Evaluation of laminated shaly sand sequences in Ahwaz oil field using (via) high-resolution square logs

Abstract

Thinly bedded and laminated shale-sand sequences are very common in most of the producing formations in Iran. Historically, traditionally well logging methods such as conventional resistivity measurement is employed to evaluate pay intervals in order to extract information about hydrocarbon saturation. However, there is the practical matter of resolution of these methods to detect thin laminated shaly sand layers. In order to cope with this limitation, other technique such as: highresolution method should be utilized. For doing this method, we receive low-resolution logs and a high-resolution log from a well logging tool that is disposed in a wellbore which has laminated shaly sand layers. Firstly, square log is produced then these logs are convolved with vertical response function of well logging tools to generate constructed log. The constructed logs are compared with low-resolution logs, if these two logs are matched we choose that square logs as optimum square logs and analyze them. But if these two logs do not match, the square logs undergo interactive refinement then these refined logs are subsequently convolved with a vertical response function of the well logging tool thereby producing a constructed log. Then these constructed logs compare with low-resolution logs. This work repeated until these logs are matched and the optimum square logs are chosen. High-resolution square log method is an iterative method, time consuming and also has very mathematical calculations because we developed a computer program with MATLAB software which can do all these works with high accuracy and low time. Keywords Laminated shaly sand (LSS) • Conventional log • Petrophysical analysis • High-resolution square log method • Convolution • MATLAB software Abbreviations LSS Laminated shaly sand LSSA Laminated shaly sand analysis RHOB Compensated gamma-gamma density average [g/cm 3 ] CGR Compensated gamma-ray [API] NPHI Neutron porosity hydrogen index GUI Graphical user interface NISOC National Iranian South Oil Company