Correct Shale Volume Estimation and Clay Typing Identification in Shaly Sand Reservoirs: Case Study of Zarga Formation, Keyi oil field, Block-6, Sudan.

Abstract

The presence of potassium (K) in Zarag formations effects the total gamma measurement and there for causes an overestimation of the shale volume estimation. We introduce a powerful technique that combine the gamma ray and photo electric factor log (PEF) in order to overcome this challenge. The clay type identification is essential step to calculate an accurate effective porosity and water saturation models. As preliminary analysis steps, first density neutron cross plot investigated to verify the lithology, second spectral core logs achieved for potassium identification, thirdly a new technique applied to correct the gamma ray from the potassium effects, and finally X-ray diffraction (XRD) and multi minerals cross plots utilized to identify the formation minerals components. The reasonable shale volume estimation provided by corrected gamma ray (CGR0) method with average of 27% and density- neutron technique with average of 20%. The dominant clay type is Kaolinite with average volume of 39%, and considerable amount of Chlorite with average volume of 18%. The Quartz and K-Feldspar excited in the matrix with average volume of 22% and 21% respectively