Reservoir Quality and Rock Properties Modeling Results—Jurassic and Triassic Sandstones: Greater Shearwater High Pressure/High Temperature (HPHT) Area, United Kingdom Central North Sea

Thomas R. Taylor¹, Mark G. Kittridge¹, Linda M. Bonnell², and Peter Winefield^3
1 Shell International E&P Inc. - Technology Applications & Research, Houston, TX
² GEOCOSM, Austin,
³ Shell International E&P - Technology Development & Research, Houston, TX

The complex burial and diagenetic histories of the Jurassic Fulmar and Triassic Skagerrak sandstones in the UK Central North Sea present significant challenges with regards to reservoir quality prediction. Commercial reservoir quality is retained despite deep burial and associated high temperatures and pressures. Shallow marine Fulmar sands are normally compacted (mean IGV = 27±3%) yet have porosities of 25 – 33%. Porosity was a) preserved through inhibition of quartz cementation by clay and microquartz coatings, and b) enhanced by dissolution of feldspar grains (~ 5%). Skagerrak fluvial sands are more compacted (mean IGV = 23±2%), exhibit minor feldspar dissolution (<1%), and have porosities of 17 – 22%. Quartz cement averages only 2±1.5% due to robust chlorite coats that cover 80% (±13%) of quartz surfaces. The diagenetic forward modeling program Touchstone simulates porosity loss due to compaction and quartz cementation. Quantitative petrographic analyses and burial history data were used to calibrate Touchstone model parameters. The results, coupled with basin modeling were applied to deeper prospects for pre-drill prediction of porosity and permeability. In parallel, petrophysical data were used to develop elastic properties amenable to quantitative seismic forward modeling. Experimental data and core-calibrated petrophysical results, reflecting variable in situ fluids and saturations, were used to build an elastic properties model. The model is robust and was used to generate fluid-filled sandstone properties, incorporating Touchstone results, for prospect-specific seismic attribute modeling. Well results from two recent exploration wells are in very good agreement with pre-drill Touchstone and elastic properties model predictions.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005