Lost circulation whole mud (whether to depleted reservoirs or to natural/induced fractures)is one of biggest causes of well kicks. In the wellbore, fluid levels can decrease and this lowers the hydrostatic pressure. Once hydrotatic pressure is less than formation pressure, it will cause a flow from the formation in permeable zones. Figure 1 illustrates loss of fluid level into a weak zone which will lead a well control incident if a wellbore is not filled up on time with correct mud weight.
Figure 1 – Lost Circulation in Drilling Leading to a Well Control Situation
Well control can be categorized into three main categories which are Primary Well Control, Secondary Well Control and Tertiary Well Control. The details are shown below;
Primary Well Control
Primary Well Control is hydrostatic pressureprovided by drilling fluid more than formation pressure but less than fracture gradient while drilling. If hydrostatic pressure is less than reservoir pressure, reservoir fluid may influx into wellbore. This situation is called “Loss Primary Well Control”. Typically, slightly overbalance of hydrostatic pressure over reservoir pressure is normally desired. The basic of maintaining primary well control is to maintain hydrostatic pressure that is heavy enough to overcome formation pressure but not fracture formations.
Figure 1 – Drilling Fluid
Not only is hydrostatic pressure more than formation pressure, but also hydrostatic pressure must not exceed fracture gradient. If mud in hole is too heavy, it will cause a broken wellbore, that will result in loss circulation problem (partially lost or total lost circulation). When fluid is losing into formation, mud level in well bore will be decreased that will cause reduction in hydrostatic pressure. For the worst case scenario, hydrostatic pressure is less than formation pressure therefore wellbore influx (kick) will enter into wellbore. Continue reading →
We’ve found this vidoe on Youtube and this is one of the most interesting stories of well control. This is about how to kill the blow out well using a nuclear bomb. We are not sure when it was happened but from what you can see, this was quite long time ago when directional technology was not good enough to successfully drill a relief well. Please see the video below and we already added the footage transcript for further learning.
Many people ask us every time about well control but many of them understand that well control is when the rigs are burn. This is not the right concept.
Well Control is a situation when hydrostatic pressure in a wellbore is less than formation pressure therefore reservoir fluid will come into a well. If a well control situation is not taking care of properly, it will result in blow like you can see in the VDO below.
The short VDO, only 1 minute and 34 seconds, clearly show that what will be happening if the well cannot be control.