Pore structure characterization and low-permeability genesis of low-permeability tuffaceous sandstone reser-voirs:a case study of the Paleocene Wenchang Formation in the Lufeng Sag within the Pearl River Mouth Basin
The Wenchang Formation in the Lufeng Sag is a typical low-permeability sandstone reservoir.The complex pore structure and reservoir heterogeneity are the keys to restricting the increase in re-serves and production in the study area.The pore throat structure of sandstone reservoirs in the study area was characterized by experimental methods such as casting thin section observation,high-pressure mercury intrusion and constant velocity mercury induction.The pore throat types of reservoirs are divid-ed based on fractal curve characteristics and pore throat structure parameters,and the pore evolution patterns of different types of reservoirs and their impact on physical properties are discussed based on the physical properties of the reservoir and the properties of interstitial materials.The findings delineate the classification of reservoirs within the study area into three distinct categories:type Ⅰ reservoirs are identified as those of exceptional quality,possessing optimal physical attributes with an average dis-charge pressure of 0.1 MPa;type Ⅱ reservoirs are acclaimed as superior,exhibit discharge pressures predominantly within the range of 0.5 to 1.0 MPa;whereas type Ⅲ reservoirs are regarded as the least favorable,characteristically have discharge pressures exceeding 1.0 MPa.The observed low porosity and reduced permeability of the sandstone reservoirs in this area emerge from a synthesis of variables in-cluding the type of fill material,degree of solubility,and the properties of alteration by-products.Pre-dominantly,the extensive infusion of tuffaceous material within the primary pore spaces,compounded by a modest extent of dissolution and erosion,is the principal contributor to the diminished porosity of these reservoirs.Concurrently,the by-products of these processes tend to obstruct the pore throats,thus playing a pivotal role in the genesis of the low-permeability attributes of the reservoirs under study.The results provide guidance for the division and effective development of low-permeability reservoirs.
tuffaceous sandstonesandstone reservoirpore structurelow-permeability genesisWen-chang FormationPaleogeneLufeng SagPearl River Mouth Basin
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