The effect of confining pressure on specific energy in Nd:YAG laser perforating of rock

For many years, the oil and gas industry were looking for an alternative method that could significantly reduce the primary drawbacks of using explosives. Perforating oil and gas wells using lasers as a new method is currently under research. In laser perforating, many parameters influence the essential factor of specific energy (i.e. the required energy to remove the unit weight of rock). One of these parameters is the confining pressure. Here, a core sample is placed in the Hoek cell and a new frame is designed to fix them. A small circular part of top side of the cylindrical sample is open in order to interact with the laser beam while the mechanical pressure exerted with the Hoek cell confines the other sides. The results show that the main disparity in specific energy and rate of penetration (ROP) occurs in the range 8–16 MPa of confining pressure. It is found that the amount of specific energy is constant at pressures higher than 16 MPa and consequently, micro cracks that appeared on sample surface at low pressure are absent at higher pressures.

► Confining pressure was applied on granite and limestone under laser radiation. ► Water and heavy oil saturated and dry samples were compared under laser radiation. ► Effect of confining pressure on the specific energy (SE) was studied. ► The main change in the SE and ROP occurs in 8–16 MPa confining pressure. ► The SE increases by increasing the confining pressure, while the ROP decreases.