Kicks and Blowouts Prediction Before and During Drilling in the Over-Pressured Sediments

摘要

Uncontrollable kicks are the most costly events that occur while drilling for oil and gas. Formation water flow sometimes turns to kicks that lead to life threatening and environmentaly disastrous blowouts. Prediction of the possible abrupt pressure surges that characterize the subsurface geological setting before drilling sheds light on some of the challenges that may be encountered along the bore-hole trajectory. This will also help curtail human error during penetration of certain zones along the well-hole trajectory, and consequently reach the objective depth safely and with less nonproductive time (NPT). Before drilling, pore andfracture pressure predictions from seismic velocity are critical for assessing the economic feasibility and safety for the whole prospective trap. Integrating the seismic velocity drifts and the sequence stratigraphy semblance at the proposed location can point to the possible pressure transgressive intervals that can cause a sudden pressure surge (PS). Moreover, modifying the drilling tolerance window (DTW) to accommodate the expected hydrocarbon column in the prospective reservoirs reduces the potential of unexpected hard kicks at the shale - sand interface. This paper briefly discusses the impact of subsurface geopressure compartmentalization on seismic velocity drift and consequently on PS. It also examines the subsurface geological setting that can cause substantial pressure increase penetrating the lithological interfaces. Therefore, the pressure transgression and expected excess pressure in pay zones should be encompassed within the numerical algorithm of the predictive model before drilling. Monitoring the logging while drilling (LWD) data slopes in shale beds can successfully point to a possible kick ahead of the drill bit. Maneuvering the mud weight and casing program while drilling within the DTW based on the modified numerical pressure profile can achieve safe drilling. Examples from onshore and deep-water wells are shown. This paper covers several geological features that correlate to open bore-hole flows or kicks that sometimes develop to a blowout if the formation flow is not controlled by the right mud weight kill. Detecting these subsurface features and their associated seismic velocities before drilling can lead to safe drilling and avoiding NPT. Moreover, this paper sheds light on the potential to enhance drilling safety in advance, even in cases where managed pressure drilling (MPD) equipment is used.