Clay Trace Research Articles

Implications of sand mobilization on stability and rheological properties of carbon dioxide foam and its transport mechanism in unconsolidated sandstone

This study reports the role of sand grain (of varying size: 60–380 μm and concentration: 0–3 wt%) on stability and properties of Pickering carbon dioxide (CO2) foam, which relates to foam transport problem during oil recovery practice in unconsolidated formation. For foams, anionic surfactant (sodium dodecyl sulfate: 0.2 wt%) and single-step silica nanofluid (0.1 wt%, size: 33–38 nm) were used and Pickering foams were prepared by mechanical agitation in the presence of different sand (comprised mainly of quartz with traces of clay), to mimic the effect of grain on foam stability. Interestingly, a varying stability exists in presence of sand. Thus, foam volume increased from 48 ml (without sand) to 58 ml when 1 wt% sand (of size ≈ 60–120 μm) was added while it further reduced to 46 and 40 ml with 2 and 3 wt% sand, respectively. On the contrary, foam stability continuously reduced with increment in sand size (from 60 to 120 to 200–380 μm), indicating unfavorable role of sand size on foam stability. Thus, sand production during oil recovery process is unfavorable for the stability of foam systems. The effect of sand concentration and size on foam properties was validated by interfacial tension and rheological measurements. Interfacial tension between CO2-nanofluid decreased till 1 wt% sand, suggesting favorable role of sand on CO2-nanofluid interaction. Similarly, CO2 foam showed maximum viscosity (72.8 mPa s) at 1 wt% sand (of size ≈ 60–120 μm) while further increase in concentration (>1 wt%) and size (>120 μm) reduced foam viscosity. These foams also exhibited viscoelastic characteristics with presence of both storage and viscous moduli. The solid-like nature of foam was least affected by the increase in deformational strain and foams exhibited dominating storage modulus over the range strain explored. Thus, the observation of this study can be used to optimize foam flooding in sandstone reservoirs which exhibit sand/fines production.

Date antropologice referitoare la unele dintre descoperirile funerare ale Epocii Bronzului de la Păuleni-Ciuc (jud. Harghita) / Anthropological data about several Bronze Age funerary discoveries at Păuleni-Ciuc (Harghita County)

The study details the anthropological analyses of 14 archaeological cases in which entire or partial human skeletons were found in the Bronze Age site of Păuleni-Ciuc, Ciomortan (Harghita county) during the excavation campaigns 2000-2002, 2007, 2009 and 2011. Two collective deposits, a ritual pit, two dwellings and other findings delivered a total of 22 individuals, among which 8 were aged seven or less. Feature 14, an oval pit researched in 2002, contained a grinding stone, an entire ceramic vessel, animal bones and the remains of 5 individuals: the skull of 15 years old female with traces of peri-mortem blow inflicted with a small object in the mandible, the skull and ribs of a seven years old child, parts of the hands and ribs of two infans I, the entire skeleton, deposited flexed on its right side, on the bottom of the pit (a woman, 17-21 years old, 160 cm height). The woman’s skeleton had traces of burning on the ribs, right tibia and cubitus, suggesting that the dead was laid on the remains of a recently consumed fire. Traces of cuts and blows were identified on the long bones. Feature 14a, a flexed skeleton of an adult (22-24 years old) male (159 cm height, robust) was found in the vicinity of the previously described situation. They could be connected. The mandible showed signs of an abnormal disposition of the teeth with rotated canines. Feature 13 was associated with the fortification, maybe with a decommissioned gate. It comprised the entire skeleton of an adult man (24-30 years old) and the remains of 4 other individuals: an adult female (represented by unburnt fragments of the skull), one infans I (cremated, with traces of clay on the skull), a new-born and a 4 years old. The robust man was partially cremated, laid flexed, on its left side, mixed with animal bones. Traces of ochre were found on its right femur. He had suffered from osteoarthritis. Pit 36, dug in the fortification, contained 7 Wittenberg vessels and the entire skeleton of a 4 years old child. Remains of two infans II were discovered in two dwellings (8 and 8A) excavated in 2000.

The composition and technology of the 3–4th century CE decorative earthen plaster of Pithalkhora caves, India

This research focuses on the characterization of ancient decorative earthen plaster of India's Pithalkhora group of caves. The restoration strategies being planned for the earthen plaster demand detailed scientific investigation to understand technology and composition so as to prepare matching plaster. The mineralogical, micro-structural and chemical characterization of the earthen plasters have been investigated by analytical tools like petrological microscope, XRF, CHN analysis, laser scattering particle size analyzer, FTIR, XRD, Scanning Electron Microscopy, thermal analyzer (DGA/DTA) as well as on-site observations. A comparative study with nearby sites portrays the earthen plaster of Pithalkhora coarser (silt: 62–100%, sand: 2–2.2%) with traces of clay (0–2%); hence it may be prone to damage by grain breakages. The chemical composition confirms that the aggregates mixed with the earthen plaster belong to that of locally available basaltic origin. SEM studies show addition of quartz and traces of clay (illite and montmorillonite) to augment the flexibility and performance of the plaster. The restoration plaster should be synthesized with aggregates of locally available basaltic rock mixed with slaked lime in addition with rice husk and other vegetal fibres as vegetal additive to overcome the shrinkage of the plaster.

Cyclic shear behaviour of fibre-reinforced mine tailings

ABSTRACT: In order to investigate techniques to improve the mechanical behaviour of mine tailings, an investigation of the cyclic shear response of fibre-reinforced mine tailings was carried out in the present study. Cyclic simple shear tests were conducted on fibre-reinforced and non-reinforced mine tailings. The tailings, produced from gold mining, were classified as sandy silt with traces of clay. Polypropylene fibres (zero and 0.5%) were added to the material. Under monotonic shear conditions, the addition of fibres unstiffens the material. Under shear stress-controlled cyclic conditions, fibres improved the material shear response and produced a stiffer material. Under shear strain-controlled cyclic conditions, no improvement was observed as a result of addition of fibres and there was no effect on material stiffness. The agreement of the strength envelopes of both monotonic and cyclic stress paths, under different cyclic loading conditions, allows the use of the same strength parameters for mixtures analysed under different loading conditions.

Cyclic shear response of fibre-reinforced cemented paste backfill

In order to investigate techniques to improve tailings backfill stability in stopes, the cyclic shear response of fibre-reinforced cemented mine tailings was studied. Cyclic simple shear tests were conducted on fibre-reinforced and non-reinforced cemented mine tailings. The tailings, produced from gold mining, are classified as sandy silt with traces of clay. Portland cement (5%) and polypropylene fibres (zero and 0·5%) were added to the material. Under monotonic shear conditions, the addition of fibres confers hardening behaviour to the cemented material. Under shear strain controlled cyclic conditions, fibres increased the shear stress values of the cemented samples after successive load cycles. The agreement of the strength envelopes of both monotonic and cyclic stress paths, under different cyclic loading conditions, allows the use of the same strength parameters of mixtures analysed under different loading conditions.

Extending Well-Productivity Life in a High-Pressure/ High-Temperature Tight Gas/Condensate Carbonate Reservoir by Acid Refracturing

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 142444, ’Extending Well- Productivity Life by Acid Refracturing in a High-Pressure/High-Temperature Tight Gas/Condensate Carbonate Reservoir in a Jurassic Formation of Northern Kuwait,’ by Mir Kabir, SPE, Qasem Dashti, SPE, J.R. Singh, SPE, and San Prasad Pradhan, SPE, KOC, and Ikhsan Nugraha, SPE, Liu Hai, and Hamed Al-Ghadhban, Schlumberger, prepared for the 2011 SPE Middle East Unconventional Gas Conference and Exhibition, Muscat, Oman, 31 January- 2 February. The paper has not been peer reviewed. Productivity of the subject well, which had been on production for 3 years after an initial acid-fracture treatment with almost 90% of its cumulative production occurring during the last year, was declining faster than expected. Review of the well’s performance indicated two possible causes: reservoir-pressure decline and reduced fracture-length/conductivity ratio. Acid refracturing was chosen to restore the well’s productivity by extending the fracture half-length to enhance fracture conductivity. The results showed that the productivity index (PI) increased by a factor of 2.5 during the post-treatment production test. However, after 3 months of production, this declined to 1.2. Introduction Several major fields in north-ern Kuwait, including Sabriyah, Raudathain, Umm Niqqa, Bahra, and Dhabi, produce gas from the Jurassic Middle Marrat formation, an important carbonate reservoir. Typical depth is 14,000 ft, reservoir pressure ranges from 10,000 to 12,000 psi, and the bottomhole static temperature averages 275°F. The Middle Marrat formation is mostly limestone (calcite>90%) with minor dolomitization. Only traces of clay and silt are found. High heterogeneity, both laterally and vertically, has been reported. Core permeability matches log permeability, and the high permeability value obtained from the core could be the result of induced fractures. Pressure-transient analyses of some wells showed dual-porosity behavior with low matrix permeability. Generally, the absolute matrix permeability is less than 1 md. The production mechanism is a combination of matrix and natural-fracture permeability. Acid Refracturing In regions where acid fracturing is common, there are questions that arise. When is the best time to refracture? What is the justification to repeat the treatment? If there is justification, what needs to be done differently in the subsequent treatment? The decision usually relies on the post-treatment production behavior compared with the pretreatment condition.