Phase state variations for supercritical carbon dioxide drilling

Abstract

A phase state prediction model during supercritical carbon dioxide (SC‐CO2) drilling is established, considering the enthalpy changes caused by the flow work variations and changes in kinetic energy, as well as the potential energy caused by the fluid velocity along with physical property variations. The results show that variations in the flow work affect the temperature field of the SC‐CO2 fluid significantly. Phase state transitions of the fluid in the drill pipes and the annulus exist; in this example, the depth of the phase transition point in the drill pipes is in the range of 600 to 1000 m, while in the annulus, it is in the range of 400 to 700 m. Different results are observed when the phase state prediction is conducted by adjusting the discharge capacities, injecting temperature and pressure. When the discharge capacity is increased, the phase transition points in the drill pipes and the annuluses move downward; the pressure of the bit nozzle upstream increases gradually, while the pressure of the bit nozzle downstream changes slightly. When the wellhead back pressure is increased, the depths of the phase transition points in the drill pipes and the annulus decrease. Moreover, the pressure variations of the bit nozzle upstream and downstream can be divided into two stages: the fast growth stage and the slow growth stage. When the injection temperature is increased, the depths of the phase transition points in the drill pipes and the annulus are reduced; the temperature drop and the pressure drop at the nozzle change slightly. © 2015 Society of Chemical Industry and John Wiley & Sons, Ltd

Study on the extension limit model of a horizontal well with supercritical carbon dioxide drilling

“…Compared with conventional drilling fluid, developing unconventional oil and gas resources under the condition of supercritical carbon dioxide drilling has many advantages when working with rocks that can be broken easily and swollen with difficultly . Recently, the feasibility of drilling a vertical well with supercritical carbon dioxide has been confirmed .…”

The effect of thermal stresses on the relation between rock failure and temperature and pressure of supercritical carbon dioxide jet

“…Supercritical carbon dioxide has a density near to that of water and a low viscosity, less than 1/10 that of water . This helps to reduce the pressure loss in liquids circulating in well‐drilling operations, reduce the pressure requirements on the pumps on the ground, and form high‐pressure jets for underbalanced drilling at the hole bottom . Compared to the conventional water‐based and oil‐based drilling fluids, the SC‐CO 2 drilling fluid performs better with respect to wellbore stability and has a wider safe mud weight window .…”

Study on filtration patterns of supercritical CO2 fracturing in unconventional natural gas reservoirs

“…Nevertheless, these techniques are not suitable for water‐sensitive reservoirs, and the waste water and pollution of groundwater resources have always been controversial. Comprehensively considering China's shortage of water resources and the concept of sustainable development requiring energy conservation and environmental protection, novel fracturing technologies that are both environmentally friendly and highly effective need further exploration …”