By means of core observation,thin section identification,image analysis,mercury penetration,petro-physical property testing and other technical methods,the low permeability reservoirs of Ess4 were studied in the north zone of Bonan Sag.The diagenesis of low permeability reservoirs of Ess4 is characterized by strong compaction,multistage of dissolution and cementation,and lime-mud matrix recrystallization.Confined by conditions of "reservoir diagenesis evolutionary sequence and reservoir pore structure",physical properties of the reservoirs in geological history were restored.The geological time when reservoirs of different lithology in different sub/micro-facies form low-permeability properties were determined based on the reservoir property evolutionary history.Genetic mechanisms of low permeability reservoirs of sandy conglomerate were investigated.There are five different genetic types of reservoirs.The characteristic of type Ⅰ reservoir is that its low permeability and extra-low permeability are caused by compaction,while its ultra-low permeability is caused by lime-mud matrix recrystallization.The characteristic of type Ⅱ reservoir is that its low permeability is caused by compaction,while its extra low permeability and ultra-low permeability are caused by cementation;The characteristic of type Ⅲ reservoir is that its low permeability and extra-low permeability are caused by compaction;The characteristic of type Ⅳ reservoir is that its physical property is improved by dissolution,while its low permeability is caused by compaction; The characteristic of type Ⅴ reservoir is that its low permeability is caused by compaction,while its extra-low and ultra-low permeability are caused by compaction and cementation.According to a matching relationship between the reservoir compaction history and the hydrocarbon accumulation history as well as results from oil testing,type Ⅳ reservoir had high permeability in the hydrocarbon accumulation period and shows low permeability now,which is the best reservoir and has the best exploration potential;Type Ⅲ reservoir had medium permeability in the hydrocarbon accumulation period and shows extra-low permeability now,which is better reservoir and has medium exploration potential;Type Ⅴ reservoir had low permeability in the hydrocarbon accumulation period and shows ultra-low permeability now,which is medium reservoir and has poor exploration potential;Type Ⅰ reservoir had extra low permeability while type Ⅱ low permeability reservoir had medium permeability in the hydrocarbon accumulation period.Both of these two types of reservoirs show impermeability now,which are poor reservoirs and have little exploration potential.
Low permeability reservoirGenetic mechanismCompaction history-accumulation historyEss4Bonan Sag
NETL
NSTL
万方数据
维普
