The effects of minerals on oil cracking in confined pyrolysis experiments

Abstract

Confined pyrolysis experiments of oil in the presence and absence of minerals were conducted to reveal the effects of minerals on the oil cracking process. The results indicated that the methane generation rates decreased in the following order: oil alone > oil with clastic minerals > oil with carbonate minerals > oil with clay minerals, and the yields of C2-5 decreased in the order: oil with clay minerals > oil with carbonate minerals > oil with clastic minerals > oil alone. That means these minerals inhibited the cracking of C2-5 into methane. The inhibiting effect were decreased in the order: clay minerals > carbonate minerals > clastic minerals. Meanwhile, the ratios of i-C4/n-C4 decreased in the order: oil with clay minerals > oil with carbonate minerals > oil with clastic minerals > oil alone. That means the efficiencies of isomerization catalysed by minerals were decreased in the order: clay minerals > carbonate minerals > clastic minerals. Meanwhile, the ratios of C2H4/C2H6 increased with the order: oil with clay minerals < oil with carbonate minerals < oil with clastic minerals < oil alone. The hydrogenation rates of olefins increased in the following order: clay minerals < carbonate minerals < clastic minerals. The extent of enrichment12C for the generated methane and ethane increased in the order: clastic minerals < carbonate minerals < clay minerals. Such carbon isotopic fractionation during methane and ethane formation was probably induced by the catalytic effect of mineral surface on the terminal methyl group of hydrocarbons. The study of minerals effects on oil cracking may enhance our understanding on the evolution of petroleum reservoirs.