ALBERT

Description: The discovery of large volumes of natural gas from volcanic reservoirs in the Xujiaweizi Sag of Songliao Basin is a milestone in exploration for natural gas reservoired in volcanic rocks in China. Assessing the ultimate gas resource potential of volcanic reservoirs presents a challenge to the operator because the characteristics of volcanic reservoirs differ considerably from conventional clastic reservoirs. There is a need for an appropriate method that provides not only an estimate of remaining resource potential, but also the geographic characteristics of these resources in Xujiaweizi Sag. Statistical analysis on pool size and spatial distributions of 543 oil pools in Nanpu Sag, 911 oil pools in Liaohe Fault Depression, 16 gas pools in Xujiaweizi Sag and the 43 largest oilfields in China suggests that fractal characteristics are common in observed distributions of pool sizes, resource abundance (defined as reserve/unit area), and spatial distribution of oil and gas accumulations. Based on this finding, a two-dimensional fractal stochastic model, using a Fourier transformation power spectrum approach, is proposed to characterize the spatial distribution and estimate the remaining gas resource potential in the volcanic reservoirs. After elimination of high-risk areas and determination of an economic cutoff on resource abundance, this model is used to predict the resource potential under different exploration risk scenarios, as well as possible geographic location of the remaining resources. The application of this model to Xujiaweizi Sag suggests that the remaining gas resource is mostly located in the southeastern part of the sag, providing information on the direction for future exploration of the natural gas in this area.