Induced Polarization Research Articles

A Mesh Mapping-Based Cooperative Inversion Strategy for Airborne Transient Electromagnetic and Magnetic Methods

Cooperative inversion is a powerful underground imaging technique that can overcome the limitations of a single detection method. However, due to the different grid divisions used by various geophysical methodologies, imposing structural constraints between grids of different scales is challenging. This paper proposes a new cooperative inversion strategy and applies it to the inversion of the quasi-two-dimensional aerial transient electromagnetic method (ATEM) with the induced polarization (IP) effect and the two-dimensional magnetic method to solve the problem of applying cross-gradient constraints under grids of different scales. The mesh mapping method is incorporated into the iterative process of cooperative inversion in this inversion strategy. The inversion of synthetic data shows that this technique can effectively employ data complementarity to increase the accuracy of the results for describing the medium boundary. The mesh mapping methodology may be applied to the cooperative inversion of geophysical methods under any grid division and successfully solves the problem of grid division mismatch in cooperative inversion.

Boosted electromagnetic wave absorption performance from synergistic induced polarization of SiCNWs@MnO2@PPy heterostructures

Boosted electromagnetic wave absorption performance from synergistic induced polarization of SiCNWs@MnO2@PPy heterostructures

Pore-scale modelling on complex-conductivity responses of hydrate-bearing clayey sediments: Implications for evaluating hydrate saturation and clay content

A majority of the accumulated gas hydrates exist in fine-grained unconsolidated sediments with clays, which pose challenges to reservoir evaluation with resistivity-based techniques. Characteristic electrical parameters derived from induced polarization (IP) measurements have potentials to describe complex formations of various lithology, pore-water salinities, and different depths from the borehole. However, there is still a knowledge gap in complex-conductivity properties of the hydrate-bearing clayey sediments. We present a pore-scale numerical study on modelling the low-frequency (<1 kHz) complex-conductivity spectra of clayey sediments containing hydrates based on the finite-element approach, with an emphasis on evaluating the hydrate saturation (sh) and clay content. Firstly, the influences of clay type, distribution form, content and sh on the complex conductivity of sediments containing hydrates were examined systematically. Secondly, power-law and linear correlations were established for evaluating the hydrate saturation and clay content, respectively, based on complex-conductivity parameters. (Effects of clay type) The in-phase conductivity of hydrate-bearing smectite is significantly higher than that of hydrate-bearing illite and kaolinite due to the higher cation exchange capacity (CEC) of smectite. Higher peak frequency and quadrature conductivity appear for the hydrate-bearing kaolinite case because the mobility of counterions in the Stern layer of kaolinite is about ten times of that for smectite and illite. (Effects of clay distribution form) The coating-clay case has much lower in-phase and quadrature conductivities than the dispersed- and laminated-clay cases because the coating clay isolates sand particles from the pore water and no electrical double layer (EDL) forms around the sand particles. (Effects of clay content) With an increasing content of the structural clay up to 60%, the in-phase conductivity decreases and increases in the frequency bands lower and higher, respectively, than the peak frequency corresponding to the EDL polarization. The effective dielectric constant increases consistently with the clay content due to the much higher CEC of clays than that of sands. (Effects of hydrate saturation) The in-phase conductivity decreases consistently with an increasing sh up to 0.40 due to the negligible conductivity of hydrates and blockage effect on conduction currents. Both the quadrature conductivity and effective dielectric constant in the EDL-polarization-dominant frequency band decrease with an increasing sh. In this work, it has been evidenced that complex-conductivity responses of hydrate-bearing clayey sediments can be understood theoretically and modelled numerically based on the interpretation of electrical conduction and electrochemical polarization mechanisms of EDLs. This study provides a theoretical and modelling foundation for the development of new IP-based geophysical techniques for hydrate-reservoir evaluation and monitoring in both the exploration and exploitation stages.

Mapping of Potential Groundwater Using Electrical Resistivity Imaging (ERI) at Low Land Area of Parit Raja Johor

Electrical Resistivity Imaging (ERI) has emerged as an important technique in geophysical surveys for gaining more information and locating hidden water. This method was used at Parit Raja, Johorto investigate the location of underground water storage. Two-dimensional (2D) geoelectrical imaging has been used for this study. The imaging method was used at three different locations in the study area to identify potential aquifer and suitable locations for boreholes that would serve as observation wells. A Schlumberger array was set up during data acquisition since it can imagine deeper profile data and suitable for areas with a homogeneous layer. For 2D subsurface images, the raw data were processed with the RES2DINV software. According to the ERI results, this area was dominant with low resistivity values of less than 10 Ωm and potential shallow aquifer depths ranging from 10 to 30 m. Furthermore, the chargeability value obtained from Induced Polarization (IP) supported this point. According to the IP data, the chargeability at that point was between 0 and 1 ms, indicating the presence of a groundwater in the study area.

3-D complex resistivity imaging using controlled source electromagnetic data: a multistage procedure using a second order polynomial parametrization

SUMMARY In some Earth materials, significant induced polarization (IP) phenomena are occurring when an electric perturbation is applied. These mechanisms are described by a frequency-dependent complex resistivity (CR). The study of the CR spectral signature allows to access indirectly to several properties of interest of the subsurface linked to the interaction between the pore space and fluids. CR is usually studied using the electrical method with a direct current approximation, neglecting by the way electromagnetic (EM) induction that can occur in the data. However, EM induction increases with frequency and offset, resulting in limitations at high frequencies or for the investigation of deep target. We implemented a frequency-dependent CR in a 3-D finite-differences (FD) modelling and inversion code for frequency domain controlled-source electromagnetic (CSEM) data to take into consideration IP information contained in EM data or reciprocally. The CSEM methods are resistivity imaging techniques using multifrequency EM fields that fully take into account EM induction with large investigation depth. Following a preliminary sensitivity study, a multistage inversion framework was designed to constrain the multiparameter inverse problem. Furthermore, to manage the increasing number of parameters, a second-order polynomial parametrization is used to describe independently frequency variation of CR norm and phase. We demonstrate the method through 1-D and 3-D synthetic data inversions for a deep-target model. We show that we were able to recover the CR and its frequency variation from CSEM data in the IP/EM coupling domain for 1-D targets. The problem of deep polarizable 3-D targets is more challenging and the resolution of the recovered CR spectrum was impacted. Nevertheless, we retrieved from a model containing several polarizable anomalies some crucial information allowing the discrimination of the targets from the non-polarizable background and from different spectral CR signatures. Our inversion strategy allows thus accessing to IP parameters of the medium in an extended frequency domain by fully taking EM induction information into account.

Rapid and Simple Method for Measuring Petroleum Asphaltenes by the Centrifugation Technique.

Asphaltenes are heavy constituents of crude oil which affect the flow and viscosity of crude oil. They also stabilize water-in-oil emulsions which makes the separation process of water from oil during the primary treatment processes for crude oils more difficult and costly. Measuring asphaltenes has great importance, especially for crude oil production companies. Gravimetric and spectroscopic measurement methods are the basic techniques used by international references such as ASTM and IP. A new methodology has been introduced as a modification of ASTM D6560 gravimetric methodology by using the centrifugation technique in the separation of asphaltenes for different oil samples with the API gravity change from 17.4 (oil S1) to 39.8 (oil S5). The new methodology has the advantages of consuming little time, and multiple sample processing and can be done in the field and also in the lab. Moreover, it has good repeatability, reproducibility, and working range values compared to the reference gravimetric ASTM and IP methods. The repeatability of the new method was found to be 8.0% at its maximum value (S1, has a low asphaltene content), while the minimum value was found to be 3.75% (S10, has the highest asphaltene content). It was found that the maximum reproducibility value was 17.0% for the S1 sample and the minimum was 0.0% for S9 and S10 samples.

Integrated geophysical investigation for lead and zinc mineralization in Wase, middle Benue Trough, Nigeria

There is an increasing demand for solid industrial minerals worldwide, as countries seek to support their economic growth. Wase, situated in Plateau State, is notable for lead and zinc mineralisation due to tectonic and hydrothermal activities in the region. The study utilises geophysical surveys to map mineralised zones of lead-zinc occurrence. These include ground magnetic survey, very low frequency electromagnetic, electrical resistivity tomography, and induced polarisation (IP). The field data were acquired using a GEMSys Overhauser magnetometer with VLF option and ABEM LS 2 Terrameter. twenty-nine (29) magnetic profiles with 50m spacing and a total length of 24.0 km were obtained and fifteen (15) very low frequency electromagnetic (VLF-EM) profiles with 10 m spacing in the E-W direction. A total length of 12.5 km was acquired across target areas of the magnetic profiles. The multiple-gradient electrode array of the ERT/IP surveys was used for data acquisition, and RES2DINV software by Geotomo was used for the inversion of the acquired data. High chargeability values corresponding to low resistivity values characterised zones with suspected lead-zinc mineralisation. Following this preliminary finding, we advise that further trenching, pitting, or core drilling be carried out to ascertain ore grade, possible beneficiation, and estimate of the reserve.

3D time-domain induced polarization modelling considering anisotropy and topography

Induced polarization (IP) method is one of the most widely used techniques in mineral exploration, hydrogeology, and environmental monitoring, becoming indispensable especially for metallic ore exploration. Topography of the surface and anisotropy of the subsurface plays an important role in the IP data interpretation and modelling leading to wrong resistivity and chargeability models if they are not considered. We developed a 3D IP forward modelling considering arbitrary anisotropy and topography using the finite element method (FEM). The newly developed algorithm is compared with the numerical solutions and analytical results for classical two-layer anisotropic models successfully. By using unstructured mesh to consider complex topography, we implement 3D IP forward modelling for arbitrary anisotropic medium under the condition of uneven terrain and investigate the effect of anisotropy and topography on IP data interpretation. Topography has a decreased or reinforcing effect on time-domain induced polarization (TDIP) response. Vertical transverse isotropic (VTI) medium has a tiny effect and can accurately locate the anomaly in the subsurface while tilted transverse isotropic (TTI) medium has a very large effect and cannot be explored. Under the comprehensive influence of complex topography and anisotropy with an angle larger than 30 degrees, it is very difficult to interpret TDIP results. The 3D inversion of the synthetic data derived by the 3D anisotropic chargeability model indicates that topography weakens the TDIP response. However, VTI anisotropic anomaly can be detected accurately in the horizontal direction, the TTI anisotropic anomaly is difficult to be explored.

Application of Induced Polarization and Resistivity to the Determination of the Location of Minerals in Extrusive Rock Area, Southern Mountains of Java, Indonesia

Mountainous areas often have a lot of natural wealth. The existence of geological appearances in the form of outcrops which are products of intrusion and alteration, indicates that the Pacitan area is a mineralized zone. In this study, geophysical measurements were carried out using the Induced Polarization (IP) method in the area where mineralization was suspected. The polarization induction method is expected to prove the presence of a mineralized zone in the Pacitan area. From the research results, line 1, line 4, line 5, line 6 and line 7 are areas with high chargeability values. So it can be proven that the area with high resistivity and high chargeability is an area with mineralization. Judging from the geological conditions on the surface, there are also outcrops which show that there is an intrusion and the result of alteration. So it can be concluded that the area has a fairly high mineralization. In measuring the correlation between magnetic anomalies and IP, the results are very supportive of each other that the area is a mineralized area, if we look at the resistivity, and chargebility.

Geophysical exploration and geological appraisal of the Siah Diq porphyry Cu–Au prospect: A recent discovery in the Chagai volcano magmatic arc, SW Pakistan

AbstractDiscovery of the Siah Diq porphyry (Cu–Au) prospect in the foothill of Dam Koh volcano is a recent exploration success story of mineralization buried under a 46 m alluvium cover in an exploratory mature Chagai belt. Acquisition of geophysical data followed by drilling and logging was key in the discovery. Integrated magnetics and induced polarization (IP) surveys in an area of 7.5 km2, pointed out magnetic-low, IP-high, and resistivity-low anomalies corresponding to porphyry Cu–Au type sulfide mineralization. Three bore holes were drilled to test the geophysical anomalies. After careful observation and geoscientific logging of core, porphyry style Cu–Au mineralization was revealed. The porphyry prospect was further characterized based on host rock lithology, petrography, alteration mineralogy, ore vein characterization, and Cu/Au geochemical assays based on core samples. Rocks hosting the mineralization include andesite, granodiorite, coarse, as well as fine grained diorite and pink granite, all highly altered, mineralized and porphyritic. Propylitic alteration was dominant in all the three bore holes and developed earlier followed by phyllic, potassic, and argillic alterations. Sulfide mineralization is present as cross-cutting stockwork veins and disseminations. Average copper and gold assays of drill core are 0.17% Cu and 0.78 ppm Au, respectively. Economically insignificant values of molybdenum and silver have been noted in some samples.

Mineralization Based on CSAMT and SIP Sounding Data: A Case Study on the Hadamengou Gold Deposit in Inner Mongolia

The Hadamengou deposit is the largest gold deposit in Inner Mongolia. However, given that the sources of ore-forming alkaline magmatic hydrothermal solutions and ore-controlling structures are still controversial, the theories behind the genesis of the deposit have been controversial. In this study, four controlled-source audio magnetotellurics (CSAMT) and spectral induced polarization (SIP) profiles in the mining area were used to obtain the underground resistivity model and the pseudo section map of the apparent frequency dispersivity based on fine inversion. In the resistivity model, there are two high-resistivity blocks with resistivity greater than 3000 Ω m and three low-resistivity channels with resistivity less than 50 Ω m. Combined with the regional geological and drilling data, it is inferred that the high-resistance bodies, R4 and R5, may be alkaline magmatic intrusions related to multiple stages of magmatic hydrothermal activities, ranging from the Precambrian to Yanshanian periods. The highly conductive channels, C3, C5, and C4, may represent the Baotou-Hohhot fault, secondary faults, and ductile shear zone, respectively, which were formed in the Precambrian era and underwent multiple activations during the Hercynian to Yanshanian period. According to the spatial relationship, it is inferred that the ductile shear zone is an important ore-controlling and ore-hosting structure. However, the Baotou–Hohhot fault may be a pre-metallogenic fault rather than an ore-controlling fault. By comparing the resistivity model with the pseudo section of the apparent frequency dispersivity, it was found that all the known gold veins are located in the superimposed area of low resistivity and high-frequency dispersivity. It is speculated that the ductile shear zone outside the alkaline magmatic rock with the superimposed characteristics of low resistivity and high-frequency dispersivity is the favorable area for mineralization.

Complex Resistivity Anisotropy Response Characteristics of Wufeng-Longmaxi Formation Shale in Southern Sichuan

Electrical exploration has become an important means of shale gas reservoir exploration and evaluation, and is expected to play a key role in the later stages of reservoir fracturing and development. At present, the research on the electrical response characteristics of shale gas reservoirs and their relationship with reservoir parameters is extensive and in-depth, but there is little research on their complex resistivity anisotropy characteristics and influencing factors, which restricts petrophysical modeling and reservoir parameter prediction, and reduces the reliability of shale gas exploration and reservoir evaluation by electromagnetic methods. In this paper, shale samples from the Longmaxi Formation and the Wufeng Formation of shale gas wells in southern Sichuan were collected, the complex resistivity of 34 shales in bedding direction and vertical bedding direction were measured, and the induced polarization (IP) parameters of shales were extracted by inversion. The electrical anisotropy response characteristics under different temperature and pressure conditions were analyzed, and the influencing factors and laws of complex resistivity anisotropy of shales were revealed. Combined with the test results of shale porosity and permeability, the evaluation model of resistivity, polarizability and porosity and permeability parameters was established. The research results have formed a set of testing methods and analysis techniques for electrical anisotropy of shale reservoirs, which are mainly based on complex resistivity parameter testing. It is helpful to understand the electrical anisotropy characteristics of shale gas reservoirs in southern Sichuan; this will provide the theoretical and physical basis for shale gas reservoir evaluation and fracturing monitoring by electrical exploration.

A novel approach to determine rock mechanical parameters using non-invasive geophysical methods

Engineering design of the major infrastructures mainly relies on determination of rock mechanical parameters. However, such indexes are traditionally acquired from the borehole tests of the construction site. The drilling test is generally time-consuming and costly procedure. Further, such tests provide geology information only at some specific points, need more equipment, are hardly carried out in the high topographic sites, and often leave ambiguity in the subsurface interpretation. Alternatively, geophysical research of ERT (electrical resistivity tomography) is swift, user-friendly, inexpensive and non-destructive, and can provide a bridge between the limited drilling tests and a true geotechnical model of the subsurface. In the present research, we introduce a novel geophysical approach to estimate rock mass integrity index (Kv) via integration between the ERT-based electrical resistivity and the limited borehole-based Kv. The obtained Kv offers 2D and 3D evaluation of rock mass integrity along all ERT profiles for large coverage of the project site where even no borehole data exist. Furthermore, uncertainty in the evaluation of water-clay distinction was removed by the integration of IP (induced polarization) with ERT. Our research, compared to the conventional geotechnical investigations, removes uncertainties in the geotechnical model and offers more accuracy in rock mass quality classification for various types of rock units. This approach removes the extensive drilling tests and offers a comprehensive assessment of rock mass integrity to achieve the proper design of engineered infrastructures in the highly heterogeneous terrains.

Development of formalin killed vaccine candidate against streptococcosis caused by Enterococcus sp. in Nile tilapia

Multiple bacteria under Streptococcus, Enterococcus and Lactococcus genera are considered to be associated with Streptococcosis. This study was conducted to develop and evaluate the effectiveness of whole cell formalin killed vaccine prepared from E. faecalis, E. hirae and E. faecium against the streptococcosis in Nile tilapia. To develop the candidate vaccine, efficacy of whole cell killed E. faecalis (strains BFF1B1 & BFTS22), E. hirae (strain BFTS29) and E. faecium (strain BFTS31) were evaluated. The vaccine prepared by mixing 3 % formalin and left for 24 h to kill the bacterial cells. Physiological saline (0.85 %) was mixed to the harvested formalin free killed cells to make final suspension for vaccine. This vaccine was administered to the fingerling tilapia (average weight 30 ± 5 g) by interperitoneal injection (IP) and bath immersion (BI) methods. The vaccinated group was monitored for 28 days to assess the developed immunity and vaccine safety into the fish. Post vaccination in vivo challenge test were performed against the pathogens. The hematological parameters (RBC, WBC, platelets and hemoglobin) and specific IgM were found significantly higher (p < 0.001) in the vaccinated fish compared to those in the non-vaccinated fish. The mean mortality in IP and BI method ranged from 10.0 ± 0.00 % to 23.3 ± 5.77 % and 18.33 ± 5.30 % to 40.0 ± 0.10 %, respectively. The relative percentage survival (RPS) in IP and BI varied from 68.78 % to 88.57 % and 59.52 % to 69.05%, respectively. Mortality was significantly lower in the immunized fish compared to those in non-immunized fish. The RPS were not different (p > 0.05) between IP and BI vaccination method. Formalin killed vaccine showed an excellent efficacy against Enterococcus sp. infection in Nile tilapia by IP method although bath immersion could also be an alternative.

Imaging hydraulic conductivity in near-surface aquifers by complementing cross-borehole induced polarization with hydraulic experiments

Precise information about the spatial distribution of hydraulic conductivity (K) in an aquifer is essential for the reliable modeling of groundwater flow and transport processes. In this study, we present results of a new inversion procedure for induced polarization (IP) data that incorporates petrophysical relations between electrical and hydraulic parameters, and therefore allows for the direct computation of K. This novel approach was successfully implemented for the Bolstern aquifer analog by performing synthetic IP experiments with a combined surface and cross-borehole setup. From these data, the distribution of K was retrieved with high accuracy and resolution, showing a similar quality compared to images achieved by hydraulic tomography. To further improve the quantitative estimates of K, we use synthetic pumping test data to inform two novel calibration strategies for the IP inversion results. Both calibrations are especially helpful for correcting a possible bias of the IP inversion, e.g., due to resolution limitations and/or to bias in the underlying petrophysical relations. The simulation of tracer experiments on the retrieved tomograms highlights the accuracy of the inversion results, as well as the significant role of the proposed calibrations.

Delineation of kaolinised and aquifer formations using electrical resistivity tomography (ERT) and induced polarization (IP) techniques

Delineation of kaolinised and aquifer formations using electrical resistivity tomography (ERT) and induced polarization (IP) techniques

Penalties From 2D Grating Coupler Induced Polarization Crosstalk in Silicon Photonic Coherent Transceivers

Silicon photonic two-dimensional grating couplers for C- and O-band dual-polarization coherent transceivers are analyzed with respect to their polarization splitting/combining performance. Due to scattered light in the grating's plane, a linear cross-polarization results. The latter is responsible for a limited polarization split ratio and a polarizations' non-orthogonality. The impact of these two quantities is evaluated by system-level simulations with regard to OSNR penalties in coherent systems. For both C- and O-band, a design modification for reduced penalties is proposed.

A Set of In-Well Receiver Array for Borehole Induced Polarization Detecting Technology in Deep Mine Exploration

With the rapid development of the economy, the demand for mineral resources has increased dramatically. Because it is difficult to explore new mines in deep and peripheral areas, new theories, technologies, methods, and equipment are needed. How to accurately and effectively carry out new mine exploration has become an urgent research topic. In this study, based on the requirements of mine exploration within a depth of 3000 m, an array receiver for borehole-induced polarization was developed. Each channel of the receiver array independently acquires data, and it is able to carry out full waveform acquisition in the dual voltage and voltage difference mode. The structure of the receiver array can be flexibly adjusted to obtain array observations of induced polarization in different ways. Experiments demonstrated that the device works well at a high temperature of 155 °C, its resolution reached 0.1 μV, and the error between the different channels was less than 3%. Its dynamic range is 180 db. Through experiments on induced polarization in a demonstration mining area, the apparent resistivity curve and the apparent polarization curve were determined to be consistent with the known well-logging information, and the interpretation results were in agreement with the stratum information.

The Influence of Magnetic Minerals on Induced Polarization Measurements in Sedimentary Rocks

AbstractInduced polarization (IP) measurements in porous sedimentary rocks are modeled in terms of pore geometrical descriptors (PGD). Using an extensive data set composed of 241 sandstone, carbonate, and arenite samples, we identified a stronger relationship between IP parameters and volumetric magnetic susceptibility versus IP parameters and PGD. This finding suggests that even small concentrations of iron minerals in rocks typically thought to lack electron‐conducting minerals can significantly influence IP measurements. The combination of magnetic susceptibility with a pore geometrical descriptor term improves the empirical prediction of IP measurements relative to the use of pore geometrical descriptor terms alone. This suggests that small concentrations of iron minerals exert a strong control on the specific capacitance, a property that remains poorly understood. The lack of any relationship between magnetic susceptibility and the PGD confirms that the magnetic susceptibility provides additional information unrelated to PGD.

Numerical Simulation Study on the Relationships between Mineralized Structures and Induced Polarization Properties of Seafloor Polymetallic Sulfide Rocks

The induced polarization (IP) method plays an important role in the detection of seafloor polymetallic sulfide deposits. Numerical simulations based on the Poisson–Nernst–Planck equation and the Maxwell equation were performed. The effects of mineralized structures on the IP and electrical conductivity properties of seafloor sulfide-bearing rocks were investigated. The results show that total chargeability increases linearly as the volume content of disseminated metal sulfides increases when the volume content is below 20%. However, total chargeability increases nonlinearly with increasing volume content in vein and massive metal sulfides when the volume content is below 30%. The electrical resistivity of disseminated metal sulfides mainly depends on the conductivity of pore water. The electrical resistivity of vein and massive sulfides mainly depends on the volume content and the length of sulfides. Increase in the aspect ratio (0.36 to 0.93) of seafloor massive sulfides causes relaxation time constants and total chargeability to decrease. Relaxation time constants and total chargeability also decrease with increase in the tortuosity of seafloor vein sulfides from 1.0 to 1.38. This study is of great value for the electrical survey of seafloor polymetallic sulfide deposits.