Micropalaeontological dissection of the Shu’aiba Reservoir, Saudi Arabia
Published:January 01, 2005
Determination of the depositional architecture of carbonate hydrocarbon reservoirs is a necessary prerequisite for pre- and syn-development modelling and simulation. Such reservoirs are typically too thin for internal bedding geometries to be confidently determined from seismic and wireline log evidence, and this aim is best achieved by integrated palaeontological and sedimentological studies. Of these, micropalaeontological analysis and biofacies interpretation of closely spaced core samples can reveal cryptic, high-frequency depositional cycles and three-dimensional palaeoenvironmental information.
In Saudi Arabia, the Shu’aiba Formation is the main reservoir in the Shaybah field, and has been subdivided into a number of biofacies (ShBf-1 to ShBf-10) within four main depositional units, of which the lower unit (Sh1) is regionally extensive, moderately deep marine and of non-reservoir significance. A thicker second unit (Sh2) displays significant lateral and vertical differentiation of a rudist-rimmed shallow carbonate platform in which discrete lagoonal, rudist bank complex and fore-bank biofacies have been determined. Deep platform sediments characterize the uppermost stacked unit (Sh3) of the main buildup, and are of early Aptian age. Flank carbonates onlap the former three units and are assigned a late Aptian age (Sh4).
This fully integrated palaeontological approach to over 50 cored wells from the Shaybah Field has significantly provided a detailed stratigraphic and palaeoenvironmental interpretation that is currently being used to successfully develop this field with 14 billion barrels of crude oil and 25 trillion cubic feet of gas in place. A satisfactory sequence stratigraphic interpretation of the Shu’aiba Formation at Shaybah remains elusive, as neither detailed seismic evidence nor correlatively valuable wireline logs are available.
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Recent Developments in Applied Biostratigraphy
In recent years the application of biostratigraphy to hydrocarbon exploration and development has become increasingly important both scientifically and economically. The demand for higher stratigraphical resolution in field development studies has resulted in the utilization of new approaches. However, in under-explored areas with little reliable primary biostratigraphical data, conventional methods using relatively coarse biozonations still have relevance. The aim of this volume is to encourage an exchange of ideas and to seed new research initiatives particularly within integrated multidisciplinary teams. The papers are divided into four main themes which cover a broad range of modern applications of biostratigraphy. The first three themes are: UK North Sea field development; outcrop analogues; and international exploration and development. The final section discusses new methodologies, such as the application of correspondence analysis and multivariate correlation of wells, and palynological processing techniques applicable to the wellsite.