The role of provenance in the diagenesis of siliciclastic reservoirs in the Upper Triassic Yanchang Formation, Ordos Basin, China

Abstract

A better understanding of the controls on reservoir quality has become essential in the petroleum exploration in recent years. Determining the original composition of the sediment framework is important not only for paleogeographic reconstructions, but it is also vital for predicting the nature of physical and chemical diagenesis of the potential reservoirs. Depositional setting and diagenesis are important factors in controlling the type and quality of most siliciclastic reservoirs. We studied the Upper Triassic Chang 8 and 6 members, where the relationship between sediment provenance and diagenesis was examined. The study attempts to clarify sediment provenance and post-depositional diagenetic microscopic analysis of grain and heavy mineral types, and measurements of the palaeocurrent direction of the Yanchang Formation sediments in the outcrops in order to determine the provenance of the studied sediments. Furthermore, the relationship between framework grains, pore types and diagenesis of the sediments was analyzed by thin section petrographic characterization using a polarizing microscope.system was used to investigate the habits and textural relationships of diagenetic minerals. On the basis of of diagenesis which may be expected in sandstones. In the Chang 8 and 6 members, the formation of chlorite rims and laumontite cement was observed where volcanic rock fragments constitute a large part of the framework grains. Furthermore, high biotite content provides abundant iron and magnesium and enables the formation of chlorite rims due to biotite hydrolysis. In addition, ductile deformation of biotite leads to strong mechanical compaction of the sediments. Conversely, high feldspar content diminishes the degree of mechanical compaction, however the dissolution of feldspar minerals in sandstones is commonly observed. Apart from feldspars, quartz and other rigid framework grains highly control the degree of mechanical compaction during the initial stage of burial (0-2 km).

Diagenetic Controls on the Reservoir Quality of Fine-Grained “Tight” Sandstones: A Case Study Based on NMR Analysis

“…These samples are derived from two principal provenance directions: samples N75, B12, L189, Z129, and Z191 are originated primarily from the Qinling and Liupanshan orogenic belts in the southwest, whereas the sands in sample H218 are derived from the Yinshan palaeocontinental terrain in the northeast. Sample S110, on the other hand, is believed to be of mixed provenance. ,, These samples were subjected to thin section petrology, scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), and NMR analyses.…”

“…Sample S110, on the other hand, is believed to be of mixed provenance. 14,15,18 These samples were subjected to thin section petrology, scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), and NMR analyses.…”

“…The tight sandstone of Chang-7 Member in the Ordos Basin was deposited within a lacustrine basin, with significant provenance variability, and under diverse sedimentary conditions . This resulted in a diversity of mineralogical composition and highly variable diagenetic evolution of the sandstones . Intense compaction, facilitated by fine grain size and high clay content, together with late-stage carbonate cementation, are deemed to be the major cause for porosity loss in the Chang-7 sandstone. ,, These conclusions are based on consideration of total porosity variation during digenetic processes, as in conventional reservoirs.…”

Origin and depositional model of deep-water lacustrine sandstone deposits in the 7th and 6th members of the Yanchang Formation (Late Triassic), Binchang area, Ordos Basin, China

“…The 7th and 6th members of the Yanchang Formation in the Binchang area of the Ordos Basin were deposited in a deep-water environment (Lei et al 2015) and are the main production formation of tight oil in China (Yang et al 2012;Ding et al 2013;Yuan et al 2015). Understanding the origin, distribution pattern, scale and continuity of this sandstone is important, and these factors must be considered during exploration and decision-making in the development of the oil field.…”

Formation mechanisms and sequence response of authigenic grain-coating chlorite: evidence from the Upper Triassic Xujiahe Formation in the southern Sichuan Basin, China

“…Studies have been performed on many sedimentary formations such as the Upper Triassic Yanchang Formation in the Ordos Basin Ding et al 2013;Zhang et al 2013;Zhu et al 2015), the Upper Jurassic in the Songliao Basin (Zeng 1996), Xujiahe Formation in the Sichuan Basin Huang et al 2010;Zou et al 2013), Middle Jurassic Shaximiao Formation in the Sichuan Basin (Lü et al 2015), Jurassic Sangonghe Formation in the Junggar Basin (Xi et al 2015), Upper Cretaceous in the Santos Basin, Brazil (Bahlis and Luiz 2013), and the Lower Vicksburg Formation in Southern Texas (Grigsby 2001). However, the clastic sequences which developed grain-coating chlorite in these sedimentary basins have varying characteristics.…”