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
Minjur Sandstone Revisited: New Advances in Sequence Stratigraphy and Modeling in the Khashm-Al-Khalta Reference Area (Central Saudi Arabia)
(1) Water Division, BRGM, Orleans, France.
(2) Mapping, SGS, Jeddah, Saudi Arabia.
In connection with the issues of CO2 geological storage in complex reservoirs, the Minjur Sandstone, in outcrop in Central Saudi Arabia, was selected as a case study for modeling and simulating the spatial distribution of sand bodies in a fluvial-deltaic system. As a first step, detailed sedimentologic mapping, sequence stratigraphy and 3D geological modeling were performed in the area of inlet/outlet maximum activity of the deltaic system.
Compared to the reference studies by Vaslet et al.(1983) and Le Nindre et al., (1987, 1990), the vertical and lateral variations around the type section were studied in detail, and interpreted with greater accuracy in terms of depositional features and sequence stratigraphy. This new survey was specifically designed to collect 3D information for numerical modeling.
High-resolution sequence stratigraphy demonstrates nine depositional parasequences, involving four environments: sabkha, tidal, estuarine and fluvial-continental. The general trend at the formation scale is a thickening-coarsening upward trend related to increasing clastic influx and development of fluvial systems. As originally described, a maximum flooding occurs near the middle of the formation with a development of tidal mud flats and carbonate facies. The lower member is dominated by subtidal, brackish and scattered fluvial environments, while the upper member is fluvial, dominated with amalgamated sand bars.
The facies variations were analyzed on the field by vertical sedimentological measured sections, spectral gamma-ray logs, and a network of georeferenced scattered observation points. These data were mapped by using high-resolution IKONOS satellite imagery and an enhanced DTM. These investigations demonstrated that the more distal deposits of the lower Minjur include disconnected, scattered and narrow sand bars. Wide meandering point bars appear upward. Above the MFS, massive and very wide sand bars resulting of an important sediment supply exhibit a maximum vertical and horizontal connectivity with a continuity of several hundred of meters.
Using mapping, logs and field observation points, a deterministic numerical model of the sand/mud distribution was built. This outcrop analogue is currently used to test by inversion various scenarios of modeling from subsurface data only, to optimize data requirements. Further CO2 flow simulations are expected to provide conclusions on response of CO2 injection to fluvial heterogeneities in each case.