Well Engineering & Construction

KICK TOLERANCE

AL-KHALIDI SEHAM JALALMISKOLC UNIVERSITY

2013

CONTENTS Introduction Casing Seat Selection Kick Tolerance Definition KICK TOLERANCE ELEMENTS Causes of Kick VOLUME OF GAS INFLUX Circulation Kick Tolerance Gas Compressibility Factor Well Kick Detection

IntroductionThe importance of kick tolerance in well operations has recently increased

due to its implications in well design, in drilling and well control .These implications are still more evident in wells currently drilled by oil industry, for which more complex planning and performance are required in comparison with the past.

Therefore

Kick tolerance is a key element when establishing a well design. The number of sections will rely on the engineered data from the set of regulations governing thesafety (kick tolerance) for each section

Casing Seat Selection

The selection of casing setting depths is one of the most critical in the well design process:

While the conservative selection of casing shoe depth could make a well design uneconomical.

The unsuitable casing shoe depth could make a well undrillable.

Information is sourced from: Seismic and geological background. Drilling data from offset wells .

Casing Seat Selection

The pressure which the formation at the casing seat must be able to withstand is the greater of:

the hydrostatic pressure of the mud used to drill the next section.

the maximum pressure exerted at the casing seat when circulating out gas influx from TD of the next hole section.

Casing Seat Selection The selection of the number of casing strings and their setting

depths generally is based on a consideration of the pore pressure gradients and fracture gradients of the formations to be penetrated :

The pore pressure and fracture pressure are expressed as an equivalent density and are plotted vs. depth. A line representing the planned-mud-density program also is plotted. The mud densities are chosen to provide an acceptable trip margin above the anticipated formation pore pressure to allow for reductions in mud weight caused by upward pipe movement during tripping operation.

A commonly used trip margin is 0.5 lbm/gal or one that will provide 200-500 psi of excess bottom hole pressure over the formation pore pressure

Casing Seat Selection

Casing Seat Selection Point a: to prevent the formation fluid into the well and to

reach the desired depth.

Point b: to prevent the fracture of formation -->

intermediate casing need to run at this depth.

Point c: Fluid density is reduced until it reaches to margin of

the curve

Point d: casing shoe of the surface casing

Casing Seat SelectionDuring the casing seat design, MAASP and

Differential Pressure criteria are used to select casing setting points.

M.A.A.S.P. =Maximum Allowable Annular Shut in Casing Pressure

Kick Tolerance DefinitionKick Tolerance is defined as the maximum kick volume that can be taken

into the wellbore and circulated out without fracturing the formation at weak point (shoe), given a difference between pore pressure and mud weight in use.

Kick tolerance may also be defined the maximum allowable pore pressure at next TD or maximum allowable mud weight which can be tolerated without fracturing the previous casing shoe.

Kick tolerance can be understood as the capability of the wellbore towithstand the state of pressure generated during well control

operations (well closure and subsequent gas kick circulation process) without fracturing the weakest formation.

Kick Tolerance DefinitionKick tolerance is the maximum height of a gas column that the open

hole section can tolerate, without formation fracture occurring. This height is then converted to a volume using the cross sectional area

and geometry of the wellbore and drill string to derive a limited 'Kick Tolerance' in barrels or ppg equivalent.

Kick tolerance is the largest volume of influx that can be removed from the well safely and is again based on the results of either a LOT . When kick tolerance is calculated the result could be best described as a measurement of well control risk when drilling the current hole section.

Kick Tolerance Definition

Kick tolerance therefore depends on: the maximum kick size. maximum formation pressure at next

TD . density of the invading fluid and the

circulating temperatures. the maximum mud weight which can

be tolerated without fracturing the weakest point in the open hole

Kick Tolerance Definition

It is very important to recognize a kick and quick shut-in the well in order to limit Kick Volume

and to carry out a successful control.

Kick Tolerance Definition

Causes of Kick

1. Lack of knowledge and experience of personnel (Human error)– Lacking of well-trained personnel can cause well control incident because they don’t have

any ideas what can cause well control problem. For example, personnel may accidentally pump lighter fluid into wellbore and if the fluid is light enough, reservoir pressure can overcome hydrostatic pressure.

2. Light density fluid in wellbore – It results in decreasing hydrostatic pressure. There are several reasons that can cause this issue such as Light pills, sweep, spacer in hole Accidental dilution of drilling fluid Gas cut mud

3. Abnormal pressure – If abnormally high pressure zones are over current mud weight in the well, eventually kick

will occur.

Causes of Kick Tolerance

4. Severe lost circulation – Due to lost circulation in formation, if the well could not be kept fully filled all

the time, hydrostatic pressure will be decreased.Lost circulation usually caused when the hydrostatic pressure of drilling fluid

exceeds formation pressure. There are several factors that can cause lost circulation such as

Mud properties – mud weight is too heavy and too viscous. High Equivalent Circulating Density High surge pressure due to tripping in hole so fast Drilling into weak formation strength zone

Causes of Kick Tolerance 5. Unable to keep the hole full all the time while drilling and

tripping

If hole is not full with drilling fluid, overall hydrostatic pressure will decrease.

6 .Swabbing causes reducing wellbore hydrostatic pressure.

Swabbing is the condition that happens when anything in a hole such as drill string, logging tool, completion sting, etc is pulled and it brings out decreasing hydrostatic pressure. Anyway, swabbing can be recognized while pulling out of hole by closely monitoring hole fill in trip sheet.

Causes of Kick Tolerance

Kick Types

Gas KicksRapid expansion as gas circulated through chokeMud gas separators and flare lines usedGas migration problemsHigher SICP than others

Gas Kicks, cont.Barite settling in OB mud Solubility of gas masks kick indicators Flammability of gas Slugging of gas at choke

Kick Types

Oil Kicks

Flammable but not as explosive as gasDensity greater than gas-lower SICPVery little expansion as kick reaches

surfaceBut, there is almost always some gas

present

Kick Types

Water kicksnot flammablevery little expansionlower SICP than gas or oil

But, there is still usually some gas present.

Kick Types

Prediction kick types

Density of gas =1-2 ppgDensity of oil = 6-8 ppgDensity of salt water =8.6-9.0

ppg

Equation for the determination of the density of kick:

Kick Types

KICK TOLERANCE ELEMENTS The following elements determine the magnitude

of kick tolerance:

Pore pressure from next TDMud weight to be usedFracture Gradient at current casing shoeType of well exploration or developmentDesign influx volume that can be safely

circulated out

When to Calculate Kick Tolerance After a leak-off test Prior to drilling ahead, If the mud weight is changed When drilling into areas of overpressure rapid pore pressure increase, increasing mud weight to compensate, kick tolerance is limited by formation

strength at the previous casing shoe.

KICK TOLERANCE ELEMENTS

Circulation Kick Tolerancewhen the top of the gas bubble reaches the shoe, the pressure at the

casing shoe is given by:

wherePf = formation pressure at next TD, psiPg = pressure in gas bubble = H x GH = height of gas bubble at casing shoe, ftG = gradient of gas = 0.05 to 0.15 psi/ftTD = next hole total depth, ftCSD = casing setting depth, ftpm = maximum mud weight for next hole section, ppg

Circulation Kick Tolerance

Maximum tolerable length (H) of gas influx in the annulus at any position between bottom hole and the casing

where FG = fracture gradient at the casing shoe in ppg Pf = pore pressure in psi

Circulation Kick Tolerance

The kick tolerance values may be increased when:

1. drilling extremely high porous and permeable zones (1-3 Darcie's)

2. using low technology kick detection equipment or using old rigs

3. several transition zones are expected in same open hole section are encountered

4. drilling from a semi-submersible rig

VOLUME OF GAS INFLUX

Flow rate into the wellbore:

Q = flow rate, bbl/min k = permeability, millidarcy Δp = pressure differential, psi L= length of section open to wellbore, ft μ = viscosity of intruding gas, centipoises Re = radius of drainage, ft Rw = radius of wellbore, ft

VOLUME OF GAS INFLUX The amount of influx volume that entering in well depends on:

underbalanced between mud weight and pore pressure reservoir porosity and permeability influx type sensibility and reliability of detection equipment reaction time of well control crew type well shut in procedure time of BOP closure

VOLUME OF GAS INFLUX

In case of a kick occurrence the type of the influx that enters the wellbore is required to be determined.

The influx gradient can be evaluated using the given ranges

VOLUME OF GAS INFLUX

A gas kick causes higher annular pressures than a liquid kick.

A gas kick has lower density than a liquid kick. A gas kick must be allowed to expand as it is pumped

to surface. The objective for the well control is to always having

a constant bottom hole pressure. This is only possible through having higher surface annular pressure that can be maintained through the adjustable choke

BEHAVIOR OF GAS KICKS

Percolation of gas through liquid in vertical open hole.

Source: SPE 130693“Snubbing Units Used Effectively in Well-Control-Recovery Efforts” by S.R. Wehrenberg, SPE, Boots & Coots, et al

BEHAVIOR OF GAS KICKS

Source: SPE 130693“Snubbing Units Used Effectively in Well-Control-Recovery Efforts” by S.R. Wehrenberg, SPE, Boots & Coots, et al

BEHAVIOR OF GAS KICKS

Gas/liqiud distribution after 1 second of simulation in relation To Wellbore inclination.

Temperature Effect.

The change in temperature along the wellbore will affect the density and the rheology of the mud, having a direct effect on the hydrostatic gradient and the frictional pressure losses during circulation. Currently, it is assumed that the temperature in the open hole section is constant; thus, no correction to the volume calculation is applied.

The effects of temperature on influx volume are described by Charles law, which states that the volume of the gas is directly proportional to the absolute temperature. Contrary to the afterflow effect, the temperature correction results in a higher kick tolerance. Therefore, the conventional constant-temperature assumption results in a conservative solution.

Z-Factor Correction.The compressibility factor, also know as z factor, takes account for

real gas behavior according to the particular gas composition of the influx. A common assumption is to utilize z=1, as if the influx behaved according to the ideal gas law.

The approach used to estimate this factor is not straightforward and requires several different methods for the numerical calculation, this makes it a hard task to perform without computer power.

The pseudo critical properties are calculated using Katz’s correlations, and the factor requires Newton-Raphson iterative method combined with Dranchuk-Abou- Kassem or HallYarborough correlations (best fit for single phase) or the Beggs-Brill correlation when multiphase is considered.

Well Kick DetectionWell Kick Detection List Look The Indicators to Prevent Blowout

Positive Indicators of a Kick1.Increase in Pit Volume2.Increase in Flow Rate

Secondary Indicators of a Kick1.Decrease in Circulating Pressure2.Gradual Increase in Drilling Rate3.Drilling Breaks4.Increase in Gas Cutting5.Increase in Water Cutting or Chloride

Well Kick Detection

Indicators of Abnormal Pressure1.Decrease in Shale Density2.Change in Cuttings Size and Shape3.Increasing Fill on Bottom After a Trip4.Increase in Flow Line Temperature5.Increase in Rotary Torque6.Increasing Tight Hole on Connections

Innovative drilling technologies

In challenging Deep HPHT wells, where kick tolerance is very narrow , it is necessary to use innovative technologies in order to be able to

drill on. Managed Pressure Drilling (MPD) ENI Near Balance Drilling (ENBD)

They allow to manage the bottom hole pressure properly.

Managed Pressure Drilling (MPD)

MPD technology is the use of a closed,pressurizable mud returns system that provides the ability to drill ahead and make jointed-pipe connections while maintaining the appropriate annular pressure profile.

ENI Near Balance Drilling

ENBD allows “walking the line” between pore pressure and fracture gradient, through precise and safe control of the annular pressure profile, during drilling.

ENBD integrates the advantages both of Continuous Circulation and Managed Pressure Drilling. Application of a continuous circulation device may give great benefit, especially in combination with annular back-pressure

Managed Pressure Drilling (MPD)

Shut in Procedures For Well Control Operation

Shut in procedures are specific procedures for closing a well in case of well control situation and personnel on the rig should get proper training and be familiar with these procedures.

The main reason to have the specific shut in procedure is to minimize kick volume entering into a wellbore when well control situation occurs. Basically, the faster to recognize kick and shut in a well, it is the better to manage a well control situation. The amount of wellbore influx that enters the wellbore are minimized when personnel respond quickly to shut the well in. It is the fact that a small amount of kick entering into the wellbore will result in lower initial shut-in casing pressure and lower casing pressure while circulating. What's more, the lower pressure at surface will reduce the chance of breaking down hole formation, generally called underground blowout.

Types of Shut-In In the drilling industry, there are 2 types of shut in which are Hard Shut-

in and Soft Shut-in.Hard shut in: It means that while drilling, choke line valves are in a

closed position. When you have the well control, you just shut in a blow out preventor. The choke valves will be opened when we kill the well. The hard shut-in is the fastest method to shut in the well; therefore, it will minimize volume of kick allowed into the wellbore.

Soft Shut In: It means that while drilling, the choke line valves are in an opened position. When the well control situation is occurred, you shut in the blow out preventor and then close choke valves to shut in the well. The soft shut in procedure allows fluid to low through the surface choke line before the well will be completely shut in. This is the bad part of the soft shut in procedure because it doesn't minimize size of the wellbore influx.

Well control

ConclusionsKick Tolerance is an important concept that can be applied both in drilling operations and in casing program design.

Application of kick tolerance concept is especially helpful in wells currently drilled by oil industry, for which more complex planning and execution are required.

Considering Kick Tolerance made drilling execution safer and more economical by reducing the probability to have an incident.

THANK YOU

AL-KHALIDI SEHAM JALALMISKOLC UNIVERSITY

2013