# Methodology and Results of Detailed 3D Seismic Exploration in the Zhezkazgan Ore District
## 2 Materials and Methods
### Benchmarking Data Specifications
A review and analysis of a previously conducted seismic exploration performed by field crews of Zhezkazgangeologiya JSC within the Zhezkazgan syncline and border areas has shown that seismogeological conditions of the study area are favorable for detailed seismic exploration. The Zhezkazgan Depression contains certain common features with marginal trough-type structures and, in particular, with an oil-bearing Pre-Ural Depression in terms of its structural position, basement immersion depth, tectonics, and composition. The distinctive signs of oil and gas potential in the form of hydrocarbon gas manifestations and accumulations of droplet-liquid oil have been established within the depression. The target reference horizons linked to the base of carbonate sediments of the Lower Carboniferous (RIII), the bottom of Mid-Visean sediments (R'II), the base of the Taskuduk suite (RII), and the base of salt-bearing Permian (RI) have been traced within the Zhezgaz-gan depression based on reflection of seismic sections obtained in different years. The faults of various orders have been confidently traced within the area by identifying areas with gaps in horizon correlation, vertical displacement of the same boundaries and the presence of diffracted waves. The velocity characteristics of the rocks of the entire section are presented as follows, based on available historical seismic data: The uppermost part of the section is represented by a very loose low velocity layer (LVL). Its thickness varies from 2-3 m to 25-35 m. The velocity in the LVL fluctuates between 500 and 1700 m/s. Stratigraphically, the low velocity layer corresponds to Quaternary system sediments. A layer of variegated clays of the Cenozoic age with a thickness of 20-60 m is traced below the LVL. The values of formation velocity are 1500-2400 m/s. The formation velocities of the weathering crust of various rocks vary between 2200 and 2700 m/s. The Low Carboniferous sediments are characterized by large velocity differentiation (from 3500 to 6500 m/s). The Tournaisian formations are noted for increased velocity values of 5000-6000 m/s due to silicified limestone beds. The velocities of the Viseansediments vary within 4000-6000 m/s with maximum velocity values apparently corresponding to the distribution zones of dense limestones, dolomites, and anhydrites. The red-colored terrigous strata of the Upper-Middle Carboniferous are characterized by velocities of 4000-5500 m/s. An overwhelming majority of the Zhezkazgan suite has a velocity of 4700-5000 m/s. According to seismic well logging data for Yu-29, the formation velocity is 4600 m/s, and for Yu-24--4500-4650 m/s. The Permian sediments have quite different velocities in various parts of the basin. The red-colored formations of the Zhidelisay suite and the light marls, sandstones, and argillites of the lower parts of the Kingir suite have a velocity of 2600 to 4000 m/s (wells Yu-29, Yu-2). The halogen formations widespread in the Zhidelisay and lower parts of the Kingir suites are characterized by a significant range of velocities, fluctuating between 3500 to 5000 m/s (well Yu-29). The upper part of the Kingir suite (dark marls, limestones, sandstones) has higher velocities in relation to the underlying red-colored deposits equal to 5000-5500 m/s (wells Yu-30, Yu-17, etc.). An overall velocity model has been developed demonstrating a sharp increase in the velocities in the upper part of the cross section up to 5600 m/s. The sharpest velocity boundaries are those at the base of loose sediments, the base of Upper Tournaisian rocks, the top of Upper Famennian limestones substages, and separate horizons within Famennian production pay. The mode of occurrence of various strata is the essential factor for the reflected waves method. The heterogeneity of the upper part of the cross section (from 100-150 to 1000 m/s) and the resulting significant horizontal velocity gradients is an unfavorable factor impacting the accuracy of velocity determination.