Drillability characteristics of sandstone with different pores under simulated bottom hole conditions

Rock drillability has an important application value in oil and gas well engineering. Accurate evaluation of rock drillability characteristics is the theoretical basis of improving the rate of penetration (ROP) in the drilling process of the deep well. Up to date, few scholars have studied the degree of rock break difficulty according to the rock’s pore structure characteristics. In order to study the influence of pore structure characteristics on sandstone drillability under the condition of the bottom hole and realize the accurate prediction of sandstone drillability. Sandstones with different pore structures were collected as the research object. The pore structure characteristics of the collected sandstone were studied by casting thin section identification. The porosity, permeability, acoustic wave, and Richter hardness of sandstone with different pore structures were tested, and the sandstone drillability experiment was carried out under simulated bottom hole conditions. The relationship between the characteristics of pore structure and drillability was analyzed by statistical method. The experiment results show that sandstone’s pore structure characteristics have an important effect on the drillability of sandstone. The porosity, permeability, and acoustic wave of sandstone have a very high correlation with the Richter hardness. The drillability of sandstone decreases exponentially with the increase of porosity and permeability. With the increase of borehole pressure, sandstone’s drillability with different pore structures generally increases exponentially. When the porosity is less than 0.19, the drillability of rock decreases gradually with the increase of porosity. When the porosity is more than 0.19, the drillability of rock decreases significantly under different borehole pressures. The characteristics of pore structure are an important factor affecting the drillability of rock, which should be paid more attention to by related scholars. The study is of great significance for revealing the mechanism of rock breaking, objectively evaluating the characteristics of drillability, and establishing the prediction model of drillability.