â⊠I could see that we were having a blowout! Gas to the surface at 0940 hours.â
0940 TO 1230 HOURS
Natural gas was at the surface on the casing side very shortly after routing the returning wellbore fluid through the degasser. The crew reported that most of the unions and the flex line were leaking. A
-in. hammer union in the line between the manifold and the atmospheric-type âpoor-boyâ separator was leaking drilling mud and gas badly. The separator was mounted in the end of the first tank. Gas was being blown from around the bottom of the poor-boy separator. At about 1000 hours, the motors on the rig floor began to rev as a result of gas in the air intake. The crew shut down the motors.
At 1030 hours the annular preventer began leaking very badly. The upper pipe rams were closed.
1230 TO 1400 HOURS
Continuing to attempt to circulate the hole with mud and water.
1400 TO 1500 HOURS
The casing pressure continues to increase. The flow from the well is dry gas. The line between the manifold and the degasser is washing out and the leak is becoming more severe. The flow from the well is switched to the panic line. The panic line is leaking from numerous connections. Flow is to both the panic line and the separator.
The gas around the rig ignited at 1510 hours. The fire was higher than the rig. The derrick fell at 1520 hours.
This excerpt is from an actual drilling report. Well control problems are difficult without mechanical problems. With mechanical problems such as those described in this report, an otherwise routine well control problem escalates into a disastrous blowout. In areas where kicks are infrequent, it is common for contractors and operators to become complacent with poorly designed auxiliary systems. Consequently, when well control problems do occur, the support systems are inadequate, mechanical problems compound the situation, and a disaster follows.
Because this book is presented as a blowout and well control handbook, its purpose is not to present the routine discussion of blowout preventers (BOPs) and testing procedures. Rather, it is intended to discuss the role of equipment, which frequently contributes to the compounding of the problems. The components of the well control system and the more often encountered problems are discussed.
The saying âit will work great if we don't need it!â applies to many well control systems. The fact is that, if we don't ever need it, anything will suffice. And therein lies the root of many of the problems encountered. On a large number of rigs, the well control system has never been used and will never be needed.
Some rigs routinely encounter kicks, and the crew is required to circulate out the kick using classical well control procedures. In these instances, the bare essentials will generally suffice. For most of these conditions, well site personnel need not be too concerned about how the equipment is rigged up or how tough it is.
In some parts of the industry, wells are routinely drilled underbalanced with the well flowing. In these cases, the well control system is much more critical, and more attention must be paid to detail.
In a few instances, the kick gets out of control, or the controlled blowout in the underbalanced operation becomes uncontrolled. Under these conditions, it is sometimes impossible to keep the best well control systems together. When it happens, every âiâ must be dotted and every âtâ crossed.
Unfortunately, it is not always possible to foretell when and where one of those rare instances will occur. It is easier and simpler to merely do it right the first time. Sometimes, the worst thing that can happen to us is that we get away with something we shouldn't. When we do, we are tempted to do things the same way over and over and even to see if we can get away with more. Sooner or later, it will catch up with the best of us. It is best to do it right the first time.
Pressure, Erosion, Corrosion, and Vibration
When everything goes to hell in the proverbial hand basket, our first question should be, âhow long is all this sâgoing to stay together?â The answer to that question is usually a function of the items listed aboveâpressure, erosion, corrosion, and vibration.
Pressure
If the well control system is rated to 10,000 psi and has been tested to 10,000 psi, I'm comfortable working up to that pressure provided none of the other three factors is contributing, though that is seldom the case. There is usually a large difference between the working pressure and test pressure for a given piece of equipment. For example, a 10,000 psi working pressure BOP has a test pressure of 15,000 psi. That means the rams should operate with 10,000 psi, and under static conditions, everything should withstand 15,000 psi.
Wellheads, valves, and all other components are the same. It is easy to understand how a valve can have a âworkingâ and a âtestâ pressure, but it is natural to wonder how a spool can have a âworkingâ and a âtestâ pressure. Since a spool has no moving parts, it seems that the two should be the same.
Vibration
When things begin to vibrate, the working pressure goes down. There are no models available to predict the effect of vibrati...