Kill mud is the mud required to kill the well in case the Kick has taken place. To calculate the kill mud weight required, first we need to calculate formation pressure due to which kick has taken place.
Shut-in Drill pipe pressure SIDPP
Shut-in drill pipe pressure (sidpp) is the surface pressure on drill string side when an influx has taken place and the well is shut. While Shut-in casing pressure SICP is the surface pressure on casing side.
There is a assumption in well-control calculation, When the kick takes place formation fluid flows into annulus and not inside the drill-pipe. Which is genrally true, as the genral direction of fluid flow is from drill pipe to annulus side.
Oil Well kick
Kick is the inflow of formation fluid into the wellbore. Generally drilling is done under overbalance condition which means borehole pressure is higher than formation pressure. This overbalance keeps the formation fluid from entering into the wellbore. But sometimes due to different reasons wellbore pressure may decrease below the formation pressure (under-balance condition), which allows the formation fluid to enter into the hole. This influx is called kick.
Kick can happen during any operation drilling,tripping and circulation. If the kick is handled successfully kick is said to be killed and if the kick flows to the surface uncontrolled its called a blowout.
Brent vs WTI crude oil price
Whenever we check for crude oil prices, we notice one thing that Brent crude oil prices are generally higher than WTI crude oil Prices.What is the reason for this Brent WTI price spread?
Brent refers to the oil produced from the North sea and has a sulphur content of 0.37% while WTI is mainly produced in North america and it is delivered at cushing, okhalama(U.S.A) where its prices are set and has a sulphur content of 0.24%. And remember Lower the sulphur content cheaper it is to refine the crude oil. WTI is sweeter than Brent crude that’s why WTI is considered superior to Brent crude, but still is priced lower than Brent crude
Oil industry 2020
Meanwhile ,the oil price that had started plummeting in November 2014 has rebounded to 99$/bbl on January 2020.The operations that were shutdown over years -when oil price reached 33 $ ,while Iran flooded the market in Early 2016 ,were resumed in 2017-18 and are operating at full phase now- creating more job prospects & higher demand in 2020.
While the Multinational Service Companies were hit by the low oil prices in 2015-16 resulting in Cost cuttings,at the same time they were taking advantage of the situation & busy planning for swallowing up the companies that could not able to sustain the weakness. The Wave of Mergers and Acquisitions that started in 2014-15 are a bit Freezing now as Industry is Prepared with Restructuring !
Difference Between Leak off test, Formation integrity test & Formation breakdown test
While Leak off test, Formation integrity test & Formation breakdown test all have the same procedure and aim, the only difference is the point to which the casing shoe will be pressured.
Leak off test procedure and calculation
Leak off test in drilling is conducted to measure the pressure at which the drilling fluid just start to leak into the formation or the formation just start to fracture.Alternatively leak-off pressure is the maximum pressure which the open hole section can bear without fracturing and from this maximum pressure we can calculate the maximum mud weight which could be used to drill this open hole section. Leak off test is conducted in the new formation after the casing has been set.
- Leak-off test
- Formation integrity test
- Formation breakdown test/Fracture test
All the above pressure tests have the same procedure and are conducted to measure the strength of the weakest part of the next hole section to be drilled. For these pressure tests it is assumed that the shallowest depth of the open hole section has the least strength because as we move deeper compaction increases (due to the weight of overlying formation) and so does the strength of the formation.if we make sure that during any operation(drilling, tripping and casing) in the open hole pressure does not exceed the leak-off pressure there will no chance of fracturing the open hole.
Leak off test Procedure
- After the casing and cementing , 3 to 5m of next hole section is drilled.
- Drill string is pulled into the casing shoe.
- Close the BOP.
- Equal volumes of Drilling mud is pumped in intervals(Generally 1-2 bbl) from the cementing unit.After pumping each volume, pressure will increase as the well is closed.
- Surface pressure and cumulative volume is plotted on a graph.
- After the test is finished, pressure is bleed-off from the surface and the BOP is open.
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