Abstract
The Nubian Sandston Group is one of the most important oil bearing formation in Sirt Basin Abadi [1]. The group is comprised of non-marine sediments of Lower Cretaceous age and is the subdivided into three formations; Lower Nubian Sandston, Upper Nubian Sandstone and Varicoloured Shale separating two sandstones, Locally the Lower Nubian Sandstone is subdivided in to upper pool, separated by the middle shale. Identify the rock lithology has important meaning for estimating the reserve of petroleum as reservoir capacity and storage ability. The lithology identification from well log based on not conventional cross plot proposed and studied, which is easier instead of rock core data observation results. However, this work carried out comparison between chart and analytical solution of matrix parameter (ρma and ΔTma) estimation values of producer shaly sand reservoir, and present the main depositional environment affects. In addition to influences of pyrite, ferruginous encrustations, organic material throughout this studied reservoir Ben Ghawar BM [2]. Consequently, variety of matrix parameters values is contributed by clay minerals present in this reservoir type. This study based on wire line data measured over than 872AT Q2 with an 646 feet produced Upper Nubian Sandstone belong to three oil fields, E Sirt Basin. This shaly reservoir divided into three main units (V59, 97II and OO82), from bottom to top according to depositional and petrophysical properties. The available cores (cut in the lower Nubian sandstone formation) of some wells drilled in 3v59 structure are analysed according to their sedimentology, petrology and diagenetic products Analysis are correlated with the results obtained from wire-line log interpretation. Analysis of these logs based on different cross plots results, with the support of petrographic and digenetic investigation, allows analysis of the mineralogical commotion, particular clay minerals, and estimation of the depositional environment. Petrography examination shows that the sands are mineralogically and texturally mature. Digenetic processes resulted in different cements of illite and chlorite. Confirmation of mineralogical identification and estimation of depositional enlivenments using different cross-plots of data derived from wire-line log analysis are fair to medium coarse sands. These values reflect quartz/kaolinite composition the latter and presence of iron carbonates (e.g. siderite and/or ankerite) and pyrite in the former. These characterize are confirmed by cross plots of ROME (MATRIX DENSITY) versus UMA (absorption cross section of matrix). Potting of PEF (photoelectrical absorption index) against log TK/K and confirm kaolinite as the most common clay mineral. Various cross plots obtained from analysis of spectral gamma-ray logs show that the sandstone is characterized by abundant thorium, minor amounts of potassium and locally uranium, interpreted as indicating fluvial continental environment. Higher amounts of potassium and the middle shale define a lacustrine environment