High Penetration Rates: Hazards and Well Control—A Case Study

Abstract

Abstract Good agreement with field data has been obtained when using a commercial kick simulator to analyse a 56 bbl gas kick taken in a 59 deg deviated wellbore. Fast kick detection and reaction are necessary when drilling at high rates of penetration since high pump rates, necessary for hole cleaning and cuttings transport, imply that a gas influx may be rapidly circulated to surface. A simulated example of a field kick is used to show how close to a blowout it is possible to be with normal rig actions and response times; the tip of the gas cloud is less than 300 ft below surface and rising fast at shut-in. Benefits of earlier detection and shut-in are illustrated through simulation. High penetration and pump rates result in dispersal of the influx along the annulus. This makes kick detection harder, since a greater proportion of the influx gas can dissolve in the drilling fluid. A simulated example emphasizes how influx detection can be significantly harder with an oil based mud than with a water based mud. Gas migration results in a stabilised bottom-hole pressure much higher than the formation pore pressure. Subsequent use of standard field methods significantly overpredicts kill mud weight: alternative interpretation methods are suggested. Based on the results of the simulations, procedural recommendations are made in order to minimize the risk of a kick and to enhance the probability of kick detection. Circulation is dangerous if a potential influx could be pumped a significant distance up the annulus during the period of circulation. So, when making a connection, dangerous periods of circulation should only be carried out after completing the connection. When the influx is dispersed along the annulus, surface pressures may take a long time to stabilise. Prompt use of the driller's method in these cases gets the gas safely out of the wellbore and lessens possible misinterpretation of shut-in pressure rise. Using simulation for well control contingency planning can help in early recognition of field hazards and in the confident choice of appropriate actions.