity.These three examples illustrate how coherency data can be used in production, development and exploration settings to improve the imaging of geological features ranging in scale from reservoir barriers to major faults.at University of Iowa on June 7, 2015 http://pgc.lyellcollection.org/ Downloaded from
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