Determining shale organic porosity and total organic carbon by combining spin echo, solid echo and magic echo

Abstract

Organic matter in shale is very important for shale evaluation. However, current methods for evaluating the structure and porosity of organic matter are time consuming and expensive. Previous low-field NMR work using magic-echo methods provided relationships between magic echo T1−T2 data and total organic carbon (TOC) of shales using partial least-squares regression (PLSR), but uncertainty in estimation of organic pores indicated further study was required. The magic echo and solid echo measurements produce additional signal in the oil shale samples compared to the standard methodologies. The difference between these signals is mainly caused by the homonuclear dipolar coupling in the organic matter; therefore, it implies the content of the organic matter. Compared to the spin echo method, the solid echo and magic echo measurements are able to access additional information of the quantity and porosity of the organic matter in shale samples. Based on this, we suggest a new method using the amplitude of magic echo, solid echo and spin echo to obtain information about quantity and porosity of the organic matter in oil shale samples. The results demonstrate the feasibility of the new method for organic matter estimation.