Low-alloy carbon steel drill pipes in the controlled yield strength grade 95 ksi showing excellent sulfide stress cracking (SSC) resistance and impact toughness have been developed. This paper describes the product, its manufacturing route, and the test program which was conducted to evaluate the mechanical properties and SSC resistance of the material in the different parts of the product.
Fifty years after the well blowout in the French sour gas field of Lacq following the failure of the drill pipe and casing [1], the risks related to the presence of wet hydrogen sulfide in the drilling fluids for stressed low-alloy steel components are well known : embrittlement of the steel and failure under stresses well below the nominal load-bearing capacity of the component.
Drilling deep wells, where sour gas is oftentimes found in the reservoir fluids, requires drill pipe materials combining high strength and sulfide stress cracking (SSC) resistance, a requirement which conventional API 5D [2] drill pipes with API 7 [3] tool joints do not meet.
Therefore, the section 10 "Drill Stem Corrosion and Sulfide Stress Cracking" of the API RP 7G document [4], as well as the section 11 of the NACE MR0175-01 standard [5], recommend corrective measures to mitigate SSC in water-based drilling fluids. Among those are the maintenance of the drill fluid pH above 10, the control of the drilling fluid pressure to minimise formation fluid inflow, the use of chemical sulfide scavengers, and the involvement of oil-based muds. Drill pipe products designed for such controlled environments have been presented in a previous paper [6].
However these operations are expensive and not always practical since they often require a subsequent chemical treatment to rinse the well bore before the actual production. In addition, the underbalanced drilling techniques, which result in less formation damage, but involve inflow of reservoir fluids into the well bore, are becoming more widely used, especially for sour gas wells [7]. These two reasons make the availability of sour service drill pipes an important issue for operators.
