Dynamic conditions of Mesozoic petroleum secondary migration, Ordos Basin

Tectonic movement of the Ordos Basin is characterized by the whole ascending and descending. The main driving forces of petroleum migration in the Mesozoic are buoyancy and abnormal pressure. The continuous oil column height in reservoirs of the Jurassic Yan'an Formation is close to the calculated oil column height required to overcome capillary pressures. The width of the discovered oil-bearing belt below the Tertiary Yanchang Formation is far less than that needed for overcoming capillary pressures. Study of the mudstone compaction curves of more than 100 wells reveals that the driving was buoyancy in the Jurassic and the upper part of Tertiary Yangchang Formation. During the period of large quantity petroleum accumulation, middle and lower reservoirs of the Yangchang Formation were very tight, the formation basically lost water alternating ability, and the extensively developed abnormal high pressure became the main dynamic force of petroleum secondary migration.