--> Quantitative Evaluation of Hydrocarbon Migration Pathways in Tight Sand Reservoirs Based on Multi-Parameters: A Case Study From Yanchang Formation of Upper Triassic in Honghe Oilfield, Southwest Ordos Basin, China

AAPG ACE 2018

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Quantitative Evaluation of Hydrocarbon Migration Pathways in Tight Sand Reservoirs Based on Multi-Parameters: A Case Study From Yanchang Formation of Upper Triassic in Honghe Oilfield, Southwest Ordos Basin, China

Abstract

The Upper Triassic Yanchang Formation (T3ch) in Ordos Basin contains a large number of tight oil resources. However, tight sand oil exploration and exploitation have been restricted by the absence of quantitative evaluation on migration pathways, so this research is carried out in Honghe Oilfield by comprehensive analysis with multi-parameters.

Firstly, many parameters are adopted to define the main carrier beds of lateral migration, such as porosity, permeability, buoyancy, residual pressure, capillary force and fluid potential gradient. According to membership function and maximum subordination principal, considering the different weight of parameters above, we use the fuzzy comprehensive evaluation method to establish a Migration Coefficient (Ks) model to evaluate quantitatively the conducting property of carrier beds. The relationship between Ks and oil-gas shows indicates that the reservoirs with Ks>0.18 are more suitable for oil migration.

Secondly, Shale Gouge Ratio (SGR) and Fault Tightness Index (IFT) are applied to analyze vertical migration characteristics along faults. Results show most of NW faults were sealing while a majority of NEE faults were opening in target layers during the critical period of migration and accumulation (135-90 Ma). Because the tectonic principal stress orientation during Yanshanian period was SSW238o, the normal stress component of it on NW faults was much bigger than NEE faults’, resulting in the above situation. Moreover, the effects of overpressure distribution should also be taken into account.

Thirdly, the regional tectonic stress field during Yanshanian period is simulated by ANSYS software to predict the fracture-developed zones in T3ch. It is found that the development of fractures in the fault zone is stronger than that in the non-fault zone, and the sand-body development area is also one of the fracture-developed zones.

Finally, the migration pathways are simulated based on results calculated above. This study develops a quantitative method for hydrocarbon migration evaluation in tight sand reservoirs based on multi-parameters. The method presented here has been tested to simulate the hydrocarbon accumulation in the tight reservoir of T3ch8, Ordos Basin, China. The good match between the simulation results and the proved enrichment area demonstrates the reliability of this method. This method is also of general applicability for tight sand reservoirs.