--> A Pore Pressure Model In A Centrifugal Hydrodynamic Paleocene Basin.

AAPG Asia Pacific Region GTW, Pore Pressure & Geomechanics: From Exploration to Abandonment

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A Pore Pressure Model In A Centrifugal Hydrodynamic Paleocene Basin.

Abstract

The Caspian basin is known for its remarkable high sedimentation rate (~1500m/MA). In this area, they are fluvio-lacustrine sediments of the Paleo-Volga deltas which filled the rapidly subsiding South Caspian basin. The high sedimentation favored the generation of overpressure. The large area covered by the productive series and their good lateral connectivity triggered centrifugal hydrodynamics (Grosjean et al, 2009) within the reservoirs as soon as they outcrop at the basin edges. Following non-economic drilling results on the southern flank of the Absheron anticline tested by well ABX-1A in 2001 and evidence for a regional hydrodynamic regime in the nearby Shah Deniz structure (SDX-4, 30 km to the west) led to the re-evaluation of the Absheron block. The consequently drilled well ABX-2, located off the crest of the structure, discovered a large gas accumulation in 2011 and emphasized the importance of hydrodynamic trapping in the area Two exploration wells were drilled on Absheron structure: - ABX-1 located on the southern part of the structure, water bearing. - ABX-2 located on the northern part of the structure which encountered gas bearing Balakhany and Fasila reservoirs. The Productive Series are of Pliocene age (Balakhany and Fasila) and are found between 5000 and 7000m depth in the Absheron area. In these reservoirs, the relationship exists between the fluid content of a reservoir and its pressure. If the reservoirs are gas bearing, they are almost fully drained. If water bearing, the reservoir is in equilibrium or close to the shale pressure. The main uncertainty was for the overburden. The first approach on this 4-way structure was based on the hypothesis of reservoir pressure equal to shale pressure within the overburden. The revised understanding is based on a pressure transfer hypothesis. It’s very likely that these sand layers have lateral continuity down dip and have pressures higher than the surrounding shale pressure resulting from the water balance effect due to their dipping nature. This study, based on the revision of well post mortems, shows a review of a pore pressure model in a geological context of hydrodynamism.