Category Archives: Applied Drilling Calculations

Maximum ROP Before Fracture Formation

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In this topic, we will apply the effective mud density formula to determine maximum ROP before fracturing formation.

Figure 1 - Max ROP before Fracturing FormationFigure 1 – Max ROP before Fracturing Formation

 

These two equations that will be used to determine the maximum ROP are listed below;

Effective mud density due to cuttings in the hole can be determined by the empirical equation below;

equation 1

Where;

ρeff is effective mud density in ppg.

ρm is mud density in ppg.

Q is flow rate in gpm.

ROP is rate of penetration in fph.

db is wellbore diameter or bit diameter in inch.

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Increase In Mud Weight Due To Cutting

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Cutting generated while drilling will increase drilling fluid density and it will finally affect equivalent circulating density while drilling. In this topic, we will talk about how to determine mud weight increase due to cutting.

 Figure 1 - Cutting Increases Mud Density

Figure 1 – Cutting Increases Mud Density

 

Effective mud density due to cuttings in the hole can be determined by the empirical equation below;

euqation pm

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Rig Derrick Load Calculation

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The drilling line is reeved over a set of crow block and down to another set of sheaves known as travelling block. The hook connected to travelling block is used to suspend the drilling load. One end of drilling line is wound onto the drawworks and this line is called “Fast Line”. Other end of the drilling line is tied into an anchor point on the rig floor and this line is named as “Dead Line”. The drilling line is reeved around the blocks several times in order to meet required load.

derrick Load Calculation 1

According to the diagram above, we can use basic physic to determine derrick load.

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Pipe Light Calculation

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Pipe light (figure 1) describes the condition of the well which well head pressure and buoyancy acting upward against a cross sectional area of pipe is greater than weight of the string. If the light pipe condition is happened and the string is not controlled by the snubbing unit, the string will be pushed out of the well.

Figure 1 - Diagram for Pipe Light Condition

Figure 1 – Diagram for Pipe Light Condition

You may see these videos showing the pipe light condition. These videos below clearly demonstrate when the pipe is in “Pipe Light” condition. You can see that the tubing string is  hydraulically pushed out of the hole by wellbore pressure.

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Kick Tolerance Concept and Calculation for Well Design

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Kick tolerance is the maximum gas volume for a given degree of underbalance which the circulation can be performed without exceeding the weakest formation in the wellbore. This article is the extended version of Kick Tolerance Calculation  which will explain more on this topic. It is very critical that drilling personnel understand its importance to well design and drilling operation.

147-Kick-Tolerance-Concept-and-Calculation-for-Well-Design-cover

There are two important factors used for determining the kick tolerance

• Kick Intensity – It is the different between the maximum anticipated formation pressure and planned mud weight. For example, the planned mud weight is 13.0 ppg and the possible kick pressure is 13.5 ppg. Therefore, the kick intensity is 0.5 ppg (13.5 – 13.0).

A zero kick intensity (swabbed kick scenario) should be used for a know area where you have less uncertainty about an overpressure zone.

 • Kick Volume – It is a gas influx entering into the wellbore from the formation. Gas kick is always used for well control calculation because it is the worst case scenario. The kick volume should be realistic figure which personal can detect the influx on the rig. In a larger hole, it allows bigger influx volume than a small hole.

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