This topic will cover about pressure profile both drill pipe and casing pressure while kill a well with wait and weight method.
Drill Pipe Pressure
Firstly, we will take a look at the drillpipe pressure. When kill weight mud is displaced in the well, drill pipe pressure drops as per the drill pipe schedule. Once kill weight mud is to the bit, drill pipe pressure is maintained until the well is killed. A pressure profile will look like the following chart.
This example demonstrates how to determine drill pipe pressure schedule for wait and weight method.
Well Information
Current mud weight = 9.5 ppg
Pump output = 0.1 bbl/stroke
Well depth = 9000’MD/9000’TVD
Drill string capacity = 0.0178 bbl/ft
Surface line volume = 15 bbl.
Shut in casing pressure = 700 psi
Shut in drill pipe pressure = 500 psi
ICP = 1600 psi at 30 spm as kill rate
Please follow steps below to determine the drill pipe pressure schedule (step down chart).
This topic will explain you how wait and weight well control controls bottom pressure constant. There are 2 steps that must be took into consideration separately. The first one is when kill weight mud is displaced to the bit and the second one is when the kill weight mud from bit to surface.
1) Displace kill weight mud to the bit
Once kill weight mud is mixed and displaced into drill pipe, drill pipe pressure will be decreased due to increasing in hydrostatic pressure. In order to control bottom hole pressure, a drill pipe pressure schedule must be developed and followed until kill mud weight to the bit.
I will give you overview about the wait and weight method on this blog post and some basic concepts and calculations will be described later.
Wait and Weight Well Control Method or someone calls Engineer’s Method is a method to control well with one circulation. Kill weight mud is displaced into drill string and kick (wellbore influx) is removed while displacing a wellbore.
Reserve Fluid System in Koomey
According to API RP53, each closing unit should have a fluid reservoir tank with a capacity equal to or at least twice the usable fluid capacity of the accumulator system and reservoir fluid is stored at atmospheric pressure
Pumping System in Koomey Unit
Pumps in the Koomey Unit provide power to charge bottles to 3,000 psi. According to API RP53, it states about the pumping system as follows:
• Two or three independent sources of power (Air, Electric or Nitrogen)
• For surface accumulators: With the accumulator removed from service, each pump system should be capable of closing the annular BOP on drill pipe, opening HCR and obtaining a minimum pressure of 200 psi over pre-charge pressure within 2 minutes.
