ORCID Profile
0000-0001-6755-0320
Current Organisation
Nanyang Technological University
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Publisher: American Chemical Society (ACS)
Date: 12-04-2018
Publisher: Elsevier BV
Date: 07-2018
Publisher: Society of Petroleum Engineers (SPE)
Date: 26-02-2018
DOI: 10.2118/189984-PA
Abstract: Proppant plays a vital role in hydraulic fracturing in tight oil/gas production because it helps to keep the fractures open during the production process. However, it is common for proppant embedment, the main type of proppant degradation, to occur under high compression load, which greatly reduces the fracture conductivity, and consequently reduces the production rate. During the process of hydraulic fracturing, the fracturing fluid only has the chance to contact and infiltrate the fractures that are in the top surface of the rock medium because of ultralow rock permeability and the short time of fluid existence, whereas the condition of other parts of the rock remain unchanged, creating inhomogeneity within the rock medium. Therefore, the present study conducted a comprehensive experimental and numerical evaluation to investigate the behavior of proppant for inhomogeneous rock media, considering the factors (effective stress, proppant concentration, and fracturing fluid) that affect proppant performance. According to the experimental results, increasing the proppant concentration reduces the proppant embedment, and, interestingly, the optimal proppant concentration is approximately 150% coverage. Furthermore, the influence of fracturing fluid on proppant embedment is more significant for high proppant concentrations, and the embedment under water-saturated conditions is higher than that under oil-saturated conditions. The numerical simulation achieved the same result as the experimental study, showing that 150% proppant coverage is the optimal proppant concentration to achieve the minimum proppant embedment. In addition, numerical modeling indicated that the inhomogeneity of the rock formation can also considerably enhance proppant embedment through differential settlement during compression.
Publisher: Elsevier BV
Date: 07-2018
Publisher: Elsevier BV
Date: 06-2019
Publisher: Springer Science and Business Media LLC
Date: 20-01-2016
DOI: 10.1038/SREP19362
Abstract: Interactions between injected CO 2 , brine and rock during CO 2 sequestration in deep saline aquifers alter their natural hydro-mechanical properties, affecting the safety and efficiency of the sequestration process. This study aims to identify such interaction-induced mineralogical changes in aquifers and in particular their impact on the reservoir rock’s flow characteristics. Sandstone s les were first exposed for 1.5 years to a mixture of brine and super-critical CO 2 (scCO 2 ), then tested to determine their altered geochemical and mineralogical properties. Changes caused uniquely by CO 2 were identified by comparison with s les exposed over a similar period to either plain brine or brine saturated with N 2 . The results show that long-term reaction with CO 2 causes a significant pH drop in the saline pore fluid, clearly due to carbonic acid (as dissolved CO 2 ) in the brine. Free H + ions released into the pore fluid alter the mineralogical structure of the rock formation, through the dissolution of minerals such as calcite, siderite, barite and quartz. Long-term CO 2 injection also creates a significant CO 2 drying-out effect and crystals of salt ( NaCl ) precipitate in the system, further changing the pore structure. Such mineralogical alterations significantly affect the saline aquifer’s permeability, with important practical consequences for the sequestration process.
Publisher: Elsevier BV
Date: 10-2017
Publisher: American Chemical Society (ACS)
Date: 27-04-2016
Publisher: Elsevier BV
Date: 07-2015
Publisher: Elsevier BV
Date: 05-2018
Publisher: MDPI AG
Date: 17-10-2018
DOI: 10.3390/EN11102795
Abstract: Fracability of unconventional gas reservoirs is an important parameter that governs the effectiveness of subsequent gas extraction. Since reservoirs are saturated with various pore fluids, it is essential to evaluate the alteration of fracability of varyingly saturated rocks. In this study, varyingly saturated (dry, water, and brine with 10%, 20% and 30% NaCl by weight) siltstone s les were subjected to uniaxial compressive loading to evaluate their fracability variation. Acoustic emission (AE) and ARAMIS photogrammetry analyses were incorporated to interpret the crack propagation. SEM analysis was carried out to visualize the micro-structural alterations. Results show that siltstone strength and brittleness index (BI) are reduced by 31.7% and 46.7% after water saturation, due to water-induced softening effect. High NaCl concentrations do not reduce the siltstone strength or brittleness significantly but may contribute to a slight re-gain of both values (about 3–4%). This may be due to NaCl crystallization in rock pore spaces, as confirmed by SEM analysis. AE analysis infers that dry siltstone exhibits a gradual fracture propagation, whereas water and brine saturated specimens exhibit a hindered fracturing ability. ARAMIS analysis illustrates that high NaCl concentrations causes rock mass failure to be converted to shear failure from splitting failure, which is in favour of fracability.
Publisher: AIP Publishing
Date: 06-08-2007
DOI: 10.1063/1.2768904
Abstract: Fe Pt : Al 2 O 3 nanocomposite thin films have been synthesized by magnetic trapping assisted pulsed laser deposition. The annealing temperature required for phase transition from low Ku fcc-FePt to high Ku fct-FePt is lowered down from about 600°C for conventional pulsed laser deposition (PLD) to 300°C for magnetic trapping assisted PLD. For the s le annealed at 300°C with fct phase FePt nanoparticles, the average nanoparticle size is estimated to be about 8.7±2.1nm, and the magnetic properties are improved which makes it a potentially good candidate for possible applications in high density data storage.
Publisher: MDPI AG
Date: 28-06-2017
DOI: 10.3390/APP7070664
Publisher: Elsevier BV
Date: 12-2017
Publisher: Elsevier BV
Date: 04-2017
Publisher: Springer Science and Business Media LLC
Date: 07-09-2016
Publisher: Springer Science and Business Media LLC
Date: 15-12-2018
Publisher: Elsevier BV
Date: 08-2017
Publisher: Elsevier BV
Date: 09-2017
Publisher: Elsevier BV
Date: 08-2015
Publisher: Springer Science and Business Media LLC
Date: 02-08-2023
Publisher: Elsevier BV
Date: 2019
Publisher: Elsevier BV
Date: 10-2018
Publisher: Springer Science and Business Media LLC
Date: 10-2018
Publisher: Elsevier BV
Date: 08-2017
Publisher: Elsevier BV
Date: 2017
Publisher: Elsevier BV
Date: 04-2018
Publisher: Elsevier BV
Date: 05-2018
Publisher: Elsevier BV
Date: 02-2019
Publisher: Springer Science and Business Media LLC
Date: 12-11-2015
Publisher: The Royal Society
Date: 10-2017
DOI: 10.1098/RSOS.170896
Abstract: The mechanical properties of any substance are essential facts to understand its behaviour and make the maximum use of the particular substance. Rocks are indeed an important substance, as they are of significant use in the energy industry, specifically for fossil fuels and geothermal energy. Attenuation of seismic waves is a non-destructive technique to investigate mechanical properties of reservoir rocks under different conditions. The attenuation characteristics of five different rock types, siltstone, shale, Australian sandstone, Indian sandstone and granite, were investigated in the laboratory using ultrasonic and acoustic emission instruments in a frequency range of 0.1–1 MHz. The pulse transmission technique and spectral ratios were used to calculate the attenuation coefficient ( α ) and quality factor ( Q ) values for the five selected rock types for both primary ( P ) and secondary ( S ) waves, relative to the reference steel s le. For all the rock types, the attenuation coefficient was linearly proportional to the frequency of both the P and S waves. Interestingly, the attenuation coefficient of granite is more than 22% higher than that of siltstone, sandstone and shale for both P and S waves. The P and S wave velocities were calculated based on their recorded travel time, and these velocities were then used to calculate the dynamic mechanical properties including elastic modulus ( E ), bulk modulus ( K ), shear modulus ( µ ) and Poisson's ratio ( ν ). The P and S wave velocities for the selected rock types varied in the ranges of 2.43–4.61 km s −1 and 1.43–2.41 km h −1 , respectively. Furthermore, it was observed that the P wave velocity was always greater than the S wave velocity, and this confirmed the first arrival of P waves to the sensor. According to the experimental results, the dynamic E value is generally higher than the static E value obtained by unconfined compressive strength tests.
Publisher: Elsevier BV
Date: 06-2016
Publisher: Elsevier BV
Date: 05-2015
Publisher: Springer Science and Business Media LLC
Date: 08-2016
Publisher: MDPI AG
Date: 21-12-2018
DOI: 10.3390/EN12010014
Abstract: Hydro-fracturing is a common production enhancement technique used in unconventional reservoirs. However, an effective fracturing process requires a precise understanding of a formation’s in-situ strength behavior, which is mainly dependent on the formation’s in-situ stresses and fluid saturation. The aim of this study is to identify the effect of brine saturation (concentration and degree of saturation (DOS)) on the mechanical properties of one of the common unconventional reservoir rock types, siltstone. Most common type of non-destructive test: acoustic emission (AE) was used in conjunction with the destructive tests to investigate the rock properties. Unconfined compressive strength (UCS) and splitting tensile strength (STS) experiments were carried out for 78 varyingly saturated specimens utilizing ARAMIS (non-contact and material independent measuring system) and acoustic emission systems to determine the fracture propagation. According to the experimental results, the increase in degree of pore fluid saturation (NaCl ionic solution) causes siltstone’s compressive and tensile strengths to be reduced through weakening and breakage of the existing bonding between clay minerals. However, increasing NaCl concentration in the pore fluid generally enhances the compressive strength of siltstone through associated NaCl crystallization effect and actually reduces the tensile strength of siltstone through the corrosive influence of the NaCl ions. Moreover, results show that AE capture and analysis is one of the most effective methods to understand crack propagation behavior in rocks including the crack initiation, crack propagation, and final failure. The findings of this study are important for the identification of fluid saturation dependent in-situ strength conditions for successful hydro-fracturing in low permeable reservoirs.
Publisher: Elsevier BV
Date: 11-2016
Publisher: Elsevier BV
Date: 10-2018
Publisher: Elsevier BV
Date: 08-2017
Publisher: IOP Publishing
Date: 15-02-2007
Publisher: Elsevier BV
Date: 04-2014
Publisher: Elsevier BV
Date: 05-2018
Publisher: MDPI AG
Date: 24-05-2018
DOI: 10.3390/EN11061338
No related grants have been discovered for tharaka Rathnaweera.