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Summary Maintaining zonal isolation for the lifetime of oil and gas wells is critical. Leakage behind casing can reduce the cost effectiveness of the well and cause health and safety risks from pressure buildup and contaminated aquifers. During the completion and production phases of the well, temperature and pressure variations can cause stresses at the cement-to-formation interface. The ability of the casing-cement system to maintain a seal at the cement-to-formation interface depends on the condition of the formation surface before slurry placement. The condition of shale will depend upon the nature of the drilling fluid used, whereas the condition of a permeable rock will depend upon the presence and nature of the filter-cake deposited during drilling and circulation. In this paper, we present an improved understanding of chemical interactions at the cement-to-formation interface and the factors that determine bond strength and the position of the plane of failure. For permeable formations, the role of the mud filter-cake for different mud types is explored. For nonpermeable formations, the presence and effect of a mud treatment are also examined. The extent and depth to which chemical alteration of the mudcake occurs when in contact with cement is determined together with measurements of the yield stress and water-content profile of the altered mudcake. The effect on bond strength of exposing swelling and nonswelling shales to inhibitive drilling fluids is presented. Laboratory-scale test equipment and as mall-scale wellbore simulator, developed for tests under realistic field conditions, are described. A flexible (i.e., lower Young's modulus) cement plays a role in bonding and is demonstrated by the simulator tests. This improved understanding enables us to confirm the key issues at the cement-to-formation interface and propose some solutions for effective zonal isolation.

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Minimising the transport of corrosive reactants such as carbon dioxide, hydrogen sulfide and chloride ions to the surfaces of carbon steel pipes by the use of polymer barrier layers is of major interest in the oil and gas sector. In these applications, there is a requirement to assess the performance of these barrier layers although it is difficult to perform long-term predictions of barrier properties from the results of short-term measurements. New methodologies have been successfully developed to study the permeability of carbon dioxide (CO2) and hydrogen sulfide (H2S) through polymer layers under variable conditions of elevated temperatures of 100 °C and pressures of the order of 400 barg. In situ variation of the temperature and the inlet pressure of the gas (or gas mixture) allowed the activation energy and pressure dependence of the permeability to be determined without outgassing of the specimen. These methodologies have been applied to the measurement of the permeability of moulded polyphenylene sulfide (PPS) to supercritical CO2 in the presence of H2S. The diffusion coefficients of sodium chloride and potassium chloride through both PPS and polyether ether ketone (PEEK) at ambient temperature and pressure have also been measured.

A review is given of the results and lessons arising from a sustained in situ diffraction study of the structure and performance of functional ceramic/cementitious materials in which synchrotron-based energy-dispersive diffraction has been the central under-pinning technique. Five particular points of discussion emerge: the demands on time resolution; the use of penetrating radiation for the in situ mode; the need for complementary techniques; re-analysing of data; spatially resolved diffraction: a new tomography. These aspects are discussed in turn using illustrative examples taken from the ®elds of cement hydration, clay intercalation, cation-exchanged zeolites, and particulate/¯uid invasion into building and archaeological objects.