Multi-technique characterization of shale reservoir quality parameters

https://doi.org/10.1016/j.jngse.2019.103125Get rights and content

Highlights

  • Multitechnique characterization approach is applied to study shale quality parameters.

  • Porosity, permeability, brittleness, elements distribution and pore size were determined.

  • Shales are clay rich, having medium pore size with ultralow permeability.

Abstract

A multitechnique characterization approach has been used to quantitatively and qualitatively evaluate all the reservoir quality parameters, crucial for the exploitation and development of unconventional shale plays. Characterization methods, in particular FTIR, XRF, NMR, MICP, HPP, LPP and High Pressure Permeameter were used on selected 20 younger and older shale samples of Cambay to determine their true petrophysics, mineralogy, brittleness and fracability potential with respect to depth. Properties mainly porosity, permeability, pore size distribution, mineralogy, brittleness, pore sizes and fracability were determined. It was found that younger cambay has medium size pores with high porosity, low silica and high clay content. On the contrary, older cambay has good pore connectivity, rich in organic and clay content, fair brittleness index and capable of producing hydrocarbons. The performed multidisciplinary analysis is first of its kind research and will go a long way in shale gas research and development in India at pilot scale. The generated data can be helpful in minimizing the research gap and hence the challenges associated with the commercial development of these prolific shales.

Introduction

Natural gas and oil extracted from unconventional shale plays is moving to the centre point of current discussion on energy, security and environment (Rao, 2011) as they can fulfil the increasing demand of energy in the country. Unconventional shale plays development at commercial level has transformed energy fortunes of many countries especially United States and reshaped them into a self-sustainable energy independent country. According to Bellelli and Troszczynska-Van Genderen (2013), with the advancement of new technologies and practices, the natural gas production in USA may increase from 23.0 trillion cubic feet (Tcf) in 2011 to 33.1 Tcf in 2040. A 44% incremental growth may be observed due to shale gas production, which is expected to grow from 7.8 Tcf in 2011 to 16.7 Tcf in 2040 (Bellelli and Troszczynska-Van Genderen, 2013; EIA, 2013). A cheap and clean energy maintaining the socio-economic balance has always been the need of the hour for every country.

In India, hydrocarbon (oil and gas) sector plays a major role in influencing India's economy and Government's Revenue. There is a natural gas deficit in the country, and it is expected that natural gas demand will reach 606 MMSCMD by 2021–2022 as against a demand of 473 MMSCMD in 2016–17 (BP Energy Outlook, 2018; IBEF, 2018). It becomes imperative for India to harness all of its energy resources especially Shale gas/oil to overcome current energy deficits and reduce heavy reliance on foreign imports. A resource potential of around 2000 TCF of Shale Gas and 96 TCF of recoverable shale gas reserves has been estimated (Rajendra, 2017) and according to preliminary data analysis, basins like Gondwana, Cambay, Krishna – Godavari, Cauvery, Assam-Arakan, Rajasthan, Vindhyan and Bengal are the most promising shale gas basins (EIA, 2013).

Despite having enormous shale oil and gas potential its exploration and exploitation in India is still at the research and development stage. A detailed understanding of promising shale basins of India is necessary for the commercial development of these reserves. Taking production from unconventional shale plays is quite difficult and challenging as compared to conventional plays. Unlike conventional reservoirs, unconventional shale plays have grain size below 2 μm, clay content exceeds 50%, organically rich, deposited in low-energy environment, Total organic content is greater than 2% and permeability is very low i.e. in the orders of nanometres (Richard, 2015). To obtain commercial gas rate at such low permeabilities, advance stimulation techniques like horizontal drilling coupled with hydraulic fracturing and microseismicity are required (Rao, 2011). Adequate information on reservoir and completion quality parameters is required before implementing or suggesting stimulation techniques. Quantitative and qualitative determination of the reservoir quality parameters is the focus of the present work as it greatly affects the economic viability of a shale play. These parameters are the collected predictive characteristic tools which are governed by the porosity, permeability, mineralogy, brittleness index, elements distribution, pore networking and its distribution (Diaz et al., 2013; Green, 2013; Speight, 2013; Glaser et al., 2013) of the shales. In this study, multitechnique characterization approach has been used to quantitatively determine all the discussed parameters, crucial for the development of shale plays at large scale (Fig. 1). This type of study will be first kind of research level investigation for Cambay Shale. It is providing with a road map for complete reservoir characterization of Cambay and may be useful for the oil and gas professionals to understand true shale oil/gas potential of Cambay Basin, Gujarat.

The study area chosen for the laboratory investigations is Cambay Shale of North Cambay Basin of Gujarat from Western India which is the main source rock in this basin having Total Organic Carbon (TOC) content values from 0.61 to 14.3 wt % (average, 2.6 wt %). More research data is required to study the mineralogical, petrophysical and pore structures of this shale as limited dataset is available. After reviewing work of various researchers (Chen et al., 2014a, 2014b; Gasaway et al., 2017; Hazra et al., 2016; Li et al., 2015; Yingjie et al., 2015; Kumar et al., 2013; Veselinovic et al., 2016; Daigle et al., 2014; Martinez and Davis, 2000; Loucks et al., 2009; Clarkson et al., 2012; Yuan et al., 2015; Schmitt et al., 2013; Wang et al., 2018; Hintzman et al., 2016; Chen et al., 2014a, 2014b; Gasaway et al., 2017; Soeder, 1988; Goral et al., 2015; Tian et al., 2013; Fauchille et al., 2017; Kong et al., 2018; Liu et al., 2016; Spencer and Weedmark, 2015; Rowe et al., 2012; Al-Otoom et al., 2005; Saif et al., 2017; Tovar et al., 2017; Shi et al., 2015), it was found that characterization methods like - Scanning Electron Microscopy (SEM), Low & High Pressure Porosity Methods (LPP and HPP), X-Ray Fluorescence (XRF), Permeability-Porosimeter, Mercury Intrusion Capillary Pressure Test, Fourier Transform Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance, CT Scanning are the most commonly used methods (Table 1) to determine the shale reservoir quality parameters. Table 2 illustrates a review on the research and development activities pertaining to the data collection using characterization methods on ultra-tight, shale low permeable formations. In this work, characterization techniques mainly LPP, HPP, MICP, NMR, FTIR and XRD are used to determine porosity, permeability, pores structure and dimensions, mineralogy, brittleness index and element distribution in the shale sections of Cambay Basin.

Section snippets

Study area: cambay basin

The Cambay basin forms a significant petroleum province with established hydrocarbon source potential. The estimates of the most likely retained in-place accumulations are the order of 2700 MMT of oil and oil equivalent of gas. The phenomenon of geology, stratigraphy and hydrocarbon prospects of this basin has been worked out by several workers. Tectonically, from North to South, the Cambay basin is divided into five tectonic blocks namely Sanchor-Patan, Mehsana-Ahmedabad, Tarapur-Cambay,

Samples and experimental methods

A total of 20 older and younger Cambay shale samples (in the form of pieces and cuttings, Table 1b) belonging to North Cambay Basin were analysed to determine shale reservoir quality parameters in the selected depth-interval. Table 1a gives the details of the selected depth intervals used for this study. A multitechnique integrated characterization approach was applied on the collected shale samples to determine the porosity, permeability, element distribution, mineralogy and brittleness index

Multi mineral analysis by Fourier Transform Infrared Spectroscopy (FTIR)

Approximately 13 samples (belonging to younger and older cambay shale) at depth interval of 1200–1400 m and 3600–3610 m were obtained in the form of cuttings and pieces and transformed into fine powder for running FTIR analysis. The samples were first put into an oxygen-rich Plasma Asher and then left for overnight drying in the oven.

FTIR spectrometer needs to be purged for the removal of undesired gases, optics protection and for improving the thermal stability of the instrument. A background

Discussions

Advance stimulation technique such as hydraulic fracturing is most commonly used to exploit unconventional shale resources at commercial scale. To design an exploitation plan, an adequate information on shale reservoir quality parameters and hydraulic parameters is always required and needed. Shale gas exploration and exploitation in India is at the research and development stage. However, tremendous efforts are going on to understand complex nature of this shale and suggesting best

Comparative assessment with US shales

A property wise comparison of Cambay (India) shale with various prominent shales of USA is illustrated in Table 12. Cambay has very high clay content which may be due to the presence of siltstones in between the shales unlike US shales which are less clay rich having ultra-low permeability and high silica content. Only Eagle ford and Haynesville shale shows low clay and silica content.

Conclusions

We have performed a multitechnique reservoir characterization on the younger and older shale of Cambay, which has an immense potential of shale oil/gas and is capable of generating 90 TCF of hydrocarbons. All the data pertaining to shale petrophysical and mineralogical properties was experimentally determined and interpreted to understand reservoir quality of this shale. Properties mainly porosities, permeability, pore size distribution, mineralogy, brittleness, pore sizes and fracability were

Author contributions

Vaishali Sharma: Methodology, Analysis, Interpretation, Writing, Reviewing, Anirbid Sircar: Reviewing, Supervision, Interpretation, Visualization, Comments.

Declaration of competing interest

There are no conflicts of interest to declare.

Acknowledgments

The authors extend their sincere thanks to Prof. Chandra Rai and Prof. Subhash Shah, The University of Oklahoma, USA, for giving an opportunity to work in IC3 centre of MPGE, OU to complete all the necessary experimentation and data generation. We are also thankful to Institute of Seismological Research for allowing us to work in their laboratory for additional data generation.

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