In early 1993, two ultraslim hole wells (3" and 3 3/8") were drilled in the Parts Basin of France. Our intention was to quantify the "concepts" associated with new and re-emerging technology. This paper details the drilling performances and the technical aspect of the drilling operations, The paper also presents the tests results of new slim hole drill pipe while performing destructive drilling and wire line coring. The validation of a mud pressure model is also presented. These experiments have confirmed the benefits of slim hole technology and highlighted the need for a dedicated surface equipment to comply with the environmental criteria. Additionally, all the required geological data concerning formations and reservoir fluids were acquired.


In today's economic environment oil companies must reduce costs, especially costs related to drilling exploration and appreciation wells. One way to achieve substantial cost reductions is to use slim hole technology. Our company decided to investigate along this direction. We based our approach on the following two facts: destructive drilling is more efficient than coring and continuous coring is not needed from the top to the bottom of the well. We also need to obtain all the data concerning formations evaluation and we must realize the proper evaluation of fluids which are trapped in these formations to satisfy our business requirements.

In order to test these objectives, we were allowed to drill two experimental wells in the Parts Basin. Our objective was to verify the feasibility of drilling an ultra slim hole (diameter <4") of a long distance >3000 ft) and to acquire all of the necessary information required by the "explorationists".

We will present the results of these two wells. We will focus on the specific problems related to slim hole drilling.


The two experimental wells were drilled in the same geologic location called "Les Talonnieres". The distance between the two wells was 50 meters. They both had the same geological profile. The area is well known with no hydrocarbon bearing reservoir We could perform our experimental tests with relative safety. Two different technical programs with complementary challenges were performed on these two wells

The first well LTR1 and the first challenge: Drill a long section of 1500m (4500 ft) 4 3/4" hole (120,6 mm) utilizing a new slim hole drill string SH 111 (see characteristics in Table I).

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