Differential compaction of dolostone reservoir and its controlling effect on physical property preservation

Key words:  dolostone  deep reservoir  tight reservoir  differential compaction  pore space type  preservation index  fracture occurrence

Abstract:

In order to clarify the evolution and preservation mechanisms of reservoir space and connectivity properties of dolomite under the action of compaction in medium-deep burial diagenetic stage, a combined measurement method of unsteady pressure attenuation porosity and permeability were used to conduct a comparative study on the compaction resistance of dolostone of porosity type, porosity-vuggy type and fracture type. The results show that the porosity and permeability of dolostone decrease correspondingly as the effective stress increases. The preservation law of physical properties of dolostone is also different due to differences in pore types and initial physical property. The porosity type is further divided into typeⅠand type Ⅱ. In the process of gradually increasing effective stress, the porosity preservation ability of dolostone from high to low is porosity type I , vuggy type , fracture type and porosity type Ⅱ, respectively. The reservoir spaces of porosity type Ⅰ and vuggy type dolostone have a strong ability to resist compaction, and their porosity evolution can be characterized by a rapid decline in the early stage which then asymptotically flattens in the later stage. The reservoir spaces of fracture type and porosity type Ⅱ dolostone have weak ability to resist compaction, and their porosity evolution rule is that the porosity decreases rapidly in the early stage and continues decreasing in the later stage. In the process of gradually increasing effective stress, the connectivity properties of porosity type I dolomite have a strong compaction resistance. When the effective stress exceeds 10 MPa, the permeability basically remains unchanged. The compaction resistance of connectivity properties of porosity type Ⅱ, vuggy type and fracture type dolostone decreases successively, and permeability decreases rapidly in the early stage and continuously in the later stage with the increase of effective stress.