Combined matrixstimulation andscale inhibition

ScaleMAT

Scale deposition is a persistent problemover the economic life of producing wells.Protecting wells from scale depositionis commonly accomplished by squeez-ing scale inhibitors in the near-wellborematrix, a process that frequently requireswells to be shut in. Every effort to reducethe required number of inhibitor squeezetreatments is essential to achieve signifi-cant overall cost reduction and maintainwell productivity.

Through the use of a new acid-com-patible scale inhibitor, the ScaleMAT*service integrates both matrix stimula-tion and scale inhibition in a singletreatment. By enabling the producer toplace a scale inhibition treatment at thesame time as a matrix stimulation treat-ment, at least one subsequent inhibitorsqueeze treatment is eliminated witheach matrix stimulation treatment.

In addition to a cost reductionadvantage, use of the ScaleMAT serviceresults in improved and efficient place-ment of the scale inhibitor: (1) effectiveplacement of the inhibitor, directlyprotecting the stimulated matrix, and(2) improved coverage of the completedinterval, as part of a properly divertedacid treatment (scale-squeeze treat-ments are commonly bullheaded).

The following features of the ScaleMATscale inhibitor are the result of innova-tive chemistry. Calcium tolerant, offering full

compatibility with the most commonmatrix stimulation fluid systemsfor both sandstone and carbonatereservoirs. This includes acids,chelating agents, and organic systems.

Tolerant to high levels of ferric ironcontamination, offering a robuststability under typical field conditions

Effective inhibition of commoncarbonate and sulfate scales

Polymer-based chemistry, offeringsuperior inhibitor retention efficiency

Applicable at bottomhole tempera-tures up to 350F

The combined treatment is illustratedabove. When formation damage, includ-ing mineral scale deposition, completelyplugs the flow path of oil or gas in thepore space, an acid or a scale-dissolvertreatment is used to remove the damageand restore productivity. The ScaleMATservice not only dissolves away thedamage, but also places an effective

scale inhibitor coating at the sametime, while the rest of the stimulationfluids are flowed back at the end ofthe treatment. This ensures long-termprotection of the stimulated matrixat a much-reduced cost compared toperforming a separate subsequentscale inhibitor squeeze treatment.

The ScaleMAT engineering serviceoffers candidate selection, treatmentdesign, treatment placement, and post-treatment monitoring of the productiondecline and the inhibitor return in theproduced water. The post-treatmentmonitoring ensures that the treatedwell remains protected from scalingand provides timely signals of protec-tion loss so the well can be retreated.The stimulation/inhibition treatmentpackage can also be customized tosuit individual well conditions.

ApplicationsMatrix stimulation in carbon-

ate and sandstone formations

Dissolution and inhibitionof common carbonate andsulfate scales

Benefits Significant cost reduction

from minimizing the numberof interventions

Maximized workoverefficiency by minimizing theshut-in time and the deferredproduction

Effective scale inhibitorplacement, directly protectingthe stimulated matrix

Improved coverage of thecompleted interval withthe scale inhibitor as partof a properly diverted matrixstimulation treatment

Features Scale inhibitor fully compati-

ble with sandstone andcarbonate stimulationfluid systems

Applicable at bottomholetemperatures up to 350F.

Tolerant of calcium as wellas high levels of ferric ironcontamination

Customizable packaging ofthe appropriate matrix simu-lation fluid with the inhibitor

ScaleAcidScale inhibitor

Dissolving away the damage and protectingthe stimulated matrix in a single treatment.

A significant number of core flow testswere conducted to ensure superiorcompatibility of the new scale inhibitorwith most of the carbonate and sand-stone stimulation fluid systems.

Scale and other damage pluggingthe pore space.

Combined acid stimulation andscale inhibitor package.

The acid is produced back afterremoving the damage; the inhibitorstays to protect.

First case historyWhen a gas well in the Gulf of Mexicorapidly lost productivity in the first5 months of production, fines migrationwas pinpointed as the main cause.A mud acid treatment was performedthat, initially, succeeded in restoringthe well's production. However, a rapiddecline was experienced, and the wellquickly lost more than 50% of its pro-ductivity for the second time.Subsequent damage analysis indicateda calcium-carbonate scaling tendencyin the produced water in addition tothe previously diagnosed fines migra-tion damage. A ScaleMAT treatmentwas designed that combined mud acidto dissolve the fines, hydrochloric acid(HCl) to dissolve the calcium carbonatescale, and simultaneous placement of ascale inhibitor for long-term protectionfrom scale deposition.

After the treatment doubled produc-tion, the producing company allowed2 months for the treatment evaluation,producing only from the stimulatedinterval. Then, an upper interval inthe same well was completed, andproduction from the two intervalswas commingled. Over the 2-monthperiod, the production decline wascarefully monitored and evaluated,which concluded a much slowerdecline than before the ScaleMATtreatment. This indicated that scalewas indeed a cause of the unexpectedproduction decline after the first acidtreatment, and that the ScaleMAT treat-ment effectively inhibited scale deposition.

Water production did not increaseupon production commingling, con-firming that all the produced waterstill originated from the stimulatedinterval. In 10 months of production,the inhibitor successfully treated morethan 125,000 bbl of produced water.

Cumulativewater

(1,000 bbl)

SIconcentration

(ppm)

Jan Feb Mar Apr May June July Aug Sep Oct1

10

100

1,000

1

10

100

1,000

MIC = 5 ppm

SI concentration Cumulative water

0

200

400

600

800

0

5

10

15

20

Gas(Mscf/D)

Water(B/D)

Jan Feb Mar Apr May June July Aug Sep Oct

ScaleMATtreatment

Acid treatmentNo scale inhibition

Gas Water

Much slower production decline after the ScaleMAT treatment.

Inhibitor return profile indicating long-term protection from scale redeposition.

ST_04_001_0 Schlumberger

January 2004 *Mark of Schlumberger

www.slb.com/oilfield

Second case historyWhen oil production decreased by50% in a Gulf of Mexico well in less than4 months, loss of production was readilyattributed to two types of formationdamage: fines migration and mineral-scale deposition. Upon collection andanalysis of produced water samples,a calcium carbonate scaling tendencywas identified. A combined mud-acidand HCl treatment was designed toremove the fines damage and dissolvethe scale deposit. In addition, a subse-quent scale inhibitor squeeze treatmentwas planned to provide long-term pro-tection of the near-wellbore matrix.

A ScaleMAT treatment that combinedall objectives in a single treatment wasproposed as an alternative. By placingthe inhibitor as part of the diverted acidtreatment instead of through a nondi-verted inhibitor squeeze, the ScaleMATservice improved coverage of thecompleted interval, and the stimulatedmatrix received direct protection.The acid-compatible scale inhibitorwas mixed in the acid and pumpedthroughout the treatment. The retentionefficiency of the scale inhibitor isenhanced when mixed in acid, so only4 hr of shut-in time were enough, asopposed to up to 12 hr of shut in timethat would be needed for a separatescale inhibitor squeeze. The well wasback on production in less than 6 hrafter the treatment was pumped.

Following the ScaleMAT treatment,oil production was restored to 90% ofthe initial well production, and the wellperformance was monitored to evaluatethe long-term production decline. Overa period of 10 months, the ScaleMATtreatment not only successfully restoredproduction, but also prevented furtherscale deposition. This was confirmedby the much slower post-treatment pro-duction decline. A total produced watervolume of 91,000 bbl was effectivelytreated.

Scaleinhibitor

concentration(ppm)

Cumulativewater

(1,000 bbl)

1

10

100

1,000

1

10

100

1,000

MIC = 5 ppm

SI concentrationCumulative water

Jan Feb Mar Apr May June July Aug Sep Oct

Jan Feb Mar Apr May June July Aug Sep Oct

Waterproduction

(B/D)

Oilproduction

(B/D)

0

20

40

60

80

100

0

300

600

900

1,200

1,500

Steady slower decline afterScaleMAT treatment

Rapid declinewith scale deposition

ScaleMAT treatment

Oil Water

Production restored. Much slower production decline is indicated here.

Inhibitor return profile indicating long-term protection from scale redeposition.