Investigation of Explosion Occurrence in Underbalanced Drilling

Abstract

fax 01-972-952-9435. AbstractThe development of mature fields has led operators to use underbalanced drilling to benefit from advantages such as reducing formation damage and increasing penetration rate. In gasified liquids, a light oil can be used as the liquid phase and nitrogen with almost 5 percent oxygen as the gas phase. Due to the simultaneous presence of oil and oxygen in the drillstring, safety considerations are a major concern in these operations.To study and simulate the occurrence of explosions, oil base liquids were aged at 150 o C and 14 MPa initial pressure in rocking and stationary reactors for 2.5 and 5 days in the presence of a gas with different concentrations of oxygen. The presence of drilling cuttings was simulated by addition of calcium carbonate to the base liquids. To cover the real penetration rates encountered in the drilling industry, volume percentages of 0.3, 0.6, 1.2, 2.4, and 4.8 of calcite were employed.The experimental results of the samples that experienced explosions show that a delay time of approximately 0.5 hours was observed. In the period leading up to an explosion, the vapor phase temperature remained relatively constant while the liquid phase temperature first increased gradually and then more rapidly. At the time of the explosion, a rapid rise in the vapor phase temperature accompanied by a sudden increase in the reactor pressure was observed. This behavior indicates that the explosion was triggered by liquid phase oxidation reactions but that the sudden energy release event was associated with combustion reactions in the vapor phase.This study signifies the important impact of the liquid phase temperature on explosion occurrence. The liquid phase acts as an initiator or an ignition source for explosions. Furthermore, it can be used as a parameter to warn of an impending explosion.

Impact of Supercritical CO2 on Shale Reservoirs and Its Implication for CO2 Sequestration

“…Traditionally, water-based fluids were used for drilling tight gas reservoirs for the recovery of oil and gas resources. , However, unconventional reservoirs vulnerable to formation damages are not ideal to drill with water-jets because it can cause excessive overbalance condition near the bottom hole, resulting from the hydrostatic pressure exerted by the produced mud . In such a scenario, underbalanced drilling (UBD) is helpful because, in place of heavy drilling fluids and muds, a light mineral oil, nitrogen foam, and sometimes compressed air are used to achieve underbalanced well conditions and the low density of such drilling fluids will cause the hydrostatic pressure in the wellbore to be lower than the internal fluid pressure of that formation, resulting in the production of reservoir fluids while drilling . However, the density of these fluids is not sufficient enough to generate enough torque for the bottom-hole motors to rotate at its maximum efficiency .…”

An Explosive Range Model Based on the Gas Composition, Temperature, and Pressure during Air Drilling

“…If the mixed gas reaches the combustion condition, an explosion will probably occur, causing accidents such as burning out the drilling tools and ruining the wells [3,4]. Gas content, temperature, and pressure are regarded as the main factors affecting the explosion range [5][6][7]. In our study an explosive range calculation model is developed for estimation of the air drilling explosive range.…”