Data Processing Methods for 3D Seismic Imaging of Subsurface Volcanoes: Applications to the Tarim Flood Basalt

Summary

Three-dimensional (3D) reflection seismology is a powerful method for imaging subsurface volcanoes. By using industrial 3D seismological data from the Tarim Basin, we illustrate how to extract the sills and the conduits of subsurface volcanoes from seismic data cubes.

Abstract

The morphology and structure of plumbing systems can provide key information on the eruption rate and style of basalt lava fields. The most powerful way to study subsurface geo-bodies is to use industrial 3D reflection seismological imaging. However, strategies to image subsurface volcanoes are very different from that of oil and gas reservoirs. In this study, we process seismic data cubes from the Northern Tarim Basin, China, to illustrate how to visualize sills through opacity rendering techniques and how to image the conduits by time-slicing. In the first case, we isolated probes by the seismic horizons marking the contacts between sills and encasing strata, applying opacity rendering techniques to extract sills from the seismic cube. The resulting detailed sill morphology shows that the flow direction is from the dome center to the rim. In the second seismic cube, we use time-slices to image the conduits, which corresponds to marked discontinuities within the encasing rocks. A set of time-slices obtained at different depths show that the Tarim flood basalts erupted from central volcanoes, fed by separate pipe-like conduits.

Introduction

The aim of most of the industrial seismic imaging projects in sedimentary basins is to explore for hydrocarbon reservoirs. In recent years, hydrocarbon exploration has expanded to basins containing large amounts of igneous rocks because many of the volcanogenic basins have considerable oil and gas reservoirs. However, because of the interface of igneous rocks in the volcanogenic basins, seismic data processing presents a series of challenges induced by various intrusions, such as reduced energy transmission, intrinsic attenuation, interference effects, refraction and scattering¹. Therefore, oil field companies are focusing their efforts on redu....

Protocol

NOTE: The data processing procedures include: synthetic seismogram calculation, synthetic-real seismic trace correlation, and geo-body extraction. Below are the step-by-step details of each procedure.

1. Calculation of Synthetic Seismogram

1. Calculate the acoustic impedance at each interval of the down-well logging curve.
   NOTE: Acoustic impedance is the product of 'seismic wave velocities' and 'density' (ρ*ν)). The data are often averaged to sampling intervals larger than 1 ft, in order to reduce the computation time and aliasing.
2. Calculate the reflection coefficients (R₀) at each interface by us....

Results

We demonstrate the usefulness of the techniques described above by applying them to 2 types of igneous bodies, horizontal sills and vertical volcanic conduits. Extraction of the sills is conducted by using the opaque rendering technique, and interpretation of the volcanic conduit is performed by using slicing technique.

Extraction of sills

Industrial drilling wells have i.......

Discussion

Here we demonstrate 2 methods for illustrating the morphology and structure of the plumbing system of buried basaltic volcanoes; one is opacity rendering, the other is time slicing.

The opacity rendering method is suitable for geo-bodies that have continuous and near horizontal interfaces with the encasing strata. With this method, one can extract the 3D morphology of magma lobes. Normally, flow directions should be along the long axis of the magma lobes. It is also important that the surface .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
The Petrel E&P software platform	Schlumberger		software version:2014