True Resistance Research Articles

Increased platelet expression of glycoprotein IIIa following aspirin treatment in aspirin-resistant but not aspirin-sensitive subjects.

Aspirin is widely used as an anti-platelet agent for cardiovascular prophylaxis. Despite aspirin treatment, many patients experience recurrent thrombotic events, and aspirin resistance may contribute to this. We examined the prevalence of aspirin resistance in a healthy population, and investigated whether the platelet proteome differed in aspirin-resistant subjects. Ninety-three healthy subjects received aspirin 300 mg daily for 28 days. Before and at the end of treatment, urine was taken to determine 11-dehydrothromboxane B2 , and blood was taken to measure arachidonic acid (AA)-induced aggregation of platelet-rich plasma and to interrogate the platelet proteome by mass spectrometric analysis with further confirmation of findings using Western blotting. In two of the 93 subjects, neither AA-induced aggregation nor urinary 11-dehydrothromboxane B2 was effectively suppressed by aspirin, despite measurable plasma salicylate concentrations, suggesting the presence of true aspirin resistance. Despite no detectable differences in the platelet proteome at baseline, following aspirin a marked increase was seen in platelet glycoprotein IIIa expression in the aspirin-resistant but not aspirin-sensitive subjects. An increase in platelet glycoprotein IIIa expression with aspirin resistance was confirmed in a separate cohort of 17 patients with stable coronary artery disease on long term aspirin treatment, four of whom exhibited aspirin resistance. In a healthy population, true aspirin resistance is uncommon but exists. Resistance is associated with an increase in platelet glycoprotein IIIa expression in response to aspirin. These data shed new light on the mechanism of aspirin resistance, and provide the potential to identify aspirin-resistant subjects using a novel biomarker.

A Computational Intelligence Approach to Solve the Inverse Problem of Electrical DC Resistivity Sounding

Electrical methods have been widely used in geophysical surveying to obtain high-resolution information about subsurface conditions, since the last few decades. Resistivity is an important parameter in judging the ground properties, especially detecting buried objects of anomalous conductivity. Electrical DC (i.e. Direct Current) resistivity sounding is the commonly used technique to obtain the apparent 2-D resistivity of the region under investigation. Acquiring the true resistivity from collected data remains a complex task due to nonlinearity particularly due to contrasts distributed in the region. In this work, a radial basis function neural network (RBFNN) metamodelling approach is proposed to solve the 2-D resistivity inverse problem. The model was trained with synthetic data samples obtained for a homogeneous medium of 100Ω.m. The neural network was then tested on another set of synthetic data. The results show the ability of the proposed approach to estimate the true resistivity from the 2-D apparent resistivity sounding data with high correlation. The proposed technique, when executed, appears to be computationally-efficient, as it requires less processing time and produces less error than conventional method.

Method for characterizing the contact resistance of metal-vanadium dioxide thin film interfaces

The standard method for determining the contact resistance of planar metal-semiconductor interfaces can underestimate the true contact resistance under normal operating conditions, as it relies on the resistivity of the semiconductor material remaining constant during measurement. However, the strong temperature dependence of the resistivity of VO2 requires a modified approach that maintains a constant power density dissipated within the film to account for Joule heating. We develop a method for measuring contact resistance in semiconductors with a high thermal coefficient of resistivity, demonstrate this method with an example, and compare the results with the standard technique.

Cooperative constrained inversion of multiple electromagnetic data sets

We evaluated a method for cooperatively inverting multiple electromagnetic (EM) data sets with bound constraints to produce a consistent 3D resistivity model with improved resolution. Field data from the Antonio gold deposit in Peru and synthetic data were used to demonstrate this technique. We first separately inverted field airborne time-domain EM (AEM), controlled-source audio-frequency magnetotellurics (CSAMT), and direct current resistivity measurements. Each individual inversion recovered a resistor related to gold-hosted silica alteration within a relatively conductive background. The outline of the resistor in each inversion was in reasonable agreement with the mapped extent of known near-surface silica alteration. Variations between resistor recoveries in each 3D inversion model motivated a subsequent cooperative method, in which AEM data were inverted sequentially with a combined CSAMT and DC data set. This cooperative approach was first applied to a synthetic inversion over an Antonio-like simulated resistivity model, and the inversion result was both qualitatively and quantitatively closer to the true synthetic model compared to individual inversions. Using the same cooperative method, field data were inverted to produce a model that defined the target resistor while agreeing with all data sets. To test the benefit of borehole constraints, synthetic boreholes were added to the inversion as upper and lower bounds at locations of existing boreholes. The ensuing cooperative constrained synthetic inversion model had the closest match to the true simulated resistivity distribution. Bound constraints from field boreholes were then calculated by a regression relationship among the total sulfur content, alteration type, and resistivity measurements from rock samples and incorporated into the inversion. The resulting cooperative constrained field inversion model clearly imaged the resistive silica zone, extended the area of interpreted alteration, and also highlighted conductive zones within the resistive region potentially linked to sulfide and gold mineralization.

Assessment of near-surface mapping capabilities by airborne transient electromagnetic data — An extensive comparison to conventional borehole data

A newly developed helicopter transient electromagnetic (TEM) system has the ability to measure very early times within just a few μs after the turn off of the primary current. For such a system, careful calibration and accurate modeling of the electromagnetic (EM) response is critical to get true resistivities of the very shallow geologic layers. We discovered that this leads to resolution of the same level or in some cases even better than what can be obtained from airborne frequency EM systems. This allowed a range of important applications where high and accurate resolution is mandatory, e.g., geotechnical applications such as urban planning, railroad and road investigations, landslides or distribution of raw materials, and assessing aquifer vulnerability. We evaluated the results of a pilot survey covering the Norsminde catchment south of Aarhus, Denmark, where we found that near-surface layers (top 30 m) can be mapped with an accuracy of a few meters in a complicated glacial sedimentary environment. The mapping of the geologic layers was assessed by a detailed analysis in which we developed a general methodology for crosschecking the EM and borehole data. This methodology is general and can easily be adapted to other data types and surveys. After rating the quality of the boreholes based on a list of predefined criteria, we concluded that the EM data matched with about three-quarters of the boreholes located within less than 15 m from the closest EM soundings. The remaining quarter of the boreholes fell into two groups in which half of the boreholes were of very poor quality or had inaccurate coordinates. Only eight of all the boreholes could not be reproduced by the data, and we attributed this to be caused by very strong lateral or vertical geologic variations not resolvable by the TEM technique.

Aspirin unresponsiveness predicts thrombosis in high-risk pediatric patients after cardiac surgery

Thrombosis occurs in up to 26% of patients with congenital heart disease after cardiac surgery and is associated with increased morbidity and mortality. Aspirin is commonly administered to reduce the risk of thrombosis, yet aspirin responsiveness is rarely assessed. In this study, we hypothesize that inadequate response to aspirin is associated with increased risk of thrombosis after selected congenital cardiac procedures considered to be high risk for thrombosis. Patients undergoing high-risk congenital cardiac surgery who received postoperative aspirin (N = 95) were studied. Response to aspirin was determined using the VerifyNow system several days after administration. Patients were monitored prospectively for 30 days for the development of a thrombosis event and the relationship between aspirin unresponsiveness and a thrombosis event was determined by the Fisher exact test. Rate of aspirin unresponsiveness (≥550 aspirin reaction units [ARU]) was 10 of 95 (10.5%) and was highest in patients weighing less than 5 kg given 20.25 mg/d of aspirin. Thrombosis events occurred in 7 patients (7.4%). Thrombosis was observed in 6 of 10 (60%) patients who were unresponsive to aspirin, compared with 1 of 85 (1.2%) patients who were responsive to aspirin (P < .001). In 2 patients who were unresponsive to the initial aspirin dose, an increase in dose resulted in an adequate therapeutic aspirin response (ARU < 550), suggesting insufficiency rather than true resistance in a subset of patients. Postoperative thrombosis is associated with aspirin unresponsiveness in this patient population. In high-risk patients, monitoring of aspirin therapy and consideration of dose adjustment or alternative agents for unresponsive patients may be justified and warrants further investigation in a prospective trial.

Time-Dependant Responses of High-Definition Induction Log and Case Studies

The process of drilling mud filtrate invading into a reservoir is time dependant. It causes dynamic invasion profiles of formation parameters such as water saturation, salinity, and formation resistivity. Thus, the responses of a high-definition induction log (HDIL) tool are time dependent. The logging time should be considered as an important parameter during logging interpretation for the purposes of determining true formation resistivity, estimating initial water saturation, and evaluating a reservoir. The time-dependent HDIL responses are helpful for log analysts to understand the invasion process physically. Field examples were illustrated for the application of present method.

A new methodology for identification of potential pay zones from well logs: Intelligent system establishment and application in the Eastern Junggar Basin, China

In recent years, as the exploration practices extend into more complicated formations, conventional well log interpretation has often shown its inaccuracy and limitations in identifying hydrocarbons. The Permian Wutonggou Formation hosts typical clastic reservoirs in the Eastern Junggar Basin. The sophisticated lithology characteristics cause complex pore structures and fluid properties. These all finally cause low well testing agreement rate using conventional methods. Eleven years’ recent statistics show that 12 out of 15 water layers have been incorrectly identified as being oil or oil/water layers by conventional well log interpretation. This paper proposes a methodology called intelligent prediction and identification system (IPIS). Firstly, parameters reflecting lithological, petrophysical and electrical responses which are greatly related to reservoir fluids have been selected carefully. They are shale content (V sh ), numbered rock type (RN), porosity (Φ), permeability (K), true resistivity (RT) and spontaneous-potential (SP). Secondly, V sh , Φ and K are predicted from well logs through artificial neural networks (ANNs). Finally, all the six parameters are input into a neuro-fuzzy inference machine (NFIM) to get fluids identification results. Eighteen new layers of 145.3 m effective thickness were examined by IPIS. There is full agreement with well testing results. This shows the system’s accuracy and effectiveness.

Benefits of a pharmacology antimalarial reference standard and proficiency testing program provided by the Worldwide Antimalarial Resistance Network (WWARN).

Comprehensive assessment of antimalarial drug resistance should include measurements of antimalarial blood or plasma concentrations in clinical trials and in individual assessments of treatment failure so that true resistance can be differentiated from inadequate drug exposure. Pharmacometric modeling is necessary to assess pharmacokinetic-pharmacodynamic relationships in different populations to optimize dosing. To accomplish both effectively and to allow comparison of data from different laboratories, it is essential that drug concentration measurement is accurate. Proficiency testing (PT) of laboratory procedures is necessary for verification of assay results. Within the Worldwide Antimalarial Resistance Network (WWARN), the goal of the quality assurance/quality control (QA/QC) program is to facilitate and sustain high-quality antimalarial assays. The QA/QC program consists of an international PT program for pharmacology laboratories and a reference material (RM) program for the provision of antimalarial drug standards, metabolites, and internal standards for laboratory use. The RM program currently distributes accurately weighed quantities of antimalarial drug standards, metabolites, and internal standards to 44 pharmacology, in vitro, and drug quality testing laboratories. The pharmacology PT program has sent samples to eight laboratories in four rounds of testing. WWARN technical experts have provided advice for correcting identified problems to improve performance of subsequent analysis and ultimately improved the quality of data. Many participants have demonstrated substantial improvements over subsequent rounds of PT. The WWARN QA/QC program has improved the quality and value of antimalarial drug measurement in laboratories globally. It is a model that has potential to be applied to strengthening laboratories more widely and improving the therapeutics of other infectious diseases.

Rapid response to selection, competitive release and increased transmission potential of artesunate-selected Plasmodium chabaudi malaria parasites.

The evolution of drug resistance, a key challenge for our ability to treat and control infections, depends on two processes: de-novo resistance mutations, and the selection for and spread of resistant mutants within a population. Understanding the factors influencing the rates of these two processes is essential for maximizing the useful lifespan of drugs and, therefore, effective disease control. For malaria parasites, artemisinin-based drugs are the frontline weapons in the fight against disease, but reports from the field of slower parasite clearance rates during drug treatment are generating concern that the useful lifespan of these drugs may be limited. Whether slower clearance rates represent true resistance, and how this provides a selective advantage for parasites is uncertain. Here, we show that Plasmodium chabaudi malaria parasites selected for resistance to artesunate (an artemisinin derivative) through a step-wise increase in drug dose evolved slower clearance rates extremely rapidly. In single infections, these slower clearance rates, similar to those seen in the field, provided fitness advantages to the parasite through increased overall density, recrudescence after treatment and increased transmission potential. In mixed infections, removal of susceptible parasites by drug treatment led to substantial increases in the densities and transmission potential of resistant parasites (competitive release). Our results demonstrate the double-edged sword for resistance management: in our initial selection experiments, no parasites survived aggressive chemotherapy, but after selection, the fitness advantage for resistant parasites was greatest at high drug doses. Aggressive treatment of mixed infections resulted in resistant parasites dominating the pool of gametocytes, without providing additional health benefits to hosts. Slower clearance rates can evolve rapidly and can provide a strong fitness advantage during drug treatment in both single and mixed strain infections.

Simplified Microarray System for Simultaneously Detecting Rifampin, Isoniazid, Ethambutol, and Streptomycin Resistance Markers in Mycobacterium tuberculosis

We developed a simplified microarray test for detecting and identifying mutations in rpoB, katG, inhA, embB, and rpsL and compared the analytical performance of the test to that of phenotypic drug susceptibility testing (DST). The analytical sensitivity was estimated to be at least 110 genome copies per amplification reaction. The microarray test correctly detected 95.2% of mutations for which there was a sequence-specific probe on the microarray and 100% of 96 wild-type sequences. In a blinded analysis of 153 clinical isolates, microarray sensitivity for first-line drugs relative to phenotypic DST (true resistance) was 100% for rifampin (RIF) (14/14), 90.0% for isoniazid (INH) (36/40), 70% for ethambutol (EMB) (7/10), and 89.1% (57/64) combined. Microarray specificity (true susceptibility) for first-line agents was 95.0% for RIF (132/139), 98.2% for INH (111/113), and 98.6% for EMB (141/143). Overall microarray specificity for RIF, INH, and EMB combined was 97.2% (384/395). The overall positive and negative predictive values for RIF, INH, and EMB combined were 84.9% and 98.3%, respectively. For the second-line drug streptomycin (STR), overall concordance between the agar proportion method and microarray analysis was 89.5% (137/153). Sensitivity was 34.8% (8/23) because of limited microarray coverage for STR-conferring mutations, and specificity was 99.2% (129/130). All false-susceptible discrepant results were a consequence of DNA mutations that are not represented by a specific microarray probe. There were zero invalid results from 220 total tests. The simplified microarray system is suitable for detecting resistance-conferring mutations in clinical M. tuberculosis isolates and can now be used for prospective trials or integrated into an all-in-one, closed-amplicon consumable.

2D and 3D separate and joint inversion of airborne ZTEM and ground AMT data: Synthetic model studies

Abstract The ZTEM (Z-axis Tipper Electromagnetic) method measures naturally occurring audio-frequency magnetic fields and obtains the tipper function that defines the relationship among the three components of the magnetic field. Since the anomalous tipper responses are caused by the presence of lateral resistivity variations, the ZTEM survey is most suited for detecting and delineating conductive bodies extending to considerable depths, such as graphitic dykes encountered in the exploration of unconformity type uranium deposit. Our simulations shows that inversion of ZTEM data can detect reasonably well multiple conductive dykes placed 1 km apart. One important issue regarding ZTEM inversion is the effect of the initial model, because homogeneous half-space and (1D) layered structures produce no responses. For the 2D model with multiple conductive dykes, the inversion results were useful for locating the dykes even when the initial model was not close to the true background resistivity. For general 3D structures, however, the resolution of the conductive bodies can be reduced considerably depending on the initial model. This is because the tipper magnitudes from 3D conductors are smaller due to boundary charges than the 2D responses. To alleviate this disadvantage of ZTEM surveys, we combined ZTEM and audio-frequency magnetotelluric (AMT) data. Inversion of sparse AMT data was shown to be effective in providing a good initial model for ZTEM inversion. Moreover, simultaneously inverting both data sets led to better results than the sequential approach by enabling to identify structural features that were difficult to resolve from the individual data sets.

Screening and Histopathological Characterization of Korean Carrot Lines for Resistance to the Root-Knot Nematode Meloidogyne incognita.

In total, 170 carrot lines developed in Korea were screened for resistance to Meloidogyne incognita race 1 to select parental genetic resources useful for the development of nematode-resistant carrot cultivars. Using the gall index (GI), gall formation was examined on carrot roots inoculated with approximately 1,000 second-stage juveniles of the nematode 7 weeks after inoculation. Sixty-one carrot lines were resistant (GI ≤ 1.0), while the other 109 were susceptible (GI > 1.0) with coefficient of variance (CV) of GI for total carrot lines 0.68, indicating low-variation of GI within the lines examined. The histopathological responses of two carrot plants from resistant and susceptible lines were examined after nematode infection. In susceptible carrots, giant cells formed with no discernible necrosis around the infecting nematodes. In the resistant carrot line, however, no giant cells formed, although modified cells were observed with extensive formation of necrotic layers through their middle lamella and around the infecting nematodes. This suggested that these structural modifications were related to hypersensitive responses governed by the expression of true resistance genes. Therefore, the Korean carrot lines resistant to the nematode infection are potential genetic resources for the development of quality carrot cultivars resistant to M. incognita race 1.

Electrical Resistivity Tomography for the Modelling of Cultural Deposits and Geomophological Landscapes at Neolithic Sites: a Case Study from Southeastern Hungary

ABSTRACTA large‐scale electrical resistivity tomography (ERT) survey was undertaken around the Neolithic tell of Szeghalom‐Kovácshalom in southeast Hungary, covering an area of almost 6 ha. High‐resolution ERT data were collected along 28 uniformly distributed transects of variable length using the roll‐along technique. A recently presented two‐dimensional fast non‐linear resistivity inversion algorithm was used to invert the ERT data and recover the true subsurface resistivity distribution along the specific cross‐sections. The algorithm calculates and stores in an efficient manner the part of the Jacobian matrix that is actually important within the inversion procedure, thus rendering it almost 4.8 times faster than the algorithm that calculates the complete Jacobian matrix, without losing quality. The algorithm was further modified to account for any non‐standard electrode configuration. A recently established iterative algorithm for sparse least squares problems (LSMR) was incorporated for the first time into the algorithm to solve the inverse resistivity problem. The effectiveness and robustness of the LSMR solver was highlighted through the processing of all the ERT lines. The processing and evaluation of the ERT data made it possible to map the thickness of the anthropogenic layer below the surface of the tell, to outline the horizontal and vertical dimensions of the palaeochannel adjacent to the tell, and to determine the general stratigraphy of geological layers up to 10 m below the ground surface. The ERT results also were used to update an older topographic map of the site showing the course of the palaeochannel around the tell. A synthetic model verified and enhanced the conclusions based on the field data. This study illustrates the added value that a systematic ERT survey can provide in reconstructing the ancient fluvial geomorphology of a microregion as well as the depth and horizontal extent of deposits associated with human habitation at archaeological sites. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Genetic implanted fuzzy model for water saturation determination

Abstract The portion of rock pore volume occupied with non-hydrocarbon fluids is called water saturation, which plays a significant role in reservoir description and management. Accurate water saturation, directly measured from special core analysis is highly expensive and time consuming. Furthermore, indirect measurements of water saturation from well log interpretation such as empirical correlations or statistical methods do not provide satisfying results. Recent works showed that fuzzy logic is a robust tool for handling geosciences problems which provide more reliable results compared with empirical correlations or statistical methods. This study goes further to improve fuzzy logic for enhancing accuracy of final prediction. It employs hybrid genetic algorithm-pattern search technique instead of widely held subtractive clustering approach for setting up fuzzy rules and for extracting optimal parameters involved in computational structure of fuzzy model. The proposed strategy, called genetic implanted fuzzy model, was used to formulate conventional well log data, including sonic transit time, neutron porosity, formation bulk density, true resistivity, and gamma ray into water saturation, obtained from subtractive clustering approach. Results indicated genetic implanted fuzzy model performed more satisfyingly compared with traditional fuzzy logic model. The propounded model was successfully applied to one of Iranian carbonate reservoir rocks.

A simple inversion of induced-polarization data collected in the Haenam area of Korea

We develop a two-stage method to invert induced polarization (IP) data. First, DC resistivity data are inverted to recover a background resistivity that is used to generate a sensitivity matrix for the IP inversion. The second stage accepts the background resistivity as the true resistivity of the medium and attempts to find a polarizability that satisfies the IP data. This is done by linearizing the equations for the background resistivity to produce a linear inverse problem that can be solved for the distribution of the subsurface polarizability. Smoothness and base-model constraints are used to stabilize the IP inversion process. These regularization methods are validated by inverting both synthetic and field data obtained in the Haenam epithermal mineralized area, Korea. As a result, the IP anomaly recovered from the base-model constraint indicates that fine-grained pyrite is disseminated in a shallow zone beneath the ridge of this site, which is confirmed by core samples.

Mapping groundwater conditions in different geological environments in the northern area of UAE using 2D earth resistivity imaging survey

A water resources database was developed and used to characterize the geological and hydrogeological settings of groundwater aquifers in the northern part of the United Arab Emirates. An intensive 2D Earth Resistivity Imaging (ERI) survey was conducted in selected areas to assess the available groundwater resources and delineate the salt-water intrusion. Drilling information of the existing monitoring wells as well as their records of water table elevations and groundwater salinity were used to measure the horizontal and vertical variations in lithology, degree of saturation, and groundwater salinity and thus to improve the interpretation of ERI data. The results of the chemical analyses of water samples collected from the wells along with the 2D ERI survey profiles were used to obtain an empirical relationship between the inferred earth resistivity and the amount of total dissolved solids. This relationship was used along with the true resistivity sections resulting from the inversion of 2D ERI data to identify and map three zones of water-bearing formation (fresh, brackish, and salt-water zones) in the coastal areas. The results indicated that the depth to the fresh-brackish interface exceeded 50 m at the upstream of the wadies and was in the order of 10 m or less in the vicinity of shoreline. Because of the high resistivity contrast between dry and water saturated fractured rocks; this method was very successful in detecting water-filled fractures and cavities in the carbonate aquifer. The application of this method was unsuccessful in clayey aquifers as it was not possible to isolate lenses of gravel and/or saturated with saline or brackish water from the surrounding clayey materials.

Heart rate and heart rate variability in resistant versus controlled hypertension and in true versus white-coat resistance

Sympathetic nervous system has an important role in resistant hypertension. Heart rate (HR) is a marker of sympathetic activity, but its association with resistant hypertension has not been assessed. We aimed to evaluate differences in HR values and variability between resistant and controlled patients and between true and white-coat resistant hypertensives (RHs). We compared office and ambulatory HR, nocturnal dip and s.d. in 14,627 RHs versus 11,951 controlled patients (on ⩽ 3 drugs) and in 8730 true (24 h blood pressure (BP) ⩾ 130 and/or 80 mm Hg) versus 4825 white-coat (24-h BP < 130/80 mm Hg) RHs. After adjusting for age, gender, body mass index, diabetes status and beta blocker use, HR values and variability were significantly elevated in resistant versus controlled patients and in true versus white-coat RHs. In logistic regression models, after adjustment for confounders, office HR (odds ratio for each increase in tertile: 1.337; 95% confidence interval: 1.287-1.388; P < 0.001), nocturnal dip (0.958; 0.918-0.999; P = 0.035) and night time s.d. (1.115; 1.057-1.177; P = 0.013) were all significantly associated with the presence of resistant hypertension. Moreover, night time HR (1.160; 1.065-1.265; P < 0.001), nocturnal dip (0.876; 0.830-0.925; P < 0.001) and 24-h s.d. (1.148; 1.092-1.207; P < 0.001) were all significantly associated with true resistant hypertension. In conclusion, both increased HR and variability are associated with resistant hypertension and with true resistance. These suggest the involvement of the sympathetic nervous system in the development of resistance to antihypertensive treatment.

Geoelectrical Inversion Study of Limestone Attributes at Mayo Boki Area (Northern Cameroon)

A geoelectrical survey using the electrical resistivity method was carried out in the Mayo Boki (Northern Cameroon), to investigate the subsurface layering and evaluation of the limestone characteristics. In addition to geological data collection, three vertical electrical soundings and one electrical resistivity profile were measured. Joint interpretation of the DC data allows us to obtain reliable 1D models of the resistivity distribution. The interpretation of the field data was carried out using the RES2DINV software, which converts the apparent resistivity as a function of electrode spacing to the true resistivity as a function of depth in two dimensions. The results obtained from the electrical resistivity survey showed that: 1) A limestone layer was put in evidence at a depth of 4 m and the thickness varies from 13 m to 44 m; 2) The limestone layer resistivity is ranged from 125 to 2410 ohm.m; 3) An area of probable limestone deposit with interesting thicknesses have been identified. These facts are useful for future mining exploration as drilling map definition and operations. The geologic section of a nearby location termed resistivity profile was delineated and its total depth was found to be 57 m, which corroborates the lithologs of the boreholes from the area. The correlation of geological data and the geoelectric section has led to envisage pursuing exploration activities. Based on the limestone layer characteristics extracted from this DC investigation, the exploration drilling operations have to be initiated in order to define the limestone resource over the area of study, which will certainly enables to built the exploitation project prefeasibility document.

Porosity Assessment of Gas Reservoir Using Wireline Log Data: A Case Study of Bokabil Formation, Bangladesh

Shale volume and porosity are the most important rock properties for petrophysical analysis, formation evaluation and estimation of hydrocarbon reserve in the oil and gas fields. This research shows how to shale volume and porosity estimation of Titas gas field (T-11) using wireline log data of Bokabil Formation in Bangladesh. Shale volume has been estimated from Gamma Ray, Self-Potential logs and True resistivity method. Porosity estimated from single log method as well as from Neutron-Density and sonic logs. Lithology is mainly sand and shale where sand is the dominant fraction. In A2 sand interval of T-11, sand and shaly sand appeared as alternating units. The shales are laminated. Shale volume percentage is ranges from 3.82 to 17.52 averaging 9.23 using Gamma Ray log which is optimistic and more reliable than other two methods. The total porosity (average) percentage is 25.09 based on sonic log which is over estimated but Neutron-density combination formula with clay corrected gives better results as averaging 18.17% which is more reliable for estimation of water saturation, formation evaluation and reserve estimation and similar as core porosity. The porosity quality is good of A2 gas sand which is potential hydrocarbon reservoir.