A well documented path to improving overall efficiency in project execution is through an integrated team approach which involves both the operator and the service suppliers. This paper describes what can be achieved when such a team adopts a fearless approach to new technology, and dares to think outside existing conventions. To be more specific, the paper covers the engineering, planning, and execution of a HTHP exploration program in the central North Sea by a Norwegian operator.Large areas of the North Sea contain the Cretaceous period of sediments which comprise of a massive hard layer of chalk that historically has posed a major drilling risk and expense to operators in the area. To mitigate expected problems an integrated team was gathered to thoroughly analyze drilling records and lessons learned from previous offset wells and re-engineer the drilling process with the aim of minimizing cost and uncertainty when drilling the most challenging chalk interval.The paper presents the hypothesis that formed the basis for the team effort, and the measures implemented based on said hypothesis. This includes an unconventional bit selection and the use of modern vibration measurement technology and mitigation techniques, as well as a key electro-mechanical modification of the advanced logging and directional suite completed by the lead service provider. The discussion and reasoning behind each step is included and the method was repeated in several wells with the same results, verifying the validity of the findings and making the paper a valuable input for drilling hard chalk.The nominal result from applying the new methodology was a doubling of the rate of penetration (ROP) in the harder layers, and the entire section of problematic strata was drilled in one single bit run. Drilling time was reduced by 12 days when compared to average figures from recent offset wells representing an estimated cost saving of 15 -20% on the overall well budget. The method and savings presented are primarily of interest to stakeholders in the central North Sea, but can also be applicable to other areas with hard chalk and stringers with similar characteristics.

Different logging operations can suffer from presence of metallic particles in the drilling fluids. Directional drilling in Arctic areas can be a challenge because of magnetic contamination in the drilling fluid. This is a challenge especially when drilling east-west relative to the magnetic north direction. Magnetic and paramagnetic particles in the drilling fluid will shield the down hole compasses and introduce additional errors to the surveying than those normally included in the uncertainty ellipsoid. The objective of the project is to remove the magnetic particles being the largest contributor to this error. On many offshore drilling rigs there is mounted ditch magnets to remove metallic swarf from the drilling fluid. These magnets will normally only remove the coarser swarf. In this project we use a combination of strong magnets and flow directors to significantly improve the performance of the ditch magnets. This combination, together with proper routines for cleaning the ditch magnets significantly helps cleaning the drilling fluid. By the combined use of flow directors and ditch magnets it was possible to extract more than five times as much magnetic contamination from the drilling fluid. This is verified by comparing the ditch magnet efficiencies from two drilling rigs drilling ERD wells. The logging tool signal strengths of several down hole instruments were unusually good and insignificant down times were observed on the logging tools. The results are anticipated to have aided to the directional drilling performance. Detailed information on how to clean the drilling fluid properly from magnetic contamination is presented. It is also shown that this cleaning is significantly better than conventional cleaning of magnetic debris from drilling fluids.

Historically, invert emulsion drilling fluids (IEFs) require organophilic clays to provide viscosity and suspension characteristics. Whilst effective, these chemicals are prone to stratification in certain conditions, slow chemical reaction times, high pressure spikes, and high equivalent circulating densities (ECDs) attributed to the solids contribution and inherent chemistry of the fluid. To help reduce such adverse effects, clay based chemicals used in IEFs can be replaced with highly sophisticated polymer viscosifiers, filtration agents, and emulsifiers, which provide a strong, stable emulsion, even with low-oil/water ratio (OWR) IEFs. Legislation governing the energy industry’s use of chemicals in Norway prohibits use of certain products that are otherwise globally used in drilling fluids. To address such restrictions, extensive research and development has resulted in availability of environmentally acceptable chemicals that produce the unique rheological and suspension characteristics inherent to clay-free IEF systems. This paper describes the first application of clay-free IEFs in the Norwegian continental shelf (NCS) with an emphasis on an impressively low ECD contribution far more consistent than previously recorded in comparable wells. Further, a treatment was developed to allow the IEFs to be used to drill into a section exhibiting temperatures greater than 160°C. Chemical consumption was substantially lower compared to previous wells using traditional IEF systems, thus reducing shipping requirements. Before planning the subject well, the environmentally acceptable chemicals intended for use were approved by governing bodies. Consequently, a vertical exploration prospect was selected as the initial well to be drilled using a clay-free IEF. This well was comparable to a previously drilled high pressure/high-temperature HP/HT well, allowing direct comparison of several of the metrics.