Formation Water and Residual Gas Analysis of Some Reservoirs in the Deep-Water Offshore Mozambique: Insights on Burial History and Field Compartmentalization

Abstract

The deep-water block of interest is located in the offshore Mozambique and hosts huge volumes of natural gas in place, distributed in several Paleogenic reservoir units. The high quality subsurface dataset acquired in the area is key for the interpretation of the geologic evolution of the reservoir units. This work aims at integrating seismic, log, core and fluid data for contributing to the understanding of the burial history of the reservoir deposits in the area. The activity focuses on the evaluation of the aquifer connectivity between the various penetrated reservoirs, on the validation of the presence of a paleo-contact in one of the reservoir units, and on the implications of burial and compartmentalization on rock matrix-pore system chemistry. The study is presented with special emphasis on the formation water analysis and its integration with other subsurface data. Water saturation and pressure data, combined with the AVO analysis of anisotropic PSDM seismic volumes, support the presence of a paleo-contact in at least one of the reservoir units. A link is suggested between the timing of the hydrocarbon trapping, the paleo-contact evolution and the fault activity in the area, from the analysis of seismic, log and pressure data. The tectonic framework and some field compartmentalization are evident on seismic and pressure data and find some positive correlation with the rock matrix-pore system mineralogical and chemical data. The assessment of the low salinity formation water sampled in the wells allows to identify trends of formation water chemical composition with burial and its relation with rock matrix mineralogy from bottom-hole core data. Water sample chemical values plotting outside the general trends correspond indeed to isolated fault blocks. Notwithstanding the significant uncertainties related to the limited representativeness of the available subsurface data and to the limited understanding of some of the involved geological processes, the study provides a positive contribution to the reservoir characterization in the area in terms of hydrocarbon migration, reservoir compartmentalization and rock burial history.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018