Seismic Prediction Technology and Application of Ordovician Subsalt Carbonate Gas Reservoir in the Central Ordos Basin: A Case Study of the S Block in the Jingbian Area

To meet the growing demand for energy, the exploration of subsalt reservoirs has become a critical focus in the development of oil and gas resources. The deep subsalt faults in the central Ordos Basin are steep and have short fault throws with significant concealment, resulting in low accuracy in fault recognition. The thin dolomite reservoirs in the target area exhibit strong heterogeneity and subtle geophysical signatures, complicating seismic prediction. To address this, a case study of Block S in the Jingbian area of the central Ordos Basin is conducted to comprehensively evaluate favorable zones for subsalt gas reservoirs. Pre-stack migration processing results are utilized, and dip-oriented filtering along with frequency-domain coherence techniques are applied to precisely characterize the spatial morphology and distribution of micro-faults. Additionally, pre-stack elastic parameter inversion technology based on rock physics analysis is employed to improve the gas reservoir prediction accuracy of thin dolomite reservoirs. Combined with factors such as structure, sedimentary period paleogeomorphology and the range of cap rock, a series of seismic prediction technologies suitable for the deep carbonate reservoirs of the Ordovician in the Ordos Basin have been developed. The seismic-geological comprehensive evaluation model of subsalt gas reservoirs is constructed. It is considered that the structural high point near the fault zone that does not break through the cap rock of MaWu6 is the most favorable area for subsalt reservoir formation. Criteria such as a Poisson’s ratio of less than 0.26 and Lamé impedance of less than 115 can be used to distinguish fluid types to some extent. Ultimately, 17 favorable areas in total for three target layers are identified through multi-factor analysis, and it is recommended to drill five wells. Among them, the recently tested J3 well obtained a gas flow of 23300 cubic meters per day in layer M, demonstrating significant effectiveness and contributing to discovering new gas-rich areas in the Hengshan region. This result expands the favorable gas-bearing area by 200 km2, providing valuable technical support for subsequent exploration decision-making and deployment.