Study on Reorientation Mechanism of Refracturing in Ordos Basin—A Case Study:Chang 6 Formation, Yanchang Group, Triassic System in Wangyao Section of Ansai Oil Field

摘要

The essence of fracture reorientation of refracturing is rockrnfailures. Therefore, the study on reorientation mechanismrnshould be started from studying rock failures, taking therninfluences of objective and subjective factors such as reservoirrnmicrofracture distribution, geostress field, rock mechanicsrncharacteristics, physical properties and the methods of wellcompletion,rninjection/production, hydraulic fracturingrntechnology upon fracture reorientation into account.rnAs a result, the conditions that rock failures occur werernanalyzed, thus the theory criteria for fracture reorientation wasrngiven, namely the critical bottomhole pressure required andrnthe conditions which the geostress field and rock mechanicsrnparameters should have. The new fractures are divided intornshear fractures and tensile fractures, which correspondrnrespectively to the two kinds of rock basic failurernmechanisms-shear failure and tensile failure. The azimuths ofrnthese two kinds of fractures are both different from the initialrnhydraulic fracture (abbr.IHF), and the critical pressure is thernfunction of the geostress field and rock mechanics parameters.rnBased on the above criteria, utilizing the refracturing data ofrnChang 6 formation, the feasibility of fracture reorientation forrnWangyao section was investigated. And three typical wellsrnwere analyzed in details, which show the refracturerncharacteristics we predict accord with that of microseismicrnmonitoring or the curve of the treating pressure.rnIt indicates that even if the geostress field keeps unchanged,rnfracture reorientations can be achieved by other ways.rnIn the certain range of parameters for reservoir physicalrnproperties, if a proper fracturing technology, such as TSO (I.e.rnTip Screen Out) with temporarily blocking treatmentrn(abbr.TBT), can be applied so as to create the treatingrnconditions that meet the demand of the above criteria, thernrefracturing can produce new fractures in Wangyao.rnAnd for refracturing treatments, with the shot holes along thernIHF azimuth blocked effectively, multi-fractures and newrnfractures can be achieved by oriented perforations.