Effect of fracture fluid flowback on shale microfractures using CT scanning

The field data of shale fracturing demonstrate that the flowback performance of fracturing fluid is different from that of conventional reservoirs,where the flowback rate of shale fracturing fluid is lower than that of conventional reservoirs.At the early stage of flowback,there is no single-phase flow of the liquid phase in shale,but rather a gas-water two-phase flow,such that the single-phase flow model for tight oil and gas reservoirs is not applicable.In this study,pores and microfractures are extracted based on the experimental results of computed tomography(CT)scanning,and a spatial model of microfractures is established.Then,the influence of rough microfracture surfaces on the flow is corrected using the modified cubic law,which was modified by introducing the average deviation of the microfracture height as a roughness factor to consider the influence of microfracture surface roughness.The flow in the fracture network is simulated using the modified cubic law and the lattice Boltzmann method(LBM).The results obtained demonstrate that most of the fracturing fluid is retained in the shale microfractures,which explains the low fracturing fluid flowback rate in shale hydraulic fracturing.

hale gas reservoir modeling and production evaluation considering complex gas transport mechanisms and dispersed distribution of kerogen

Stimulated shale reservoirs consist of kerogen,inorganic matter,secondary and hydraulic fractures.The dispersed distribution of kerogen within matrices and complex gas flow mechanisms make production evaluation challenging.Here we establish an analytical method that addresses kerogen-inorganic matter gas transfer,dispersed kerogen distribution,and complex gas flow mechanisms to facilitate evaluating gas production.The matrix element is defined as a kerogen core with an exterior inorganic sphere.Unlike most previous models,we merely use boundary conditions to describe kerogen-inorganic matter gas transfer without the instantaneous kerogen gas source term.It is closer to real inter-porosity flow conditions between kerogen and inorganic matter.Knudsen diffusion,surface diffusion,adsorption/desorption,and slip corrected flow are involved in matrix gas flow.Matrix-fracture coupling is realized by using a seven-region linear flow model.The model is verified against a published model and field data.Results reveal that inorganic matrices serve as a major gas source especially at early times.Kerogen provides limited contributions to production even under a pseudo-steady state.Kerogen properties’influence starts from the late matrix-fracture inter-porosity flow regime,while inorganic matter properties control almost all flow regimes except the early-mid time fracture linear flow regime.The contribution of different linear flow regions is also documented.

An optimization model for conductivity of hydraulic fracture networks in the Longmaxi shale,Sichuan basin,Southwest China

Shale gas is an important unconventional resource.The economic recovery of shale gas is only possible when a fracture network with sufficient conductivity is created by hydraulic fracturing,that,if effectively propped,connects fracturing fractures and natural fractures.Focusing on the Longmaxi shale in the Sichuan Basin,Southwest China,we built an optimization model for conductivity of multi-grade fractures based on equivalent seepage theory.We then experimentally analyzed the conductivity of self-propped and sand-propped fractures,and optimized the propping patterns of multi-grade hydraulic fractures in shale gas reservoirs.We concluded that the propping effectiveness of fracture networks could be improved by using low concentrations of small-sized sands and by focusing on creating a large number of self-propped fractures.By applying this understanding to the optimization of fracturing designs for the Longmaxi shale,we successfully created networks of well-propped fractures.

Changes in Total Factor Productivity,Technological Progress and Efficiency of Banana Industry in China

Based on the DEA-based Malmquist index method,the total factor productivity was calculated for 5 major banana production areas in 2003-2004,and it was further divided into technological progress and technical efficiency.The results show that the total factor productivity of banana industry in China was 1.3% in the sample period,mainly due to technological progress,the average growth rate was 2.6%,while the pure technical efficiency and scale efficiency was -0.1% and -1.2% respectively.The improvement of total factor productivity in banana industry in China relied mainly on technological progress,cultivation of new banana varieties,management of high quality cultivation,popularization and application of water conservation and fertilizer saving technology,and injury-free picking technologies.The pure technical efficiency and scale efficiency of banana production were negative,indicating that the management level of banana was not high.The effect of scale economy of this industry through agglomeration and consolidation is still to be practiced.Banana growers should promote the improvement of large scale and management level of the banana industry at the same time of promoting the technological progress.

Evaluation on the anisotropic brittleness index of shale rock using geophysical logging

The brittleness index plays a significant role in the hydraulic fracturing design and wellbore stability analysis of shale reservoirs.Various brittleness indices have been proposed to characterize the brittleness of shale rocks,but almost all of them ignored the anisotropy of the brittleness index.Therefore,uniaxial compression testing integrated with geophysical logging was used to provide insights into the anisotropy of the brittleness index for Longmaxi shale,the presented method was utilized to assess brittleness index of Longmaxi shale formation for the interval of 3155e3175 m in CW-1 well.The results indicated that the brittleness index of Longmaxi shale showed a distinct anisotropy,and it achieved the minimum value at β=45°-60°.As the bedding angle increased,the observed brittleness index(BI_(2_β))decreased firstly and increased then,it achieved the lowest value at β=40°-60°,and it is consistent with the uniaxial compression testing results.Compared to the isotropic brittleness index(β=0°),the deviation of the anisotropic brittleness index ranged from 10%to 66.7%,in other words,the anisotropy of brittleness index cannot be ignored for Longmaxi shale.Organic matter content is one of the main intrinsic causes of shale anisotropy,and the anisotropy degree of the brittleness index generally increases with the increase in organic matter content.The present work is valuable for the assessment of anisotropic brittleness for hydraulic fracturing design and wellbore stability analysis.

Allele-defined genome reveals biallelic differentiation during cassava evolution

Dear Editor,Generation of heterozygous genomes by hybridization between or within species can help maintain plant diversity and serve as a potential source of new species(Baek et al.,2018).Moreover,genomic heterozygosity is associated with genomic coadaptation,developmental stability,and heterosis.Accurate definition of alleles in haplotypes is necessary to precisely characterize allelic variation controlling agriculturally important traits(Shi et al.,2019).Currently,most released genomes have mosaic assembly of haplotypes due to random selection or collapse of alleles during genome assembly(Shi et al.,2019),which masked allelic variation and functional differentiation of divergent alleles in heterozygous species.

Comparison of the clinical features and therapeutics of COVID-19 in cardio-cerebrovascular disease(CCVD)and non-CCVD patients

Cardio-cerebrovascular disease(CCVD)is a major comorbidity of coronavirus disease 2019(COVID-19).However,the clinical characteristics and outcomes remain unclear.In this study,102 cases of COVID-19 from January 22,2020 to March 26,2020 in Xixi Hospital of Hangzhou were included.Twenty cases had pre-existing CCVD.Results showed that compared with non-CCVD patients,those with CCVD are more likely to develop severe disease(15%versus 1%),and the proportion of pneumonia severity index grade IV was significantly higher(25%versus 3.6%).Computed tomography images demonstrated that the proportion of multiple lobe lesion involvement was significantly higher in the CCVD group than in the non-CCVD group(90%versus 63.4%).Compared with non-CCVD group,the levels of C-reactive protein,fibrinogen,D-dimer,and serum amyloid-A were higher,whereas the total protein and arterial partial Pa02 were lower in the CCVD group.Although no statistical difference was observed in the outcomes between groups,CCVD patients received more intensive comprehensive treatment to improve COVID-19 symptoms compared with non-CCVD patients.Integrated Chinese and Western medicine treatments have certain advantages in controlling the severe conversion rate and mortality of COVID-19.In addition,given that COVID-19 patients are usually related to coagulation disorders and thrombosis risk,the application of Chinese medicine in promoting blood circulation and removing stasis should be strengthened.

Influence of pore pressure on tensile fracture growth in rocks： a new explanation based on numerical testing

The diffusion of pore fluid pressures may create both spatial and temporal effective stress gradients that influence or control the development and evolution of fractures within rock masses. To better understand the controls on fracturing behavior, numerical simulations are performed using a progressive fracture modeling approach that shares many of the same natural kinematic features in rocks, such as fracture growth, nucleation, and termination. First, the pinch-off breaking test is numerically performed to investigate the tensile failure of a rock specimen in a uniform pore pressure field. In this numerical simulation, both mechanical and hydrological properties of a suite of rocks are measured under simulated laboratory conditions. The complete tensional failure process of the rock specimen under pore pressure was reproduced. Second, a double-notched specimen is numerically extended to investigate how the water flow direction or pore pressure gradient influences the fracture growth. An exhaustive sensitivity study is conducted that examines the effects of varying both hydrological and mechanical boundary conditions. The simulation results indicate that local fluid pressure gradients strongly influence the state of stress in the solids and, thereby, fracture growth. Fracture and strength behavior is influenced not only by the pore pressure magnitude on a local scale around the fracture tip, but also by the orientation and distribution of pore pressure gradients on a global scale. Increasing the fracture growth rate increases the local model permeability and decreases the sample strength. The results of this study may provide useful information concerning the degree of hydrological and mechanical coupling action under geologic conditions.

A minimum volume prediction of spacer based on turbulent dispersion theory: Model and example

During cementing operations involving cement slurry contamination,problems often occur due to the inaccurate calculation of the space fluid volume.This study,based on the turbulent dispersion theory,developed a minimum volume calculation model of spacer fluid to prevent cement slurry contamination.This model was used to analyze influence factors and practical calculations.The results indicated that the minimum volume of spacer fluid increase with the eccentricity of casing and injection rate and decrease with the density of cement slurry.Additionally,the better rheological properties of the cement slurry and spacer fluid would increase the volume of the spacer fluid.Furthermore,this model fitted actual field data better than other heat calculation models.

Treatment Effects of Integrated TCM and Western Medicine Treatment Scheme on COVID-19: A Single-armed Clinical Trial

Backgroud:The outbreak of COVID-19 has brought unprecedented perils to human health and raised public health concerns in more than two hundred countries.Safe and effective treatment scheme is needed urgently.Objective:To evaluate the effects of integratedTCM and western medicine treatment scheme on COVID-19.Methods:A single-armed clinical trial was carried out in Hangzhou Xixi Hospital,an affiliated hospital with Zhejiang Chinese Medical University.102 confirmed cases were screened out from 725 suspected cases and 93 of them were treated with integrated TCM and western medicine treatment scheme.Results:83 cases were cured,5 cases deteriorated,and 5 cases withdrew from the study.No deaths were reported.The mean relief time of fever,cough,diarrhea,and fatigue were(4.78±4.61)days,(7.22±4.99)days,(5.28±3.39)days,and(5.28±3.39)days,respectively.It took(14.84±5.50)days for SARS-CoV-2 by nucleic acid amplification-based testing to turn negative.Multivariable cox regression analysis revealed that age,BMI,PISCT,BPC,AST,CK,BS,and UPRO were independent risk factors for COVID-19 treatment.Conclusion:Our study suggested that integrated TCM and western medicine treatment scheme was effective for COVID-19.