Abstract
AbstractTight sandstone reservoirs are widely distributed worldwide. The Upper Triassic Chang 6 member of the Yanchang Formation is characterized by low permeability and porosity. The facies model offers a unique approach for understanding the characteristics of various environments also heterogeneity, scale, and control of physical processes. The role of subsurface facies features and petrophysical properties was unclear. Notable insufficient research has been conducted based on facies and petrophysical modeling and that demands to refine the role of reservoir properties. To tackle this problem, a reservoir model is to be estimated using various combinations of property modeling algorithms for discrete (facies) and continuous (petrophysical) properties. Chang 6 member consists of three main facies, i.e., channel, lobe main body, and lobe margin facies. The current research is aimed at comparing the applicability and competitiveness of various facies and petrophysical modeling methods. Further, well-log data was utilized to interpret unique facies and petrophysical models to better understand the reservoir architecture. Methods for facies modeling include indicator kriging, multiple-point geostatistics, surface-based method, and sequential indicator simulation. Overall, the indicator kriging method preserved the local variability and accuracy, but some facies are smoothed out. The surface-based method showed far better results by showing the ability to reproduce the geometry, extent, connectivity, and facies association. The multiple-point geostatistics (MPG) model accurately presented the facies profiles, contacts, geometry, and geomorphological features. Sequential indicator simulation (SIS) honored the facies spatial distribution and input statistical parameters. The porosity model built using sequential Gaussian simulation (SGS) showed low porosity (74% values <2%). Gaussian random function simulation (GRFS) models showed very low average porosity (8%-10%) and low permeability (less than 0.1 mD). These methods indicate that Chang 6 member is a typical unconventional tight sandstone reservoir with ultralow values of petrophysical properties.
Highlights
A lot of research has been done on tight sandstone reservoirs by many authors around the globe
The inferences were drawn from the evaluation of facies and petrophysical modeling methods, and statistical results that were performed during this research: (1) Sequential indicator simulation (SIS) was proved to be more robust and honored the spatial distribution of facies, but the connectivity between facies lacks, and the geobody dimension was not clear
The indicator kriging (IK) modeling results were suitable for facies interpretation and facies associations
Summary
A lot of research has been done on tight sandstone reservoirs by many authors around the globe. The oil in a tight sandstone reservoir with permeability less than 0.1 mD and porosity less than 10% can be referred to as tight (sandstone) oil [1,2,3,4,5,6,7,8,9]. Tight (sandstone) oil emerged as an important unconventional oil resource in the petroleum sector. Accumulations of tight oil exist in China in different basins, especially in the Chang 6 reservoir located in the Ordos Basin. Most of the reservoirs in the Ordos Basin are characterized by ultralow permeability with substantial heterogeneity. The current research is focused on reservoir modeling that has become a unique approach to access the reservoir quality, characterization, reserve estimation enhancement, and field development, future production
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