Geological Controls on Seismic Signatures of Volcanic Gas Reservoirs: A Case Study from the Changling Fault Depression of Songliao Basin, China
The Songliao basin in northeastern China is a Mesozoic rift basin characterized by Mesozoic and Cenozoic hydrocarbon systems. The Changling fault depression located at the south of the Songliao Basin, in which volcanic rock reservoirs are extensively distributed in the Yingcheng Formation, has a good exploration prospect for the favorable accumulation conditions of natural gas. Although great success was obtained in this area, we are still facing great challenges for exploration of volcanic gas reservoirs. Volcanic rocks were buried in depth and lack of sufficient outcrops in the surface of the earth. In addition, scare well data and low resolution seismic data in deep formations make it difficult to provide information for distribution, period, age, cycle, occurrence, and rock facies of volcanic rock and hence make challenges for identification of gas reservoirs and the thickness of effect reservoirs. These kinds of problems together would greatly affect the exploration of volcanic gas reservoirs.
3-D reflection seismic and well log data were
gathered to understand seismic indicators of volcanic gas reservoirs, the
geological factors controlling these seismic indicators, and thereby predict
the distribution of volcanic gas reservoirs. In this paper, the volcanic rock facies were described through an analysis of seismic features in conjunction
with well logs and seismic attributes like instantaneous amplitude,
instantaneous frequency, attenuation attribute in vertical and horizon were
extracted to recognize volcano craters and gas reservoir. Under the constraints
of volcano craters, two types of volcanic reservoirs including crevice eruption
and central eruption are indentified corresponding to the distinct seismic
signatures. Additionally, we have applied the broadband frequency constrained
simulated annealing inversion with global optimization to implement our
observations. The results indicate that the volcanic rock has larger impendence
values compared to the clastic rocks while the gas-bearing volcanic rock has
lower impendence values compared to volcanic rock. This is consistent with the
analysis of rock physics from well log. The distinct seismic signatures of the
volcanic gas reservoirs are governed by the different types of eruption
patterns and deep-seated faults.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California