Monopiles supporting offshore wind turbines can experience permanent non-recoverable rotations (or displacements) during their lifetime due to the cyclic nature of hydrodynamic and aerodynamic loading exerted on them. Recent studies in the literature have demonstrated that conventional cyclic p–y curves recommended in different codes of practice (API-RP-2GEO and DNVGL-RP-C212) may not capture the effects of long-term cyclic loads as they are independent of the loading profile and the number of applied cycles. Several published methodologies based on laboratory scaled model tests (on sands) exist to determine the effect of cyclic lateral loads on the long-term behaviour of piles. The tests vary in terms of the pile behaviour (rigid or flexible pile), number of applied loading cycles, and the load profile (one-way or two-way loading). The best-fit curves provided by these tests offer practical and cost-efficient methods to quantify the accumulated rotations when compared to Finite Element Method. It is therefore desirable that such methods are further developed to take into account different soil types and the complex nature of the loading. The objective of this paper is to compare the performance of the available formulations under the actions of a typical 35-h (hour) storm as per the Bundesamt für Seeschifffahrt und Hydrographie (BSH) recommendations. Using classical rain flow counting, the loading time-history is discretized into load packets where each packet has a loading profile and number of cycles, which then enables the computation of an equivalent number of cycles of the largest load packet. The results show that the loading profile plays a detrimental role in the result of the accumulated rotation. Furthermore, flexibility of the pile also has an important effect on the response of the pile where predictions obtained from formulations based on flexible piles resulted in a much lower accumulated rotation than tests based on rigid piles. Finally, the findings of this paper are expected to contribute in the design and interpretation of future experimental frameworks for Offshore Wind Turbine (OWT) monopiles in sands, which will include a more realistic loading profile, number of cycles, and relative soil to pile stiffness.

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Chemical radioactive sources are commonly deployed in logging-while-drilling (LWD) assemblies to measure formation bulk density and neutron porosity. These measurements are widely used in porosity evaluation, lithology determination, clay volume estimates and fluid identification. Deploying logging tools with chemical sources poses Health, Safety and Environment (HS&E) risks requiring specific procedures throughout the entire process of planning, logistics and execution of well construction. Obtaining similar, identically equal or better formation bulk density and neutron porosity measurements without chemical sources has many advantages, particularly from the HS&E perspective in both standard and high-risk developments. Advances in LWD technology have enabled the neutron porosity measurement to be obtained by employing an electronic neutron generator instead of a chemical source. These electronic neutron generators have been used for many years in different wireline tools and are now also available in LWD tools. The bulk density measurement has, until recently, only been measured utilizing a chemical source. Recent developments use the gamma rays induced by the interaction of high-energy neutrons (from the electronic neutron generator) with the formation as an "in-situ" source for subsequent derivation of bulk density. Studies of the sourceless neutron-gamma-density (SNGD) data acquired in 15 to 20 horizontal and vertical wells have shown the accuracy obtained is within the specified limits, as compared to the traditional gamma-gamma-density (GGD) data. The typical density differentials observed in these environments are in the 0.01 to 0.02 g/cm3 range, which results in a porosity and saturation "error" in the order of 0.002 to 0.004 V/V. This level of accuracy is probably acceptable in a number of applications (e.g., infill drilling in mature fields), but may not be acceptable in other scenarios (e.g., more complex lithologies, extremely tight reservoirs), unless the HS&E considerations are overriding. The HS&E benefits are important to keep in focus as they have a direct human benefit through the entire process of equipment preparation, transportation, wellsite operation and potential bottomhole assembly abandonment. Associated with this there is also the economic benefits related to less rig time required for source handling, and the potentially large savings in a lost-in-hole (LIH) abandonment scenario, in the locations where this is applicable. All these different aspects, HS&E, financial and technical, associated with the SNGD system need to be evaluated from a holistic viewpoint to ensure the most appropriate, fit-for-purpose acquisition program is selected in each case.

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