The reservoir property modeling of volcanic reservoir: An application to the Shahejie Formation, Zaoyuan oilfield, eastern China

Abstract

As an increasing number of volcanic reservoirs has been discovered all over the world, the study of volcanic reservoirs has caught more attention. However, researchers mainly focus on the characterization of the external architecture of volcanic rock mass and the superimposed relationship between the rock mass, while paying little attention to the fine anatomy of the internal structure of the rock mass, making it difficult to effectively guide the development of the volcanic reservoir. Taking Zao35 block in Huanghua depression, Bohai Bay Basin, China, as an example, we find a workflow of establishing a high-resolution volcanic stratigraphic structure model and reservoir properties models by integrating well- and seismic-data analysis. The seismic data indicate that the volcanic activities consist of three stages: Stages I and III have positive seismic amplitude reflections, whereas stage II has a negative seismic reflection. The well data indicate that the lithology column of target formation in our study area consists of eight volcanic strata and seven mudstone strata. According to the lithology interpreted using well data, stages III, II, and I consist of five, one, and two volcanic eruption periods, respectively. We have established a structure and stratigraphy model with eight zones of volcanic rock and seven zones of mudstone barrier (15 zones in total) to effectively distinguish volcanic rocks (products of the eruption period) from sedimentary rocks (products of the volcanic dormant period). Based on the seismic attribute analysis, we have combined the sequential indicator simulation and local anisotropy from the seismic amplitude attribute. The model of volcanism can be reproduced by sequential indication simulation of local variogram with variable range directions. Based on the principle of “facies control” (perform lithology simulation in different regions according to lithofacies), we have used the sequential indication method to simulate volcanic rocks. The simulation results have a very good agreement with the shape of lava flows spreading around the crater. To describe the internal structure of the volcanic rock body, reveal internal lithology distribution characteristics, and reservoir physical properties, we provide an effective research method for the development of volcanic reservoir geologic research.