Title : Depositional environment characterization and petrophysical analysis of PUC (B) sand reservoir, area 90 East Sirt Basin-Libya
Abstract:
The objective of this paper is to interpret the depositional enviroments of the main reservoir intervals PUC(B)sandstone, in order to evaluate the dry well A2-90. The area of study located in northeastern part of sirt basin, eastern Libya. Henceforth, there are five wells have been selected from study the area, these are the A1-90, A2-90 B1- 90, C1-90, and D1- 90. In addition, to determine different types of facies in the PUC (B) reservoirs sedimentological description for 263 feet of cores have been carried out. Matching cores to log motifs have been carried out to verify lithofacies identified. Stratigraphic cross sections, 3-D cross section window to correlate the reservoir lithofacies. Isopach maps to show the facies distribution and their trends. Based on cores sequences examination integrated with GR log motif analysis of the PUC (B) sand reservoir indicting a fluvial depositional environment based on thick blocky clean sandstone associated with thick trough cross beeded at the base of channel and laminated sets at top.
More over fining upward dirtying trend bell shape Gamma ray integrated with cross-bedded both planner and trough types including bedsets of unidirectional lamina sets also overbank or levee are shown as horizons light gray heterolithic horizon of silts and shales. The fluvial was dominated during Pre-Upper Cretaceous time. The stratigraphic cross-section, which has been made between the studied wells, has subdivided into braided system in the lower part graduates up in to meandering stream in the upper part depending on GR log correlation. The Braided system thickness vary between (410-620ft), and subdivided into five channels, they show highest thickness in south to southeast direction according to thickness maps.
The characteristics features of the braided channel is shown by the boxer trend, cylindrical log shape of thick clean sandstone with thick cross-bedded. The meandering system thickness vary between (180–220ft) and subdivided into two channels. The channels are consisting of small sets of sandstones, take dirtying trend bell shape gamma ray, fining upward cycle of deposition. Dry hole analysis for the well A2-90 was based on correlation of petrophysical analysis of PUC (B) sandstone reservoir with the nearest oil well A1-90. Facies changes, poor reservoir quality, decreased porosity and high content of shale are the causes of dry well A2-90.
