Quantitative evaluation of adsorbed and free water in deep shales:a case study on the Wufeng-Longmaxi Formations from the Luzhou area,southern Sichuan Basin,China

Deep shale gas reservoirs commonly contain connate water, which affects the enrichment and migration of shale gas and has attracted the attention of many scholars. It is significant to quantitatively estimate the amounts of adsorbed and free water in shale matrix pores, considering the different impacts of pore water (adsorbed water and free water) on shale gas. In this paper, pore water in six deep shale samples from the Wufeng-Longmaxi Formations in the Luzhou area, southern Sichuan Basin, China, was quantitatively evaluated by saturation-centrifugation experiments. Further, the impact of shale material composition and microstructure on the pore water occurrence was analyzed. The results show that amounts of adsorbed and free water are respectively 1.7967–9.8218 mg/g (mean 6.4501 mg/g) and 9.5511–19.802 mg/g (mean 13.9541 mg/g) under the experimental conditions (30℃, distilled water). The ratio of adsorbed water to total water is 15.83%–42.61% (mean 30.45%). The amounts of adsorbed and free water are related to the pore microstructure and material compositions of shale. The specific surface area of shale controls the amount of adsorbed water, and the pore volume controls the amount of free water;organic pores developed in shale solid asphalt contribute specific surface area and pore volume, and inorganic pores developed in clay mineral contribute pore volume. Therefore, the pores of shale solid asphalt accumulate the adsorbed water and free water, and the pores of clay minerals mainly accumulate the free water.

Advanced near-infrared light approaches for neuroimaging and neuromodulation

Almost all physiological processes of animals are controlled by the brain,including language,cognitive,memory,learning,emotion and so forth.Minor brain dysfunction usually leads to brain diseases and disorders.Therefore,it'is greatly meaningful and urgent for scientists to have a better understanding of brain structure and function.Optical approaches can provide powerful tools for imaging and modulating physiological processes of the brain.In particular,optical approaches in the near-infrared(NIR)window(700-1700 nm)exhibit excellent prosperities of deep tissue penetration and low tissue scattering and absorption compared with those of visible windows(400-700 nm),which provides a promising approach for scientists to develop desired methods of neuroimaging and neuromodulation in deep brain tissues.In this review,variable types of NIR light approaches for imaging and modulating neural ions,membrane potential,neurotransmitters,and other critical molecules for brain functions and diseases are summarized.In particular,the latest breakthrough research of brain imaging and brain regulation in the NIR-II window(1000-1700 nm)are highlighted.Finally,we conclude the challenges and prospects of NIR light-based neuroimaging and neuromodulation for both basic brain research and further clinical translation.

Prediction of decline in shale gas well production using stable carbon isotope technique

Prediction of shale gas production is a challenging task because of the complex fracture-pore networks and gas flow mechanisms in shale reservoirs.Empirical methods,which are used in the industry to forecast the future production of shale gas,have not been assessed sufficiently to warrant high confidence in their results.Methane carbon isotopic signals have been used for producing gas wells,and are controlled by physical properties and physics-controlling production;they serve as a unique indicator of the gas production status.Here,a workable process,which is combined with a gas isotope interpretation tool(also known as a numerical simulator),has been implemented in Longrnaxi shale gas wells to predict the production decline curves.The numerical simulator,which takes into account a convection-diffu-sion-adsorption model for the matrix and a convection model for fractures in^(13)CH_(4) and ^(12)CH_(4) isotopologues,was used to stabilize the carbon isotope variation in the produced gas to elucidate gas recovery.Combined with the production rates of the four developing wells,the total reserves ranged from 1.72×10^(8) to 2.02×10^(8) m^(3),which were used to constrain the trend of two-segment produc-tion decline curves that exhibited a transition from a hyperbolic equation to an exponential one within 0.82-0.89 year.Two-segment production decline curves were used to forecast future production and estimate ultimate recovery.