Yiyu Lu

Bio: Yiyu Lu is an academic researcher from Chongqing University. The author has contributed to research in topics: Hydraulic fracturing & Oil shale. The author has an hindex of 24, co-authored 115 publications receiving 1971 citations.

Investigation on the physics structure and chemical properties of the shale treated by supercritical CO2

Abstract: Shale gas is the second largest source of unconventional fuel in the world. Supercritical carbon dioxide (SC-CO2) fracturing not only allows effectively breaking paper to the shale gas recovery but also could the replace of methane with carbon dioxide. In this method CO2 adsorption in the shale affects the physical and chemical structure of the shale formations. Therefore, the change of reservoir physical properties will affect the efficiency of fracturing. The main objective of this study is to investigate supercritical CO2 (SC-CO2) effects on the physical structure (porosity, deformation, and mechanical properties) and chemical structure (mineral components) of the shale. Four types of experiments were conducted: (1) pore characteristics by low-pressure nitrogen adsorption. (2) the mineral composition of the shale test. (3) The CO2-induced (adsorption-induced and pressure-induced) deformation of the shale teste. (4) The triaxial compressive strength and tensile strength of samples test. The results show that shale pore properties could be change by the SC-CO2. The specific surface of the shale decreased and the porosity and average pore size increased. The mineral content of the shale minerals (except quartz) decreased after SC-CO2 treatment. The samples exhibited swelling strains caused by SC-CO2. At low pressures, shale deformation was mainly caused by adsorption, while deformation at higher pressures was mainly caused by pressure. After the SC-CO2 treatment, the tensile strength, triaxial compressive strength, and elastic modulus of the shale decreased. The strength decreased as the treatment time increased. The changes in the strength of shale could be explained by two mechanisms: the dissolution effect of SC-CO2 and the adsorption/pressure-induced strain. It indicate that supercritical carbon dioxide can change the characteristics of shale reservoir, and it could reduce the fracturing pressure of supercritical carbon dioxide fracturing and enhance the efficiency of fracturing.

VALIDITY OF CUBIC LAW FOR FLUID FLOW IN A DEFORMABLE ROCK FRACTURE - eScholarship

Abstract: The validity of the cubic law for laminar flow of fluids through open fractures consisting of parallel planar plates has been established by others over a wide range of conditions with apertures ranging down to a minimum of 0.2 µm. The law may be given in simplified form by Q/Δh = C(2b)3, where Q is the flow rate, Δh is the difference in hydraulic head, C is a constant that depends on the flow geometry and fluid properties, and 2b is the fracture aperture. The validity of this law for flow in a closed fracture where the surfaces are in contact and the aperture is being decreased under stress has been investigated at room temperature by using homogeneous samples of granite, basalt, and marble. Tension fractures were artificially induced, and the laboratory setup used radial as well as straight flow geometries. Apertures ranged from 250 down to 4µm, which was the minimum size that could be attained under a normal stress of 20 MPa. The cubic law was found to be valid whether the fracture surfaces were held open or were being closed under stress, and the results are not dependent on rock type. Permeability was uniquely defined by fracture aperture and was independent of the stress history used in these investigations. The effects of deviations from the ideal parallel plate concept only cause an apparent reduction in flow and may be incorporated into the cubic law by replacing C by C/ƒ. The factor ƒ varied from 1.04 to 1.65 in these investigations. The model of a fracture that is being closed under normal stress is visualized as being controlled by the strength of the asperities that are in contact. These contact areas are able to withstand significant stresses while maintaining space for fluids to continue to flow as the fracture aperture decreases. The controlling factor is the magnitude of the aperture, and since flow depends on (2b)3, a slight change in aperture evidently can easily dominate any other change in the geometry of the flow field. Thus one does not see any noticeable shift in the correlations of our experimental results in passing from a condition where the fracture surfaces were held open to one where the surfaces were being closed under stress.

Mathematical Theory Of Elasticity

Abstract: THE appearance of a treatise in English upon the mathematical theory of elasticity is an event the potential importance of which may be judged by the that the author, in his frequent suggestions for collateral reading, refers to only three such, those of Southwell, Timoshenko, and Love. In spirit and content Sokolnikoff}s book differs greatly from each and all of these. It may be described by a possible sub-title: “A pure mathematician surveys topics related to certain problems in the mathematical theory of elasticity”. It is symptomatic of the change in outlook of American mathematics over the past few decades. Mathematical Theory Of Elasticity Prof. I. S. Sokolnikoff with the collaboration of Asst. Prof. R. D. Speche. Pp. xi + 373. (New York and London: McGraw-Hill Book Co., Inc., 1946.) 22s. 6d.

Some Basic Problems Of The Mathematical Theory Of Elasticity

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