Microseismic Technique Research Articles

Probing predominant flow areas of enhanced geothermal systems with fuzzy-genetic inversion model: Impacts of initial conditions of fracture network distributions

Predominant flow areas in fractured reservoirs, causing a large amount of fluid loss, are the primary reason for a failed practical enhanced geothermal system project. However, in practical situations, the existed geophysical exploration methods (e.g., microseismic techniques and tracer techniques) are unable to clear all the actual fracture network distribution in fractured reservoirs, so it is difficult to verify the existence state of predominant flow areas. This study aims to create an inversion method based on a fuzzy-genetic algorithm for identifying fracture network distributions, through discussing the influences of different initial guessed fracture network distributions on inversion results. Results show that the random distribution and the fracture aperture range have an obvious impact on inversion results (inversion accuracy rate = 70%). An increase in fracture length scope (>120−210 m) and number (>170) decreases inversion accuracy. Curved-fracture network distribution also leads to a decrease in the accuracy of inversion results. This study would provide suggestions for deep geothermal exploration.

Identification of goaf instability under blasting disturbance using microseismic monitoring technology

Micro-seismic (MS) technique can be used to appreciate rock failure process and severity of damage by quantifying micro-earthquakes in terms of time, location, grade, and energy release. Based on 3D laser detection and high-precision micro-seismic monitoring, this study analyzes the MS activity, stress and displacement evolution linked with the instability/failure property of hidden goaf incorporating several blasting disturbances in an open pit mine. MS monitoring outcomes reveal two arch fracture zones in the goaf roof, and MS occasions are mostly intense at rock-intersecting interface of north–south goafs. Evolution of apparent stress, apparent volume, and displacement reveals that the goaf is currently in a stable state. The current investigation offers a novel field method and view of inspecting the stability of goaf subjected to blasting disturbance in mines.

Combined effects of solution environment and freeze-thaw cycling on the crack propagation characteristics in sandstone during loading

The failure of ancient rock ruins is affected by freeze-thaw cycles is an important phenomenon in cold region. The degree of freeze-thaw damage be significantly influenced and show an obvious difference during the complex solution environments. However, few studies have been conducted to investigate the combined effects of complex solution environments and freeze-thaw (F-T) cycles to the crack propagation mechanism of loading freeze-thawed sandstones. To study the coupling effects of complex solution environments and freeze-thaw on argillaceous sandstone in ancient ruins, the physical and mechanical properties were investigated through weighing tests, ultrasonic tests, and uniaxial compression tests. The complete failure process of each sample was concurrently monitored using a combination of AE and MS techniques. The crack propagation mechanism at different scales was systematacially investigated through a comparative analysis of microseismic (MS) and acoustic emission (AE) signal characteristics. Additionally, the orthogonal test was designed to effectively analyse the sensitivity of the primary influencing factors to freeze-thawed damage. The findings indicate that:(1) NaCl concentration influences the frost heave force and salt crystallization pressure. While pH levels impact the integrity of the rock structure, leading to significant changes in volume expansion and frost heave force. These aspects are regarded as the main causes of sandstone softening. (2) Compared to the NaCl concentration, varying pH have a more pronounced effect on the freeze-thawed damage. (3) The micro-cracks propagation during loading process is classified into three stages: initial compaction, incubation, and rapid propagation. The macro-cracks propagation is divided into two stages: uniform propagation and rapid propagation. With the increase of NaCl concentration and acidity of solution, the relative duration of incubation in micro-cracks propagation decreased, while the relative duration of uniform propagation in macro-cracks increased. When NaCl concentration and acidity surpass a specific threshold, both the micro-cracks and macro-cracks rapidly propagate from the beginning of the loading process.

Rockburst and microseismic characteristics around lithological interfaces under different excavation directions in deep tunnels

Sandstone (hard rock) and siltstone (relative soft rock) appeared alternately during tunnel boring machine (TBM) excavation of two headrace tunnels at the Neelum–Jhelum hydropower station in Pakistan. Rockbursts occurred frequently near these sandstone-siltstone interfaces, seriously threatening the safety of personnel and equipment. In situ rockburst investigations and microseismic monitoring were conducted to study the characteristics of these rockbursts and their associated microseismic activities around the lithological interfaces under different excavation directions (i.e., the TBM passing though sandstone and siltstone in different sequences). The results show that the rockburst frequency and intensity are greater during excavation from sandstone to siltstone than those during excavation from siltstone to sandstone within 15 m around the lithological interfaces. Moreover, the number of miroseismic events, the amount of microseismic radiated energy and the proportion of high-energy or large microseismic events are higher during excavation from sandstone to siltstone than those during excavation from siltstone to sandstone in the selected zone. In addition, the differences in the rockburst and microseismicity characteristics between sandstone and siltstone are also analysed in the selected zone. Finally, a simple 3D numerical model is employed to assess the rockburst risks in different excavation directions, the results of which agree well with field rockburst results. The formation mechanisms of different rockburst risks under the two excavation directions are discussed and analysed with microseismic data and numerical results. This study may be valuable for predicting rockburst based on microseismic techniques and managing rockburst risks in similar projects.

Machine Learning Optimizes Duvernay Shale-Well Performance

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 189823, “Machine Learning Applied To Optimize Duvernay Well Performance,” by Braden Bowie, SPE, Apache, prepared for the 2018 SPE Canada Unconventional Resources Conference, Calgary, 13–14 March. The paper has not been peer reviewed. This paper discusses how machine learning by use of multiple linear regression and a neural network was used to optimize completions and well designs in the Duvernay shale. The methodology revealed solutions that could save more than $1 million per well and potentially deliver an improvement in well performance of greater than 50%. The work flow described rigorously analyzes the relationships between a significant number of well-completion variables, predicts results, and performs optimizations for ideal outcomes. The work flow is not Duvernay-specific and can be applied to other basins and formations. Introduction A fundamental problem for machine learning in many industries is that a responding variable is controlled not by one but by a number of predictor variables. Inferring the relationship between the responding variable and the predictor variables is of key importance. Interactions between predictor variables and noise in the data complicate matters further. This problem can be solved with multiple linear regression or a neural network, both of which use all of the predictor variables together. However, care must be taken to obtain a model that is truly predictive and not merely a result of overfitting the data. In unconventional oil and gas reservoirs, well performance generally is characterized either at the well level by detailed technical work such as rate-transient analysis, microseismic, and other techniques or at the field level by statistical methods with ranges for production performance. Refinement of this statistical interpretation generally involves normalizing for only one or two key parameters, such as lateral length or tonnage. Additionally, wells usually are grouped or excluded entirely from the population for various reasons, such as substandard completion design. This introduces bias in the selected wells and reduces the sample size. As a result, this approach is limited to the key variables identified and the bias introduced by the well population selected. The idea of using a neural network has been executed successfully in the past to optimize completions. However, data sets were limited. Recently, the use of machine learning has grown substantially by integrating more variables in the analysis, which reduces reservoir uncertainty. The goal of the work flow described in the complete paper is to improve on previous methodology by rigorously and statistically refining estimates for well performance without excluding wells and to recommend which variables are and are not influencing well performance. The goal was accomplished through machine learning in the form of a multiple linear regression and a neural network, comparing the results from both.

Characteristics of microseismic waveforms induced by hydraulic fracturing in coal seam for coal rock dynamic disasters prevention

Coal rock dynamic disasters have been a persistent threat to mine safety. Hydraulic fracturing(HF) technique has been proved to be an effective method for preventing coal rock dynamic disasters in underground coal mines. In order to monitor the crack extent of HF in coal seam, highly precision microseismic(MS) data acquisition apparatus and sensitive sensors are employed to monitor the cracks induced by coal seam HF in Xieqiao Coal Mine. Lots of effective and weak MS waveforms induced by HF are successfully recorded. Some useful methods such as wavelet transformation, Hilbert-Huang transformation, envelope analysis and curve fitting method help to make comprehensive insights into the amplitude-frequency, time-frequency, duration and peak following attenuation characteristics of these HF induced MS waveforms. The frequency, duration time and peak following attenuation characteristics of MS waveforms induced by mining, blast and coal seam HF are statistically studied. The results show that these characteristic parameters, peak frequency, duration time and peak following attenuation, are very sensitive to distinguish these three typical kinds of induced MS waveforms. Further study shows that the principles of fractures’ propagation influenced by the pressurized water and the backfill effect of pores by large volume of pressurized water injection and the pressurized water itself are the key factors influencing the characteristics of MS waveforms. The conclusions are the theoretical basis of locating the cracks and monitoring the effect of HF in coal seams by using MS technique, which can provide the basis reference for designing optimized, safe and effective HF program to prevent the coal rock dynamic disasters, and will be of great significance to coal mine safety.

Dynamic Stability Analysis of Rockmass: A Review

There are a series of human or natural activities, including earthquakes, explosions, and rockbursts, which have caused a number of safety accidents in geotechnical engineering. This review paper summarized the theories and methods for dynamic stability analysis of rockmass. First, numerical simulation methods, including finite element method (FEM), discrete element method (DEM), finite difference method (FDM), boundary element method (BEM), discontinuous deformation analysis method (DDA), and numerical manifold method (NMM), are summarized. Second, the laboratory experiments, containing shaking table test, split-Hopkinson pressure bar test (SHPB), improved true-triaxial test, dynamic centrifugal model test, acoustic emission (AE) technique, and dynamic infrared monitoring, are considered. Third, the in situ tests including microseismic (MS) technique, velocity tomography, stress-strain monitoring, and electromagnetic radiation monitoring are considered. Finally, some comprehensive analysis methods based on statistical theories are also provided. It is pointed out that the study foundation for the dynamic stability of rockmass is weak to explain the mechanism. So, a set of general comprehensive theories integrating the different methods, including theoretical analysis, numerical methods, laboratory experiments, and in situ tests, should be completely established. This is the most effective way for further investigation.

Tomographic fracture imaging: Examples of induced fracture and reservoir-scale observations during wellbore stimulations, Niobrara and Bakken plays, USA

Classic microseismic techniques have been unable to adequately resolve many of the questions that have been asked with respect to reservoir stimulation and production in the Bakken and Niobrara unconventional resource plays as they have matured over the last few years. This has become evident especially in relation to the infill drilling and restimulation phases of field development. In support of efforts to design efficient continued development of operations in these areas, Whiting Oil and Gas has utilized a different, but related, technology to enhance understanding of the subsurface environment during and after reservoir stimulation treatments. We present two separate field examples of a novel reservoir monitoring technology that utilizes microseismic surface geophone arrays and seismic emission tomography (SET) methodologies to directly image both natural and hydraulically induced fracture systems. Tomographic fracture imaging (TFI) was developed with the goal of directly identifying and mapping active induced or natural fracture systems, as opposed to inferring them from a population of microseismic hypocenters as is done in classical microseismic data acquisition and analysis. Examples shown here consist of results from a purpose-designed array intended to monitor the stimulation efficiencies of three wellbores on a single Niobrara drill pad that was completed within a very short timeframe, and the results of a much larger reservoir-scale study showing the 4D reservoir effects of field production over a nine-month period by the TFI reprocessing of legacy microseismic data in the Bakken. These examples represent clear empirical evidence that the TFI technique is effective in detecting and localizing active fracture networks that are highly correlative to other wellbore data, even though much remains to be researched about the exact mechanisms involved in the generation of seismic energy within fracture networks.

Application of Downhole Micro-seismic Technique in Shale Gas Fracturing Optimization of Fuling, China

The downhole micro-seismic method has successfully applied to well fractory fracturing development in Jiaoshiba block, Fuling shale gas reservoir in September 2015. The new concept and understanding have accumulated. Combing the actual construction condition of micro-seismic monitoring in JY AA-BB well groups, we reviewed briefly the downhole micro-seismic monitoring technology and then summarized multi-disciplinary experience and understanding. The staged fracturing process level improved and productivity increased with the further development of shale gas field. Results show that the understanding of micro-seismic method has played a guiding role in the optimization of fracturing process and site construction adjustment of other wells in the same area, which increased the productivity and created a huge economic benefits with a broad market prospects.

Technology Focus: Seismic Applications (March 2017)

Technology Focus My career in the oil and gas industry started in 1975. Shortly thereafter, a theme that became wildly popular in conferences, workshops, and internal boardrooms was better integration of seismic with other oilfield disciplines. Initial progress was slow, but, if we fast-forward to today, we see that significant strides indeed have been made. A good representation of integration papers appeared this past year, so that is the theme we will use. Advancement of the integration of seismic with other oilfield disciplines has been fueled by two factors. First, evolutionary advances in seismic technologies naturally led to more-powerful integration. A simple example is the progress made in bandwidth. In this regard, advances in seismic sources, field recording equipment, and data processing all benefited interpretation, inversion, and reservoir modeling. For example, in the 1980s, a commonly used vibrator sweep in land surveys was 12–48 Hz. Today, sweeps start as low as 2 Hz and often go up to more than 100 Hz. The benefits to resolution and derisking have been striking. Second, several developments in seismic were motivated in direct response to the needs of interpreters and engineers. For instance, the appearance of creative, new, high-channel-count survey designs provided full-azimuth, densely sampled data that led to striking advances in imaging complex structures (especially in subsalt settings) and provided the wherewithal for characterizing natural fractures and stress in both conventional and unconventional plays. Indeed, this tighter integration of seismic with geomechanics energized the rise of the microseismic technique. Six integration papers were selected. Three are presented here in summary format, and three are listed for additional reading. They come from all over the world, cover a range of reservoir lithologies, and deal with a suite of geologic settings. Let’s keep the progress moving. Recommended additional reading at OnePetro: www.onepetro.org. SPE 183289 Seismic Reservoir Characterization of Carbonate Reservoirs—Case Study of the Mishrif Formation, Zubair Field, Iraq by J.M. Rodrigues, Eni, et al. IPTC 18956 Seismic-Driven Lithofacies for Geological-Model Infilling in a Deep Offshore Turbiditic Field—Case Study by Victoriano Da Silva, Total E&P, et al. SPE 181872 Microseismic Mapping Improves Understanding of a Complex Reservoir: A Case Study in a Southern Sichuan Shale Gas Field by Yang Wang, Halliburton, et al.

Monitoring of induced microseismicity in an onshore oilfield from Abu Dhabi, United Arab Emirates: Implications for carbonate reservoir monitoring

We present the first pilot study of a microseismic monitoring survey using a single vertical downhole array in an onshore oilfield in Abu Dhabi, the United Arab Emirates. The microseismic data are acquired continuously for 27 days in conjunction with gas and water injection in the Lower Cretaceous Thamama and Shuaiba reservoirs. The aim of this pilot study is to verify the ability of microseismic monitoring to reveal information about fracture system and fluid flows within the carbonate reservoirs in response to fluid injection. For the majority of the data, the signal to noise ratio is less than 1dB, which makes it very challenging to find well-defined P and S waves simultaneously. However, a total of ninety microseismic events are detected using the combination of amplitude ratio, hodogram and apparent velocity analysis. The occurrence of detected events shows a strong relationship with the injection rates. Subsequently, the probabilistic global grid-search strategy is employed to obtain locations of these events. The spatial distribution of the events detected in the Thamama II reservoir correlate well with NW-SE oriented pre-existing fault and fracture systems in the oilfield. By contrast, the events detected in the Shuaiba reservoirs are scattered without a major trend and depth constraint probably due to various azimuths of injectors. The high b values retrieved from Gutenberg-Richter formula suggest that the reservoirs are stiff. Moreover, the different behaviors of the released seismicity and b values for lower (Thamama II reservoir) and upper (from Shuaiba I to Shuaiba IV reservoirs) group of events indicate that microseismicity is induced more easily in Thamama II reservoir than Shuaiba reservoirs. It is reasonable because the injection in Thamama II reservoir just started a year ago while that in Shuaiba reservoir has been going on for the past 20 years. Therefore, it is more likely for Thamama II to induce more microseismicity than Shuaiba reservoirs. Overall, this study demonstrates that the microseismic technique can be considered as a potentially important monitoring tool to reveal information about fracture systems in the carbonate reservoirs of Abu Dhabi oilfields.

Performance and feasibility analysis of two microseismic location methods used in tunnel engineering

The location of microseismic (MS) sources is of fundamental importance in MS monitoring and risk warning. Location accuracy, efficiency and stability are affected by location methods heavily. In this paper, feasibility of two location methods (TDP&S and TDP-S methods) recently used in MS monitoring in tunnel is studied. An efficient global-optimization algorithm, particle swarm optimization (PSO), is introduced to analyze the performance (efficiency, accuracy and stability) of the two methods successfully in a tunnel engineering condition. Results obtained via numerical experimentation show that in a tunnel engineering condition the locations of MS sources with PSO algorithm could be accurately obtained using both the two location method. The relative location errors are mostly in 5.0%. The solution efficiency is greatly improved when using TDP-S location method (the average solution speed increase is 73.9%). And it is less sensitive to the MS source position. However, the TDP&S method is better when there are errors in arrival-times. We should dynamically choose the better location method according to the actual situation. The two methods should be used together to meet the engineering demand sometimes. The two location methods with PSO algorithm were used to find rockburst events in the deeply-buried tunnels of the Jinping II hydropower station in China. The results in this real engineering application agreed with the numerical experimentation results. These results will lay a foundation of the development of MS technique in tunnel engineering.

Stability analysis and reinforcement evaluation of high-steep rock slope by microseismic monitoring

The stability of excavated high-steep rock slopes is most significant in the long-term safety of large-scale hydropower projects. Dagangshan rock slope had an unloading fractured zone (XL-316) and a fault (f231) during excavation, which resulted in a high risk of slope instability. Anti-shear tunnels were constructed for enhancing the overall shear resistance and reinforcing the slope at six different elevations. The microseismic technique was employed to investigate microseismic activities during excavation and after reinforcement. An integrated method of microseismic energy density and the magnitude-frequency relation based on microseismic monitoring was proposed to analyse the stability and reinforcement effect of the slope. During excavation, a large number of microseismic events took place with few low-magnitude events and numerous high-magnitude events. The aggravated damage occurred in the major discontinuities during excavation. The number of low-magnitude microseismic events increased after reinforcement, and the b value obviously increased, which means the slope stability was substantially enhanced. Microseismic activities were evidently reduced, and the accumulated microseismic energy increased slowly. The stresses were transferred towards the edge of the anti-shear tunnel, and a small number of low-energy events occurred. The targeted reinforcement has served well for its purpose and improves the mechanical performance of the discontinuities. The application of the proposed method was verified by 3D RFPA-Centrifuge software. The proposed method can be considered as an effective way to evaluate the reinforcement effect and stability of high-steep rock slopes.

Monitoring on CO2 migration in a tight oil reservoir during CCS-EOR in Jilin Oilfield China

Jilin Oilfield is conducting a large-scale demonstration project on CO2 EOR (enhanced oil recovery) and storage in China. CO2 separated from a nearby natural gas reservoir (15–30 mol% CO2) is injected into the northern part of H59 oil block with permeability and porosity of 3.5 mD and 12.7%, respectively. After about six years of operation, nearly 0.26 million tons of CO2 (0.32 HCPV (hydrocarbon pore volume)) has been injected into the thin oil layers with well-developed natural fractures. In order to track the movement of CO2 in the oil reservoir, a microseismic monitoring program has been implemented to map the CO2 flow anisotropy and estimate its sweeping efficiency. Gas tracer testing has also been conducted to examine the inter-well connectivity. The temporal change of produced CO2 has been analyzed in a real-time mode to monitor the dynamic response in production wells. It is demonstrated that the migration of CO2 in the thin oil layers can be successfully detected by the microseismic technique, and the sweeping profiles of CO2 obtained from the inverted microseismic are in good agreement with the produced CO2 rate from production wells as well as the reservoir's petrophysical properties.

Integrated Analysis of the Formation Mechanism of Cracks in a Concrete Dam Using Microseismic Monitoring and Numerical Simulation

The dam of Guanyinyan hydropower station is composed of a concrete gravity dam in the left bank and a rockfill dam in the right bank. During the operation of the hydropower station, several surface cracks occurred in the concrete gravity dam, which threatened the stability of the dam. To evaluate the evolution trend of the cracks and forecast the potential risk of the dam, the microseismic (MS) monitoring technique and finite-element method were used. First, the concrete three-point bending field test was performed to prove the reliability of the MS technique in monitoring the concrete cracks. The MS monitoring results were consistent with the simulation results. Then, the MS monitoring system was installed in the dam body. By analysing the MS activities before and after the impoundment, the evolution trend of the cracks and potential risk of the dam were evaluated and forecasted. The simulation results were also consistent with the monitoring results. These results can provide significant references for the operation safety of the dam and also present a new thought for the risk evaluation of similar dam engineering.

APPLICATION OF MICROSEISMIC AND CALCULATIONAL TECHNIQUES IN ENGINEERING-GEOLOGICAL ZONATION

Data on engineering-geological conditions is the basis for seismic microzonation (SMZ). It is usually based on different data of field geological works in the investigated area, including drilling data, ground- penetrating radar (GPR) sensing, etc. At the same time seismic properties of soils (mainly velocities of p- and s- waves) are obtained by seismic exploration. This technique is used for sites. While the quality of initial engineering-geological map strongly affects selection of such typical sites. Practice of seismic microzonation has shown that such maps must be refined before usage of the main SMZ techniques (earthquakes and explosions recording, etc.) which are relatively labor-intensive. For practical realization of SMZ in the Republic of the North Ossetia-Alania we had to use combined microseismic technique to refine engineering-geological- data, especially in instrumental gaps regions. As a result new statistical method for different site type allocation was developed. It is based on histograms of different site parameters, obtained from microseisms processing. Mobile seismic stations was used to investigate large areas in a short terms, exploration grid size was from 100 up to 500 meters in some places. H/V technique was used for predominant period estimation. Numerical models were used for data control in reference sites. As a result new refined engineering-geological maps of Vladikavkaz, Beslan, Alagir, Ardon and other cities were obtained in a short time.

Microseismic monitoring of the hydraulic-fracture growth and geometry in the Upper Bahariya member, Khalda concession, Western Desert, Egypt

Three-component, downhole geophones are installed in production wells at the Khalda and Kahraman sites to monitor hydraulic fracturing treatment in a nearby well. Locatable microseismic events were distributed in space around the treatment well using the hypocenter-velocity inversion method. The E?W oriented microseismic pattern aligns with the proposed specifications of fracture model design at both the Khalda and Kahraman sites. Due to the small magnitude and long separation distance between the treatment well and the recording string, microseismicity was dominantly observed during the main fracturing operation at both the Khalda and Kahraman sites, with calculated magnitudes less than??0.3?Mw. In addition, the calculated confidence for locatable events was generally average or low. The seismic zone through the mainfrac treatment was estimated to spread over 58?m height and 320?m length at the Khalda site, while the zone of the Kahraman site was enclosed within 25?m height and 250?m length. The stimulated reservoir volume (SRV) at the Khalda site was estimated to be 433?200?m3, with asymmetrical wings around the stimulation well, but at the Kahraman site the stimulation imaging was marginally successful and the stimulated SRV was only 247?000?m3. In general, the two microseismic experiments at Khalda and Kahraman were relatively successful in locating the microseismic events and calculating the SRV within the producing horizon, elucidating the importance of the microseismic technique in monitoring reservoir stimulation.

Microseismic Techniques for Avoiding Induced Seismicity during Fluid Injection

Abstract Induced seismicity is inherently associated with underground fluid injections, including during geologic carbon sequestration. If fluids are injected in proximity to a pre-existing fault or fracture system, the resulting elevated pressures can trigger dynamic earthquake slip, which could both damage surface structures and create new migration pathways. The goal of this research is to develop a fundamentally better approach to geological site characterization and early hazard detection. We combine innovative techniques for analyzing microseismic data with a physics-based inversion model to forecast microseismic cloud evolution. The key challenge is that faults at risk of slipping are often too small to detect during the site characterization phase. Our objective is to devise fast-running methodologies that will allow field operators to respond quickly to changing subsurface conditions.

Rock Burst Intensity Classification Based on the Radiated Energy with Damage Intensity at Jinping II Hydropower Station, China

Based on the radiated energy of 133 rock bursts monitored by a microseismic technique at the Jinping II hydropower station, in Sichuan province, China, we analyzed the advantages and disadvantages of qualitative classification methods for the rock burst intensity. Then, we investigated the characteristics, magnitude, and laws of the radiated energy, as well as the relationship between the rock burst radiated energy and intensity. Then, we selected the energy as an evaluation index for the rock burst intensity classification, and proposed a new rock burst intensity quantitative classification method, which utilized the hierarchical clustering analysis technique with the complete-linkage method. Next, we created a new set of criteria for the quantitative classification of the rock burst intensity based on radiated energy and surrounding rock damage severity. The new criteria classified the rock burst intensity into five levels: extremely intense, intense, moderate, weak, and none, and the common logarithms of the radiated energy of each level were >7 lg(E/J), >4 lg(E/J) and 2 lg(E/J) and 1 lg(E/J) and <2 lg(E/J), and <1 lg(E/J), respectively. Finally, we investigated the factors influencing the classification, and verified its feasibility and applicability via several practical rock burst examples.

A nonlinear microseismic source location method based on Simplex method and its residual analysis

Source location is one of the most valuable features of the microseismic technique due to its ability to delineate the unstable areas. In this paper, the precise formulas of the station residual and event residual are derived for the L1 norm statistical standard and the L2 norm statistical standard based on the residual analysis. Then, the error space for microseismic source location is proposed and analyzed. Based on the above research, a nonlinear microseismic source location method using the Simplex method is developed. This new method can search the microseismic source directly in the error space through four deformations of the simplex figures, and it is able to make use of both P-wave and S-wave velocities. Finally, the performance of the Simplex microseismic source location method is tested and verified by laboratory experiments. Test results show that the Simplex microseismic source location method can improve the accuracy and stability of the source location greatly when P-wave and S-wave velocities are involved simultaneously and correctly. The results also demonstrate that the L1 norm statistical standard always provides more accurate and reliable solutions than the L2 norm statistical standard when there are some major but isolated errors in the input data. However, none of the optimization methods are able to function when the errors in the input data are systematic and extreme, which indicates that an early detection and correction of these errors is of primary importance for microseismic source location.