gc spe permian study group

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Successful Stimulation of Open Hole

Carbonate Formations

Using Coiled Tubing

A Presentation for the Gulf Coast

Permian Basin Study Group

Presented By:

Jeff Harris

BJ Services (Coiltech)

Midland, Texas

GETTING THE MOST FROM

HORIZONTAL OIL AND GASWELL ACID TREATMENTS

TECHNOLOGY

Why the titles? What¶s this to

do with acidizing HorizontalWells?

Too many CT jobs are performedthe same way they were done

³back when´

Our own in-

house survey

But first ...

How many of you

have had experiencesin stimulating HZ

wells?

Economically have

your Hz wells proven

to be ««.Good

Fairor Poor?

(be honest)

How were yourwells stimulated?

Did you know only40% of the Hz wells

drilled are likely to

become economicallyviable

Hopefully after thisdiscussion we can

increase our ³luck´

when stimulating Hz

wells!!!!

Part One

Some Simple

Basics

What does a simple

horizontal well look like?

A Basic Horizontal WellA horizontal well may be drilledA horizontal well may be drilled

into a gas or oil bearing strata,into a gas or oil bearing strata,

as well as being used for water, steam or miscibleas well as being used for water, steam or miscibleflood injection.flood injection.

Lateral Section

Build Section Fractures

A Basic Horizontal Well

50 to more than 1500 metres of lateral

section depending upon objectives«..

HeelToe

Target formation

150 to more than 5000 ft of lateral section

depending upon objectives...

Horizontal wellsare expensive to

drill andstimulate so why

horizontally?

The decision to drill a well

horizontally may depend uponmany factors

and can include

the necessity for greater exposure of

narrow target zones to the wellbore

a reduction of solids migration to thewellbore because of reduced drawdown

intersection of naturally occurring

vertical fractures

Part Two

Formation

Simply put the extremes of the

types of rock we drill into

for oil or gas are

a tight, low perm carbonate

a fractured carbonate with good

porosity and permeability

a sandstone

Consider

A very tight,

low perm/low porosity

carbonate reservoir

No upward folding to cause

stress fractures

Low Perm / Low Porosity

Carbonate Reservoir

(tombstone)

When there are No

fractures and low

permeability...« Matrix Acidizing has

ONLY VERY LIMITEDEFFECTIVENESS IF ANY!

Now Consider

a fractured carbonatereservoir with good

porosity and permeability

Carbonate Reservoir

The best example of this type of reservoir is

formed by an upward folding of the formation to

causes stress fractures

Horizontal wellsdrilled into this type of

formation areespecially suited to

squeezed matrix acidstimulation techniques

Carbonate

Reservoir

Fractures

Horizontal

Wellbore

Intersecting

Fractures

Vertical drill -

may not

intersect

fractures

³K ill the Geologist´

Finally «..

«.. sandstone reservoirs - a

topic for discussion on

another day!!!

Part Three

Formation Damage

(typically carbonate reservoirs)

Fact : Almost all horizontalwells are very susceptible to a

variety of formationdamaging mechanisms while

drilling.

Drilling damage acrossthe wellbore may look

like «.....

Drilling Damage

FracturePlugging Pore Plugging

Filter Cake

Shallow

MatrixDamage

Wellbore Crushing

Also possible damage

from rock polishing, aqueous

phase trapping, the use of poor fluid choices etc.

Drill fines may be as

small as 2 microns!!

Shallow Matrix

Damage

Wellbore

Crushing

Drilling damage alongthe wellbore may look

like ...«..

Drilling fluid

Overbalanced finesOverbalanced finesmigration into fracturesmigration into fractures

Open Hole SectionOpen Hole Section

Compressed Filter Cake -Compressed Filter Cake -considered to be 2 to 5 mm thickconsidered to be 2 to 5 mm thick

Drilling Fluid &

Cuttings

Loosely held fines

Formation damage one finds

restricting flow in vertical wellsmay also occur in horizontal

wells- for example

Fluid incompatibilities

Oil wetting the formation

Anhydrite or soft rock smearing

Sulphur deposition in high H2S wells

Horizontal Well Drilling DamageHorizontal Well Drilling Damage

The heaviest damage is to be expected at the heelThe heaviest damage is to be expected at the heel

Part Four

Designing Horizontal

Well Acid StimulationPrograms

Horizontal well stimulationprogram design requires

intercompany teamwork!

Geologists, reservoir engineers, mud

engineers, technologists, laboratory

and specialised service company staff all have a role in designing the best

stimulation program possible

Before recommending any

stimulation treatment wecarefully carryout many

tests and observations.

Well data

Geology reports

Drill cuttings

Drilling mud

Stimulation Program

Acid solubility

Service Company

Experience

Target zones

Drill Bit

Fractures

Well fluids

Stimulation

package design

Computer modelling

SEM analysis

Drilling reports

losses

Other information

Core flow studies

porosityGas shows

Hz Well Stimulation ProgramPossibilities

Fracturing

Enzyme Squeeze Treatments

Acidizing

Oil or Water Based Fluids

Carbonate

SandstoneOther specialised treatments

Roto-Jet

Assuming the drilling fluids

have been designed to beacid compatible «...

«.. then acid is the best stimulation

media for removing drill fines, drill

cuttings, filter cake, crushed and

polished rock, and acid soluble LCM

both around the near wellbore and

into any extending fractures

But how do we conveythe acid to the damaged

areas of the wellbore andformation, as well as

squeezing acid into thefractures?

By ««...

Bullheading aciddown tubing - NO,

NO, NO!!!

Why? Because acid

will go where IT wantsto go - not where YOU

want it to go. THERESULT

Oh No!Oh No!

Not Another Water Well!Not Another Water Well!

I should have listened toI should have listened to

Jeff Jeff

By ««...

Bullheading acid down tubing

using diverting agents (wax

beads, benzoic acid, salt) -NO!!!

Pumping acid down productiontubing placed at various depths

along the lateral section - NO!!!

By ««...

Pumping acid down a work

string RIH to the toe while

pumping acid down thebackside of the workstring

hoping to palce acid all alongthe OH lateral - NO!!!

By ««...

Pumping acid down a work

string RIH to the toe with holes

along the length of the lateralhoping to obtain limited entry -

I don¶t think so!!!!

Why? Because acid

will go where IT wantsto go - not where YOU

want it to go. THERESULT

Oh No!Oh No!

The acid still wentThe acid still went

where it wanted to gowhere it wanted to go

Then How?????

I know of a couple of methods

that have worked for me.

Let¶s talk about them -

The first tool I was given for OH

acidizing was a rotating jetting

This tool rotates 360° at a

controlled speed, induces cyclic

stress on the drilling damage anddevelops high impact pressure.

The tool was developed for

removing hard scales, but I thought

³what a great acidizing tool this

could be for open hole´

The first jobs went great - well productivity

increased as much as 7 fold. That promptedan SPE paper (SPE 54467).

The first candidates were deeper

wells that had fairly high BHTand the acid reacted almost

instantly as the tool was runalong the length of the OH.

Then someone read the SPE

paper and wanted to use the tool

and procedure on a San Andres

open hole horizontal!!

Since the San Andres doesn¶t have a

very high BHT, the customer wanted some type of diversion to

insure that the acid went where he

wanted it to go!

I suggested a method that had

worked for me over the years

FOAMFOAM

But wait a minute ««..

Foam as a diverting agent!

Surely it¶s only good forshaving!!!

Not so!

A 75% quality foam willprovide a thick, viscous, non-

damaging fluid media that is a

useful diverting agent in both

vertical and Hz wells

Obviously the foam must beacid compatible «..

«.. such foams are able

to divert acid very

effectively

So the

customer said³OK, let¶s try

But I want to be sure this FoamTechnology is working «...

I want to use isotope tracers in the

acid stages´.

Sounded like a good idea to me«..

another trip into the hole$

After stimulating and logging

four wells, using tagged acid

stages and foam diversion

stages«.

It was confirmed that the acid

went where he wanted it togo!!!!

The following illustration is the

basic procedure used on those

four wells

Over time there have been

variations of this procedureused to ³fit the purpose´

Foam Diverted Acid Squeeze

1. Coil tubing is RIH to the toe and the

wellbore is cleaned underbalanced at a

designed penetration speed to get 360°/nozzle

coverage with the rotating jetting tool

Foam Diverted Acid Squeeze

2. Circulation continues until returns are clean

3. Foam is pumped to the BHA

Foam Diverted Acid Squeezing

4. The OH is filled with foam

- it is not necessary to fill the well completely

with foam

5. Close in the well, start PUH and

acidizing by pumping calculated volumes

of acid and foam stages

6. Continue pumping acid and foam stages

along the target intervals of the open hole

until desired acid coverage is achieved

7. Flush CT and OH (gas lift if desired)

Are the results always as good

as the examples in the SPEPaper?

As far as increasing

productivity«.

The answer is«.not always«.

There is an additional benefit that

has made using the rotating jetting

tool and foam diverted acid squeeze

stimulations beneficial«.

Less acid/foot«.A lot less acid/foot«.

7 to 10 gal/ft has produced the sameresults as the 35 to 50 gal/ft used with

other methods.

The San Andres wells we have

stimulated in the last 3-4 yearshave had laterals >5000 ft long

With 1.75´ coiled tubing and the 1.75´

tool, pumping rates <1.5 bpm meant long

job times«. some over 40 hours.

Our customers (field personnel) weren¶ttoo crazy about sitting on these jobs for

hours and hours and «. So «.

We were ask if there was some

way to cut the job time!!!!

We requested a larger

rotating tool and got it«.plus larger coiled tubing

and equipment.

Now we were able to pump 3 -

3.5 bpm and the job time was cutin half«.18 to 20 hours«.field

personnel happier but still not

that happy!

I had heard about a new self-

diverting acid system that was inhigh demand in Saudi - So I

looked into it - a year or so later!

This is what I learned about the

self -diverting acid system Single Surfactant System

Stimulates and diverts in a single stage - design and

operation less complicated Break mechanisms: hydrocarbon, water, internal

breaker and system also breaks on spending of acid

Matrix Acidizing Applications Are Delayed Viscosifying System

Self Diverting Acid

Viscosified Diverted Acid

Staged Acid

Application

For carbonate and sandstone acidizing

Acid Type - HCl, HF

Surfactant added to acid

Concentration range - 40-80 gpt in acid

HCL concentration range - 20-28%

Internal breaker recommended for - Wells with no Oil/Condensate- Wells with no Formation Water Production

Application

Incompatible - some mutual solvents,

surfactants, corrosion inhibitors

Temperature stable to 275ºF

Surfactant type - amphoteric, worm-like

micelle

Wettability - water wets limestone

The next slide is a graph thathelped me understand how the

system worked.

I also sent this information to the customer

(Production Eng and Field Forman) and

pointed out that we could cut job time even

more«.It wasn¶t a hard sell!!

Viscosity of Spent Acid vs. calculated %HCL concentration

28% HCL initially -- Ambient Temperature and 150F

0 5 10 15 20 25 30

%HCL (calculated)

V i s c o s i t y ( c P ) @ 1

7 s e c - 1

Divert S 75F

Divert S with CI-25

Divert S 150F

2-Dec-05 REVISION DATE GIVEN REQUIRED

REVISED by J. Harris PUMP PUMP COILCOIL INTERVAL RATE RATE TIME SPEED

STEP DIRECTION FT FT FT FLUID GALLON BBL BPM SCFM MIN FPM

1 DOWN 0 5023 5023 WATER 1,055 25.1 0.25 0 100.5 50.0

2 DOWN 5023 6400 1377 WATER 723 17.2 0.25 0 68.9 20.0

3 DOWN 6400 8088 1688 WATER 20,103 478.6 3.5 0 112.5 15.0

4 UP 8088 7700 388 Load Hole w/Acid 1,680 40.0 3.5 0 11.4 34.0

Close CT Annulus

5 UP 7700 7200 500 ACID 3,500 83.3 3.5 0 23.8 21.0

6 UP 7200 7000 200 Do Not Pump 0 0.0 0 0 9.5 21.0

7 UP 7000 6400 600 ACID 4,200 100.0 3.5 0 28.6 21.0

8 UP 6400 5023 WATER Flush * 6,476 154.2 3.5 0 44.1

* Do not wash at high rate via nozzel or acidize across

the curve

TOTALS Total fluid pumped 37,736 Total time (mins) 399.2

Gallons of Acid 10,000 9,380 Total time (hrs) 6.7

Gallons of water 28,356 Acid Pump time (hrs) 63.8

BBL of water 675

NOTE: 10,000 gal of Acid to contain 2 drums of Low PH Scale Inhibitor.

The first well was a Terry County

producer with a 4 3/4´ OHlateral. MTD was 8088 ft.

Pump Schedule

Th lt f th S lf Di ti

The results of the Self -Diverting

Acid System are impressive«.

The field is ~30 years old and average

oil production is 10 -12 BOPD

After the well was put on production

the oil was up to 40 BOPD

At the end of one month it was

45BOPD

Last week it was producing 50 BOPD

Th d ll T C t

4-Jan-06 REVISION DATE GIVEN REQUIRED

REVISED by J. Harris PUMP COIL

COIL RATE Acid TIME SPEED

STEP DIRECTION FT FT FT FLUID GALLON BBL BPM Gal/ft MIN FPM

1 DOWN 0 5288 5288 WATER 1,110 26.4 0.25 0 105.8 50.0

2 DOWN 5288 5737 449 WATER 236 5.6 0.25 0 22.5 20.0

3 DOWN 5737 8716 2979 WATER 35,179 837.6 3 0 248.3 12.0

4 UP 8716 8696 20 Load w/Acid 1,050 25.0 3 0 8.3 2.4

Close CT Annulus5 UP 8696 8440 256 ACID 770 18.3 3 3 6.1 41.9

6 UP 8440 8360 80 ACID 400 9.5 3 5 3.8 21.0

7 UP 8360 8280 80 ACID 240 5.7 3 3 1.9 42.0

8 UP 8280 7830 450 ACID 2,700 64.3 3 6 21.4 21.0

9 UP 7830 7670 160 ACID 800 19.0 3 5 6.3 25.2

10 UP 7670 7410 260 ACID 1,040 24.8 3 4 8.3 31.5

11 UP 7410 7010 400 ACID 2,400 57.1 3 6 19.0 21.0

12 UP 7010 6880 130 ACID 520 12.4 3 4 4.1 31.5

13 UP 6880 6130 750 ACID 5,250 125.0 3 7 41.7 18.0

14 UP 6130 6030 100 ACID 600 14.3 3 6 4.8 21.015 UP 6030 5860 170 ACID 850 20.2 3 5 6.7 25.2

16 UP 5860 5288 572 WATER Flush * 10,500 250.0 3 0 83.3 25.0

* Do not wash at high rate via nozzel or acidize across

the curve

TOTALS Total fluid pumped 63,645 Total time (mins) 592.3

Total Acid 17,250 Total time (hrs) 9.9

Gallons of water 46,395 Acid Pump time (hrs) 2.3

BBL of water 1,105

NOTE: 17,250 gal of Acid to contain 5 drums of Low pH Scale Inhibitor

INTERVAL

The second well was a Terry County

Water Injection Well

The post- job injection rates are

the same as pre- job rates«. but injection pressures were

30% less

This well is a multi-lateral and this

was the last lateral to be

stimulated.

Other Case Results

East Texas - self diverting acid stages

between acid stages down 2 3/8´ Tbg.

Pre-job production - 0 MCFD Post-job production - 1500 MCFD

Saudi - Hz Injection Well - the diverting

stages were foamed-the surfactant wasused to stabilize the foam (SPE 93536)

Pre-job injection - 17,000 BWD @ 1643 psi

Post-job injection - 77,000 BWD @ 1180 psi

One More Case Result

Saudi - Hz Oil Producer - Acid stages

using diverting acid stages between.

(SPE 94044) Post job results - Production increase of

76,000 BOPD.

Thank you allfor coming today

Any questions? AnyHz OH wells you

gc spe permian study group

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