Integrated Analysis of Borehole and Surface Seismic Data to Resolve Seismic Uncertainties in the Gulf Of Suez
Authors: El-Hateel Mohamed S , Ahmad Parvez , A Ismail Ahmed Hesham , Henaish Islam A M , Ashraf Ahmed 
Published: May 2016

Seismic imaging in the Gulf of Suez is severely affected by salt plays, strong multiple contamination and raypath distortion etc. Consequently, geophysicists face challenges while interpreting the existing surface seismic and planning new wells, both in time as well as depth domain, and encounter surpirses while drilling. Borehole seismic is commonly used to address some of the seismic issues, which could also result in big uncertainties if not planned properly in challenging environment.

In this paper, we present case studies from two areas in the Gulf of Suez where borehole seismic surveys were conducted in different configurations in wellbores with different geometries. Logging programs were defined after pre-survey ray trace modeling simulating different scenarios and careful planning considering the operational and geological challenges and logistics. Full waveform processing of well data resulted in much higher resolution 1D to 2D images in time and depth. Borehole seismic images were integrated with the existing surface seismic. In the first area, integrated analysis helped in horizon and structural interpretation revealing features not seen on low resolution surface seismic time and depth cubes. Seismic uncertainties for shallow as well as deep targets were resolved and fault interpretation was refined. Additionally, integrated analysis helped to detect new faults successfully, indicating new promising area for future development drilling. In the second area, integrated analysis confirmed presence of multiples in the surface seismic resulting in the target horizon deeper than expected, which was interpreted shallower all over the area. Analysis also confirmed change in the depositional environment in the area indicating a new block to be studied and estimated.

Introduction

In this paper, we present case studies from Ras Fanar (Gulf of Suez West Concession) and Ras Budran (Gulf of Suez East Concessions) fields in the Gulf of Suez Offshore, Figure 1. Both oilfields were discovered in 1978 and are operated by Suez Oil Company, joint venture of RWE Dea and Egypt General Petroleum Corporation (EGPC). Surface seismic data in the Gulf of Suez is affected by strong contamination by multiples, weak subsalt reflection strength, and strong raypath distortion (Domenico, 1977 and Lewis et al, 1995), and is of low resolution typically. Therefore, existing conventional surface seismic in these fields is no exception making the interpreter's job difficult. Both explorationists and reservoir characterization specialists have identified the importance of borehole seismic or commonly known as Vertical Seismic Profiling or VSP (Hardage, 1985) over the years as aid to the above. Suez Oil Company also conducted standard zero offset (source position at some distance from the well) Checkshots or VSPs to address a few of these challenges in the area, but the problem remained unsolved since most of the wells drilled are deviated from a single platform. Even the time-depth relationship could be inaccurate in such complex subsurface environment. The problem is more serious due to severe ray paths bending and oblique incident angles when the well deviation increases, which is very common in the current drilling campaign. It can be addressed by acquiring data in appropriate survey configuration in different well geometries after pre-survey modeling and proper planning. Integrated approach can further help in data interpretation and resolve seismic uncertainties.