Well Engineering & Construction KICK TOLERANCE AL-KHALIDI SEHAM JALAL MISKOLC 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.ThereforeKick tolerance is a key element when establishing a well design.The number of sections will rely on the engineered data fromthe 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 SelectionThe 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 SelectionThe 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 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 DefinitionKick 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 andquick shut-in the well in order to limit Kick Volume and to carry out a successful control.
Causes of Kick1. 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 mud3. Abnormal pressure –If abnormally high pressure zones are over current mud weight in the well, eventually kick will occur.
Causes of Kick Tolerance4. 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 Tolerance5. Unable to keep the hole full all the time while drilling and trippingIf 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 asdrill string, logging tool, completion sting, etc is pulled and it bringsout decreasing hydrostatic pressure. Anyway, swabbing can berecognized while pulling out of hole by closely monitoring hole fill intrip sheet.
Kick TypesGas Kicks Rapid expansion as gas circulated through choke Mud gas separators and flare lines used Gas migration problems Higher SICP than othersGas Kicks, cont. Barite settling in OB mud Solubility of gas masks kick indicators Flammability of gas Slugging of gas at choke
Kick Types Oil KicksFlammable 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 TypesWater kicks not flammable very little expansion lower SICP than gas or oil But, there is still usually some gas present.
Kick TypesPrediction kick types Density of gas =1-2 ppg Density of oil = 6-8 ppg Density of salt water =8.6-9.0 ppg
Kick TypesEquation for the determination of the density of kick:
KICK TOLERANCE ELEMENTSThe 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
KICK TOLERANCE ELEMENTSWhen 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.
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 casingwhere FG = fracture gradient at the casing shoe in ppg Pf = pore pressure in psi
Circulation Kick ToleranceThe kick tolerance values may be increased when:1. drilling extremely high porous and permeable zones (1-3 Darcies)2. using low technology kick detection equipment or using old rigs3. several transition zones are expected in same open hole section are encountered4. drilling from a semi-submersible rig
VOLUME OF GAS INFLUX Flow rate into the wellbore:Q = flow rate, bbl/mink = permeability, millidarcyΔp = pressure differential, psiL= length of section open to wellbore, ftμ = viscosity of intruding gas, centipoisesRe = radius of drainage, ftRw = radius of wellbore, ft
VOLUME OF GAS INFLUXThe amount of influx volume that entering in welldepends 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 INFLUXIn 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 KICKSPercolation of gas throughliquid 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 KICKSSource: SPE 130693“Snubbing Units Used Effectively in Well-Control-RecoveryEfforts” by S.R. Wehrenberg, SPE, Boots & Coots, et al
BEHAVIOR OF GAS KICKSGas/liqiud distribution after 1 second ofsimulation in relationTo 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 DetectionIndicators 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 technologiesIn 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 DrillingENBD 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
Shut in Procedures For Well Control OperationShut 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. Whats more, the lower pressure at surface will reduce the chance of breaking down hole formation, generally called underground blowout.
Types of Shut-InIn 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 doesnt minimize size of the wellbore influx.
ConclusionsKick Tolerance is an important concept that can beapplied both in drilling operations and in casingprogram design.Application of kick tolerance concept is especially helpful inwells currently drilled by oil industry, for which more complexplanning and execution are required. Considering Kick Tolerance made drilling execution safer and more economical by reducing the probability to have an incident.
THANK YOUAL-KHALIDI SEHAM JALAL MISKOLC UNIVERSITY 2013