BALAKHANY SAND HIGH-RESOLUTION SEISMIC INTERPRETATION OVER DEEP WATER GUNASHLI AND CHIRAG AREAS
(Provisional abstract pending approval from AIOC partners)

N. Sadigova¹, A. Narimanov¹, J. Howie^2
1 State Oil Company of Azerbaijan Republic, 73, Neftchilar Ave., Az 1004, Baku, Azerbaijan
² BP Exploration, Chertsey Road, Sunbury in Thames, Middlesex, TW16 7LN, United Kingdom

The ACG Oil Field is situated to the SE of Baku, offshore Azerbaijan in water depths of between 60m and 280m. The ACG megastructure is comprised of four linked culminations, which are, from west to east Shallow Water Gunashli, Deep Water Gunashli, Chirag and Azeri fields. The development of ACG is progressively stepping eastwards into deeper water. The trap, which forms the giant ACG Field, is a WNW-ESE trending, steeply dipping thrusted anticline. Within structural closure there are a number of crestal faults oriented along strike as well as mud volcanoes of varying size, which complicate the structural geometry. The main ACG reservoirs were deposited in a range of environments associated with a large river-dominated lacustrine delta. Pereriv reservoirs are laterally extensive and vary little in thickness reflecting sand-rich depositional systems and low relief palaeo-topography. Laterally persistent lacustrine shales separate the Pereriv into five distinct reservoirs and record the interplay between lacustrine expansion across a low-relief floodplain and fluvial deposition. The Pereriv and Balakhany sediments record sand-prone and shale-prone stacking patterns associated with alternation between more proximal and distal environments of deposition.

The Balakhany X and VIII intervals have significantly greater development and production potential than the Balakhany IX and VII. Detailed study of the stratigraphic spatial distribution of these sands is very important to enhance the understanding of the hydrocarbon presence within them. There remain significant uncertainties in identifying the lateral distribution of Balakhany VIII sands at the crest of Chirag and Balakhany VII sands through the Deep Water Guneshli and Chirag areas. These uncertainties are primarily caused by a truncated rock property volume at the upper levels of Balakhany interval.

The Balakhany Sand High-resolution Seismic Identification Project was carried out to improve the visualization and understanding of the sand depositional architecture. This included sand body size and shape, the location and connectivity of the Balakhany intervals across the ACG field. The primary objective was to identify individual or amalgamated sand bodies within the Balakhany X, IX, VIII and VII intervals across the DWG and Chirag fields based on the current available 3D seismic dataset (2001).

The sand body geometries were not identified through conventional lithostratigraphic or chronostartigraphic event mapping. They were identified directly from a lithology (Vshale) volume. This volume was generated with the Hampson-Russell EMERGE software, which inverts the data derived from direct ties to several of the best quality well data.

A striking observation from this work is the overall northwest-southeast depositional trend seen at the all Balakhany horizons, however it is recognised that there is a subordinate north-south trend.

Balakhany X sand bodies appear to be a combination of bars and channels. The sand bodies that observed in the Deep Water Guneshli area could be well connected to each other although this is not proven. Balakhany VIII sand body areas are more extensive in comparison with Balakhany X sands. The Balakhany IX interval has a higher value of Vsh than Balakhany VIII and X and therefore contains significantly less sand than the other Balakhany intervals. The Balakhany IX interval is dominated by channel-like sand geometries.

A large Balakhany VII sand body is present at the south flank of Deep Water Guneshli, but it remains questionable as to how many individual bodies are at this interval.

From the work completed to date, it is concluded that mapping individual and amalgamated sand bodies using Vshale volume does identify target areas for development and an understanding on sand body size, distribution and possible connectivity.