RAVVA    Celebrating 16 Years of Technical Excellence      Innovating Development | Slim Hol...
Ravva – Innovating DevelopmentSlim Hole DrillingThe ‘Slim Hole Drilling’ concept is considered as one of the most cost eff...
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Cairn India Limited - Ravva | Slime Hole Drilling

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http://www.cairnindia.com The ‘Slim Hole Drilling’ concept is considered as one of the most cost effective methods in oil & gas field development. It involves drilling smaller diameter holes and using small diameter production casing and tubing. It is an emerging technology expected to make step-improvements in the efficiency and economy of well construction.

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Cairn India Limited - Ravva | Slime Hole Drilling

  1. 1.               RAVVA Celebrating 16 Years of Technical Excellence Innovating Development | Slim Hole Drilling
  2. 2. Ravva – Innovating DevelopmentSlim Hole DrillingThe ‘Slim Hole Drilling’ concept is considered as one of the most cost effective methods in oil & gas fielddevelopment. It involves drilling smaller diameter holes and using small diameter production casing andtubing. It is an emerging technology expected to make step-improvements in the efficiency and economyof well construction.The narrow-gap criterion says that if the drill string to hole diameter ratio is greater than 0.8, it is classifiedas ‘slim hole’. If one can extract less rock, then the well costs should fall. Thus, the use of small diameterwell bore reduces the overall cost of exploration, drilling and reserve development. Slim hole drilling applications are:  Continuous coring  Conventional rotary drilling  Downhole motor drilling  Coiled-tubing drilling.The table here shows some of the wells drilled in the Ravva exploration campaign, the hole sizes, targetdepths, casing policy, production hole sizes & the year of completion for the respective wells.As evident from the table, the initial period of the campaign saw a three casing policy being deployed todrill the wells. The data received from these initial wells was then processed to determine the right casingpolicy for future wells. It can be seen in the table that wells drilled in the later part of the campaign have atwo casing policy. The surface hole was dropped and the intermediate 12 ¼” hole extended from surfaceto intermediate depth and the 8 ½” production hole was extended to cover the longer hole section. Thechanges in the casing policy with slim well design have resulted in substantial cost savings.Slim Hole Drilling advantages are:  Considerably less usage of drilling mud  Smaller casing sizes (major cost reduction factor)  Can be used for High Angle and Horizontal  Wellbore from existing wells  Could be used for CO2  Flood Injection holes or wells  Reduced drilling time due to rapid drillingThe advantages of a smaller hole size and the reduction in the volume and size of oil, wet drilling cuttingshelps in minimising the environmental impact associated with the use of oil base mud. The reduction indrilling fluid volume and treatment cost, higher rates of penetration, better hole cleaning capabilities,savings in consumables (such as bits, mud, cement, and diesel oil), less tangible cost, and easierequipment mobilisation, produce significant operational gains. By using slim hole technology, a reductionof 40% to 70% in well costs can be realised. Tubular costs alone are reduced by 40% t50 % with anoverall reduction of around 17% in the well cost. In addition to cost savings, the operations can beperformed safely due to the smaller size of equipment involved. It has also been seen that slim holes donot hinder production.Although substantial savings are realised by using the slim hole concept, there are elevated risks as well.There is a lack of good contingency in the event of unexpected hole condition or geological conditionrequiring an extra casing to be run prior to reaching the total depth. Usually, very slow drilling ROPs areassociated with the erratic directional responses, and can restrict the use of MWD tools.Effective pre-planning between the drilling, exploration, and the engineering team to accurately definepossible geological targets and their potential drilling problems can minimise these risks associated withdrilling slim holes and provide higher levels of success in meeting planned objectives.

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