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Proactive breakthrough prevention

I m p r o v i n g o p e n h o l e co m p l e t io n s w i t h i n f l o w c o n t r o l d e v ic es a n d s w e l la b l e zo n a l

i so l a t io n c a n b e t h e m e a n s t o a v o id i n g p r o b l em s a ss o ci a t e d w i t h e a r l y w a t e r a n d

g a s b r e a k t h r o u g h a n d r e s u l t i n g r e d u c e d o i l p r o d u c t io n .

Drilling horizontal wells was a significant

step for the oil industry. Even though thecomplexity and cost of drilling rose,

economic returns to the operator rose as

 well.

Horizontal drilling meant increased

production by maximizing the reservoir

contact, and it meant drilling fewer wells

than with vertical drilling. Horizontal wells

also enabled reserves to be produced from

zones previously thought too difficult to reach, such as thin oil zones. And horizontal wells helped avoid

drawdown-related problems associatedwith vertical wells, such as water and gas coning.

 Although horizontal completion technology and techniques improved over the years, horizontal wells continue to

face challenges related to uneven influx of reservoir fluid to the well bore, which results in early water and gas

 breakthrough. While some operators and regions can hold these problems to a manageable level, for others it

substantially lowers overall productivity.

Most oil companies are familiar with the problems associated with early water and gas breakthrough. In the worst

cases, the well has to be abandoned and valuable reserves left in the ground. Water and gas coning in the heel is

often blamed for this. While this may be true for high-rate, long horizontal wells with low drawdown, coning in

the heel may not be the only reason for early breakthrough.

For example, in homogenous formations with minor differences in permeability along the well bore, pressure

Article By Geirmund Saetre, Halliburton

Published Jan 5, 2009

Heterogeneous reservoir without inflow control evidences early water and gas

 breakthrough. (Images courtesy of Halliburton)

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drop from heel to toe inside the tubing can lead to uneven drawdown across the well bore. The drawdown can be

higher in the heel and eventually lead to a breakthrough of water and gas.

 Another reason for water and gas breakthrough is related to uneven permeability and fractures or differences in

fluid mobility, which occurs in wells with high-viscosity oil. Since it becomes easier for the reservoir fluid to be

produced through one section compared to the other, having an even drawdown under conditions of uneven

permeability or uneven fluid mobility can lead to premature breakthrough of water or gas.

Seeking solutions

One common way to handle these conditions is to wait until they occur. But by then it may be too late, and costly

intervention operations may not give the desired results.

The most effective way to solve the problem is to manage it at its origin — in the reservoir before the fluid enters

the well bore.

In relatively homogenous reservoirs with higher drawdown in the heel, one solution is to balance the drawdown

from heel to toe. This can be done by applying a controlled pressure drop from the annulus to the production pipe

in the heel using inflow control devices (ICD), which in turn reduces the drawdown and the fluid rate from this

particular section.

In a heterogeneous reservoir, where the drawdown is more equally distributed along the well bore, the drawdown

should be reduced in high-permeability sections to allow low-productivity sections to flow more oil. Today it is

 becoming common practice to achieve this equal distribution through the use of ICDs.

 While using ICD technology may have a positive impact on initial overall production, the main benefit is to delay

potential water or gas breakthroughs and allow more oil to be produced throughout the life of the well. Imagine,

for example, the improvement in field economics that would follow if water and gas breakthroughs could be

delayed two or three years.

The EquiFlow ICD creates a controlled pressure drop across the production tubing and is an integral part of the

completion string. The pressure drop is achieved by directing flow through a set of tubes inside the ICD. This

device can be combined with screen technology if sand control is needed. In addition, the ICD does not require

additional installation time.

Determining placement, number of units, and configuration of the ICDs has traditionally been done using

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numerical, steady-state near-wellbore software. This is a quick and effective method to run multiple scenarios

and completion configurations to quantify the benefit of the ICD.

Since steady-state software does not offer the capability to investigate the long-term effects of the ICD on the

reservoir, Halliburton has linked its QuikLook reservoir simulator with the AGR NETool nodal analysis package.

This software package makes it possible to investigate the long-term effects of an EquiFlow ICD completion on

the reservoir and its production performance, including recovery factor, cumulative production, and time to

 water/gas breakthrough.

If the formation is competent and stable, openhole completions can often increase reservoir contact and reduce

completion cost. An important factor for a successful openhole completion is reliable zonal isolation. With the

introduction of Halliburton’s Swellpacker isolation system, this is now possible.

The Swellpacker system is based on elastomers that swell and expand in contact with oil or water to seal off the

annulus. With nearly 14,000 Swellpacker systems installed by over 175 operators, they are now considered

standard completion equipment.

Zonal isolation enables breaking down the reservoir into fewer sections, and when combined with ICDs, provides

an incremental flow control down to every basepipe joint.

 When using zonal isolation to its full potential, operators achieve more than just isolation; they have an effective

 way to manage the reservoir flow and increase recovery.

Putting the technology to work

 An operator had completed several wells in a block and experienced high water cut with some of the early

openhole completions. Experience had shown that several large fractured zones connected to an aquifer. While

the completion had recently been improved by isolating unwanted fractures, it was believed oil production could

 be further improved.

The planned well was modelled to design the configuration and placement of the EquiFlow completion system.

Data from offset wells were used for the modelling exercise.

 After the well was drilled, logging-while-drilling (LWD) data provided updated well information and helped

identify highly fractured zones. The LWD data also helped verify the pre-modelled assumptions and allowed for

optimum placement of the EquiFlow ICD and openhole packers. The highly fractured zones were blanked off, as

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they were prone to produce high water cut.

Installation of the ICD/packer system together was successful. Acid stimulation was performed through the

EquiFlow ICD modules, which improved the fluid injection profile to help ensure even placement of the acid and

help avoid pumping most of the fluid into high-permeability zones or fractures. Injectivity improved while

acidizing, as indicated by a decrease in injection pressure, suggesting that the well was successfully stimulated.

 A significant drop in water cut was observed a few days after the well was put on production, which indicates the

fractures were successfully isolated as planned. Two more wells were completed with the EquiFlow ICD and

Swellpacker system and are producing with water cuts well below the field average.

 While horizontal drilling helps mitigate some of the challenges associated with water and gas coning in vertical

 wells, today’s operators continue to seek ways to improve recovery of their reserves. Actively applying inflow

control technology and zonal isolation systems allows operators to manage the reservoir flow and maximize the

 value of their horizontal wells.

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