Drilling In Carbonate Formations With Karst And Open Fractures - Ptil
Drilling in carbonate formationswith karst and open fracturesEigil Sørensen, Principal engineerPetroleum Safety Authority
Drilling in carbonateformations with karstand open fracturesReport Acona has prepared at the request ofthe Petroleum Safety Authority Norway.The report deals with karstified formationsHow to identify karstHow to reduce risk while drilling
Drilling in carbonate formations withkarst and open fractureskarst andopen fracturesCarbonate constitutes a large group of minerals. One of theearth's most common minerals is calcium carbonate, CaCO3,lime, which occurs in many different forms, for examplelimestone, marble and chalk.Karst is a disintegrate/degrade phenomenon with caves andcracks, often occurring in limestone.
Drilling in carbonate formationswith karst and open fracturesKarstification and cave formation mainly occurs along weakness zones, cracksand faults where freshwater can flow and gradually expand cracks and cavities.The speed of this process depends on the mineralogy and the solubility of therock.Also requires that formations have been above sea level / groundwater level.
Profile which illustrating stages in development of karst5Fra Esteban og Klappa, 1983
Examples of karstEvenestangen, NordlandSalangen, Troms6Kristihola, Fauske, Nordland
Then it will last for a few years250 million yearsKarst formation has been buried down totoday's depth, 1800 – 3000 mPangaea
Drilling in carbonate formations with karst andopen fracturesDuring the burial history, karstified formations have for a period of time beenraised above sea levels and subjected to erosion and karstification beforethey were again buried.In the Barents Sea this is primarily known from the Lopphøgda area.In the Norwegian Sea, the northern part of Norlandsryggen is affected.Utsirahøgda in the Johan Sverdrup area represents example in the North Sea.
Drilling in carbonate formations withkarst and open fracturesDrilling in carbonate formations with karst and open cracks poses a riskbecause there may be sudden and large loss of drilling fluid, and therebysevere weakening of the primary barrier.Ongoing exploration drilling in areas with carbon-dominated formations in theBarents Sea has raise awareness to this issue.In 2016 the Petroleum Safety Authority Norway decided to start a project withknowledge acquisition and mapping of methods and tools that could reducerisk.
Drilling in carbonate formations with karst andopen fracturesNorwegian Oil and Gas Association:Sharing to be better #13Total mud loss followed by a kick in "karstified carbonates“.During cutting of core, the bit dropped 2m and an immediate severe mud loss wasfollowed by a kick.
Drilling in carbonate formations withkarst and open fracturesThe area Norlandsryggen is also mentioned in the report with Well 6608/8 ( Drilledin 1997 ). Major mud losses ( 1700 l/min) followed by wellcontroll situations.The combination of an open fracture system and significant overbalance wasprobably the cause of the massive loss of drilling fluid.
Drilling in carbonate formations withkarst and open fracturesThe report has examples of several places on the globe where one drillsfor oil in carbonate reservoirs.The main author have also experience from carbonate reservoir in Iran.
Seismic methods3D seismic with optimal acquisition and processingparameters is the most important tool for identifying bothkarst-related features and potential loss zones associatedwith faults
Lopphøgda in 3D with eroded carbonatesGipsdalengruppen eroderte og karstifiserte karbonatavsetningerDoliner og erosjonskanalerSynkehull
Drilling in carbonate formations withkarst and open fractures derThe risk of drilling can be significantly reduced by using new drillingmethods with the common term "Managed Pressure Drilling" - MPD.One technology that recently has been applied in some wells in the BarentsSea is called CML (Controlled Mud Level).This equipment allows drilling with a bottom hole pressure that can beadjusted to near the pore pressure. This is done by adjusting the level ofdrilling fluid in the riser.
Report and contactsderACONA reportMain author : Tore Amund Svanå, toreamund@gmail.comCo-author : Bjørn GjørvPetroleum Safety Authority: Eigil Sørensen
Summaryder The industry has experience with karst Drilling technology and methods to deal with the issuehave been developed Risk can be managed and reduced by paying necessaryattention to the issue of karst
Report (Acona) can be downloaded from: www.ptil.noThank you for your attention
The risk of drilling can be significantly reduced by using new drilling methods with the common term "Managed Pressure Drilling" - MPD. One technology that recently has been applied in some wells in the Barents Sea is called CML (Controlled Mud Level). This equipment allows drilling with a bottom hole pressure that can be
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