Shale formations are known for their chemical interactions with water based muds which may result in swelling, bit balling or even closure of the wellbore. As a result, eco-friendly water based fluids with inhibitive characteristics are required for drilling through shale formations. The aim of this study is to provide a deeper insight into drilling through shale formations by providing few approaches for different circumstances. Many inhibitors developed so far are introduced with their mechanism of shale inhibition presented. It appears that silicate based muds and thermally activated mud emulsion (TAME) are the best option to mitigate shale related issues, but more studies are required to provide a permanent solution for this very complicated issue, especially under HPHT conditions.

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Shale reservoirs have gained the attention of many in recent years due to their potential as a major gas resource. Production from this kind of formation, however, requires an accurate estimation of brittleness and employments of hydraulic fracturing. There have been many studies as to how brittleness can be estimated, but few research works were carried out so far indicating how brittleness indices vary in gas shale formations. The aim of this paper is to evaluate the variation of brittleness in one of the gas shale reservoirs located in the north Perth Basin of Australia. The results obtained indicated that the lower part of the Carynginia shale should be selected for a hydraulic fracturing job due to a high brittleness index, although a careful analysis of Total Organic Content (TOC) might be required before initiating any plans. The mineralogical report and interpretations revealed that the space created by cross-plotting the elastic parameters is able to identify dominant minerals contributing into brittleness. Performing a series of true triaxial tests, which are capable of simulating the real field condition by applying three independent principal stresses, implied that as the stress anisotropy increases, a transition takes place from brittle towards the ductile behaviours. However, when this anisotropy becomes significant, samples regain their strength. This study, therefore, recommends more studies to get a practical conclusion on brittleness under true triaxial conditions.

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