Study on the Charge Parameters of Explosive Seismic Exploration Used in Carbonate Strata

摘要

As one of the major methods used for geophysical exploration, Seismic exploration applies the propagation law of explosion excitation seismic waves in different strata to detect geological conditions underground. The vibration characteristics of explosion excitation seismic waves will influence the quality of the reflection or refraction waves produced by strata interface while received by the earth surface. The vibration characteristics of seismic waves caused by explosion excitation in strata are influenced by many factors, such as the self-identities of explosive, the geometrical shape and structure of explosive package, the buried depth and lithological characters of strata for explosive excitation, etc. In order to improve the signal-to-noise ratio of seismic exploration work in the area of carbonate stratum, this paper focuses on the research into the vibration characteristics of explosive seismic waves in carbonate strata caused by the specialized explosives with standard explosive package (the detonation velocity is 5300m/s, the density is 1.6g/cm~3, the diameter of the columnar explosive package is 5.0cm). Dynamic numerical simulation method and General explicit dynamic analysis program LS-DYNA are used to explore the optimum parameters of a single explosive package in a single excitation well. The applicable weight and minimum buried depth of standard explosive package in carbonate strata can be determined by comparing and analyzing the vibration waveforms and strengths of the monitoring points, the results of the numerical simulation tests performed with explosive packages of different weights at one same buried depth and with explosive packages of the same weight at different buried depths. The results show that: 1. Increasing only the weight of standard explosive package has limited effects on promoting the strength of seismic waves just below the package. 2. When the buried depth of standard explosive package is less than 4ms, the reflected waves from the upper free surface will influence the seismic waves transmitted downward by the explosive package, and may possibly change the characteristics of the seismic waves' forms. With the increase of the buried depth, the influence of the reflected waves from the upper free surface will gradually weaken. 3. With the application of the method of a single explosive package in a single excitation well to explosion excitation, the weight of explosive package should be in the range of 4kg～8kg, up to a maximum of 10kg to ensure a higher gain efficiency of vibration. 4. When the weight of standard explosive package is 10kg, the critical depth of burial in carbonate strata is 4m～6m below the bedrock surface.