Evaluation of shale gas reservoir in Barakar and barren measures formations of north and south Karanpura Coalfields,Jharkhand

India recognizes the strategic importance for developing shale gas resources like other countries in the world. Shale gas reservoirs are known to be difficult for extracting gas in comparison to conventional reservoirs. Recently, due to high prices of gas, rising demand and enhancement in recovery technologies has attracted the Indian energy industries to explore the shale gas resource. Coal and lignite are the prime source of energy in India and these resources are well explored, while shale is ignored, despite it being associated with coal and lignite bearing formations. The paper presents reservoir characteristics of shale horizons in Barren Measures and Barakar formations of north and south Karanpura coalfields. Shale core samples were collected from exploratory boreholes in air tight canisters. In-situ gas content and adsorption capacities ascertained to be 0.51–1.69 m³/t and 3.90–5.82 m³/trespectively. Desorbed gas derived from canisters contains CH₄, C₂H₆, C₃H₈, CO₂, N₂ and O₂ and varies from 76.19–82.63, 0.38–0.76, 0.10–0.50, 8.65–12.34, 9.89–19.34 and 0.56–2.24 vol. % respectively. The permeability and porosity determined under reservoir simulated confining pressure is varying from 0.41–0.75 mD and 0.89–2.28 % respectively. The plots of Rock Eval S₂vs TOC and HI against Calc. VRo% indicates that all shale samples belong to Type III kerogen, which is prone to generate gas. It is evaluated that insitu gas content, sorption capacity, saturation level and low permeability of shale beds are critical parameters for development of shale gas resource in the studied area.     

Erratum: Properties of a pair of fracture networks produced by triaxial deformation experiments: insights on fluid flow using discrete fracture network models

Results of a series of deformation experiments conducted on gabbro samples and numerical models for computation of flow are presented. Rocks were subjected to triaxial tests (σ1 > σ2 = σ3) under σ3 = 150 MPa confining pressure at room temperature, to generate fracture network patterns. These patterns were either produced by keeping a constant confining pressure and loading the sample up to failure (conventional test: CT), or by building up a high differential stress and suddenly releasing the confining pressure (confining pressure release test: CPR). The networks are similar in overall density but differ primarily in the orientation of smaller fractures. In the case of CT tests, a conjugate fracture set is observed with one dominant fracture zone running at about 20° from σ1. CPR tests do not show such a conjugate pattern and the mean fracture orientation is at around 35° from σ1. Discrete fracture network (DFN) methodology was used to determine the distribution of flow and hydraulic head for both fracture sets under simple boundary conditions and uniform transmissivity values. The fracture network generated by CT and CPR tests exhibit different patterns of flow field and hydraulic head configurations, but convey approximately the same amount of flow at all scales for which DFN models were simulated. The numerical modelling results help to develop understanding of qualitative differences in flow distribution that may arise in rocks of the same mineralogical composition and mechanical properties, but under the influence of different stress conditions, albeit at similar overall stress magnitude.

     

Cubic law with aperture-length correlation: implications for network scale fluid flow

Previous studies have computed and modeled fluid flow through fractured rock with the parallel plate approach where the volumetric flow per unit width normal to the direction of flow is proportional to the cubed aperture between the plates, referred to as the traditional cubic law. When combined with the square root relationship of displacement to length scaling of opening-mode fractures, total flow rates through natural opening-mode fractures are found to be proportional to apertures to the fifth power. This new relationship was explored by examining a suite of flow simulations through fracture networks using the discrete fracture network model (DFN). Flow was modeled through fracture networks with the same spatial distribution of fractures for both correlated and uncorrelated fracture length-to-aperture relationships. Results indicate that flow rates are significantly higher for correlated DFNs. Furthermore, the length-to-aperture relations lead to power-law distributions of network hydraulic conductivity which greatly influence equivalent permeability tensor values. These results confirm the importance of the correlated square root relationship of displacement to length scaling for total flow through natural opening-mode fractures and, hence, emphasize the role of these correlations for flow modeling.     

Investigations on a Large Collection of Cosmic Dust From the Central Indian Ocean

We collected 1,245 spherules from the Central Indian Ocean basin by Magnetic cosmic dust collection (MACDUC) experiment raking the deep sea floor. This collection ranks among the large deep sea collections of cosmic dust. For this study, 168 particles are analyzed with SEM-EDS to characterise their cosmic nature and identify the processes that their morphological features, textures and chemical compositions reveal. All the three basic types of cosmic spherules have been identified: I-type, S-type and the G-type. The silicate or the S-type spherules are dominant in this collection. In all, 115 spherules were sectioned, polished and analyzed for major elements. I-type spherules are mainly composed of Fe and Ni oxides, some have metallic cores where appreciable amounts of Co is observed in addition to glassy phases with lithophile elements are also observed in these spherules. These evidences are supportive of the view that the I-type spherules could be metal grains from carbonaceous/unequilibrated chondritic bodies. The S-type spherules show elemental composition of Mg, Al, Si, Ca, Fe, and Ni approximately similar to chondritic compositions. In addition, some other rare particles such as an S-type sphere which contains a large zoned relict chromite crystal, other spheres with a semi-porphyritic/barred olivine texture are also observed. While most the S-type spherules appear to have carbonaceous chondrites as their parent bodies, the relict grain bearing spherule shows distinctly an ordinary chondritic parent body.     

Physical Habitat Assessment of River Denwa Using GIS Techniques

Physical habitat of any aquatic ecosystem is an integral part upon which the biological structures of resident communities are built. Degradation of the physical habitat has serious consequences on aquatic communities and is among the leading causes of stream impairment worldwide. Therefore, a sound habitat assessment approach is necessary to assess the condition of running water and to determine if habitat degradation is responsible for any degradation in biological condition. The present study was focused on Physical Habitat Assessment of Denwa River, a sub tributary of river Narmada in central India, for generating a Habitat Suitability map. The Denwa River originates from Satpura ranges in central India and flows through entire Pachmarhi plateau supporting a diversity of habitats for aquatic flora and fauna. A survey was carried out to assess the physical characteristic of Denwa river (84 kms) from its origin to the confluence point of Tawa Denwa river. Six reaches have been identified in study area on the basis of their physiographic conditions. For Habitat Assessment measurement, Rapid Bioassessment Protocols for Stream and Wadeable rivers by United States Environmental Protection Agency (USEPA, 841-B-99-002) have been used. Seven parameters from this protocol have been chosen for physical characterization. GIS techniques have been used to develop a Habitat Suitability Map of the study area based on scores to illustrate its suitability to support aquatic life. The present paper discusses in detail the suitability of the different reaches of the River Denwa for supporting the aquatic biodiversity.     

A Method to Represent a Well in a Three-Dimensional Discrete Fracture Network Model

In discrete fracture network (DFN) modeling, fractures are randomly generated and placed in the model domain. The rock matrix is considered impermeable. Small fractures and isolated fractures are often ignored to reduce computational expense. As a result, the rock matrix between fractures could be large and intersections may not be found between a well introduced in the model and the hydraulically connected fracture networks (fracture backbones). To overcome this issue, this study developed a method to conceptualize a well in a three-dimensional (3D) DFN using two orthogonal rectangular fractures oriented along the well's axis. Six parameters were introduced to parameterize the well screen and skin zone, and to control the connectivity between the well and the fracture backbones. The two orthogonal fractures were discretized using a high-resolution mesh to improve the quality of flow and transport simulations around and along the well. The method was successfully implemented within dfnWorks 2.0 (Hyman et al. 2015) to incorporate a well in a 3D DFN and to track particles leaving an injection well and migrating to a pumping well. Verification of the method against MODFLOW/MODPATH found a perfect match in simulated hydraulic head and particle tracking. Using three examples, the study showed that the method ensured the connectivity between wells and fracture backbones, and honored the physical processes of flow and transport along and around wells in DFNs. Recommendations are given for estimating the values of the six introduced well parameters in a real-world case study.     

Moment analysis for compounds undergoing sequential chain reactions with first-order decay

Temporal and spatial moment analysis of one-dimensional equations governing fate and transport of parent compounds along with their transformation products is useful for parameter estimation of model parameters, and for understanding the average attributes of contaminant behavior. The objective of this paper is to present analytical expressions for the lower order moments of members in a sequential chain reaction, where members undergo first-order decay to produce the next member in the chain. Specifically, moments up to second order are discussed for the first two members. For the case of purely advective transport (Peclet number tending to infinity), temporal moment expressions are provided for more members of the chain. The sensitivity of temporal moments is examined with respect to Peclet number and transformation rates. Spatial moments are derived by two methods—one using Fourier transforms and another using moment generating differential equations. The behavior of lower order moments for the first few members of a chain can be elucidated from their mathematical expressions. However, expressions for higher order moments tend to be very complicated especially for members further down the chain.     

A note on ‘composite dike’ in basement granite in the vicinity of Srisailam sub-basin near Akkavaram,Telangana

A composite dike has been noticed in basement granite in the vicinity of Srisailam sub-basin near village Akkawaram, Mahabubnagar district, Telangana. It is trending N-S and traced over an extent of 600m in eastern flank of Akkavaram outlier and comprises rocks of mafic and felsic composition characterized by both gradational and abrupt contacts. On the basis of petrographic studies, felsic part of dike is designated as bostonite and mafic as dolerite. Geochemically, they are grouped into (i) trachyte to trachydacite and (ii) basalt categories. Such dissimilar mineralogical and chemical characters in a single dike may be due to coexistence of magma of contrasting composition and provides vital information for understanding the two phase liquid. Interestingly, high uranium values (0.022% U₃O₈) recorded in parts of felsic portion.