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Slide 1:                           RAVVA Celebrating 16 Years of Technical Excellence Innovating Development | Slim Hole Drilling
Slide 2: Ravva – Innovating Development Slim Hole Drilling 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. The narrow-gap criterion says that if the drill string to hole diameter ratio is greater than 0.8, it is classified as ‘slim hole’. If one can extract less rock, then the well costs should fall. Thus, the use of small diameter well 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, target depths, 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 to drill the wells. The data received from these initial wells was then processed to determine the right casing policy for future wells. It can be seen in the table that wells drilled in the later part of the campaign have a two casing policy. The surface hole was dropped and the intermediate 12 ¼” hole extended from surface to intermediate depth and the 8 ½” production hole was extended to cover the longer hole section. The changes 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 drilling The advantages of a smaller hole size and the reduction in the volume and size of oil, wet drilling cuttings helps in minimising the environmental impact associated with the use of oil base mud. The reduction in drilling 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 easier equipment mobilisation, produce significant operational gains. By using slim hole technology, a reduction of 40% to 70% in well costs can be realised. Tubular costs alone are reduced by 40% t50 % with an overall reduction of around 17% in the well cost. In addition to cost savings, the operations can be performed safely due to the smaller size of equipment involved. It has also been seen that slim holes do not 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 condition requiring an extra casing to be run prior to reaching the total depth. Usually, very slow drilling ROPs are associated 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 define possible geological targets and their potential drilling problems can minimise these risks associated with drilling slim holes and provide higher levels of success in meeting planned objectives.