Africa / Middle East
PHASE I : SEDIMENTOLOGY
PHASE II : PETROPHYSICS
This study examines the Tertiary clastic sequence from the Niger Delta Basin containing sediments generally described as an upward and updip (south-to-north) transition from marine deep water and pro-delta sediments (Akata Formation), through alternating sand/shale paralic deposits (Agbada Formation), to continental deposits (Benin Formation) [Ejedawe, et al., 1984]. Production thus far has been principally from the Agbada Formation, which is at least 3,000 m thick. It is an alternating sequence of sands, silts and clays deposited principally in delta-front, tidal/estuarine, distributary channel, and delta-plain environments. Reservoir quality has been shown to be related to depositional environment (in association with lithology and geometry) and burial depth. The underlying and interbedded Akata Formation, which is reportedly up to 7,000 m thick, includes clays, silts and sands deposited in deeper water environments by slump/slide/debris flow, bottom current, turbidity current, and pelagic/hemipelagic processes, also locally exhibits reservoir potential (Shanmugam et al., 1995). The overlying and interfingering Benin Formation is composed of fluviatile sands and conglomerates, with local coaly deposits; and is about 2,000 m thick (Weber and Daukoru, 1975). The Benin Formation locally contains (heavy) oil and gas stringers, where the oil-bearing sands are associated with coal (Avbovbo and Ogbe, 1978).
The sedimentological study, "Phase I: Sedimentology", was completed by Core Laboratories in 1996. "Phase II: Petrophysics", is the second phase of the sedimentological study that characterizes the reservoir properties of the Tertiary Niger Delta reservoirs. The reservoir quality of each lithofacies will be determined by analysis of petrophysical properties. Results of the study together with the Phase I report results will be integrated to characterize hydraulic flow units and enhance reservoir modeling program. Phase II was completed in June 1999.
This reservoir study includes regional coverage of all of the lithofacies occurring in the Tertiary reservoirs of the Niger Delta region. More than 6,300 feet of conventional core from wells listed in Table 1, from both onshore and offshore areas have been described in detail. Each lithofacies has been sampled for petrographic, mineralogical, and grain size analysis. Lithofacies sequences were identified as an aid in interpreting depositional environment. In addition, a photographic atlas has been produced that exhibits the lithofacies present throughout the region, with their characteristics.
The primary study objectives of Phase I are as follows:
Other objectives include the identification of certain formation damage problems, such as fines migration, clay swelling, water sensitivity, and sanding that are related to the studied lithofacies. Sequence stratigraphy will be applied to a limited degree to the studied cores to fit them into the regional stratigraphic framework.
The primary study objectives of Phase II are to:
A secondary objective of the study is to compare porosity-permeability measurements made during this study with those measured immediately following coring to examine the possibility of core-shed diagenesis.
PRESENTATION OF RESULTS:
Both Phase I and II are now available in HTML formats.
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