No abstract

This paper details a study that was completed at the end of 1999 to investigate the suitability of using existing, high quality, conventionally processed 3D seismic data (hereafter 3D data) to replace specifically commissioned 2D seismic site survey data (hereafter 2D site data). For this study, three wells from an existing dataset of six in the West Delta Deep Marine Concession, offshore Egypt (WDDM) were investigated. A prescriptive workflow was developed using the 3D data and the results compared to those obtained from a conventional previously commissioned 2D digital site survey dataset. For this dataset from WDDM, the results obtained from the 3D data and the 2D data were similar, the main difference being that more numerous, smaller probable hazards were prognosed by the 3D data. After undertaking this investigation and following an independent review of the results, a recommendation was made to operate the 2000 WDDM drilling campaign using hazard prognosis from the conventional 3D data, i.e. not to acquire well-specific, new digital site surveys. This recommendation was followed and five exploration wells were drilled in 2000 with no specific, digital site survey data being acquired. No safety, operational or environmental implications were encountered as a result of this replacement and significant operational savings accrued to the operating partnership.

This paper documents a study that used high quality, conventionally processed, speculative 3D seismic data for two specific purposes: first, to identify and avoid any health, safety, security and environmental (HSSE) issues regarding the water bottom and, secondly, to avoid shallow (<1 s below the mud line) geohazards when drilling the wells. The study integrated existing legacy well data, new 3D data from the BM-S-52 concession and a targeted programme of water-bottom grab samples from the BM-S-52 concession, Santos Basin, offshore Brazil. Two aspects of the analysis are described: the first addresses the problem and solution adopted for characterizing the water-bottom environment in this area; the second addresses the interpretation of the data for shallow geohazards. The results of this case study have been accepted by the regulatory authorities as representing sufficient evidence of risk evaluation that no further dedicated site-survey data acquisition is required. This has led to savings in time and in costs which would otherwise have been expended on deep-water site-survey campaigns. Furthermore, the use of 3D seismic data for well-location planning brings benefits in improved imaging of the near-mud-line geology, full coverage over the whole concession, operational flexibility for changing well location and timely availability of data. The analysis workflow may also be applicable in other, similar deep-water areas.

Slope channels are increasingly being recognised as highly prospective deep water exploration targets . An extensive dope channel system is exceptionally well developed in the West Delta Deep Marine Concession, offshore Nile Delta, operated since 1995 by BG with partner Edison . Withm the concession the Scarab, Saffron, Simian, and Channel 12 & 13 systems have all recently been successfully tested by a number of exploration Wells (Figure 1) . When gas-charged these Upper Pliocene E[ Wastani Formation channels are spectacularly imaged by 3D seismic, both in time sections and through a variety of amplitude extractions . Remarkable variations are revealed in their stratigraphic architecture, with changes apparent both withm individual channels and between the different channel systems .A variety of trap types are evident . The majority of the channels exhibit well developed flatspots to the north where dip-closure is evident . Up-dip closure varies between dip, fault and perched contacts . Typically, the shale-dominated channel margins provide the lateral seals . Gas trapeed witkin the structures is derived from a mixture of biogenie and thermogenic activity .An extensive program of core and wireline log acquisition and analysis kas enabled high resolution definition of the channel-fill sediments and their depositional geometries . The channels veere initiated by the introduction of coarse sediments to the shelf edge possibly at times of relative sea-level faal . Gravity transport of this material down-dope either initially caused slumping or followed the love topography of pre-existing slump stars . In some channels there was significant erosion in areas up depositional dip prior to infill/backiill from love and high-density turbidites, debris flows, slumps and slides . Subsequent channel evolution varies from backfilling, plugging by slumping to re-incision .Tere is an excellent match between the seismic expression of the channels and their fill and a channel model kas been developed based on integration of the well and seismic data . The model reveals significant variations in the architecture and likely production characteristics of the channels . Internat connectivity is promoted by the thin-bedded turbidite, laminated and levee facies . Detailed examination of the seismic data also reveals insights into the smaller state channel depositional architecturen and a vide variety of channel types have been identified . Some elements of the channels are characterised by near-vertical aggradational stacking of nested channels . In other channels the sands are laterally extensive and display welt developed accretion surfaces .

No abstract