This paper discusses the differences of hydrocarbon expulsion and compositions between stylolite and matrix in carbonate rocks.Samples were taken from the Ordovician and Carboniferous carbonate rock cores containing stylolites of Wells Zuo 3

Chi 53 and Wuke 1 in the Dachigan Structure Belt of the Eastern Sichuan Basin.The stylolite and matrix were studied through observation of core and cast thin sections and various tests such as whole rock X-Ray diffraction for mineral components and TOC content

Rock-Eval pyrolysis

solvent extraction and fractionation of extract and so on.The results indicate that there is a relatively large compositional difference between stylolite and matrix in carbonate rocks

and this is intimately related to pressure solution of carbonate mineral.Because of pressure solution

the stylolite contains more indissoluble materials such as dolomite

pyrite

and organic matter than the matrix.The mineral grains in stylolies mainly display basal cementation and matrix-supported fabric.While the mineral grains in the matrix mainly represent linear contact and close contact in concave and convex shapes.This makes stylolite to have better physical properties compared with the matrix

thus acting as important passages for expulsion of fluids in carbonate rocks in geological history.Therefore

the hydrocarbon expulsion effect of stylolite is more evident than that of the matrix.For the stylolite-bearing carbonate rocks with low organic abundance

the organic matter in the stylolite can be a prominent supplement of hydrocarbon generation in carbonate source rocks.In addition

the soluble organic matters relatively abundant in the stylolite have certain effects on Rock-Eval pyrolysis parameters.