Occurrence and Its Implications of Organic Matter Bound in Interlayer of Montmorillonite in Source Rocks

Jingong Cai¹, Yujin Bao², Longfei Lu¹, Jinli Xu², and Deshun Zheng^1
1State Key Laboratory of Marine Geology, Tongji University, Shanghai, China
²Institute of Earth Sciences, Shengli Oil Company, Dongying, China

To discuss characteristics of combination between organic matter and interlayer of montmorillonite mineral, we study an organo-clay complexes, less than 2 nanometer, extracted from crushed source rocks in depth 1000-3500m, Shahejie Formation, Oligocene, Jiyang sag, east China. The complexes is mainly composed of interstratified illite-smectite(I-S) and illite minerals, and has higher content of TOC and chloroform “A”. The diffraction peak (d001) of complexes is 1.3-1.4nm at 250 centigrade degree, and move to 1.0nm until heating to 550 centigrade degree in XRD curves. While the complexes was treated by H₂O₂ and chloroform and then heated from 250 centigrade degree to 550 centigrade degree, it is similar to that of untreated in XRD curves, suggesting there is organic matter in interlayer of montmorillonite with higher stability. The exothermic peaks with extraordinary stable occur at 350 centigrade degree in DTA curves, for unprocessed and processed of complexes, and movements of temperature range is in accordance with the XRD observations. This is a symbol characteristic that organic matter can enter in the interlayer space of montmorillonite minerals. The organic matter in the complexes is released in temperature range 250-650 centigrade degree, mainly at about 450 centigrade degree, and the components in complexes, with higher content of C5 and C25, is similar to that of crude oil by PY-GC analysis. Our findings indicate that organic matter can enter interlayer of montmorillonite forming highly stable organo-clay complexes with unique characteristics in temperature range 250-650 centigrade degree, which play an important role in organic matter preservation in source rocks.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas