Origin and Sources of Minerals and Their Impact on the Hydrocarbon Reservoir Quality of the PaleogeneLulehe Formation in the Eboliang Area, Northern Qaidam Basin, China

Abstract

The Lulehe sandstone in the Eboliang area is a major target for hydrocarbon exploration in the northern Qaidam Basin. Based on an integrated analysis including thin section analysis, scanning electron microscopy, X-ray diffraction, cathodoluminescence investigation, backscattered electron images, carbon and oxygen stable isotope analysis and fluid inclusion analysis, the diagenetic processes mainly include compaction, cementation by carbonate and quartz, formation of authigenic clay minerals (i.e., chlorite, kaolinite, illite-smectite and illite) and dissolution of unstable materials. Compaction is the main factor for the deterioration of reservoir quality; in addition, calcitecement and clay minerals are present, including kaolinite, pore-filling chlorite, illite-smectite and illite, which also account for reservoir quality reduction. Integration of petrographic studies and isotope geochemistry reveals the carbonate cements might have originated from mixed sources of bioclast- and organic-derived CO2 during burial. The quartz cement probably formed by feldspar dissolution, illitization of smectite and kaolinite, as well as pressure solution of quartz grains. Smectite, commonly derived from alteration of volcanic rock fragments, may have been the primary clay mineral precursor of chlorite. In addition, authigenic kaolinite is closely associated with feldspar dissolution, suggesting that alteration of detrital feldspar grains was the most probable source for authigenic kaolinite. With the increase in temperature and consumption of organic acids, the ratio of K+/H+ increases and the stability field of kaolinite is greatly reduced, thereby transforming kaolinite into mixed layer illite/smectite and illite. Within the study area, porosity increases with chlorite content up to approximately 3% volume and then decreases slightly, indicating that chlorite coatings are beneficial at an optimum volume of 3%. A benefit of the dissolution of unstable minerals and feldspar grains is the occurrence of secondary porosity, which may enhance porosity to some extent. However, the solutes cannot be transported over a large scale in the deep burial environment, and simultaneous precipitation of byproducts of feldspar dissolution such as authigenic kaolinite and quartz cement will occur in situ or in adjacent pores, resulting in heterogeneity of the reservoirs.

The Importance of Physiochemical Processes in Decarbonisation Technology Applications Utilizing the Subsurface: A Review

“…Where expulsion of petroleum is not retarded by low rock permeability, high pore pressure does not develop, organic porosity compacts and kerogen shrinks, and hence the source rock thins, causing fracturing (Brown, 2000). Maturation of kerogen and decarboxylation of organic matter may release CO 2 (Chen B. et al, 2019).…”

Influence of preferred orientation on the bioactivity of hydroxyapatite: a potential tooth repair and implant surface coating material

“…The evidence was the high calcium level recorded for 7 days of immersion for HApS2 in SBF relative to that of HApS1. The high pH value of 12.6 after dissolution suggested that calcium mineral was in association with carbonate [32]. The solution reached a supersaturation and interacted with phosphate in solution to form amorphous calcium phosphate (ACP) [14].…”

Role played by clay content in controlling reservoir quality of submarine fan system, Forties Sandstone Member, Central Graben, North Sea

“…The Paleocene turbidite sandstones of the Central North Sea contain about half of the total recoverable oil reserves within the region (2.99 billion barrels), with estimated reserves of approximately 6.01 billion barrels (Brennand et al, 2009). Therefore, quantitative evaluation of the sandstones reservoir quality is crucial for understanding of reserve estimations and development of continued hydrocarbon production strategies (Chen et al, 2019;Marchand et al, 2015;Morad et al, 2010). Reservoir quality is strongly influenced by depositional parameters (e.g., primary sediment composition, grain size, sorting, and clay content, which constitute depositional facies) (Bell et al, 2018;Marchand et al, 2015;Porten et al, 2016;Stammer, 2014) and diagenetic alterations (Morad et al, 2010;Oluwadebi et al, 2018).…”