Print this pageAAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
Prediction of Unayzah Reservoir Quality Ahead-of-the-Bit
(1) Saudi Arabian Oil Company, Dhahran, Saudi Arabia.
(2) Commonwealth Scientific and Industrial Research Organization, Perth, WA, Australia.
Recent research at Saudi Aramco have examined the feasibility of predicting areas of good reservoir quality - “sweet spots” - in the Permo-Carboniferous Unayzah reservoir away from areas of well control using stratigraphic forward modeling. The Unayzah Group reservoir interval was deposited above the Hercynian Unconformity over a 56 Ma. time period during the upper Carboniferous to lower Permian in central and eastern Saudi Arabia, and consists of a succession of sandstones and siltstones that reflect changing climatic conditions, from glacial and peri-glacial conditions in the lower Unayzah (Unayzah-C and lower -B), to fluvial, lacustrine and ultimately eolian conditions in the upper Unayzah (upper Unayzah-B and -A). Stratigraphic Forward Modeling has been applied to predict the distribution of facies, grain size, porosity, and reservoir architecture in this diverse suite of rocks. Initial conditions and paleotopography were established above the Hercynian Unconformity, with sediment erosion, transport, and deposition modeled along this surface; lower Unayzah (especially the Unayzah-C) sediments were modeled as the products of fluvial depositional systems intercalated with repeated glacial advances and retreats. Modern analogues for this interval include glacial outwash plains in front of retreating glaciers in Iceland and Argentina. Middle Unayzah sediments were modeled as predominantly fluvial and lacustrine systems that arose during glacial retreat and collapse, while upper Unayzah sediments were modeled as the result of primarily eolian deposition. Modern analogues for upper Unayzah eolian sedimentation occur in modern-day Saudi Arabia. Model results correspond to observed sedimentary facies and initial reservoir quality in cores and logs, and with stratal geometries defined to the limit of seismic resolution. Results from this research will be used in conjunction with diagenetic modeling in Saudi Aramco’s on-going reservoir quality prediction effort to develop better pre-drill risk estimates for exploration efforts in this interval.