Research on velocity and acceleration geophones and their acquired information

Based on the research of two geophone types （10 Hz moving-coil velocity and piezoelectric acceleration） and their velocity and acceleration parameters, frequency response functions have been determined, as well as the differences between them. Also, shock- vibration tests have been accomplished, not only to explain the two shock response signal differences, but also to analyze the response signal characteristics and its ability to carry information. In addition, seismic data acquisition experiments have been carried out under comparable conditions in the field. A contrast analysis of shot gathers and stack profiles acquired with the two geophone types is given in this paper. The results show that the acceleration signal from the acceleration geophone has a better advantage in terms of high signal-to-noise ratio, high accuracy, high resolution, and quantity of information to better meet current and future requirements for seismic exploration.

Analysis of geophone properties effects for land seismic data

The properties of the seismic geophones are important factors for high-resolution seismic exploration and have a great influence on data quality. For this reason, we have tested three kinds of geophones currently used in several regions with different geological features： desert, saline-alkali farmland, and carbonate areas in mountainous regions in order to test their property indexes. Based on the geophone vibration equation and from the property index effects ofgeophone and the connection of the geophones on seismic data, we analyzed seismic data quality acquired inthe tested regions and suggest that suitable geophone property indexes, reasonable choice of geophone types, and the suitable geophone connection can enhance the signal/noise ratio of seismic data.

Locating microseismic sources based upon L-shaped single-component geophone array:A synthetic study

We have developed a type of L-shaped single-component geophone array as a single station(L-array station)for surface microseismic monitoring.The L-array station consists of two orthogonal sensor arrays,each being a linear array of single-component sensors.L-array stations can be used to accurately estimate the polarization of first arrivals without amplitude picking.In a synthetic example,we first use segmentally iterative ray tracing(SIRT)method and forward model to calculate the travel time and polarization of first arrivals at a set of L-array stations.Then,for each L-array station,the relative delay times of first arrivals along sensor arrays are used to estimate the polarization vector.The small errors in estimated polarization vectors show the reliability and robustness of polarization estimation based on L-array stations.We then use reverse-time ray-tracing(RTRT)method to locate the source position based on estimated polarizations at a set of L-array stations.Very small errors in inverted source location and origin time indicate the great potential of L-array stations for source localization applications in surface microseismic monitoring.

Application of a New Qeneration of Geophonesto Improve Seismic Acquisitionin Onshore-offshore Transition Areas

In this paper, we review the differences between velocity geophones （VG） and acceleration geophones （AG） and their effect on seismic signals acquired in onshore-offshore transition areas. We present a new generation of Land Piezoelectric Geophone （LPG） and analyze its performance. Our field experiments demonstrate that our new LPG can be used to substitute for VGs in order to eliminate phase, frequency and energy differences between different geophone systems commonlv used in transition areas.

Determination of Direction of Arrival of Seismic Wave by a Single Tri-axial Fiber Optic Geophone

A fiber Bragg grating (FBG) geophone and a surface seismic wave-based algorithm for detecting the direction of arrival (DOA) are described. The operational principle of FBG geophone is introduced and illustrated with systematic experimental data, demonstrating an improved FBG geophone with many advantages over the conventional geophones. An innovative, robust, and simple algorithm is developed for obtaining the bearing information on the seismic events, such as people walking, or vehicles moving. Such DOA estimate is based on the interactions and projections of surface-propagating seismic waves generated by the moving personnel or vehicles with a single tri-axial seismic sensor based on FBGs. Of particular interest is the case when the distance between the source of the seismic wave and the detector is less than or comparable to one wavelength (less than 100 m), corresponding to near-field detection, where an effective method of DOA finding lacks.

A wireless geophone based on STM32

Seismic geophone is the key instrument for seismic data acquisition in the fields of oil and gas exploration and other relevant fields.It plays an important role in data quality,subsequent processing and interpretation.Aiming at the shortcomings of the existing geophones,such as large volume,heavy weight,unable to monitor in real-time,and heavy workload of data transmission and storage,this paper designs and implements a wireless geophone based on STM32 embedded microcontroller.It is mainly composed of STM32 microcontroller,acceleration sensor,global positioning system(GPS)module,Wi-Fi module and real-time seismic data receiving and processing module.Firstly,the acceleration of vibration in three directions is sensed by the acceleration sensor;secondly,the sampling and analog-to-digital conversion of the vibration data is controlled by the microcontroller;thirdly,the vibration and GPS data are sent to the personal computer(PC)through Wi-Fi,and the personal coomputer PC-side software module completes the reception,display,monitoring and storage of the seismic data;finally,the feasibility and effectiveness of the designed wireless geophone are verified through actual seismic data acquisition experiments.

Distributed Fiber Optic Interferometric Geophone System Based on Draw Tower Gratings

A distributed fiber optic interferometric geophone array based on draw tower grating （DTG） array is proposed. The DTG geophone array is made by the DTG array fabricated based on a near-contact exposure through a phase mask during the fiber drawing process. A distributed sensing system with 96 identical DTGs in an equal separation of 20 m and an unbalanced Michelson interferometer for vibration measurement has been experimentally validated compared with a moving-coil geophone. The experimental results indicate that the sensing system can linearly demodulate the phase shift. Compared with the moving coil geophone, the fiber optic sensing system based on DTG has higher signal-to-noise ratio at low frequency.

One-way wave equation seismic prestack forward modeling with irregular surfaces

Mathematical geophone （MG） and equal-time stacking （ETS） principles are used to implement seismic prestack forward modeling with irregular surfaces using the oneway acoustic wave-equation. This method receives seismic primary reflections from the subsurface using a set of virtual MGs. The receivers can be located anywhere on an irregular observing surface. Moreover, the ETS method utilizes the one-way acoustic wave equation to easily and quickly image and extrapolate seismic reflection data. The method is illustrated using high single-noise ratio common shot gathers computed by numerical forward modeling of two simple models, one with a flat surface and one with an irregular surface, and a complex normal fault model. A prestack depth migration method for irregular surface topography was used to reoroduce the normal fault model with high accuracy.

Seismic effort of blasting wave transmitted in coal-rock mass associated with mining operation

Microseismic effects during the transmission of seismic waves in coal and rock mass associated with mining operation were studied by on-site blasting tests and microseismic monitoring in LW704 of Southern Colliery,Australia,by using spread velocities,amplitudes and frequency contents as the main analysis parameters.The results show that the average P-wave velocity,mean values of combined maximal amplitudes and frequencies of the first arrivals are all reduced significantly along with goaf expanding and intensity weakening of overlying strata during mining process.A full roof fracturing can make the average P-wave velocities,combined maximal amplitudes and frequencies of first arrivals reduce to about 69.8%,92.2% and 60.0%,respectively.The reduction of the above seismic parameters reveals dynamic effects of the variation of strata structure and property to the wave transmission and energy dissipation of blasting wave.The research greatly benefits further study on stability of surrounding rock under the destructive effort by mine tremor,blasting,etc,and provides experimental basis for source relocation and parameter optimization of seismic monitoring as well.

Review of Fiber-optic Distributed Acoustic Sensing Technology

A distributed optical-fiber acoustic sensor is an acoustic sensor that uses the optical fiber itself as a photosensitive medium,and is based on Rayleigh backscattering in an optical fiber.The sensor is widely used in the safety monitoring of oil and gas pipelines,the classification of weak acoustic signals,defense,seismic prospecting,and other fields.In the field of seismic prospecting,distributed optical-fiber acoustic sensing(DAS)will gradually replace the use of the traditional geophone.The present paper mainly expounds the recent application of DAS,and summarizes recent research achievements of DAS in resource exploration,intrusion monitoring,pattern recognition,and other fields and various DAS system structures.It is found that the high-sensitivity and long-distance sensing capabilities of DAS play a role in the extensive monitoring applications of DAS in engineering.The future application and development of DAS technology are examined,with the hope of promoting the wider application of the DAS technology,which benefits engineering and society.

Design and Application of a Multichannel Analysis Surface Waves Acquisition System for the Pavement Layers Investigation

This study aims to design and develop a pavement non-destructive quality testing device with the MASW method. Unlike the traditional acquisition techniques that plants geophones on the pavement, the presented approach uses no-tip geophones, placed directly on the pavement surface to preserve its integrity. To proceed, a seismograph using an Arduino Due microcontroller connected to a Raspberry Pi 4 nano-computer was developed. The receivers consist of 6 4.5 Hz GD geophones connected together by a graduated tape to control the inter-trace distance and to in order to acquire data in land-streamer. The recording is triggered by a KY-038 sound sensor. The Arduino acts as an analog-to-digital converter while the Raspberry is used as a real-time data visualization and processing interface. The obtained seismic data has been processed using the Geopsy open-source software which allows the analysis and inversion of the dispersion curves. The studied system has been tested in 4 different sites. The obtained seismic VS and VP velocities as a function of the depth allowed to deduce the elastic properties of the pavement layers and to decide on their mechanical quality with the possibility of integrating the results in the road data banks.

3-D Tunnel Seismic Advance Prediction Method with Wide Illumination and High-Precision

Tunnel seismic advance prediction can effectively reduce the construction risk during tunnel excavation.Compared with the 2-D method,the 3-D method is more conducive to describing the spatial characteristics of the geological body by adding the seismic data in the vertical direction.However,some drawbacks still need improvement in the current 3-D tunnel seismic prediction method.(1)The geometry is complex,which is destructiveness,high cost,and time-consuming,and will delay the tunnel construction schedule.(2)Illumination of the anomalous body is insufficient,and the precision of migration imaging is low.(3)Shot points are far away from the tunnel face,the energy loss at the shot points is more serious.(4)The received signals at the tunnel wall have the surface wave with strong energy when the shot points are placed on the tunnel wall.(5)The geometry is not linear,so the directional filtering method cannot be used to extract the reflection wave.To overcome the drawbacks of the current prediction method,a new 3-D symmetrical tunnel seismic prediction method is proposed.Six geophones are installed on the tunnel wall,two on the left side,two on the right side,and two on the top side.Twenty-four shot points are placed on the tunnel face and near both sides of the tunnel wall,twelve shot points on the left side and twelve shot points on the right side.The shot points will move along with the forward excavation of the tunnel.The wavefield analysis,illumination statistics,and 3-D reverse time migration imaging are used to evaluate the proposed method.The result of modeled data indicates that the proposed 3-D geometry has some advantages:(1)the geometry is simple and the geophone installation time is short;(2)it has high illumination energy,wide illumination range,and can improve the prediction distance and imaging accuracy;(3)the proposed 3-D method can better estimate the velocity of surrounding rock and is more conducive to extracting the reflection wave with high resolution.

A rigorous real-time acoustic positioning method for ocean bottom seismic exploration

The conventional technique for positioning seafloor geophones in ocean bottom seismic exploration encounters several challenges,including the significant impact of outliers on positioning results,underutilization of high-precision observations,and low efficiency in real-time data processing.These issues inevitably affect the quality of seismic exploration outcomes.To address these challenges and enhance the accuracy of geophone positioning,this paper proposes a rigorous real-time acoustic positioning method for geophones based on sequential adjustment and Baarda's outlier detection approach.The proposed method comprises three key steps:grouping the original acoustic observations,constructing the intra-group acoustic positioning model,and synthesizing the positioning results across the different groups.The validity and practicality of this approach are confirmed through a simulation experiment as well as the field experiment conducted in the Bohai Sea,China.The results demonstrate that the proposed method effectively eliminates outliers in the original observations and maximizes the utilization of high-quality observations.Compared to traditional acoustic positioning methods,it significantly reduces positioning errors from meters to decimeters,and in some cases can achieve centimeter-level precision.When the sound velocity profile in the operating sea area is measured,the method can attain the posterior standard deviation at the millimeter level and positioning errors within 10 cm.When the sound velocity profile is unknown,the method can achieve the posterior standard deviation at centimeter-level and positioning errors of approximately 20 cm.

Progress of Optical Fiber Sensors and Its Application in Harsh Environment

Fiber sensors have been developed for industry application with significant advantages.In this paper,Fiber sensors for oil field service and harsh environment monitoring which have been investigated in Tsinghua University are demonstrated.By discussing the requirements of practical applications,the key technologies of long-period fiber grating(LPFG)based fiber sensor,optical spectrum analyzer for oil detection,laser induced breakdown spectroscopy(LIBS)system for soil contamination monitoring,and seismic sensor arrays are described.