Quantitative Forecast Method of Reservoir-seal Assemblage for Gas in Deep-water Area with Sparse Wells: A Case Study of Lingshui Depression, Qiongdongnan Basin

doi:10.19657/j.geoscience.1000-8527.2018.04.16

Abstract

Abstract:

Recent exploration shows that hydrocarbon resources in northern South China Sea are dominated by gas. Compared to oil, the requirement of cap rocks for gas reservoirs is stricter. Therefore, research on the reservoir-seal assemblage for gas is important for hydrocarbon exploration. Using statistics and geoscientific investigation, sandstone reservoir porosity of 12% is defined as the lower limit for the gas effective reservoir in the Qiongdongnan Basin, and the mudstone displacement pressure of 1 MPa was defined as the lower limit for the gas effective cap rock. Based on logging data, we conducted quantitative window forecasting for the reservoir-seal assemblage for gas in a single well, and the results show that one reservoir-seal assemblage window is developed in the well W22-1(Lingshui Depression). We proposed a new quantitative prediction method for reservoir-seal assemblage in the areas with very few or no wells, based on the velocity inversion section. Taking the Lingshui Depression of the Qiongdongnan Basin as an example, we predicted that there is one reservoir-seal assemblage window developed in the depression, which includes the Lingshui-Yinggehai formations. Results of this study broaden the natural gas exploration layers in the Lingshui Depression, and may also be applicable to other deep-water area and underexplored area.

Key words: Qiongdongnan Basin, effective reservoir, effective cap rock, reservoir-seal assemblage for gas, forecast window

CLC Number:

TE122.3

LIU Jingjing, LIU Zhen, SUN Zhipeng, SUN Xiaoming. Quantitative Forecast Method of Reservoir-seal Assemblage for Gas in Deep-water Area with Sparse Wells: A Case Study of Lingshui Depression, Qiongdongnan Basin[J]. Geoscience, 2018, 32(04): 796-806.

Figures/Tables 10

Fig.1 Tectonic units of the Qiongdongnan Basin(modified from Liu Zhenghua, 2011)

Fig.2 Schematic diagram of the geological cross section AA' of the Lingshui Depression,Qiongdongnan Basin

Fig.3 Histogram of sandstone porosities with different testing results in different formations of the Qiongdongnan Basin

Fig.4 Crossplot between displacement pressure of mudstone cap rock for the gas reservoirs discovered and their depths in the Qiongdongnan Basin

Fig.5 Window prediction of reservoir-cap assemblage for well W22-1 in the Qiongdongnan Basin

Fig.6 Absolute velocity section of Line AA' in Lingshui Depression, Qiongdongnan Basin

Fig.7 Sketch map of 2D effective reservoir window and effective cap-rock window

Fig.8 Prediction map of effective reservoir window on Line AA' in the Lingshui Depression, Qiongdongnan Basin

Fig.9 Prediction map of effective cap-rock window on Line AA' in the Lingshui Depression, Qiongdongnan Basin

Fig.10 Prediction map of the effective reservoir-cap assemblage for gas window on Line AA' in the Lingshui Depression, Qiongdongnan Basin

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