A fast identification method based on the typical geophysical differences between submarine shallow carbonates and hydrate bearing sediments in the northern South China Se a

Bottom simulating reflector(BSR)has been recognized as one of the indicators of gas hydrates.However,BSR and hydrate are not one-to-one correspondence.In the Xisha area of South China Sea(SCS),carbonate rocks wildly develop,which continuously distribute parallel to the seafloor with high amplitude on seismic sections,exhibiting reflections similar to BSRs in the Shenhu area nearby.This phenomenon causes some interference to hydrates identification.In this paper,the authors discussed the typical geophysical differences between carbonate rocks and hydrates,indicating that the main difference exists in relationship between porosity and velocity,causing different amplitude versus offset(AVO)characters.Then the authors proposed a new model assuming that the carbonates form the matrix and the hydrate fill the pore as a part of the matrix.The key modeling parameters have been optimized constrained by Pvelocities and S-velocities simultaneously,and the model works well both for carbonate rock and gas hydrate bearing sediments.For quantitative identification,the authors calculated the velocities when carbonates and hydrates form the matrix together in different proportions.Then they proposed a carbonate and hydrate identification template(CHIT),in which the possible hydrate saturation(PHS)and possible carbonate content(PCC)can be both scaled out for a group of sample composed by P-velocity and S-velocity.If PHS is far larger than PCC,it is more likely to be a hydrate sample because carbonates and hydrates do not coexist normally.The real data application shows that the template can effectively distinguish between hydrates and carbonate rocks,consequently reducing the risk of hydrate exploration.

Percutaneous biliary stent combined with brachytherapy using 125I seeds for treatment of unresectable malignant obstructive jaundice:A meta-analysis

BACKGROUND Malignant obstructive jaundice(MOJ)is a common pathologic manifestation of malignant biliary obstruction.Recently,several clinical trials have explored the clinical effectiveness of intraluminal^(125)I seed-based brachytherapy for MOJ patients,and various outcomes have been reported.AIM To assess the efficacy and safety of percutaneous biliary stents with^(125)I seeds compared to conventional metal stents in patients with unresectable MOJ.METHODS A systematic search of English-language databases(PubMed,Embase,Cochrane Library,and Web of Science)was performed to identify studies published prior to June 2020 that compared stents with or without^(125)I seeds in the treatment of unresectable MOJ.The outcomes analyzed included primary outcomes(stent patency and overall survival)and secondary outcomes(complications and liver function parameters).RESULTS Six randomized controlled trials and four retrospective studies involving 875 patients were eligible for the analysis.Of the 875 included patients,404 were treated with^(125)I seed stents,while 471 were treated with conventional stents.Unadjusted pooled analysis demonstrated that compared to conventional stents,^(125)I seed stents extended the stent patency time[hazard ratio(HR)=0.36,95%confidence interval(CI)=0.28-0.45,P<0.0001]and overall survival period(HR=0.52,95%CI=0.42–0.64,P<0.00001).Subgroup analyses based on the type of^(125)I seed stent and type of study design showed consistent results.However,there were no significant differences in the occurrence of total complications[odds ratio(OR)=1.12,95%CI=0.75-1.67,P=0.57],hemobilia(OR=1.02,95%CI=0.45-2.3,P=0.96),pancreatitis(OR=1.79,95%CI=0.42-7.53,P=0.43),cholangitis(OR=1.13,95%CI=0.60-2.13,P=0.71),or pain(OR=0.67,95%CI=0.22-2,P=0.47).In addition,there were no reductions in the levels of serum indices,including total bilirubin[mean difference(MD)=10.96,95%CI=-3.56-25.49,P=0.14],direct bilirubin(MD=7.37,95%CI=-9.76-24.5,P=0.4),alanine aminotransferase(MD=7.52,95%CI=-0.71-15.74,P=0.07),and aspartate aminotransferase(MD=-4.77,95%CI=-19.98-10.44,P=0.54),after treatment.Publication bias was detected regarding the outcome overall survival;however,the conclusions were not changed after the adjustment.CONCLUSION Placement of stents combined with brachytherapy using^(125)I seeds contributes to a longer stent patency and higher overall survival than placement of conventional stents without extra complications or severe liver damage.Thus,it can be considered an effective and safe treatment for unresectable MOJ.

Migration and accumulation characteristics of natural gas hydrates in the uplifts and their slope zones in the Qiongdongnan Basin,China

Various factors controlling the accumulation of natural gas hydrates(NGHs)form various enrichment and accumulation modes through organic combination.This study mainly analyzes the geological and geophysical characteristics of the NGHs occurrence in the uplifts and their slope zones within the deep-water area in the Qiongdongnan(QDN)Basin(also referred to as the study area).Furthermore,it investigates the dominant governing factors and models of NGHs migration and accumulation in the study area.The results are as follows.(1)The uplifts and their slope zones in the study area lie in the dominant pressure-relief direction of fluids in central hydrocarbon-rich sags in the area,which provide sufficient gas sources for the NGHs accumulation and enrichment through pathways such as gas chimneys and faults.(2)The top and flanks of gas chimneys below the bottom simulating reflectors(BSRs)show high-amplitude seismic reflections and pronounced transverse charging of free gas,indicating the occurrence of a large amount of gas accumulation at the heights of the uplifts.(3)Chimneys,faults,and high-porosity and high-permeability strata,which connect the gas hydrate temperature-pressure stability zones(GHSZs)with thermogenic gas and biogenic gas,form the main hydrate migration system.(4)The reservoir system in the study area comprises sedimentary interlayers consisting of mass transport deposits(MTDs)and turbidites.In addition,the reservoir system has developed fissure-and pore-filling types of hydrates in the pathways.The above well-matched controlling factors of hydrate accumulation enable the uplifts and their slope zones in the study area to become the favorable targets of NGHs exploration.