Time-lapse geophysical technology-based study on overburden strata changes induced by modern coal mining

To study the impact of modern coal mining on overlying strata and its water bearing conditions,integrated time-lapse geophysical prospecting integrating 3D seismic,electrical and ground penetrating radar method were used.Through observing and analyzing the geophysical data variations of all stages of pre-mining,mining and post-mining as well as post-mining deposition stable period,impacts of coal mining on stratigraphic structure and its water bearing were studied and modern coal mining induced stratigraphic change pattern was summarized.The research result shows that the stratigraphic structure and the water bearing of surface layer during modern coal mining have self-healing pattern with mining time;the self-healing capability of near-surface strata is relatively strong while the roof weak;water bearing selfhealing of near-surface strata is relatively high while the roof strata adjacent to mined coal beds low.Due to integrated time-lapse geophysical prospecting technology has extra time dimension which makes up the deficiency of static analysis of conventional geophysical methods,it can better highlight the dynamic changes of modern coal mining induced overburden strata and its water bearing conditions.

Continuous TDEM for monitoring shale hydraulic fracturing

Monitoring and delineating the spatial distribution of shale fracturing is fundamentally important to shale gas production. Standard monitoring methods, such as time-lapse seismic, cross-well seismic and micro-seismic methods, are expensive, time- consuming, and do not show the changes in the formation with time. The resistivities of hydraulic fracturing fluid and reservoir rocks were measured. The results suggest that the injection fluid and consequently the injected reservoir are characterized by very low resistivity and high chargeability. This allows using of the controlled-source electromagnetic method （CSEM） to monitor shale gas hydraulic fracturing. Based on the geoelectrical model which was proposed according to the well-log and seismic data in the test area the change rule of the reacted electrical field was studied to account for the change of shale resistivity, and then the normalized residual resistivity method for time lapse processing was given. The time-domain electromagnetic method （TDEM） was used to continuously monitor the shale gas fracturing at the Fulin shale gas field in southern China. A high-power transmitter and multi-channel transient electromagnetic receiver array were adopted. 9 h time series of Ex component of 224 sites which were laid out on the surface and over three fracturing stages of a horizontal well at 2800 m depth was recorded. After data processing and calculation of the normalized resistivity residuals, the changes in the Ex signal were determined and a dynamic 3D image of the change in resistivity was constructed. This allows modeling the spatial distribution of the fracturing fluid. The model results suggest that TDEM is promising for monitoring hydraulic fracturing of shale.

Time-Lapse 3-D Seismic Wave Simulation via the Generalized Multiscale Finite Element Method

Numerical solution of time-lapse seismic monitoring problems can be challenging due to the presence of finely layered reservoirs.Repetitive wave modeling using fine layered meshes also adds more computational cost.Conventional approaches such as finite difference and finite element methods may be prohibitively expensive if the whole domain is discretized with the cells corresponding to the grid in the reservoir subdomain.A common approach in this case is to use homogenization techniques to upscale properties of subsurface media and assign the background properties to coarser grid;however,inappropriate application of upscaling might result in a distortion of the model,which hinders accurate monitoring of the fluid change in subsurface.In this work,we instead investigate capabilities of a multiscale method that can deal with fine scale heterogeneities of the reservoir layer and more coarsely meshed rock properties in the surrounding domains in the same fashion.To address the 3-D wave problems,we also demonstrate how the multiscale wave modeling technique can detect the changes caused by fluid movement while the hydrocarbon production activity proceeds.

Characteristics of coda Q-value in the midnorthern part of Ningxia

On the basis of previous studies, this paper in studying the coda Q-valuc of near shocks, has proposed using the sampling depth to describe the effect of lapse time on the Q-value, and has investigated the dependence of coda wave of earthquakes on frequency and sampling depth. Analysis of digital seismograms recorded by the Yinchuan Telemetric Seismic Network, Ningxia, shows that not only the coda wave Q-value of shocks is strongly dependent on frequency but also its dependence on Samling depth cannot be neglected. In the commonly used formula that describes the dependence cbaracteristics of coda Q-value of endquakes, Q = Qof', the parameter Qo rises obviously whilc n drops when the sampling depth increases, and their changes can be fitted by linear relations. This paper has explained such a characteristic. Whether this characteristic exists universally needs to be verified by more study results because the genetic mechanism of coda wave of earthquakes is more complex.

Using a 3-D multicellular simulation of spinal cord injury with live cell imaging to study the neural immune barrier to nanoparticle uptake

Development of nanoparticle （NP） based therapies to promote regeneration in sites of central nervous system （CNS; i.e, brain and spinal cord） pathology relies critically on the availability of experimental models that offer biologically valid predictions of NP fate in vivo. However, there is a major lack of biological models that mimic the pathological complexity of target neural sites in vivo, particularly the responses of resident neural immune cells to NPs. Here, we have utilised a previously developed in vitro model of traumatic spinal cord injury （based on 3-D organotypic slice arrays） with dynamic time lapse imaging to reveal in real-time the acute cellular fate of NPs within injury foci. We demonstrate the utility of our model in revealing the well documented phenomenon of avid NP sequestration by the intrinsic immune cells of the CNS （the microglia）. Such immune sequestration is a known translational barrier to the use of NP-based therapeutics for neurological injury. Accordingly, we suggest that the utility of our model in mimicking microglial sequestration behaviours offers a valuable investigative tool to evaluate strategies to overcome this cellular response within a simple and biologically relevant experimental system, whilst reducing the use of live animal neurological injury models for such studies.