Diagenetic Sequence, Genetic Mechanism and Hydrocarbon Charge of Silurian Tight Sandstone Reservoirs in the Eastern Tarim Basin, Northwest China

Abstract

The Silurian sandstones have recently become one of the most important exploration targets in the Tarim Basin, with a considerable amount of profitable hydrocarbon pools discovered in the Central Tarim Basin. Previous exploration activities indicate that the Silurian sandstones in the Eastern Tarim Basin have a great hydrocarbon exploration potential. The Silurian reservoirs comprise a set of tight marine sandstones in the Eastern Tarim Basin, whose diagenetic sequence, genetic mechanism and hydrocarbon charge are still poorly understood. The complex relationship of hydrocarbon generation, the timing of the peak expulsion of the source rocks and the evolution of the reservoirs remains unclear. The purpose of this research is to make these problems clear to provide the theoretical guidance for the oil and gas exploration and the evaluation of the Silurian reservoirs. An integrated description and analysis have been carried out on core samples from eleven wells selected from the Eastern Tarim Basin. By using a range of petrographic and geochemical analyses, the genesis and occurrence of individual diagenetic events were documented to reconstruct the diagenetic sequence and diagenetic model for the Silurian sandstones. Additionally, the tight nature of the Silurian reservoirs can mainly be attributed to the compactional processes and the cementation. In particular, the destructiveness of the compactional processes to original porosity is far greater than that from the cementation. The Silurian sandstones have lost 10.06%-34.41% porosity, an average of 26% (around 75% of original porosity) because of the compactional processes, and 1.34%-31.66% porosity, an average of 5.9% (around 17% of original porosity) because of the cementation. Furthermore, the fluid inclusion analyses also indicate that the Silurian sandstones have experienced three phases of hydrocarbon charge. The first two phases occurred during the eodiagenesis stage (from the Late Silurian to the Early Devonian and from the Late Carboniferous to the end of the Late Permian), when the Silurian sandstones were not tight and had a porosity of greater than 20%. The third phase occurred during the stage B of mesodiagenesis (since the Late Cretaceous), when the Silurian sandstones were fully tight.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018