Gas kick behavior in horizontal wells is different from the gas behavior in normal wells (vertical and deviated wells). Gas follows Boyle’s gas law when it moves up to the shallower section of the wellbore. However, in the horizontal section, there is no change in volume because gas will move up to high side of the wellbore and there is no change in pressure.
The gas kick volume will increase when the kick is circulated out of the horizontal section because the reduction in hydrostatic pressure results in expanding of gas as per Boyle’s gas law (see below).
P1 x V1 = P2 x V2
After we’ve learnt several topics in regard to horizontal well control, today we will talk about how to prevent well control situation both while drilling and while tripping. Since the horizon well control is quite tricky when compared to normal well control due to long reach horizontal section, the best way is to prevent it.
How To Prevent Kick While Drilling (Horizontal Wells)
Drilling horizontal wells are always in the development phase and people know the geological area pretty well. Additionally, they can accurately determine reservoir pressure of the target sand for the horizontal candidate. Hence, drilling engineers can plan the well with less chance of being underbalance condition. However, there are several scenarios where the well control occurs in horizontal wells. We will need to understand what circumstances can create well control situations in the known well bore pressure like the horizontal wells.
The swab in the horizontal wells is similar to swabbing in normal well. Swabbing effect can occur when the pipe is pulled off bottom for making up connection or when tripping out of hole. High rate of swab entering into the well can happen if swabbing occurs when tripping out of the hole. The length of horizontal section will be exposed to the differential swab pressure. On the other hand, the swab will be small when the pipe is pulled off bottom for making connection. In this case, you may see several small gas behind the bit which will show on the surface later. Continue reading
Currently, horizontal wells are widely drilled around the world because the production from the horizontal wells is outperform normal vertical or deviated wells at the same location. The productivity of the well increases because of longer penetration into a pay zone and/or more intersection of reservoir fractures (see Figure 1) .
Figure 1: A normal well and a horizontal well
Well control for the horizontal wells has the same fundamental principle during the circulation of influx from the well. There are some corrections which adjust for frictional pressure between true vertical depth and measure depth since the horizontal wells usually have very long depth in comparison to wellbore true vertical depth.
Driller’s method is a preferred method for horizontal well control because it does not require drill pipe pressure schedule. Personnel can start circulate the first circulation to remove kick and displace the well with kill weight fluid using the second circulation method. However, if Wait and Weight method is planned to used, personnel should use a well control kill sheet with horizontal well feature to simulate the profile. It is very difficult to determine drill pipe schedule because there are several factors associated with calculations as well bore profile, size of pipe, hole size, etc. Continue reading