Seismic Response Identification of Karst Reservoir in Lower Permian Maokou Formation in Southern Sichuan Basin

doi:10.7657/XJPG20210503

Abstract

Abstract:

Oil and gas resources are very abundant in Block Y101 in southern Sichuan basin, and fractures and caves are very developed in the karst reservoirs of the Lower Permian Maokou formation which is the primary gas pay zone. However, the reservoir is thin and laterally heterogeneous, and the velocities of different lithologies of the Lower Permian Maokou formation and the overlying Upper Permian Longtan formation are very different. This results in a strong reflector with “two troughs and one peak”, which shields the karst reservoir in the underlying Maokou formation, and makes it difficult to identify and predict the seismic response of the karst reservoir. To identify the seismic response of the karst reservoir, a technical flow for wavelet reconstruction and waveform decomposition is established in frequency domain based on forward modeling. First, a karst reservoir model of the Maokou formation is established according to the drilling, logging and geological data in the study area, then forward modeling is conducted with acoustic wave equation based on finite difference methods, then the strong reflector is removed through frequency-domain wavelet reconstruction and waveform decomposition after multi-wavelet decomposition, and finally the seismic response of the karst reservoir is identified. Field application in Block Y101 has verified the effectiveness of the method. The frequency-domain wavelet reconstruction and waveform decomposition based on forward modeling can eliminate the shielding effect of the strong reflector, and the reservoir seismic response coincides with the well data.

Key words: southern Sichuan basin, Maokou formation, karst fracture and cave, forward modeling, karst reservoir, seismic response, frequency-domain wavelet reconstruction, wave equation, waveform decomposition

CLC Number:

TE112.24

LI Yuan, CHEN Sheng, WANG Peng, LIU Wei, FAN Kun, SUN Fu. Seismic Response Identification of Karst Reservoir in Lower Permian Maokou Formation in Southern Sichuan Basin[J]. Xinjiang Petroleum Geology, 2021, 42(5): 529-540.

Figures/Tables 12

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