Online Journal for E&P Geoscientists

Wharton, Stanley R.^*1; Lawrence, Paul ¹; Bakhiet, AbdelFattah ¹; Tang, David ¹; Gregory, Arthur ¹
(1) Saudi Aramco, Dhahran, Saudi Arabia.

Jurassic carbonates represent some of the most productive reservoirs in Saudi Arabia. The main challenge associated with prospecting for these carbonate reservoirs is their heterogeneity. This is due to their depositional and tectonic history, as well as stratigraphic and/or diagenetic influences. To assess the heterogeneity of these reservoirs, an integrated approach using seismic chronostratigraphy, well log correlation, and 3D seismic multi-attribute analysis, including unsupervised neural network seismic facies classification, was applied. The study area is located on the flanks of a large Jurassic carbonate intrashelf basin.

A seismic 2D chronostratigraphy model was built using a set of 2D traverse lines within the Callovian-Oxfordian sequences. An associated Wheeler diagram was then generated to define the major transgressive and regressive phases on the Arabian Platform. A flattened seismic volume, based on the 2D chronostratigraphy, was used to generate 3D seismic attribute volumes from existing regional surveys and included seismic facies block analysis to assess the seismic stratigraphy. The seismic facies 3D block volumes were then visualized and interpreted to define the geometry of prograding clinoforms within the carbonate sequences.

Waveform classification analysis of the upper Oxfordian Hanifa revealed distinct lateral facies changes between carbonate shoal and distal basinal areas. A proportional slicing technique generated at the top of the sequence showed a strike-dominated depositional trend for the shoal facies, and a dip-oriented depositional trend for the basinal deposits. Core data and electrofacies logs corroborated the seismic facies distribution with the sporadic oolitic deposits, located in a north-south shoal belt, and the poorer facies within the intra-shelf basin.

The integrated application of seismic chronostratigraphy, multi-attribute 3D seismic analysis, and unsupervised seismic facies classification, to assess the seismic stratigraphy and the seismic facies variations, proved beneficial in defining heterogeneities in the Jurassic carbonate depositional systems. Use of pre-conditioned, flattened seismic volumes permitted the definition of significant stratigraphic geometries and showed the potential for new stratigraphic play concepts.