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
Understanding and Managing Water Advance in a Heterogeneous Carbonate Reservoir: from Integrated Subsurface Approach
(1) ADCO, Abu Dhabi, United Arab Emirates.
Rapid and uneven water advance is observed in heterogeneous platform-interior carbonate reservoirs in the south of a super-giant Middle East Field, producing since the early 1960s. Crestal oil production is supported through peripheral water injectors typically 5-7km from the producing area. Historical production imbalance has accentuated water movement in the south of the field, with wells ceasing to flow naturally even with relatively low water cut.
A multidisciplinary approach has been used to understand controls on water encroachment. This involved integration of geology (core facies, correlation, reservoir properties), geophysics (seismic attributes, fault / fracture characterization), petrophysics (openhole & time-lapse cased hole logs) and reservoir engineering data (simulation 
models
, production / injection).
Water advance is focused in certain areas of the field, and within limited stratigraphic layers. In particular, two prominent ‘water fingers’ are present within most reservoir units at the limit between the platform interior and thick prograding platform margin belt.
Stratigraphic water fingering is controlled mainly by vertical variations in reservoir quality, particularly permeability within the 5 main Reservoir Units (named 1 - 5 from bottom to top). Water advance is less rapid in the lower two and the uppermost Reservoir Units (1, 2 and 5) which show interbedded stylolitic dense layers and lower matrix permeability (typically 1-10md). Within Units 3 and 4, water movement is more advanced and initially concentrated along super-high (darcy scale) permeability layers a few feet thick. Sequence stratigraphic analysis calibrated with core confirms that such layers are associated with 3rd & 4th Order sequence boundaries, with partial cementation but preserving vuggy porosity. Within Units 3 and 4, poorer reservoir quality facies (more cemented, coral-rich in Unit 3) and non-reservoir carbonate mudstones (within Unit 4) act as isolated local baffles to horizontal
water movement.
Controls on the location of the two prominent areal water fingers include faulting / fracturing, stratigraphic contrast between the platform margin and interior, and production / injection imbalance. An improved understanding of water movement is being used to predict future water breakthrough, refine infill drilling locations, plan future Artificial Lift requirements, design selective well completions and optimize field development.