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o =D SmU, 01PetrcMmErOmalADC/SPE 35119Field Examples of Gas Migration RatesR.D. Grace,* Grace, Shursen, Moore & Assocs., and J.L. Shursen, ConsultantSPE and IAOCMemberCopyWht 1993, IADCISPE DrIIlnw Confe,anc.sThis paper was ~pa fed fw prewn latcm at Uw 1S% WCASPE Onll lngCmfweti held mNW Orleans, Lowmana, 12-15 Mardi 199sThm paper wss seklod fcf pmmantnbonby the bUIC/SPE Progmn Commttea fol lmwngreview of mfonn8tmn ccmtdned m an ab$trsci wbrmttad by the author(6) Contents of I(Wpape r as p resen ted have no tW reviewed by the%.ae ty of Petro !wm Engmeerao r theInmrnaucmalAssouahcmof OrillIcgContractors and are sub)ed to correcocmby lm aulhor[a)The mater ia l, as presentec , @es not necassanly ref fed any powtmn of the IADC or SPE,The!r offiis, C+memkers Papers p+esenwd at lAOC/SPE moatmgs are subjecf 10pabltca.tmn revww by Edtooal Ccmmma ofthe IAOC and SPE Perrmsmonto CCPYIS re$mcfed tosn ebstr ti ofnot mcfe than300 wcfds I ltusfrabonsmay n.d beaped The abstractshouktcmlam WWXUJCWSachmwk@mwnt & where and bywhom thep- wfw presented WntaLkanan, SPE P O Box 8 333.s3s Rchwdmn TX 75083-3836 U,S.A

IntroductionIn recent years gas migration rates have become the center ofconsiderable controversy. Historically, field personnel haveused a rule of thumb that gas migrated at the rate of 1000feet per hour. Early basic research i llustrated that the factorsaffecting the rate of bubble rise were quite complex. For ex-ample, the rate of rise was affected by the properties of theinflux, mud properties, the eccentricity of the hole, and thesize of the annulus, to name a few.

The rate of rise was also affected by the manner in whichthe influx entered the wellbore. rf the influx was dispersed inthe mud as small bubbles, the rise characteristics were differ-ent than if the influx entered the wellbore as a continuousbubble, A dispersed influx generally migrated much slowerthan a continuous bubble.

It was generally expected and observed that as an influxbegan to migrate toward the surface, the surface pressurewould begin to increase. The incremental changes in surfacepressure were uti lized to determine the rate of rise and predictthe travel of the influx. In addition, these techniques wereused to model the well control problem, expand the influx,protect the casing shoe, and otherwise analyze the problem.However, in many instances, the variables were too complexto permit accurate calculations and analyses in field operationsand the old rules of thumb were util ized.

Recently, additional research has been presented thatchallenges the traditional concepts of influx migration.2 Itwas suggests that what had been done in the past was oflen inerror, that the rate of rise was as high as 18,000 feet per hour,

and the pressure increases at the surface could not be reliedupon to properly analyze and predict influx migration andbehavior.In aneffort to further illuminate this interesting and vitalsubject, this paper chronicles several well-documented in-stances of influx migration under a variety of conditions.Field Examples

Example I One of the most interesting examples ofinf lux migration, or the lack thereof, occurred at the E.N. RossNo. I near Jackson, Mississippi.3 While on a trip at 19,419feet with 17.4 ppg oil base mud, a 260-barrel sour gas influxwas taken. The top of the influx can be calculated to be at13,274 feet with a shut-in surface pressure of 3700 psi. Thewe Ilbore schematic is presented as Figure 1.

Since the influx entered the wellbore in a continuousbubble and was significantly less dense than the mud, it wasanticipated that the migration would occur rapidly. However,that was not the case as indicated by the fact the surface pres-sure remained essential ly constant for the next 17 days whilesnubbing equipment was being rigged up.

After 17 days, the surface pressure slowly began to declineto approximately 2000 psi. Migration is most often accom-panied by an increase in surface pressure. However, in thisinstance, the influx was migrating from the 7 inch liner intothe 9-5/8 inch casing. Therefore, the influx shortened and thesurface pressure declined. As illustrated in Figure 2, the topof the influx reached 10,200 feet.

Six days later, during snubbing operations, analysis con-firmed that the top of the influx was indeed at approximately10,200 feet, [n a total of 23 days, a significant influx had mi-grated a total of only 3274 feet.

ExampIe 2 In this example, a directional well was beingdrilled with a I I.2 ppg gel polymer mud system. The plasticviscosity was 29 and the yield point was 29,

The wellbore schematic is presented as Figure 3. As ilhrs-trated, 7 inch casing had been set at 2610 meters and a 6 inchhole was being cored at 2777 meters measured depth, 2564meters true vertical depth. The angle of the wellbore was 38degrees at an azimuth of 91 degrees.

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2 FIELD EXAMPLES OF GAS MIGRATION RATES IADCLSPE35119

With the bit at 1884 meters on a trip out of the hole, thewell kicked and was shut in. The kick occurred at 0700 hoursand a 12 barrel influx was recorded. The shut-in drillpipepressure was 830 psi and the shut-in casing pressure was 1040psi, Analysis of the pressure data was conclusive. The top ofthe influx was at 1428 meters or 4685 feet. While operationswere being conducted to strip back to bottom, the influx mi-grated reaching the surface at 1030 hours for a migration rateof 1339 feet per hour.

Example 3 At the Santa Fe Energy Bilbrey4 (Figure 4),a 200-barrel kick was taken while on a trip at 14,080 feet,The density of the dispersed water base mud was 11.7 ppg,As shown in Figure 4, the top of the influx was at 8442 feet,The kick occurred at 1600 hours, The influx reached the sur-face at 1000 hours the following morning for an average mi-gration rate of approximately 47o feet per hour.

Calculations based upon the rate of pressure increase indi-cated the influx was initially moving at a rate of 290 feet perhour. Calculations based upon incremental pressure increasesnear the end resulted in the estimation that the influx wasmoving at a rate of 400 feet per hour.

Example 4 The ability to calculate influx behaviorbased upon changes in surface pressure has been the subject ofconsiderable debate. At a blowout near Abilene, Texas, theopportunity was presented to test these techniques as well asto observe the migration rate of the gas through water.

The wellbore schematic is presented as Figure 5. The wellwas controlled by pumping mud down the drillpipe. How-ever, the upper formations were supercharged during theblowout. During the kill operations, a hole developed in thedri llpipe at 980 feet. After any pumping operation, gas wouldenter the drillpipe and migrate to the surface.

On one occasion, afler pumping fresh water down thedrillpipe, the gas migrated to the surface in one hour and 15minutes for a migration rate of 784 feet per hour. On anotheroccasion, as the gas migrated, water was pumped in four 2-barrel increments and the resulting change in surface pressurewas noted. The volume of water was carefully measured inthe suction tank of a service company cement pump truck.

Us the 4-% inch drillpipe, two barrels of water represents142 feet of hydrostatic and 122 psi. On each occasion, thesurface pressure declined by 120 psi when two barrels werepumped. It should be noted that although the water beingpumped was incompressible, the other f luids in the wellborewere extremely compressible. The annulus contained somecombination of oil, gas, mud, water, and cement. Thedrillpipe below 980 feet contained water, cement, mud, andgas.

Lhample 5 The wellbore schematic for the next exam-ple is presented as Figure 6. As illustrated, 7 inch casing wasset at 2266 meters. After coring to a total depth of 2337 me-ters in 6 inch hole, a trip was commenced to retrieve the core.The gel polymer mud density was 10. I ppg, plastic viscosity14 centipoise, yield point 16 pounds force per 100 square feet,

and funnel viscosity of 40 seconds per liter. The drill stringwas pulled to 757 meters where a gain of 3 barrels was ob-served. The well was shut in with a total of six barrels gained.The shut-in drillpipe and shut-in casing pressure were equal at350 psi. The kelly was picked up, the choke opened, and thewell circulated. When the well was shut in the second time,the total gain was 1 I5 barrels and the shut-in drillpipe pres-sure and shut-in casing pressure were equal at 1350 psi,

it seems ironic that the influx did not migrate when the topof the influx was only 1335 meters from the surface in 10. Ippg mud. For three days attempts were made to lubricate mudinto the hole. However, the shut-in surface pressures re-mained stable at 1320 psi indicating that the influx was refus-ing to migrate.

During the next 24 hours, the drill str ing was stripped backto the bottom of the hole. A total of 7 barrels of gas was bledfrom the annulus during the stripping process. The remainderof the gas was at total depth and had to be circulated to thesurface.Summary and ConclusionsInflux migration is a complicated phenomena, As illustratedin these examples, the influx may or may not migrate. In mostinstances, i t can be anticipated that the influx wil l migrate andif i t does migrate, its rate can and usually will vary throughoutthe process. Normally, the migration rate will increase as theinflux approaches the surface.

[t can generally be anticipated that the surface pressure willincrease as the influx migrates toward the surface and the in-crease in surface pressure can be used to analyze the condi-tions in the wellbore. However, as illustrated in Example 1, itis possible that, depending on the geometry of the wellboreand the physical propert ies of the influx, the surface pressurecan actually decrease asthe influx migrates upward.

[n the examples presented, the highest rate of migrationwas 1339 feet per hour, which was observed in the wellboreinclined to 38 degrees. In the vertical wells, the highest mi-gration rate observed was 784 feet per hour in fresh water. Ontwo occasions, one in 17.4 ppg oil base mud and one in 10.7ppg water basemud, the influx did not migrate.

In the examples studied and presented, the surface pres-sures could be relied upon to predict influx behavior and mi-gration rate. [n all cases, well control personnel must relyupon the conditions at the well to make every effort to analyzeand model the condition of the well. This analysis and modelwill serve as the best effort to react to the conditions of theblowout and prevent further deterioration of the situation.Failure to do so can cause a serious well control problem tofurther deteriorate into a major disaster.References1. Rader, D. W., Bourgoyne, A. T. and Ward, R. H.,

Factors Affecting Bubble Rise Velocity of Gas Kicks,

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lADC/SPE 35119 R.D. GRACE 3

Journal of Petroleum Technology May 1975, pages 571-585,

2. Tarvin, J. A., et. at., Gas Rises Rapidly Through DrillingMud, IADC/SPE Drill ing Conference, February 1994.

3. Grace, R. D., ~, GulfPublishing Company, 1994.

4. Grace, R.D., Burton, Mike, and Cudd, Bob: Mud Lubri-cation - A Viable Alternative in Well Control,SPE/IADC Well Control Conference. 1995.

S1 Metric Conversion FactoraCp x 1. 0 E-03 = Pa. sft X 3.048 E-01 = mft x 9.290304 E-02 = m3ft3 x 2,831685 E-02 = m3in x 2,54* E+OO . cm

Convm to n fa ao f IS exact

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Ps -3.700 psi

65

Top of Liner at 13,9 eet

TD -

feet

E. N. ROSS No. 2Conditions after initial kick

Figure L624

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Ps -1.961 @

Top of Liner at 13,

TD

.

.928

-0,

;4FG) uD

/Top of fish at 18.046 feet7 5/8 inch Liner at 18,.245 feet

: End of fish at 19.140 feet

feet

E. N. Ross No. 2Bubble migrotion

Figure 2625

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,,ShuL in DrillplpeAPressure

= 840 PS1

End of S+_ring ~1887 met_ers

7 inch casing Q2610 met_ers

J-.cjMud11,2 ppg

Figure 3

h Shut_ In Laslng Pressure= 1040 PSI

~ 12 Barrel Gain

ToLal DePLh - 2777 meLersaL 38 degrees

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WELL BORE SCHEMATIC WITH IN FLUXSANTA FE ENERGYCO.BI LBREY 28-A FEDERAL NO. ILEA COUNTY NEW MEXICONOVEMBER 1989

FIGIJRE d .

BIT AT 1494

MuD DENSITYPm =II,7VGAL

FG .13.5*/GAL

TOC - 5500

J/9,XfSURFACE PRESSPt = 2700 PSI13 3/8 AT 626

9 5/0 AT 4650

MUD

TOP OF GAS INFLUXWITH 200 BBL GAINB422 GAS

L 7 AT 12,097DST 13,913Q= 10 m AT 5100 PSI FTPSIBHP =8442 PSI

II

TOTAL OEPTH 14,080

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Ho .e in(Q

Drlllplpe980 Feet

Bridge

8Q!

5/8720

T

inchFeeL

Cas

DePLh

lr lg

4583 feetFigure 5

628

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Shut- in DrlllplpePressure A= 1320 PS1

End of SLrlng757 met_ers

)(Mud101 ppg

Gas

k Shut In Casing Pressure 1320 PS1

TOP of Gas - 1335 mel_ers

115 Barrel Gain

7 Inch Q 2266 meters

ToLal DePLh - 2337 met_ers

lgure b

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