Characterization of Fractured Basement Reservoir, Melut Basin, Southeast Sudan

Yassin, Mohamed A.; Hariri, Mustafa M.; Abdullatif, Osman M.; Makkawi, Mohammad H.

Basement reservoirs can be of different types; fractured granitic, fractured quartzite, and/ or fractured Schist and Gneiss. In the fractured basement reservoirs, hydrocarbon is entrapped within the fractures network within the basement rocks. Porosity and permeability in basement reservoirs is controlled by the fractures and not by the rocks matrix as in the conventional reservoirs. Hydrocarbon hosted fractured basement reservoir was reported in many locations in Sudan since 2007 and the Melut basin is one of those areas. This study aimed at characterization of the fractures system within the basement reservoir in Ruman area, Melut basin to understand their nature, distribution and possible origin. To achieve this goal fractures, faults and lineaments were studied in different scales and in both surface and subsurface levels. Information utilized in this study includes; well- log data, gravity, 3-D seismic data and satellite images. Compatible and parallel NW-SE, NNW-SSE to N-S, WNW- ESE to E-W and NE-SW trends were observed from the interpreted data of satellite images, gravity, wells and seismic data. This trends compatibility is evident from Rose-Diagrams generated for the faults detected from seismic data and fractures observed from the FMI-log (for five wells). The same trends can also be noticed in the gravity data and lineaments determined from satellite images.

Three stages model were suggested for the origin of those fractures associated with the basement and hosting hydrocarbon. The early formed fractures are developed during the emplacement and cooling of the igneous pluton. The second stage fractures are related to the regional Proterozoic tectonic events and the third stage fractures are associated with the formation of the Mesozoic faults which were devolved during Melut basin rifting and mostly parallel to the faults. This major fault might also act as a conduit for hydrocarbon migration from the sedimentary sequences to the fractured basement.

This study delineated the possible origins of the fractures systems hosting hydrocarbon in the basement rocks. Additionally, the study characterized and defined the possible trends of those fractures and how are they related to different origin. The study outcomes and methodology can be utilized as a guide for hydrocarbon exploration and development in Melut rift area and other areas of similar geological and structural settings.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013