Abstract:

Cambrian-Ordovician dolostone in Tarim Basin is an important oil and gas reservoir with the characteristics of deep buried depth and old geological age. According to the preliminary tests of properties, several dolostones with good porosity and permeability: stromatolite dolostone, crystalline dolostone and patchy dolostone, are chosen. In order to fully consider the impact of buried depth, rock composition and structure on reservoir physical property, an in situ simulation experiment to research the permeability changing law of these dolostones under the buried condition is designed, and the causes and influence factors are analyzed. At the same time, its petrology characteristics and pore types are studied by means of optical microscope and scanning electron microscope. Of all the samples for this experiment, stromatolite dolostone shows the best permeability, whose pore system has good connectivity and compressive resistance, and is composed of  fenestral pores and intercrystal pores, so its good permeability can be maintained under the deep buried condition. Crystalline dolostone with good permeability owes to its larger intercrystal pores, which depends on the content, size and crystal shape of the dolomite. Patchy dolostone reviews poor permeability under the deep buried condition, as its stylolite pores under high confining pressure is difficult to preserve.

Key words: dolostone, deep buried depth, simulation experiment, permeability, pore