Petrophysical Evaluation and Reservoir Heterogeneities and Their Impact on the Water Movements. Case Study: Abu Madi - El Qar'a Gas Field, Nile Delta, Egypt

Abu Madi Formation of Abu Madi-El Qar’a gas field constitutes the main gas producing horizons in
the onshore north Delta Basin, since 1975. The facies complexity of the reservoirs is the main controlling
factor for the irregular and differential water movements. The results of interpretation of the available
subsurface geological, geophysical and borehole data have been integrated in the form of petrographical,
mineralogical, sedimentological and petrophysical studies to delineate the lithofacies, lithostratigraphy,
depositional environments, structure and geometry of Abu Madi reservoirs in the study field.
Abu Madi Formation has been distinguished into a number of sand levels, named: Level III, III-A, II
and I, where Levels II and III are the main pay zones in the study field. The optical microscopic
examination indicates that these levels are partially of the same mineralogical composition. Meanwhile,
the analyzed core samples showed anisotropic permeability with horizontal permeability values greater
than vertical permeability (Cafiero, 1994).
In some sandstone levels, the permeability curves showed severe drop in the permeability values, with
a remarkable reduction in porosity, sometimes, accompanied by slight increase in GR readings.
The sequence stratigraphy indicates that Abu Madi Formation; down cutting the Qawasim Formation
and filled by braided alluvial deposits in its lower part (Level III), followed up section by Level III-A,
which is estuarine to embayment sediments. Based on the characteristics of wireline logs, Level III is
subdivided into three subdivisions, Lower, Middle and Upper units. The Lower and Middle units represent
a channel fill phase while the upper unit is heterogeneous with rapid lateral facies change producing a
poor lateral continuity (Alfy, 1992).
The stratigraphical and structural interpretations of the reflection seismic data indicate that the Sidi
Salem and Qawasim formations are the sedimentation base of Abu Madi reservoir. Faulted and tilted
blocks of the Qawasim and Sidi Salem formations gave rise to the irregular paleorelief, on which Abu
Madi Formation deposited under a fluvial environment with tidal and marine-marginal influx (Sarha,
1994).
The dipmeter data helped to identify the significant textural and structural features and to identify the
bed boundaries of Abu Madi levels. A number of isoparametric maps and cross sections have been
constructed, throw light on the early unexpected water production and the rapid differential rises of the gas
water contacts and their relationship with the reservoir heterogeneity in the studied field. However,
recommendations concerning the problems of water advancement through Abu Madi reservoirs are given.