Experimental research of the conditions for the transfer of rock pressure by saliniferous rocks to the casing

Abstract

The analysis of field data from casing failure on the fields of the Borislav and Dolinsky oilfield regions has been carried out. It has been found that the most significant negative factors that have a bearing on the preservation of the integrity of the casing strings are the presence of saliniferous rock intervals in the borehole log and not taking into account the possible impact of rock pressure when designing casing strings in these rocks. In saliniferous rocks, under certain conditions, rock pressure can be transferred to the column. To study the thermobaric conditions of the external pressure transfer to the casing from the saliniferous rock, experimental tests have been carried out on the core materials of the rocks of the Vorotyshchensk floor, sampled at different depths of the Oriv-Ulychniansk field. For this purpose, a special laboratory installation was made, which allows to study the stress conditions and rock flowage on exposure to formation temperature and rock pressure. Because it was difficult to directly measure the radial pressure transmitted to the pipe and the temperature inside the chamber during the experiments, the installation was calibrated by pressure and temperature. This made it possible to determine the temperature inside the chamber by the value of the voltage supplied to the heating element, and the value of the radial pressure supplied to the pipe - by the value of the pressure inside the pipe. Based on the results of experimental research, the depen-dences of the lateral earth pressure coefficient of saliniferous rocks on temperature were obtained at various values of normal stresses. It was found that when the temperature rises to 70 ° C and higher, the value of the lateral external pressure on the pipe approaches the vertical component of the pressure. According to the results of the experimental research, the temperature and pressure conditions for accounting for rock pressure were recommended when calculating casing strings for external overpressure in the intervals of occurrence of saliniferous rocks of the Carpathian fields.