DEPARTMENT OF PETROLEUM ENGINEERINGINDIAN SCHOOL OF MINES, DHANBAD

 WATER AND GAS CONING:

MODELLING AND SOLUTIONS

 Prof. A.K. Pathak     Department of Petroleum Engineering ISM Dhanbad  

Shubham Saxena2012JE1152B.Tech. Petroleum EngineeringISM Dhanbad

Water Coning and Gas ConingEncroachment of gas from the gas cap and water from the water aquifer into the oil producing zone.

The previously defined Water-Oil Contact (WOC) and Gas-Oil Contact (GOC) now become deformed from its plane shape to form a cone or a crest.

GOC

WOC

Effects•Reduction in oil production rate.Water and gas have much higher mobility than oil

•Corrosion of production facilities•Loss of gas cap drive•Loss in water drive

•There is expense to lift, dispose or re-inject produced waters, as well as the capital investment in surface facility construction and to address other environmental concerns.

•Unwanted production of water estimated to cost the petroleum industry about $45 billion a year.

Payzone and water coning with time

1. Perforation Squeeze-off and Re-completion High permeable layers in contact with the water zone are often times responsible for the high water influx.These could be isolated by cement squeeze operation below the perforated zone or cementing water producing perforated zones.

In some cases, an entire perforation is completely squeezed off and the well is re-completed higher up the structure away from the oil-water-contact (OWC).

Cement squeeze operation may not be feasible or effective if adequate zonal isolation is not possible due to absence of shale barrier streaks.

These are injected into the formation, if the production of unwanted water is traceable to fracture paths.

Selective relative permeability modifier that is capable of reducing relative permeability to water without affecting relative permeability to the oil and/or gel treatment.

Typically cross linked polymers, products like MaraSEAL and OrganoSEAL-R systems can be easily mixed and have a long working life.

2. Use of Chemicals, Polymers and Sealants

3. Water Coning Control with Dual Completions in Vertical Wells

In a dual completion string  we separately produce the oil and water zones and thus counter the cone developmentTwo perforations – one in the oil zone& one in the water zone below the original oil-water contact.

The top completion is placed as high as possible, within the top 20 percent of the oil zone and the second perforation placed at some depth below the oil water contact.

DWS technology controls water coning by employing a hydrodynamic mechanism of water drainage  in-situ below the well’s completion.  This localized drainage is generated by a second completion - downhole water sink - installed at, above, or beneath the oil or gas-water contact.

The two completions are hydraulically isolated inside the well by a packer. 

The bottom (water sink) completion employs submersible pump. The submersible pump drains the formation water from around the well and prevents the water from breaking through the oil column and getting into the oil-producing perforations.

4. Dual completion technology with Downhole Water Sink (DWS)

Types of DWS Completions(i) A DWS well is dual - completed for oil production

and water drainage (water sink). Water is produced from annulus and and oil is

produced from production tubing.The two completions are hydraulically isolated

inside the well by a packer. The bottom (water sink) completion employs

submersible pump and water-drainage perforations.

(ii) A similar DWS well but with water produced production tubing and oil from annulus.

(iii) DWS with both Oil and Water produced from separate production tubing It is very costly.Not possible for less

diameter or slim wells.GLV can be equipped to

lift up both water and oil.

(iv) DWS configuration for gas wells including dual completion with gravity gas/water separationWater from the aquifer underlying the oil zone which has entered the wellbore is allowed to fall down through a smaller diameter liner with a pump pumping the water into another aquifer beneath it.

The two basic Variants.

Variant A:DWS- water injection 

Variant B: DWS- water production

Downhole separator• Downhole separator installation reduces 

the production of excessive water. • The device is coupled with electric 

submersible pumps that allow upto 50% of the water to be separated and injected downhole to avoid lifting and surface-separation costs.• Separating water downhole reduces the 

lifting costs of excess water. Typical downhole separators are 50% efficient. The excessive water is injected into other formation.

Cusping in Horizontal Wells

Flux model in horizontal wells

Formation of water crest

Tail-Pipe Water Sink Completion

Bilateral Water Sink Technology

DEVELOPNMENTSMathematical models have been developed to predict the performance of oil wells with 

water coning problems after water breakthrough. Muskat and Wyckoff (1935) and Muskat, (1949) observed that coning is a rate-sensitive phenomenon, which develops only after certain equilibrium conditions are unbalanced by increasing the pressure differential beyond critical limits.

Wyckoff (1935) also determined the critical oil rate analytically solving Laplace equation for single-phase flow and for a partially penetrating well. 

Wheatly, also observed that the value of the well radius does not significantly affect the critical rate of production. This is contrary to Schol’s (1972) observation.

Guo and Lee (1993) demonstrated that the existence of the unstable water cone depends on the vertical pressure gradient beneath the wellbore. “If the vertical pressure gradient is higher than the hydrostatic pressure gradient of the water, the unstable water cone can be observed and the associated critical oil rate exists”

Water and Gas coning featuresHigh pressure gradient/high fluid velocity (production rate)

stimulates water coning.

Completion at the topmost part of the oil zone (preferably the top 45 percent) away from the oil-water-contact delays the time to water breakthrough.

Critical oil rates for water-free oil productions are typically uneconomical for all practical purposes.

The gas produced in gas coning is not very economical as compared to the oil.

After water breakthrough in the wellbore, water production increases rapidly and significant resources and efforts have to be put into water disposal and oil/water separation facilities.

The development of the water cone creates bypass oil problem and consequently shortens the producing life of the well.

A corollary is that more money is spent on infill drilling to recover bypassed oil reducing the economic gains of the field.

CONCLUSIONSOut of the various method to control and retard water and gas influx DWS seems to work best.

 Producing below critical rate or halting production can be uneconomical at times. While Polymer injection damage the payzone. The control of water coning/cresting with Downhole Water Sink (DWS) technology in both vertical and horizontal wells has been analyzed in this study. The application of the technology in controlling water coning creates a hysteresis effect.

DWS may not be economical for low producing wells.

Reference1.Ajayi, A. and Konopczynski, M. Intelligent-Well Technology Reduced Water Production in a Multilateral Oil Producer. SPE 102982, Proceedings of SPE ATCE, SanAntonio.2.Baker Hughes. Intelligent Production Systems. http://www.bakerhughes direct.com/cgi/bot/resources/ExternalFileHandler.jsp?bookmarkable=Yes&path=private/BOT/public/intelligent_wells/index.html&channelId=-546906632,3.DOWNHOLE WATER LOOP (DWL) WELL COMPLETIONFOR WATER CONING CONTROL --- THEORETICAL4.Water Production & Solution Part-1 by Dr. AminianWater Coning in Horizontal Wells: Prediction of Post-Breakthrough Performance

5.Makinde F. A1., Adefidipe, O. A., and Craig, A. J. Petroleum Engineering Department, Covenant University, Ota, Nigreia 6.PREDICTING THE BEHAVIOR OF WATER AND GAS CONING IN HORIZONTAL WELLS by T.Sh. Salavatov, Al Sayed Ghareeb Azerbaijan State Oil Academy7.A Study to Prevent Bottom Water From Coning in Heavy-Oil Reservoirs: Design and Simulation Approaches by Shugao Dai , Binshan Ju8. Well Control by Bill Bailey,John Elphik, Firki Kuchuk. Schlumberger2000.

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