Key Factors of Oil-Gas Reservoir-Forming in Ordovician Carbonate Reservoirs in Gucheng Uplift, Tarim Basin, Northwest China

Abstract

Abstract

The Ordovician carbonate reservoir of Gucheng uplift, which is one of the most important and complex fault-controlled marine carbonate reservoirs in China, is located in the east of Tarim Basin, Northwest China. The understanding for reef flat reservoir and dolomitization reservoir once sustained hydrocarbon exploration of the Lower Paleozoic platform carbonate in the Tarim Basin. However, the ancient carbonate reservoir in Gucheng uplift has experienced significant tectonic and diagenesis throughout its long geological history. These processes have greatly complicated the reservoir properties. Especially the strong heterogeneous characteristics of the carbonate reservoir and destruction of oil-gas reservoirs increase the exploration risk in the study area.

Synthetically analyzing on drilling core, thin section, fluid inclusion analysis, bitumen reflectance, and seismic interpretation, the key factors to form Ordovician oil-gas reservoirs of Gucheng area are studied as below. First, two sets of source rocks, Xidashan Formation of lower Cambrian and Heituwa Formation of Middle Ordovician, controlled the distribution of oil and gas in Gucheng uplift. Secondly, Caledonian paleostructure together with faults and unconformities provided pathways for hydrocarbon migration and accumulation. Thirdly, origin and distribution of solid bitumen, homogenization temperature of fluid inclusions, and burial-thermal evolution revealed that Permian Tectonic Heat Event was critical to the accumulation and adjustment of oil-gas reservoirs. Permian Tectonic Heat Event refer to the thermal effect of igneous rock on oil-gas reservoirs. And natural gas evolved from oil cracking at high temperature. Fourthly, two sets of important carbonate reservoirs, including the karst dolomitization reservoir of lower Ordovician and the reef flat karst reservoir of Middle Ordovician, were controlled by paleostructural geofluid processes, which was essential to reservoir accumulation. The formation and evolution of oil-gas reservoir-forming in Gucheng area withstood three stages, including the primary oil-gas pools, the destruction of paleo-oil reservoir into cracking gas, and the reformation of oil-gas reservoir. Therefore, the western area of Gucheng with good source-reservoir-cap, fairly poor faults and little magma activities are the favorable plays for hydrocarbon exploration. Our method may be useful in characterizing similar ancient marine carbonate reservoirs in other areas.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016