Abstract. This paper describes a series of experiments designed to investigate the influence of litho!ogy on the compactional loss of porosity and permeability in mudstones. Two intact samples of London Clay with clay fractions of 40% and 67% were compacted to 33 MPa effective stress. Clay fraction, permeability, porosity, pore size distribution, and specific surface area were measured and their evolution was monitored throughout the compaction process. Electron microscopy was combined with mercury porosimetry to trace the collapse of the pore structure with increasing effective stress. In both cases, porosity loss occurred primarily by the collapse of large pores. This process is more obvious in the coarser-grained sample because throughout the compaction process it has a much broader range of pore radii and a much greater mean pore radius. Consistent with the pore size distributions, the permeability of the coarser sample ranges from ,• 1040 rn s 4 to 1042 rn s 4 while that of the finer-grained sample ranges from ~ 4 x 1042 rn s 4 tO 5 x 104'* rn s 4 during progressive compaction from 2 to 33 MPa. The compressibility of the finer-grained sample is greater than that of the coarser-grained sample (0.15 as opposed to 0.07). However, in both cases the compressibility is much lower than that inferred for lithologically similar samples compacted over geological timescales. The demonstration that both porosity and litho!ogy (clay fraction) influence the permeability of mudstones should allow the development of more realistic porositypermeability relationships which take into account lithological variations exhibited by mudstones.

Abstract. We report the results of a series of hydraulic conductivity tests carried out on seven natural, well-characterised specimens of London Clay mudstone. The clay fractions of the samples range from 27% to 66% and enabled a test of the influence of clay fraction on the hydraulic conductivity, pore size distribution, compressibility and specific surface area of natural mudstones. s over a porosity range of 48% to 25%. At a given porosity the hydraulic conductivities of two silt-rich samples (27 and 33% clay fraction) were 40-250 times greater than those of the five clayrich samples. Variations in hydraulic conductivity are directly related to pore size distributions and are accurately predicted by a model which uses pore size distribution as its primary input. Clay-rich samples have unimodal pore size distributions with modal throat radii around 60-120 nm. Silt-rich samples have bimodal pore throat size distributions. One modal size is similar to that observed in clay-rich samples with a second modal value at 3-6 gm. Compaction under effective stresses up to 10 MPa results in the preferential collapse of larger pores, so that the rate of loss of hydraulic conductivity is greater in the silt-rich samples. Differences in hydraulic conductivity between silt-rich and clay-rich mudstones therefore decline with decreasing porosity. The range of porosity-hydraulic conductivity relationships means that hydraulic conductivity is not easily predicted from porosity alone; additional constraining parameters such as grain and pore size distributions are required.

Résumé -Fatigue des tiges de forage : état de l'art -La rupture des tiges de forage est un problème coûteux dans l'industrie de ce secteur. Bien que de nombreux spécialistes se soient penchés sur ce point, la fréquence des ruptures demeure toujours importante. Les ruptures par torsion ou par tension restent toutefois limitées, car les causes en sont connues et peuvent être aisément corrigées, en revanche, les ruptures par fatigue sont plus difficilement appréhendées. Le présent article se propose d'établir un état de l'art sur la fatigue des tiges de forage. La prédiction et les calculs d'un dommage de fatigue sont ici abordés selon la méthode simpliste du cumul de dommage (somme de Miner) mais aussi de façon plus complexe, par l'utilisation des éléments de la mécanique de la rupture. Les méthodes d'inspection et leurs limitations sont discutées, des recommandations sont également émises. Par ailleurs, des tests de fatigue sont mis en oeuvre face au risque humain ou environnemental. Cette étude précise les conditions de chargement, la fréquence des essais, le nombre et la taille des éprouvettes. Nous rappelons les effets d'un environnement corrosif ainsi que leur prévention, bien que ce sujet ne soit pas l'objet principal de cet article. Le dernier chapitre résume les différentes façons d'améliorer les tiges de forage. À ce titre, il aborde la géométrie, le design des connexions, les propriétés de l'acier telles que la résilience, le rechargement dur des tool-joints et l'inspection des garnitures de forage.

The influence of pore pressure on the elastic strain of rocks is basic to reservoir compaction and subsidence problems and in reservoir engineering and environment studies. Biot's coefficient is an important parameter used to determine the influence of pore pressure on rock deformation. This paper presents measurements of Biot's coefficient on limestone samples and interprets these measurements. The coefficients used in poroelastic studies first are defined as Biot's coefficient and compressibility coefficients proposed by Zimmerman. Then, the experimental apparatus and procedures used to measure these coefficients are described. Finally, the results, which confirm the theoretical framework of poroelasticity, are presented and discussed. The compressibility coefficients and Biot's coefficient increase with porosity according to a law that is formally similar to a Hashin-Shtrickman's type law. For porosities in the 4.5% to 23% range, Biot's coefficient increases from 0.34 to 0.83.