A COMPUTER PROGRAM FOR THOMAS-STIEBER ANALYSIS OF SHALY SAND BEDS

Abstract

Thin shaly sand beds are capable of yielding a reasonable amount of hydrocarbon if discovered and evaluated. Regrettably, most thin beds are usually bypassed if direct log interpretation techniques are applied in their evaluation due to their low vertical resolutions and ability to only characterize an average of multiple beds which often result to a significant under estimation of oil and gas in the sedimentary unit. The main goal of this thesis is to give a better and less uncertain estimate of sand fraction and porosity in a challenging shaly sand reservoir. In the present work, this is accomplished through study of Gamma ray log based on the methods suggested by Thomas — Stieber. The Thomas — Stieber approach for thin bed analysis is reviewed and discussed. An example is used to demonstrate the usefulness of the method for evaluating the porosity of sand beds and net sand thickness containing laminated and or/dispersed shale using synthetic data. The Thomas Stieber equations considering different shale distribution types viz, dispersed, laminated, structural and their combination, for sand-shale sequence has been employed in calculating. parameters such as total porosity, sand porosity, shale and shale fraction. A computer program based on the published literature has been developed in MATLAB to generate a set of modelled squared logs for gamma ray, sand fraction curve and total porosity curve. These curves have been employed to estimate different properties of shaly sand sequences.