Stripfing T1 Relief Well Planning

Contingency Relief Well Planning

& Dynamic Kill Modeling

Well: Stripfing T1 Well

Version: 1.0

Prepared by: Date _______________________________ _________________ Khaled Abdelaal

OMV E&P – Austria

Stripfing T1 Well Contingency Relief Well Planning

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Relief Well Planning

The Stripfing T1 (STRI T1) is an exploration deep gas well which will be drilled vertically to 5105m

depth. The well will penetrate the Hauptdolomite primary reservoir at 4250m MD. The Jurassic formation

will be penetrated at ~ 3600m which considered being abnormal pressure zone. The Jurassic zone will be

drilled within the 12 ¼” Hole using RSS assembly with 1.71 SG mud weight where the maximum

expected formation pressure will be 1.65 SG.

For simplicity, the blowout depth (target intercept) is assumed to be at 3600m MD; which expected to

be the over-pressurized Jurassic zone. The casing program for the relief well will be similar like

Stripfing T1 well. A 9 5/8” casing will be set at (80 – 100) m above the target intercept depth to

maximize the anticipated fracture gradient at casing seat for the subsequent dynamic killing operation.

The planned relief well is aligned with the Stripfing T1 (Target well) at an incident angle of 6˚ for

eventual intersect, rather than aiming directly at the blowout wellbore. This will provide the best chance

of success for a first-attempt intersects & facilities milling operations if required. It also allows steering of

the bit for a repeated attempt instead of plug-back and sidetrack.

Two different basic relief well designs were chosen using two possible relief well locations. The Two

well paths were created and checked in terms of Anti-collision with neighbor wells and found to be fine:

- Relief Well 1: 5355284 m N ; 34355 m E.

- Relief Well 2: 5355420 m N ; 34110 m E

Due to the number of wells that may be drilled and produced in the future in the field, determining an

appropriate relief well surface location during an actual event may be a significant challenge (needs to be

confirmed with Geologists). The required materials for drilling the relief well such as wellheads,

casing,....etc were considered for the relief well as if it ever becomes necessary to do so.

The magnetic ranging tool relies on measuring the magnetic pattern generated by induced current in a

steel object, and thus can only function when there is casing or drill string at the intercept point. The

worst condition would be a long open-hole section with no presence of drill string or fish. The closest

intercept to the blowout formation in this case would be limited to the deepest casing or liner shoe. This

would require an off-bottom dynamic kill, which can be difficult to design. In our relief well it is assumed

to have a BHA in the open hole;

The table below summarizes all possible scenarios & ranging options:

Target well

accessible from

surface

Casing or drill

string present at

interception point

Passive

ranging

possible

Active

ranging

possible

1 Y Y Y Y

2 Y N N Y

3 N Y Y N

4 N N N N


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Passive ranging is the easiest solution as it does not require extra equipment besides a normal MWD

(while drilling relief well) and RADAR software to interpret the readings as we approach the offset well.

The good survey accuracy of the target well is crucial as it will reduce the attempts to intercept it. If there

are offset wells nearby such to affect the magnetic pole strength active ranging may be a better option; it

will depends on the number of surrounding wells which already known specifically surrounding, their

position accuracy and if they are cased; as a rule of thumb MWD can detect magnetic disturbance within

15m approximately).

Active ranging is required when there is no other magnetic source in the target well (open hole for

example) and therefore we need to put one by running a magnet with wireline, plus we need a sub in the

BHA while drilling the relief well. This requires the target well to be accessible from surface which may

not be the case if there is a blowout ongoing. If there is no magnetic source (casing/fish) and no access to

surface (case 4) we can’t do magnetic ranging either passive or active and we need to move the

interception point higher up where we have the casing.

In the event of an actual well control emergency where a relief well would become necessary, the blowout

rate estimations, relief well plan, and dynamic kill design would be specifically tailored to the actual

wellbore geometry and directional plan, exit path(s) and any possible restriction(s).


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Relief Wells Summary

- The design for relief well 1 is based on Fly-by intercept concept, a 3D shape that consists of

four phases: drill, locate, ranging, tracking and intercept. This profile has less probability of

missing the target well.

- The design for relief well 2 is based on Direct intercept concept, a 2D “J“ shape that consist of

two phases: drill, locate.

Required Equipment

Below is a list of standard equipment & materials typically required for relief well operations:

- 2 x 8 ½” Concave Type Mills

- 2 x 6 ¾” Bent Housing Adjustable Mud Motors or RSS

- 2 x MWD

- Appropriately Sized Monels

- 2 x Appropriate Sized Floats

- Gyro

- Ditch Magnets

Item Relief Well 1 Relief Well 2

Surface Location5355284 m N

34355 m E

5355420 m N

34110 m E

Casing Program

18 5/8" @ 850m MD

13 3/8" @ 3050m MD

9 5/8" @ 3620m MD

18 5/8" @ 850m MD

13 3/8" @ 3073m MD

9 5/8" @ 3582m MD

Intercept Point 3678m MD / 3600m TVD 3710m MD / 3600m TVD

Expected LOT @ 9 5/8" casing 2.08 SG EMW 2.01 SG EMW

Kill Mud Weight

Concept Fly-by intercept Direct intercept

Kickoff depth 2200m MD 1600m MD

Hold Angle 26.3˚ inclination 19.5˚ inclination

Drop point depth 3084m MD -

Build / drop rate 2.0˚ / 30m 2.0˚ / 30m

Depending on the maximum anticipated formation pressure


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FIG 1: Pore & Fracture Gradient


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FIG 2: Potential Relief Well locations


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FIG 3: Relief Well 1 (Directional Plot)


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FIG 4: Relief Well 2 (Directional Plot)


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Dynamic Kill Modeling

There is no software available in the Gänserndorf - drilling department to perform the dynamic kill

modeling which provides the critical information such as blow out rate, kill mud weight, kill mud volume,

kill pump rate, maximum pump pressure and hydraulic horsepower required. These outputs can then be

used to review the availability of equipment and services as part of contingency planning. The OLGA

Advanced Blowout Control (ABC) simulator is the latest advanced generation tool developed by

Scandpower’s SPT Group can be used to perform such calculations.

Two different blowout scenarios could be simulated for the Stripfing T1 well:

- An uncontrolled & unrestricted flow at surface through the 13 3/8” casing at 3000m TVD through

the 12 ¼” open-hole interval at 3600m TVD with no drill-string in the wellbore

- An uncontrolled & unrestricted flow at surface through the 13 3/8” casing at 3000m TVD through

the 12 ¼” open-hole interval at 3600m TVD with drill-string in the wellbore

The output from the OLGA software can be represented in a table below:

Case Flow Rate

(MMSCF/D)

Kill Rate

(bpm)

Kill Vol

(bbls)

Pressure

(psi) HHP

No Drill-string

Drill-string on Bottom

Remarks:

- There is high probability that formation collapse and a corresponding bridging over of the

produced solids, would occur during a blowout. Any solids that would be produced will be

moving at moderate velocity once in the wellbore and will most likely not be able to be ejected

causing a pile up of solids which in theory could slow or plug the blowout.

- It is recommended to have at least 5 to 7 wellbore volumes available for a dynamic kill operation

with a direct relief well intersection. Additional volume may be required if a direct intersect is not

possible. The potential delivery of such large volumes of kill fluid in a short duration can pose

substantial challenges to a kill operation.

- In addition, building, transporting, and conditioning this mud volume until it is ready for the kill

operation will be a massive undertaking in an actual event. Significant planning will be required

to determine how to best solve this problem.

- Off-bottom kill: depending on the actual distance of the intersect above the blowout zone, the

required pump rate, kill mud weight and equivalent circulating density (ECD) for an off-bottom

kill will all be significantly higher than for a kill on bottom. For example, kill mud weight and

ECD can both exceed formation fracture gradient in open hole, resulting in massive losses. If

identified by simulation runs during the planning phase for the original target well, this problem

may be addressed by running a deeper or additional string of casing or liner. Otherwise, options

may be very limited if a blowout occurs.


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- Dual relief wells; A very prolific reservoir, off-bottom kill and high formation pressure, or a

combination of these, can form a scenario in which pump rate and pressures exceed the ratings of

normally available equipment. One option is to conduct the kill operation through two separate

intersections by two relief wells, which cuts the pump rate per well by half and should reduce

pump pressure by about 70%. It may not be possible to synchronize simultaneous intersects, so

continuous pumping of sea water or mud will be necessary after the first intersect to maintain

control until the second intersect is made. At that point, kill mud can be pumped through both

wells.

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Stripfing T1 Relief Well Planning