Hidden characteristics and sealed property evaluation of carbonate baffles and barrier in X Oilfield,Iraq
Based on core samples,experimental data,and production logging tests,this study analyzes the hidden character-istics of baffles and barriers in the Cretaceous Mishrif Formation of the X Oilfield in Iraq.By using permeability as the main discriminant parameter for baffles and barriers,a combination of macroscopic and microscopic mutual verification,dynamic and static data integration,and the permeability values of abnormal interval of formation pressure gradient,was employed to determine the criteria of baffles and barriers with sealing ability.To account for production-induced pressure abnormalies,the lower permeability limit of the production zone was determined using production logging tests.The upper limit of the non-per-meable layer was defined based on microstructure analysis,excluding the influence of permeable layers within abnormal pres-sure intervals on the statistical results.The findings reveal that the hidden baffles and barriers in bioclastic limestone manifest in various lithologies,including mudstone with grains,wackstone,packstone,and calcsparite grainstone,with diverse and complex biological shell clasts.Lithologic baffles and barriers form in low-energy environments,whereas physical baffles and barriers develop in high-energy environments with cementation.The correlation between porosity and permeability is poor,with baffles and barriers often having pore throats less than 0.5 μm,with variable microstructure.The thickness ranges from several centimeters to dozens of meters,with lateral pinch-out and diverse overlapping styles.The low permeability character-istics of baffles and barriers have weak logging responses,leading to potential misinterpretations or missed identifications.Specifically,baffles exhibit permeability less than 0.5×10-3 μm2 and thickness greater than 2.5 m,while barriers have per-meability less than 0.65×10-3 μm2 and thickness over 1m.It is concluded that MA and MB1 zones exhibit good sealing per-formance and shoud be treated as separate development units with distinct well patterns.MB1 and MB2 have poor sealing performance,posing a risk of vertical water breakthrough in separate waterflood development.Although MB2 and MC have good sealing performance,treating them as one development unit is inadvisable,as bottom injection and top production yield poor results.The evaluation of the sealing properties of baffles and barriers supports the feasibility of separate waterflood de-velopment in thick reservoirs,providing a geological basis for adjusting development strategies.
bioclastic limestonebaffles and barriersealed propertythick reservoirhidden characteristicsseparated de-velopment
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