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. [click to continue…]
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. [click to continue…]
Driller’s method and wait and weight method (engineer’s method) are widely used to circulate wellbore influx while maintaining bottom hole pressure constant. There are a lot of opinions regarding which method is the best for well control operation therefore this article will discuss about pros and cons of both methods.
The driller’s method requires two circulations to kill the well. The first circulation is to circulate influx out of the well with original mud weight. The second circulation is to kill the well with kill weight fluid. During the first circulation, the bottom hole pressure remains constant due to maintain drill pipe pressure constant while circulating. For the second circulation, in order to maintain constant bottom hole pressure, casing pressure is held constant while circulating kill mud to the bit. Once the kill mud passes the bit, the drill pipe pressure will be held constant until the kill weight mud is on surface and there is no sign of influx in the annulus.
Wait and Weight Method
The Wait and Weight method requires only one circulation. The influx will be circulated out while the kill weight mud is displaced into the well simultaneously. While pumping the kill fluid from surface to the bit, drill pipe pressure schedule must be strictly followed. After that the drill pipe pressure is maintained constant until the kill mud returns back to surface. Some people call the Wait and Weight method as “Engineer’s Method” because there are more calculations compared to the Driller’s method.
Comparison between Driller’s Method and Wait and Weight Method
After we publish this article “Hard Shut-In Procedure while Drilling with a Subsea BOP Stack”, there are some people asking us about what about the shut-in procedure while tripping with a subsea stack. So today we will focus on this topic.
For the shutting in procedure with subsea stack, there are 3 steps which are stab valve, space out, and shut in and the details for the procedure are below.
1st step: stab valve
Stab the full opening safety valve into the string and then make it up to the drillstring. Close the valve.
Learning from the past oilfield disaster will help you realize about well control, safety management, etc which you can apply to mitigate the future catasrophe. Today, we would like to share the information about Enchova Central which blown out years ago. This is very good information for everybody.
The Enchova Central platform, which was the place where two big catastrophies occurred was situated in the Campos Basin close to Rio de Janeiro and was administered by Petrobras. The initial incident was on August 16, 1984, when there was fire and an explosion. Most of the people and personnel at the time of the incident were saved with a helicopter or lifeboat. However, 42 workers lost their life in this catastrophe.
It was the most consequential and grave occurrence when there was an issue in the functioning of the lowering mechanism of a lifeboat due to which there was a malfunction with the bow hook. Consequently, the lifeboat was left hanging vertically till there was a rupture in the stern support and following this the lifeboat drowned 10 to 20m to the sea, which resulted in the death of 36 personnel. Around 6 personnel lost their lives on trying to jump 30 or 40m from the platform to the sea.
Nowadays, deepwater drilling is one of the important parts of drilling in the world and there are a lot of ongoing deepwater operations. Our team will start focus on subsea well control and this topic is about hard shut in procedure while drilling with a subsea stack. This is quite similar to surface stack but it is quite tricky how you space out the well properly because the BOP is way down below approximately thousand feet from sea surface.
There are 3 steps which are space out, shut down and shut in and the details for the procedure are below.
Underbalanced drilling becomes very famous in several places of the world because there are some advantages over normal drilling operations. Today we would like to share the basic underbalanced drilling 101 for everybody who is interested in this topic. It is presented by Shell and we also add full VDO transcript for anybody who cannot catch the information from this presentation.
Underbalanced Drilling 101 Full VDO Transcript
This presentation introduces the concept and equipment used in underbalanced drilling operations. The key differences between underbalanced drilling and conventional overbalanced drilling are at both the conceptual and the technical level. At the conceptual level the subsurface drilling conditions needs to be investigated further, the rotating drill bit cuts away rock to deepen the well. The drill cuttings are lifted to the surface by the circulating drilling fluid.
Women nowadays are dominating the world of men especially when it comes to jobs. They work side by side with males in a man’s industry, which is considered as a great achievement. Back in the days, women should stay at home, serve her husband, cook for the family, care for the children and do the household chores. This happened for many decades until some brave ladies stood up and fought for women’s rights. They showed that women can do almost anything and they can perform the work of a man. In fact, there are women who work in the oilfield, which is a tough job. People, mostly men and unbelievably some women, don’t want to accept that Eve’s daughters can work hard and do laborious jobs too.
Good thing these days men have embraced this fact and offer wider opportunities to the ladies. There are several male jobs that are now handled by women. These jobs include being a CEO, lawyer, doctor, rescuer, military work, police, a taxi driver, a construction worker, an electrician, a race car driver, engineer, oilfield worker and the list goes on. Some of these jobs were once performed by men and are not allowed for women.
Fracture gradient is one of the critical information which drilling engineers need to know in order to design drilling programs. For the well control stand point, the fracture gradient directly affects on how much influx volume can be successfully contained in the wellbore. If the wellbore pressure is over the fracture pressure, formations would be broken down and this situation will result in loss of drilling fluid into formations. Additionally, it might lead to well control situation because of loss of hydrostatic pressure. Fracture gradient is quite straight forward for land operation because it will not be reduce due to water column. However, the fracture gradient will be reduced in deepwater environment. In this article, we will discuss why water depth can cause the reduction in fracture gradient.
Basically, the fracture gradient is related to fluids occupying in pore spaces of rock and weight of rock which are called overburden pressure. Generally, the overburden of a typical sedimentary is about 1.0 psi/ft (19.2 ppg). Rocks will be fractured when the wellbore pressure exceeds the confining stresses acting on it. If we make a general assumption that the overburden pressure causes the minimum confining stress of the rock. Then the formation fracture gradient will not be 1.0 psi/ft if the location is offshore.
Note: this assumption is made in order to help you get more understanding on how and why water depth can decrease the formation fracture gradient.
Why does the water depth reduce fracture gradient?