The seismic sequence stratigraphic analysis revealed four depositional sequences(DS-1,DS-2,DS-3 and DS-4).The accompanying systems tracts were interpreted and mapped in the study area based on the log motifs of the re...The seismic sequence stratigraphic analysis revealed four depositional sequences(DS-1,DS-2,DS-3 and DS-4).The accompanying systems tracts were interpreted and mapped in the study area based on the log motifs of the reference well and the spatial distribution of the recognized constrained surfaces:maximum flooding surfaces(MFSs),sequence boundaries(SBs)and transgressive surfaces(TSs)on the seismic data.Depositional systems in the study area comprise lowstand systems tracts(LSTs),transgressive systems tracts(TSTs)and highstand systems tracts(HSTs).The LSTs are represented by coeval facies dominated by deposition basinward of the shelf-edge during maximum regression and are characterized by shallow-water deposition from gravity flows and/or traction processes within the shelf-edge or canyon-head delta.The sediments associated with lowstand systems tracts recognized in the study area are the fluvial channel sands and slope fans(SF).The transgressive sand units were interpreted as shoreface sands deposited in the shelf region during rising sea levels.Highstand systems tracts are characterized by intervals of coarsening and shallowing upwards,with both fluvial and deltaic sands prograding laterally into neritic shales.In the study area,the units are very thick.The highstand and lowstand system tracts exhibit blocky log patterns and are associated with the reservoirs while the transgressive system tracts serve as seals to the reservoirs.The environment of sediments deposition in this area is delta plain,shelf,slope to toe of slope.展开更多
Abnormal pressure prediction was undertaken in“Safety”field,onshore Niger Delta,Nigeria using amplitude variation with offset(AVO)velocities information.Each of the methods used form an integral part of a process th...Abnormal pressure prediction was undertaken in“Safety”field,onshore Niger Delta,Nigeria using amplitude variation with offset(AVO)velocities information.Each of the methods used form an integral part of a process that produces AVO Analysis,AVO velocity inversion,extraction of seismic velocity from AVO velocities inversion results and pore pressure prediction.Pore pressure predicted from the seismic velocity has a better resolution than the pressure predicted from the interval transit time.The pore pressure within the field ranges from 14.7psi to 3916psi.Overpressured and underpressured zones were delineated on the field from the pressure predicted from the seismic velocities.Within the field,the overpressured zones were delineated at depth 6855 fte7802 ft.Over pressure top was delineated at a depth of 6855 ft with a pore pressure of 3053psi and a corresponding hydrostatic pressure of 2722psi.The under-pressured zones were also delineated at depth 7883 fte9288 ft.The under pressure top was delineated at a depth of 7883 ft with a pressure of 1093psi and a corresponding hydrostatic pressure of 3122psi.Porosity values within the over pressure zone ranges from 23%to 53%which could be considered as relatively high.This could be as a result of the fact that the pore fluid cannot be expelled rapidly thereby causing the pore fluid to increase rapidly since they are no longer compacted;thus leading to overpressure.As a result of overpressure top which is directly above the reservoir top within the shale zone,drilling this reservoir vertically could not be suggested so as to avoid possible blow out.It was also observed that the primary cause or mechanism of overpressure within this field could be disequilibrium compaction.展开更多
文摘The seismic sequence stratigraphic analysis revealed four depositional sequences(DS-1,DS-2,DS-3 and DS-4).The accompanying systems tracts were interpreted and mapped in the study area based on the log motifs of the reference well and the spatial distribution of the recognized constrained surfaces:maximum flooding surfaces(MFSs),sequence boundaries(SBs)and transgressive surfaces(TSs)on the seismic data.Depositional systems in the study area comprise lowstand systems tracts(LSTs),transgressive systems tracts(TSTs)and highstand systems tracts(HSTs).The LSTs are represented by coeval facies dominated by deposition basinward of the shelf-edge during maximum regression and are characterized by shallow-water deposition from gravity flows and/or traction processes within the shelf-edge or canyon-head delta.The sediments associated with lowstand systems tracts recognized in the study area are the fluvial channel sands and slope fans(SF).The transgressive sand units were interpreted as shoreface sands deposited in the shelf region during rising sea levels.Highstand systems tracts are characterized by intervals of coarsening and shallowing upwards,with both fluvial and deltaic sands prograding laterally into neritic shales.In the study area,the units are very thick.The highstand and lowstand system tracts exhibit blocky log patterns and are associated with the reservoirs while the transgressive system tracts serve as seals to the reservoirs.The environment of sediments deposition in this area is delta plain,shelf,slope to toe of slope.
文摘Abnormal pressure prediction was undertaken in“Safety”field,onshore Niger Delta,Nigeria using amplitude variation with offset(AVO)velocities information.Each of the methods used form an integral part of a process that produces AVO Analysis,AVO velocity inversion,extraction of seismic velocity from AVO velocities inversion results and pore pressure prediction.Pore pressure predicted from the seismic velocity has a better resolution than the pressure predicted from the interval transit time.The pore pressure within the field ranges from 14.7psi to 3916psi.Overpressured and underpressured zones were delineated on the field from the pressure predicted from the seismic velocities.Within the field,the overpressured zones were delineated at depth 6855 fte7802 ft.Over pressure top was delineated at a depth of 6855 ft with a pore pressure of 3053psi and a corresponding hydrostatic pressure of 2722psi.The under-pressured zones were also delineated at depth 7883 fte9288 ft.The under pressure top was delineated at a depth of 7883 ft with a pressure of 1093psi and a corresponding hydrostatic pressure of 3122psi.Porosity values within the over pressure zone ranges from 23%to 53%which could be considered as relatively high.This could be as a result of the fact that the pore fluid cannot be expelled rapidly thereby causing the pore fluid to increase rapidly since they are no longer compacted;thus leading to overpressure.As a result of overpressure top which is directly above the reservoir top within the shale zone,drilling this reservoir vertically could not be suggested so as to avoid possible blow out.It was also observed that the primary cause or mechanism of overpressure within this field could be disequilibrium compaction.
