Rock stress state influence on permeability of carbonate reservoirs

Abstract

The relevance of the discussedissue is caused by the fact that the oil fields of the Perm region are determined by the widespread occurrence of fractures in carbonate reservoirs and the influence of fractured rocks on oil filtration in the reservoir. The paper considers the effect of changes in the stressed state of rocks (effective pressure) on the porosity and permeability of core samples in various lithologic-facies zones of Tourne-Famennian carbonate sediments. The Tourne-Famennian carbonate deposits of the Upper Kama Region fields are characterized by a complex geological structure. On these deposits the lithological-facial zones are distinguished with different filtration-capacitive properties due to the geological conditions of sedimentation. The main aim of the study is to assess the dynamics of the fracture and matrix permeability of core samples of carbonate objects depending on the change in effective pressure. Object: Tourne-Famennian carbonate reservoirs of the Gagarinsky and Ozernoe fields. Methods: filter systems with simulation of reservoir conditions UIG-5VG and AFS-300 and installation of microfocus X-ray. Results. A series of experiments analyzed in this work allowed establishing that in carbonate Tourne-Famennian collectors (permeability up to 350 mD), characterized by fracturing, while reducing the load, the permeability of the collector is not fully restored. Accordingly, in the areas of development of fractured reservoirs from the very beginning of the operation of the wells, it is preferable to limit the reduction of their bottomhole pressure. It was also established that in Tourne-Famennian deposits of the Upper Kama Region for various types of seismic waves there is a physical velocity limit associated with the structure of the pore space. At the same time, in perspective, it is possible to isolate the densest parts of the deposits in terms of the wave velocity, which, in their turn, are subject to formation of cracks. The task should be solved on the basis of integrated accounting of core research data, hydrodynamic studies of wells, 3D seismic exploration and analysis of well operation.

Keywords

• fractures opening
• fracture permeability
• matrix permeability
• stress state
• longitudinal velocity
• 3d seismic survey
• bottomhole pressure