Effect of hydraulic fracturing induced stress field on weak surface activation during unconventional reservoir development

Unconventional reservoirs usually contain many weak surfaces such as faults,laminae and natural fractures,and effective activation and utilization of these weak surfaces in reservoirs can significantly improve the extraction effect.In hydraulic fracturing,when the artificial fracture approaches the natural fracture,the natural fracture would be influenced by both the original in-situ stress field and the hydraulic fracturing-induced stress field.In this paper,the hydraulic fracturing-induced stress field is calculated based on the relative position of hydraulic fracture and natural fracture,the original in-situ stress,the net pressure inside the hydraulic fracture and the pore pressure of the formation.Furthermore,the stability model of the natural fracture is established by combining the Mohr-Coulomb rupture criterion,and extensive parametric studies are conducted to explore the impact of each parameter on the stability of the natural fracture.The validity of the proposed model is verified by comparing with the reservoir characteristics and fracturing process of the X-well 150e155 formation in the Songliao Basin.It is found that the stress field induced by the hydraulic fracture inhibits the activation of the natural fracture after the artificial fracture crossed the natural fracture.Therefore,for similar reservoirs as X-well 150e155,it is suggested to connect natural fractures with hydraulic fractures first and then activate natural fractures which can effectively utilize the natural fractures and form a complex fracture network.

Realization of^(87)Rb Bose–Einstein Condensates in Higher Bands of a Hexagonal Boron-Nitride Optical Lattice

Ultracold neutral atoms in higher bands of an optical lattice provide a natural avenue to emulate orbital physics in solid state materials.Here,we report the realization of^(87)Rb Bose-Einstein condensates in the fourth and seventh Bloch bands of a hexagonal boron-nitride optical lattice,exhibiting remarkably long coherence time through active cooling.Using band mapping spectroscopy,we observe that atoms condensed at the energy minimum of L point(K_(1)and K_(2)points)in the fourth(seventh)band as sharp Bragg peaks.The lifetime for the condensate in the fourth(seventh)band is about 57.6(4.8)ms,and the phase coherence of atoms in the fourth band persists for a long time larger than 110 ms.Our work thus offers great promise for studying unconventional bosonic superfluidity of neutral atoms in higher bands of optical lattices.

Emerging Trends of Drug-Resistant HIV-1 among Drug-Treated Patients in Former Blood Donors in Hubei,China:a Three-Year Surveillance from 2004 to 2006

This study aimed to evaluate emerging trends of drug resistance to nucleoside reverse transcriptase inhibitors (NRTIs) and nonnucleoside reverse transcriptase inhibitors (NNRTIs) among 290 former blood donor HIV-1 infected patients in Hubei, China, from 2004 to 2006, all of whom had received anti-HIV-1 therapy. The presence of NRTI- and NNRTI-associated mutations were established by sequencing; genotypic and predicted phenotypic drug resistance were evaluated using HIVdb Program version 5.0.1 (http://hivdb.stanford.edu/ pages/algs/HIVdb.html). Genotypic drug resistance analysis showed significant increases in percentages of patients carrying HIV-1 strains with M41L, T215Y/F, D67N, K103N, G190A/S, Y181C/F or L210W mutations. Of the variants' predicted phenotypic drug resistance, highly significant increases were detected in percentages of patients carrying HIV-1 with high resistance to zidovudine (AZT) or stavudine (D4T) in NRTIs, and to delavirdine (DLV), efavirenz (EFV) or nevirapine (NVP) in NNRTIs; intermediate resistance to abacavir (ABC), AZT, D4T, didanosine (DDI) or tenofovir disoproxil fumarate (TDF) in NRTIs, and to etravirine (ETR) in NNRTIs; and low and potential low resistance to lamivudine (3TC), ABC, emtricitabine (FTC) or TDF in NRTIs, and to ETR in NNRTIs.

Oscillatory-like expansion of a Fermionic superfluid

We study the expansion behaviors of a Fermionic superfluid in a cigar-shaped optical dipole trap for the whole BEC-BCS crossover and various temperatures.At low temperature(0:06(1)T_F),the atom cloud undergoes an anisotropic hydrodynamic expansion over 30 ms,which behaves like oscillation in the horizontal plane.By analyzing the expansion dynamics according to the superfluid hydrodynamic equation,the effective polytropic index y of Equation-of-State(EoS)of Fermionic superfluid is extracted.The y values show a non-monotonic behavior over the BEC-BCS crossover,and have a good agreement with the theoretical results in the unitarity and BEC side.The normalized quasi-frequencies of the oscillatory expansion are measured,which drop significantly from the BEC side to the BCS side and reach a minimum value of 1.73 around 1/k_Fa=-0:25.Our work improves the understanding of the dynamic properties of strongly interacting Fermi gas.