Gas-bearing reservoir distribution in a volcanic environment: Case of the Yingcheng Formation, China

As a special type of lithologic body, gas-bearing strata, composed of rhyolite, an igneous rock with a volcanic composition, are characterized by deep burial, complex lithology, poor stratification, and a complicated gas-bearing distribution. These characteristics lead to difficulties in the prediction of gas-bearing reservoir parameters and thus restrict the exploration and exploitation of such reservoirs. The unique and complex volcanic model contains different types of facies and subfacies because the volcanic eruption usually experiences different explosion-effusion periods. Our study focuses on the vertical and lateral gas-bearing reservoir distribution in a volcanic environment in the Cretaceous Yingcheng Formation of the Songnan Gas Field, using seismic facies-controlled nonlinear stochastic inversion to integrate the volcanic facies information. First, we built the volcanic facies model for the Songliao Basin to introduce the comprehensive characteristics of the volcanic facies during a volcanic eruption and analyzed the well-tie logging facies and seismic facies to guide the facies analysis of the target layer. Then, based on this facies analysis, we depicted the gas-bearing reservoir in detail through the use of seismic facies-controlled nonlinear random inversion. Finally, we predicted the distribution of the gas-bearing reservoir by the inversion results. The predicted results were found to agree well with the actual drilling data. The inversion method effectively predicts the velocity distribution of the gas-bearing reservoir, which provides a good foundation for the subsequent description of gas-bearing reservoirs in the Yingcheng Formation.