Distribution Prediction of Lower Jurassic Shell Limestone Reservoir in Yuanba Area of Sichuan Basin

Abstract

Abstract:

The shell limestone in the first submember of the Da’anzhai member (D1sm) of the Lower Jurassic Ziliujing Formation is an important natural gas reservoir in Yuanba area, Sichuan Basin. In this paper, we conducted an integrated study based on cores, thin sections, porosity and permeability data, oil test data, well logging data, and seismic data in order to predict the distribution of the shell-shoal limestone reservoir in the D1sm. The D1sm are composed of mainly shelly limestones and argillaceous shelly limestones. The shelly limestones have an average of porosity of 2.36% and an average of permeability of 0.02×10^-3 μm², while the argillaceous shelly limestones have an average of porosity of 4.59% and an average of permeability of 0.21×10^-3 μm². The shelly limestones in the D1sm comprise the high-energy shoal microfacies that developed in the shallow lake subfacies, and the argillaceous shelly limestones are interpreted as moderate-energy or subhigh-energy shoal microfacies. The classification of seismic waveform shows that the reflection characteristics of the high-energy shoal microfacies are well continuity, low frequency, moderate to large amplitudes, and wave troughs in the seismic profiles, and that the reflection characteristics of the moderate-energy shoal microfacies are well continuity, low frequency, moderate to small amplitudes, and wave troughs. These two types of waveforms distributed from southwest to northeast along the central part of the study area. The natural gamma data cube of the shelly limestones and argillaceous shelly limestones was constructed after rejecting the mudstones and muddy siltstones by giving the threshold value of 46 API. The distribution of shelly limestones (high-energy shoal microfacies) and argillaceous shelly limestones (moderate-energy shoal microfacies) was precisely mapped; the result shows that the favorable exploration area of natural gas has enlarged by about 518 km². The conclusions of this study provide a solid foundation for the increase of the natural gas reserves and production of the Da’anzhai member in Yuanba aera.

Key words: Sichuan Basin, Yuanba area, Da’anzhai member, limestone, reservoir prediction

CLC Number:

HE Zhiyong, LIU Haitao, XIAO Wei, DU Hongquan. Distribution Prediction of Lower Jurassic Shell Limestone Reservoir in Yuanba Area of Sichuan Basin[J]. Geoscience, 2017, 31(01): 142-149.

Figures/Tables 9

Fig.1 Sedimentary sequence comprehensive column of two different types of reservoir wells

Fig.2 The reservoir characteristics diagram of the lower part of the 1st submember of Da’anzhai member in Yuanba area

Fig.3 Depositional model of the lower part of the 1st submember of Da’anzhai member in Yuanba area

Fig.4 Cross plot porosity and permeability of different types of shelly limestone reservoir

Fig.5 Waveform classification attribute map of the lower part of the 1st submember of Da’anzhai member in Yuanba area

Fig.6 Histogram of impedance distribution of the lower part of the 1st submember of Da’anzhai member in Yuanba area

Fig.7 Cross plot of GR and shale content of the lower part of the 1st submember of Da’anzhai member in Yuanba area

Fig.8 Connected well’ GR inversion profile through YB101-YB102-YB11-YB107

Fig.9 Sedimentary facies of the lower part of the 1st submember of Da’anzhai member in Yuanba area

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