One Year Experience in Slim Hole Drilling

Abstract Further to previous research and experimental wells drilled in 1993, in 3" and 3 3/8" ("Les Talonnieres", SPE Paper n•28299), and the decision to built the fitted for purpose Slim Hole rig FORASLIM 1 commissioned in April 1994 (SPE Paper n•28867, a Fitted for purpose Rig) 6 Slim Hole wells have been drilled for ELF AQUITAINE : 2 in the Paris Basin and 4 in (Gabon) West Africa. Eighteen months of experience allow to make a global review of what are the achievements in terms of geological data acquisition, drilling performances, and economical results. This permitted to point out the weaknesses and the corresponding needed improvements to reach a mature Slim Hole technology fully comparable to the conventional approach. The paper describes and analyses the operational results of each well as different prospects were drilled in respect of depth, geology. One significant experiment in a well drilled in 3 3/8" with high pressure at 3310 m (11 000'), requiring the use of mud weight of 1,75 sg (14,5 ppg) is in particular described. Beside the review of drilling performances and geological data acquisition, an economical review will be made. A cost comparison with conventional approach provides an estimation of the benefits of the Slim Hole approach. The potential use of a Slim Hole drilling offshore and for deep wells is finally presented.