Study On The Favorable Reservoir Characteristics Of The Yanchang Formation In The Ma Huangshan Area In The Ordos Basin

Ordos basin is situated in the west part of North China platform. It is the second largest basin and an important area for oil and gas exploration in China. Several giant fields have been discovered in recent years. The Triassic sandstone still holds great exploration potentials. The basin contains large resources of oil, coal and gas, and is one of the main supply bases for China's “West to East Gas Pipeline”.The study area is located at the west margin of Ordos basin, the Mahuangshan region. There are rich hydrocarbon resources in Chang 4+5, Chang 6 and Chang 8 of the Yanchang Formation in the Triassic system. As a major oil and gas producing region in the Mesozoic Ordos basin, its exploration and development is of special significance to production uplift and reserve increase for Changqing oil field. In order to further understand the rules of hydrocarbon gathering in this area, it is necessary to conduct detailed research on sedimentary facies and reservoir characteristics. This thesis is based on the project titled “study of micro sedimentary facies and reservoir characteristics of Yanchang formation in Southern Ordos basin”. It systematically characterizes the petrology, facies, pore distribution, various diageneses of Yanchang formation in upper Triassic by applying outcrop studies, core description and analysis, thin section observation, por-perm measurements, and other methodologies. Reservoir controlling factors are subsequently investigated. Major conclusions of the thesis include:1.The study area is mostly made of delta front sedimentary sub-facies which is further classified into distributary channel, distributary mouth bar, distal bar, sheet sand, distributary bay and other micro-facies. Distributary channel and mouth bar are the main types of reservoir sands.2.The rock types of Chang 4+5, Chang 6 and Chang 8 in the study area are primarily comprised of feldspar clast sandstone and clast feldspar sandstone. The clasts in Chang 4+5 and Chang 6 are mainly from metamorphic rocks.3.Major diageneses experienced in the study area include compaction, pressolution, cementation, dissolution, dolomitization and fracturing. Strong compaction and cementation are the primary causes for the low permeability in the study area. Dissolution of feldspars may tremendously improve reservoir properties.4.Based on the analyses of controlling factors, reservoir characteristics and their variations across key exploration areas, reservoir evaluation standard is established using por-perm and lithology-reservoir quality relationships in combination with pore types and pore structures, and other characteristics.