If abnormally pressured formations are encountered while drilling with mud weights insufficient to control the zone, a potential kick situation has developed.
KICK IT WITH YOU FULL
Because a normal formation pressure is equal to a full column of native water, abnormally pressured formations exert more pressure than a full water column.
In well control situations, formation pressures greater than normal are the biggest concern. Abnormal formation pressures are greater pressures than in normal conditions. These abnormal formation pressures are often associated with causes for kicks. Because the formation pressure exceeds the wellbore pressure, fluids begin to flow from the formation into the wellbore and the kick occurs. A permeable zone is drilled while using a mud weight that exerts less pressure than the formation pressure within the zone. Insufficient mud weight is the predominant cause of kicks. Reasons for this imbalance explain the key causes of kicks: In almost all drilling operations, the operator attempts to maintain a hydrostatic pressure greater than formation pressure and, thus, prevent kicks however, on occasion the formation will exceed the mud pressure and a kick will occur. Kicks occur as a result of formation pressure being greater than mud hydrostatic pressure, which causes fluids to flow from the formation into the wellbore.
It is interesting to note that an average kick requires approximately 0.5 lbm/gal (60 kg/m 3), or less, mud weight increase. For example, if a kick required a 0.7-lbm/gal (84-kg/m 3) mud weight increase to control the well, the kick could be termed a 0.7-lbm/gal (84-kg/m 3) kick. If gas enters the borehole, the kick is called a "gas kick." Furthermore, if a volume of 20 bbl (3.2 m 3) of gas entered the borehole, the kick could be termed a 20-bbl (3.2-m 3) gas kick.Īnother way of labeling kicks is by identifying the required mud weight increase necessary to control the well and kill a potential blowout. If this negative differential pressure is coupled with high permeability and high porosity, a severe kick may occur.Ī kick can be labeled in several ways, including one that depends on the type of formation fluid that entered the borehole. If the formation pressure is much greater than the hydrostatic pressure, a large negative differential pressure exists. Pressure differential is the difference between the formation fluid pressure and the mud hydrostatic pressure. Yet another factor affecting kick severity is the “pressure differential” involved. For example, sandstone is considered to have greater kick potential than shale, because sandstone has greater permeability and greater porosity than shale. A rock with high permeability and high porosity has greater potential for a severe kick than a rock with low permeability and low porosity. Another factor affecting kick severity is “porosity.” Porosity measures the amount of space in the rock containing fluids. One factor, for example, is the “permeability” of rock, which is its ability to allow fluid to move through the rock. Several factors affect the severity of a kick. 5 Kick detection and monitoring with MWD tools.4.8 Cut mud weight (secondary indicator).4.7 Drilling break (secondary indicator).4.6 String weight change (secondary indicator).4.5 Improper hole fill-up on trips (primary indicator).4.4 Pump pressure decrease and pump stroke increase (secondary indicator).4.3 Flowing well with pumps off (primary indicator).4.2 Pit volume increase (primary indicator).4.1 Flow rate increase (primary indicator).
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