A kick must be circulated out of the well, after the initial kick response and the formation flow is stopped, to allow routine operations to be resumed. The kick must be circulated to the surface while wellbore pressure is maintained constant to avoid additional kicks. Well control experts are often strongly opinionated on selecting the better method to circulate an influx out of the wellbore.
Driller’s Method is one of the eldest methods for circulation of kick out of well. It is the easiest method.
The Driller’s Method is a widely used kick circulation method. It requires almost no calculations, and that makes it practical for application during conventional drilling. Two circulations are necessary for the removal of kick in this method. Kick is taken out of the wellbore in first circulation by use of existing mud. During the first circulation, calculations are done, kill sheets are completed and the mud is weighted up to the required kill weight. In the second circulation, the original mud is replaced by kill mud and further drilling process continues. DM circulates the kick by maintaining the bottomhole pressure constant or, preferably, slightly above the formation pressure, which is controlled based on the pump pressure. This is achieved by adjusting the choke opening.
Advantages
Circulation begins immediately. It starts as soon as the stabilized pressures are recorded. The driller has no need to follow a drill pipe schedule, since the pump pressure is always held constant as the mud weight is changed. There are also less hole problems related to stopping circulation. The Driller’s Method more easily responds to nozzle plugging problems as there is no break in circulation.
It requires less arithmetic calculations. Simple calculations related to ICP, FCP and new kill mud weight. Especially favorable in case of deviated hole and tapered drill string because complex calculations are needed in other methods.
Mostly used in gas kick cases. As it provide less time for gas migration to surface. As the circulation stop in other methods so there are chances of gas to expand and due to its low
Chapter 10
density it will move upward. It will try to pass through the mud and continues to expand while moving up.
It is commonly followed in ballooning formations. Ballooning is a phenomenon occasionally encountered in some formations. Ballooning can be defined as flowback from the well after shutting the pumps off, which is preceded by losses while the pumps were running. Ballooning is often misinterpreted as a kick. If it is decided to kill the well with the Wait & Weight Method, mud weight may be increased due to incorrect measurement of formation pressure. Due to the additional mud weight, BHP increases even further. This can induce more losses and worsen the ballooning problem. Since the Driller’s Method does not require any increase in mud weight during the first circulation, no additional BHP is exerted on the formation. After the first circulation of the Driller’s Method, the situation can be assessed and further course of action can be decided (i.e., drilling ahead with no mud weight increase if ballooning continues).
It provides best features in rigs having slow fluid mixing capability. It provides us more time for making of Kill Mud. If we have to arrange heavy density additives or chemicals then it is useful as it provide us more time for this operation. Especially in cases of offshore wells.
Deepwater wells as chances of hydrates formation due to stop circulation. If gas kicks are taken in deepwater wells, there is a possibility of hydrate formation in the BOP’s or choke/kill lines.
The high pressure and low temperature conditions in deepwater are ideal for formation of hydrates when free water comes into contact with gas. Possible long periods of non-circulation with the Wait & Weight Method will make conditions more favorable for hydrate formation due to cooling of mud. Hence, non-circulating times in deepwater wells with a gas influx should be minimized. By establishing circulation as soon as possible with the Driller’s Method, the mud can be kept warm, and hydrate formation may be prevented.
Disadvantages
More time is required for two circulations.The Wait & Weight Method involves only one circulation while the Driller’s Method involves two circulations. This sounds as if we can always save time by following the Wait & Weight Method. But other factors need to considered. If the time required to mix kill mud is significant, we may not save any time with the W&W Method.
We may not be able to circulate all the influx out with just one circulation due to hole conditions, such as gas remaining in the high pockets of the well, poor hole cleaning and bad mud properties. Additional circulations are almost always required for complete removal of the influx and the addition of safety factors in the mud weight. Therefore, the time element may not be significant, and most experts agree that doing it right is more important than doing it faster.
Maximum choke pressure when the top of the influx reaches the surface will be higher if the influx is gas. More wear on surface equipment. The Driller’s Method has a higher risk of surface equipment failure, because a higher surface pressure is expected during Driller’s Method.
Maximum casing pressure during the circulation is observed when the top of the gas bubble gets to surface. This may be defined as PMax. The gas flow rate through the mud gas separator is maximum at the same time when PMax is observed. Peak Gas Flow Rate must not exceed the gas handling capacity of the mud gas separator. PMax and peak gas flow rate will be lower with the Wait & Weight Method if kill mud gets into the annulus before the top of the bubble gets to surface. If the Wait & Weight Method is followed, there is a good chance that kill mud will enter the annulus before the top of the bubble gets to surface, and we will likely have lower surface pressures compared with the Driller’s Method.
It produces maximum on-choke time. As Choke operator will have to continuously operate choke for making constant SICP and ICP value and for making constant BHP.