Diagenetic heterogeneity, pore throats characteristic and their effects on reservoir quality of the Upper Triassic tight sandstones of Yanchang Formation in Ordos Basin, China. (December 2018)

• Record Type: Journal Article
• Authors: Dou, Wenchao; Liu, Luofu; Wu, Kangjun; Xu, Zhengjian; Liu, Xiaoxiang; Feng, Xu
• Is Part Of: Marine and petroleum geology. Volume 98(2018)
• Page Start: 243
• Page End: 257
• Publication Date: 2018-12
• Subjects: Tight sandstones -- Yanchang Formation -- Ordos basin -- Diagenetic heterogeneity -- Pore throats characteristic -- Reservoir quality; Submarine geology -- Periodicals; Petroleum -- Geology -- Periodicals; Géologie sous-marine -- Périodiques; Pétrole -- Géologie -- Périodiques; Petroleum -- Geology; Submarine geology; Periodicals; Electronic journals; 551.468
• DOI: 10.1016/j.marpetgeo.2018.08.019
• Languages: English
• ISSNs: 0264-8172

Abstract

Abstract: Upper Triassic tight sandstones in Ordos Basin are typical tight oil reservoirs in China. Using a combination of thin sections, SEM, BSE, EDS and mercury injection, 48 sandstone core samples from 17 wells in the study area were collected to investigate the diagenetic heterogeneity, pore-throat characteristics and their correlations with reservoir quality. Five diagenetic types were identified according to their specific diagenetic evolution pathways. Type A sandstones are characterized by abundant authigenic chlorite rims, rare quartz cement and high porosity. Type B sandstones underwent moderate compaction, moderate dissolution and moderate cementation. Samples from Type C are characterized by intense dissolution and large amounts of carbonate cements, they can be subdivided into two categories according to if pore throats in larger size were still reserved (Type C2 ) or not (Type C1 ) after late-stage cementation. Type D sandstones underwent intense compaction, moderate dissolution and minor carbonate cementation. Type E sandstones are characterized by the most intense compaction. Depending on the pore-throat size distributions from MICP analysis, three sandstone types with their own specific pore-throat characteristics were identified. Type Ⅰ sandstones generally contain a certain amount of mesopores (including a few macropores) and pore spaces are dominant intergranular pores, intragranular pores and even oversized pores. These sandstones generally correspond to Type A, B, C2 and D sandstones and thus represent good-quality reservoir. Type Ⅱ sandstones usually contain dominant transitional pores (77% in average) and their pore systems mianly consist of clay intercrystal microporosity and a few isolated intergranular or intragranular pores. Type Ⅲ sandstones are representative by relatively abundant micropores (17.7% in average) and pore spaces are dominant clay intercrystal microporosity. Type Ⅱ and Type Ⅲ pore structures generally correspond to Type C1 and E and thus represent poor-quality reservoir. This study gives insights into the link between different diagenetic features, pore structures and their impact on reservoir quality and this will be helpful for reservoir prediction. Highlights: Diagenesis was mainly governed by composition, depositional environment and fluid flow. Five diagenetic types were identified according to different diagenetic evolution pathways. Pore-throat characteristics were investigated by petrographic observations and MICP test. The diagenetic types are associated with pore-throat types and further with petrophysical properties.