kick tolerance concept and calculation for well design

8/10/2019 Kick Tolerance Concept and Calculation for Well Design

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by DrillingFormulas.Com on May 16, 2013

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.

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.

Tolerance Concept and Calculation for Well Design http://www.drillingformulas.com/kick-tolerance-concept-and-calc

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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.

Maximum Allowable Annular Surface Pressure (MAASP) and Kick Tolerance

Weakest formation point in the open hole is assumed to be at the shoe depth of the previous casing. The well

bore will be fractured if a summation of hydrostatic and surface pressure exceeds the weakest pressure (Leak

Off Test pressure). The maximum surface pressure before breaking the formation is called Maximum

Allowable Shut In Casing Pressure (MASICP).

Make it simpler for your understanding. MASICP is the total of kick tolerance budget. It consists of pressure

from kick intensity and hydrostatic pressure loss due to gas.

Kick Tolerance Example Calculation

Previous casing shoe (9-5/8 casing) at 6,000 MD/ 6,000 TVD

Predicted formation pressure at TD (10,000MD/10,000TVD) = 14.0 ppg

Pore pressure uncertainty = 1.0 ppg

Planned mud weight = 14.5 ppg (0.754 psi/ft)

Gas gradient = 0.1 psi/ft

LOT = 16.0 ppg

Hole size = 8-1/2

Drill Pipe = 5

BHA + Drill Collar = 7

Length of BHA+Drill Collar = 400 ft

Annular capacity between open hole and BHA = 0.0226 bbl/ft

Annular capacity between open hole and 5 DP = 0.0459 bbl/ft


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Calculation Steps

Maximum anticipated pressure = 14.0 + 1 = 15.0 ppg

Maximum Allowable Shut In Casing Pressure (MASICP) = (LOT MW) x 0.052 x Shoe TVD

Maximum Allowable Shut In Casing Pressure (MASICP) = (16 14.5) x 0.052 x 6,000 = 468 psi

Kick Intensity = 15.0 14.5 = 0.5 ppg

Underbalance due to kick intensity = 0.5 x 0.052 x 10,000 = 260 psi

As you can see, when the well is in underbalance condition (260 psi), the shoe will not be broken because the

MASICP is more than underbalance pressure (468 > 260).

We know that 0.5 ppg kick intensity we will have 208 psi (468 260 = 208 psi) before shoe broken.

It means that gas bubble can replace mud in equivalent to 208 psi before fracturing the shoe. With this


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relationship, we can determine height of gas kick by the following equation.

Height of gas kick = remaining pressure, psi (mud gradient, psi/ft gas gradient, psi/ft)

Height of gas kick = 208 (0.754 0.1) = 318 ft.

Determine gas kick volume base on height of gas kick

We need to separate into two cases and compare the smallest volume.

1st case Gas at the bottom

Volume of gas kick = Annular capacity between open hole and BHA x Height of gas kick

Volume of gas kick (bbl) = 0.0226 bbl/ft x 318 ft = 7.2 bbl


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2nd case Gas right below casing shoe

For this case, we need to convert gas at the shoe to the bottom condition by applying Boyles Laws.

Volume of gas kick = Annular capacity between open hole and 5 DP x Height of gas kick

Volume of gas kick (bbl) = 0.0459 bbl/ft x 318 ft = 14.6 bbl

Convert to the bottom hole condition


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Volume at the bottom = (volume of gas kick at shoe x Leak off test) formation pressure

Leak off test = 0.052 x 16 x 6,000 = 4,992 psi

Formation pressure (gas kick condition) = 0.052 x 15 x 10,000 = 7,800 psi

Volume at the bottom = (14.6 x 4992) 7800 = 9.3 bbl

We can compare the kick volume from two cases like this.

1 st case : kick volume = 7.2 bbl

2nd case : kick volume = 9.3 bbl

The smallest number must be selected to represent maximum kick volume therefore kick volume is 7.2 bbl.

We wish this article could help you get more understanding about Kick Tolerance.


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Ref book: Formulas and Calculations for Drilling, Production and Workover, Second

Edition

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kick tolerance concept and calculation for well design

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