?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.relation=https%3A%2F%2Fepisodesplatform.eu%2Feprints%2F2163%2F&rft.title=Cotton+Valley+Hydraulic+Fracture+Imaging+Project%3A+Phase+II+(CGU+21-9)+Fracture+Imaging+Using+Microseismic+Event+Locations.&rft.creator=Urbancic%2C+Ted&rft.subject=Collective+properties+of+seismicity&rft.subject=Cotton+Valley&rft.subject=Unconventional+hydrocarbon+extraction&rft.description=Hydraulic+fracturing+is+widely+used+to+stimulate+production+in+oil+and+gas+fields%0D%0Athroughout+the+U.S..+However%2C+currently+no+method+exists+that+can+provide+well+operators+with%0D%0Ainformation+on+fracture+dimensions+in+real+time.+The+Cotton+Valley+Hydraulic+Fracture+Imaging%0D%0AProject%2C+as+initiated+by+a+consortium+of+companies+(UPR%2C+Texaco%2C+Amoco%2C+Arco%2C+Chevron)%2C+was%0D%0Aestablished+to+determine+if+the+monitoring+of+microseismicity+was+feasible%2C+if+microseismicity%0D%0Acan+remotely+provide+accurate+measurements+of+fracture+geometry+(azimuth%2C+height%2C+length%2C%0D%0Awidth%2C+asymmetry)+and+growth%2C+and+if+recording+%2F+analysis+procedures+can+eventually+be%0D%0Aimplemented+to+allow+for+real+time+monitoring+(Walker%2C+1997).+The+presence+of+microseismicity%0D%0Awas+confirmed+during+the+Phase+I+treatment+of+well+CGU+22-10+in+May%2C+1997+(see+Figure+1+for%0D%0Alayout).+The+analysis+for+fracture+dimensions+involved+the+testing+of+various+location+techniques%0D%0A(forward+modeling+and+inversion+schemes)+by+ARCO%2C+ESG%2C+Los+Alamos%2C+and+Sandia+National%0D%0ALabs.+To+locate+events%2C+ARCO+employed+a+series+of+model+curves+derived+from+pre-fracture%0D%0Ashots+in+the+treatment+well+and+visual+curve+matching+for+data+recorded+in+both+monitoring+wells.%0D%0AESG+examined+inversion+approaches+that+could+potentially+result+in+the+real-time+determination%0D%0Aof+event+locations+and+source+parameters+(characteristics+of+source+size%2C+strength%2C+energy+and%0D%0Astress+release).+The+ESG+analyses+concluded+that+it+is+possible+to+use+automatically+determined+Pand+S-wave+arrivals+for+a+subset+of+signals+recorded+in+the+two+monitoring+wells%2C+direction%0D%0Avectors+(hodograms)%2C+and+the+inclusion+of+velocity+variations+to+effectively+locate+events+to+an%0D%0Aaccuracy+on+average+better+than+50+ft.+(Urbancic%2C+1998).+Both+Los+Alamos+and+Sandia+considered%0D%0Athe+effect+of+array+decimation+on+location+which+resulted+in+varying+degrees+of+success.%0D%0AA+Phase+II+was+implemented+in+July%2C+1997%2C+with+the+fracturing+of+well+CGU21-9.+The%0D%0Atreatment+took+place+over+three+days+(July+14%2C+16%2C+and+18)+and+was+supplemented+with%0D%0Aperforation+shots+on+July+17.+Although+signals+were+recorded+from+sensors+located+in+three+wells%0D%0A(triaxial+geophones+in+wells+CGU21-9+and+CGU22-9%2C+48+hydrophones+in+CGU22-7)%2C+only+the%0D%0Aarray+in+well+CGU22-9+provided+interpretable+data.+In+their+analysis+of+the+Phase+II+data%2C%0D%0AWithers+and+Dart+(1997)+were+able+to+locate+164+events+of+1%2C826+detected+events+by+incorporating%0D%0Adirectionality+into+their+forward+modelling+approach.+The+small+number+of+located+events+was%0D%0Aprimarily+a+result+of+generally+weaker+signals+as+compared+to+those+recorded+during+Phase+I%2C+and%0D%0Athe+large+percentage+of+events+that+were+deficient+in+P-wave+energy%2C+making+analysis+by+their%0D%0Atechnique+difficult.+As+shown+in+Figure+2%2C+the+derived+locations+were+scattered+and+markedly%0D%0Adifferent+from+the+expected+trend+of+N70E%2C+raising+questions+as+to+whether+the+technique%0D%0Aemployed+was+appropriate+or+whether+the+geometrical+constraints+imposed+by+single-well%0D%0Amonitoring+limits+does+not+allow+for+events+to+be+located+to+any+degree+of+accuracy.&rft.publisher=Gas+Research+Institute&rft.date=1998-06&rft.type=Reports&rft.type=NonPeerReviewed&rft.format=text&rft.language=en&rft.identifier=https%3A%2F%2Fepisodesplatform.eu%2Feprints%2F2163%2F1%2F6.pdf&rft.identifier=++Urbancic%2C+Ted++(1998)+Cotton+Valley+Hydraulic+Fracture+Imaging+Project%3A+Phase+II+(CGU+21-9)+Fracture+Imaging+Using+Microseismic+Event+Locations.++Technical+Report.+Gas+Research+Institute.+++++