A Multi-Point Geostatistical Seismic Inversion Method Based on Local Probability Updating of Lithofacies

In order to solve the problem that elastic parameter constraints are not taken into account in local lithofacies updating in multi-point geostatistical inversion, a new multi-point geostatistical inversion method with local facies updating under seismic elastic constraints is proposed. The main improvement of the method is that the probability of multi-point facies modeling is combined with the facies probability reflected by the optimal elastic parameters retained from the previous inversion to predict and update the current lithofacies model. Constrained by the current lithofacies model, the elastic parameters were obtained via direct sampling based on the statistical relationship between the lithofacies and the elastic parameters. Forward simulation records were generated via convolution and were compared with the actual seismic records to obtain the optimal lithofacies and elastic parameters. The inversion method adopts the internal and external double cycle iteration mechanism, and the internal cycle updates and inverts the local lithofacies. The outer cycle determines whether the correlation between the entire seismic record and the actual seismic record meets the given conditions, and the cycle iterates until the given conditions are met in order to achieve seismic inversion prediction. The theoretical model of the Stanford Center for Reservoir Forecasting and the practical model of the Xinchang gas field in western China were used to test the new method. The results show that the correlation between the synthetic seismic records and the actual seismic records is the best, and the lithofacies matching degree of the inversion is the highest. The results of the conventional multi-point geostatistical inversion are the next best, and the results of the two-point geostatistical inversion are the worst. The results show that the reservoir parameters obtained using the local probability updating of lithofacies method are closer to the actual reservoir parameters. This method is worth popularizing in practical exploration and development.

Analysis of the possibility for seismic early warning in the Balkan Peninsula

This study analyses the possibility for seismic early warning (EW) in the Balkan Peninsula. A number of characteristics of seismic record were evaluated for EW utility. Some tests checked the possibility to locate events reliably by Golitsyn’s method, using one seismic station (SS). The distance and relevant travel time from some crustal faults to the nearest SS and big towns were appraised. EW procedures for most of the seismic zones in the Balkan Peninsula are not reliable, excepting the Vrancea zone, because of the small density of the SS, crustal depth of the earthquakes and fault crowdedness of the region.

Physics-constrained deep learning for ground roll attenuation

We propose a method to combine unsupervised and supervised deep learning approaches for seismic ground roll attenuation. The method consists of three components that have physical meaning and motivation. The first component is a convolutional neural network to separate a seismic record into ground roll and signal, while minimizing the residual between the sum of the generated signal and ground roll from two sub-networks and the input seismic record. The second component creates a maximum separation of signal and ground roll in the FK domain, by training a supervised classifier. The third component is a convolutional neural network mapping signal to ground roll, which overcomes the problem of finding appropriate masks in traditional methods. Each component in our method is closely related to and motivated by the wave characteristics of the ground roll. Test results on field seismic records demonstrate the effectiveness of combining these components in preventing signal leakage and removing ground roll from seismic data.

Geo-Chemical Techniques for Earthquake Forecasting in Nigeria

Regardless of the doubt caused by some rounds on the impossibility of earthquake forecast, more and more countries, even at the highest governmental levels, realize that doing nothing is the ostrich position of dread before the real difficulties associated with the creation of a real forecasting system. Nigeria in times past was believed to be aseismic. However, the seismic record of Nigeria from 1933-2021 have demonstrated in contrast to the idea, numerous quakes have been recorded in Nigeria throughout the years. With the development of observation techniques and theoretical knowledge of geochemistry, geochemical observation of faults gas has become a hotspot once more in recent years. Rn, Hg, H2, etc., are used for geochemical observations. 222Rn has a half-life of 3.825 days, a magnitude 5.0 earthquake will be detected through precursory phenomena at a distance not greater than 142 km. Mercury and other elements are used as important detectors for earthquake prediction and they play an important role in revealing the relationship between fluid in the fault zone and the occurrence of earthquakes, the range for a magnitude 5.0 earthquake is limited to 200 km. Hydrogen concentrations have been monitored for precursory variations in many fault systems, using either discrete sampling and laboratory analysis or continuous monitoring of ground gas, using hydrogen-sensitive fuel cells. Precursory changes in groundwater chemistry are often attributed to the mixing of fluids from two or more chemically distinct aquifers, the physical mechanism responsible for the mixing of fluids is, however, not well established.

Necessity of recording seismological and seismic properties associated with geodynamic tensions in deep well drilling

The paper reviews the major ways of reducing failure cases during drilling works on the territory of Azerbaijan and South Caspian basin, as well as in oil-gas bearing structures of the Caspian Sea considering geodynamic tension of reservoirs, seismic activity and the occurrences of velocity changes. If not considering such aspects as seismodynamic activity of the territory and geodynamic tensions, failure and complication risks in the process of deep well drilling sharply increase. Physical-chemical features of rocks in the same formation are not similar and various patterns of complicated seismic record can be seen. It is necessary to study in detail the patterns of seismic record in different directions of seismic profile passing near the location selected for the project well. Foremost, it is significant to reveal the interval of drilled reservoir, where the complicated record is occurred and specify the reasons for the sharp difference in wave field patterns. Moreover, while conducting drilling works in the areas with complicated features, the failure case risks should be considered as well.

Rescue Work and Progress of Analog Seismograms in China

Rescue work involving scanning and digitization research on historical analog seismograms nationwide in China was launched in 2017. A series of results have been accomplished. There are more than 13 million analog seismic records existing in China, and about 3 million of them were scanned by December 2019. The Second Monitoring and Application Center of China Earthquake Administration completed the phased construction of the “China Analog Seismic Record Rescue Project” in 2019, which has received a great deal of funding support. Most of the analog seismograms and geophysical records in China will be scanned in the following decade, the corresponding stations and instrument parameters will be also collected during this project to provide retrieval and download service. This article first introduces the survey statistics about scanning and digitalization progress of analog seismic records in China. Second, a management and service system for the storage and query of large scale of seismograms has been established based on distributed database and search engine. Finally, future prospects of the rescue work of analog seismograms are mentioned.

Wave Field Characteristics of Small Faults around the Loose Circle of Rock Surrounding a Coal Roadway

The geological conditions of coal roadway excavation are complicated. Seismic advanced detection is strongly influenced by the loose circle of fractured rock surrounding the competent coal seam. However, the three-dimensional wave field characteristics of small fault advanced detection in the condition of the loose circle of coal roadway have not examined. In this paper, numerical modeling and field tests were conducted to address this knowledge gap. The results indicate that when a seismic source near the tunnel face is excited, the body waves and a Love channel wave propagate in the tunneling direction toward the small fault, then produces reflected body waves whose amplitude is relatively weak, and a reflected Love channel wave whose amplitude is relatively strong. When reflected body waves and the reflected Love channel wave enter the loose circle of surrounding rock, the former's signal is unrecognizable in seismic record; but the latter converts to a Love wave whose amplitude is strong in the loose circle of coal seam. The Love wave which has a large interval from other wave trains in the time domain is easily recognizable in seismic record, which makes it suitable for advanced detection of small fault. The signal-to-noise ratio of seismic record of X component is higher than those of Y component and Z component.