Characteristics of the Chang 7 Tight Sandstone Reservoir in the Luopangyuan Area, Ordos Basin
DOI:
https://doi.org/10.54097/kq13eh08Keywords:
Ordos Basin, Yanchang Formation, Chang 7 Member, tight sandstone reservoir, reservoir characterization, diagenesisAbstract
This study aims to systematically characterize the Chang 7 tight sandstone reservoir in the Luopangyuan area of the Ordos Basin to provide a geological foundation for tight oil exploration and development. Core samples from three wells were analyzed using an integrated suite of experimental techniques, including conventional thin-section petrography, field-emission scanning electron microscopy (FE-SEM), constant-rate mercury intrusion capillary pressure (MICP) analysis, and micro-computed tomography (micro-CT) scanning. Results indicate that the reservoir lithology is predominantly lithic arkose and feldspathic sandstone, characterized by fine grain size, moderate sorting, and subangular to angular grain roundness. The average porosity is 8.2%, and the average permeability is 0.32×10⁻³μm²—consistent with an ultra-low-permeability reservoir classification. Pore space is dominated by dissolved intergranular pores (37.3%) and feldspar dissolution pores (34.5%). The pore-throat system is typified by fine pores coupled with fine to micro-fine throats. Compaction and cementation are the primary diagenetic processes responsible for reservoir densification, whereas feldspar dissolution plays a critical role in enhancing reservoir quality. Based on comprehensive petrophysical and diagenetic evaluation, the reservoirs are classified into three types: Type IVa, IVb, and V. Effective reservoir intervals account for 54% of the total net sand thickness, with Type IVa being the most prevalent. These findings offer actionable geological insights for tight oil exploration not only in the Luopangyuan area but also in analogous tight sandstone systems.
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