Vertical and horizontal pressure depletion trends captured by AVA Geostatistical Inversion conditioned reservoir modeling: An example from Late Messinian lacustrine turbidities reservoirs, Nile Delta, Egypt.

Abstract

AVO and seismic inversion has been successfully applied during the exploration phase of the Late Messinian Abu Madi Formation in the central Nile Delta of Egypt. Several gas condensate discoveries were made using this technique as a Direct Hydrocarbon Indicator (DHI) and risk mitigation tool. Deterministic inversion was further employed to delineate the overall lateral extent of the field and gross reservoir character during the appraisal phase of one particular field. A comprehensive well data acquisition programme for several wells revealed a complex lateral and vertical reservoir stacking patterns with highly heterogeneous reservoir parameters. The reservoir sequence is attributed to lacustrine turbidities deposited in semi-isolated Late Messinian Basins. Informally, the Abu Madi Formation can be subdivided in to upper and lower members. Intraformational shale barriers and baffles are commonplace. The stacked reservoir sands cannot be visualised and differentiated by the existing deterministic inversion products but each sand package displays complex vertical and lateral pressure trends. This paper describes an AVA Geostatistical Inversion process integrated with rock physics modelling (using differential effective medium theorem) of the wells to generate high resolution multiple rock property models with the aim of capturing reservoir heterogeneity and the observed pressure trends. The probabilistic representations of lithology, water saturation, permeability and effective porosity captured the range of uncertainty remaining after appraisal drilling to provide equi-plausible models to further de-risk future development of the field. Flow simulation modelling is used to monitor and predict pressure depletion trends to optimise further infill drilling and effectively manage the reservoir. Introduction The Late Messinian Abu Madi Formation is a prolific producing reservoir in the Nile Delta of Egypt. The first discoveries were made from the late 1960's onwards focused along the Abu Madi Valley trend (Rizk, 2002). A number of fields were subsequently discovered within this north-south trending incised valley trend. More recently exploration focused to the west of the Abu Madi Valley trend in the central Nile Delta area. Despite near-continuous exploration from the mid-1960's the area yielded no commercial discoveries. Following a phase of extensive 3D seismic acquisition and interpretation several fields were discovered from 2007 onwards. Most discoveries have made on structurally robust traps which usually comprises some stratigraphic trapping elements (facies changes and sand pinch-out). All discoveries were supported by positive AVO responses which generally conform to the mapped structural traps.

Seismic reservoir characterization and pressure depletion of the Abu Madi Formation in the NW Khilala field, onshore Nile Delta, Egypt

“…The well data are interpreted to investigate the petrophysical parameters of the Abu Madi reservoir, which is subdivided into upper and lower Abu Madi sand intervals separated by shale layers (Abu Madi Formation is characterized by an average effective porosity of 23%, average saturation Well log correlation (Fig. 5, after Vaughan et al, 2014) shows that the UAM reservoir shales out laterally, while the LAM reservoir thins laterally. Wells shows subtle variations in the UAM Reservoir.…”

“…Most discoveries have been made on structurally controlled traps, which usually include some stratigraphic trapping elements (facies changes and sand pinch-out). All discoveries were associated with positive AVO responses, which generally followed the mapped structural traps (Vaughan et al, 2014).…”

“…The separation of sands and shales in the Vp/Vs domain allowed for accurate mapping of the intraformational shale between the Upper Abu Madi and Lower Abu Madi reservoirs and refinement of the top Abu Madi Formation flooding surface interpretation (Vaughan et al, 2014).…”