Characterization of shale pore structure by successive pretreatments and its significance

Abstract Organic matter (OM) or hydrocarbons occur in shales in different forms, and occurrence forms closely relate to pores and surfaces. Therefore, establishing the complex relationships among hydrocarbons or OM, pores and surfaces is highly necessary and requires stepwise removal of OM or hydrocarbon with different occurrence forms to obtain the pore structure progressively but with minimal effects on the mineral compositions and rock framework. In this paper, 11 organic rich shales and 3 organic lean shales from Dongying Sag were successively treated with Dichloromethane (CH2Cl2) and Sodium Hypochlorite (NaOCl), and raw, extracted and oxidized shales were analyzed by XRD, Rock-Eval VI pyrolysis, N2 adsorption and mercury intrusion porosimetry. Results show that there were minimal changes of mineral compositions, OM or hydrocarbon characteristics and pore structure of organic lean shales during pretreatments, indicating that pretreatments have minimal destruction on minerals. However, OM or hydrocarbon characteristics and pore structure of organic rich shales changed progressively, while there are minimal changes of mineral compositions, indicating that pretreatments can separate OM or hydrocarbon occur with different forms but also maintain the original mineral compositions and “recover” the original pore structure of organic rich shales. This research: (1) Demonstrates the necessity of pretreatment before pore structure detection, and recovers the original pore structure of shales abundant in OM. (2) Illustrate the complex relationships among OM or hydrocarbons, pores and surfaces. Analysis of these complex relationships will benefit shale oil potential evaluation.