Enrichment Factors and Current Misunderstanding of Shale Oil and Gas:Case Study of Shales in U.S., Argentina and China

Shale gas enrichment is uneven, and production is different whether for different shale reservoirs or in different shale oil and gas reservoirs. It is necessary to systematically analyze compare the relationship between geology, petroleum system and oil and gas enrichment of different shale oil and gas plays in the world, to find out the main enrichment factors of shale oil and gas for the purpose of best choice of exploration and development technology. Based on the observation and description of outcrop and core, property testing of shale samples, reservoir characterization, petroleum system analysis, and production test, the shale reservoirs in the United States, Argentina, and China were studied. Results show that the organic-rich shale with content of high brittle minerals is mainly distributed in the shallow water sedimentary and tectonic background far away from the orogenic provenance. The high quartz content and high gamma value are not the evaluation criterion of high quality shale reservoir. The high quality carbonate-rich shale reservoir should be rich in carbonate and of low gamma value instead of being rich in quartz and high gamma value. The "shale reservoirs" are actually fine grained organic-rich shale reservoirs or the organic-lean fine-grained reservoirs adjacent to the source rocks. The natural fractures have both positive and negative effects on shale oil and gas enrichment. Therefore, the shale oil and gas accumulation is controlled by the coupling of tectonic and sedimentary environment, lithofacies, mineral composition, and natural fracture. These controlling factors vary in different basins and different shales with specific properties.