As the industry continues to expand into ultradeepwater plays, an increasing number of tight tolerance wells warrant the use of an efficient system for determining early influxes or losses during drilling, tripping, and cementing operations. The narrow mud weight window for the majority of these wells requires an advanced solution in order to operate in all such conditions without compromising on safety. This paper describes a new early detection flow monitoring system and setup for floating rigs, and presents its application via a case study of a very high-profile ultra deepwater well. Good well surveillance for floating rigs requires precise measurements combined with an efficient smart process adapted to deepwater conditions in order to raise a reliable alarm in any condition, while minimizing the risk of false alarms. Careful sensor selection and sizing, together with particular attention to installation is required in order to achieve this degree of accuracy for all the drilling phases. The solution described in this case study provides drilling surveillance for all hole sizes, with flow up to 2000 gpm for accurate and early detection, and significantly increased safety during drilling, tripping, and cementing operations. This case study describes how kicks can be detected with a high degree of reliability much earlier than with the standard pit volume and flow paddle monitoring. In addition to this, it has shown its value by characterizing, in real time, the consequences following a packoff event and also by differentiating between a wash out and pump failure. Crew confidence in this detection system rapidly led to modifications of the operational procedures. For instance, flow checks were previously done for every pipe connection, taking up expensive rig time. Due to results obtained in the previous hole sections, the drilling procedures were updated in order to significantly reduce time spent flow-checking, while still maintaining maximum safety during the operations.
Highly pressurized hydrocarbon systems, heavy equipment, constantly changing environments, sweltering temperatures and rough terrain, remote locations with complex logistics – this isn't a scene from your favorite space flick, just your typical oil and gas operations. These characteristics underscore the industry's inherent safety risks, and with the recent uptick in U.S. onshore drilling, more operators are re-evaluating their safety capabilities. While organizations use safety KPIs to grade their safety performance, these numbers are usually influenced by a myriad of factors - location, job type, formation, hydrocarbon type (oil, gas, condensate), equipment, service provider, and procedures - but they don't tell the whole story. In her 2011 testimony to the U.S. Senate Committee on Energy & Natural Resources on risk management in offshore oil and gas, MIT professor Nancy Leveson stated that "flaws in safety culture" is the leading cause of major incidents in the oil and gas industry1. A 2013 Norwegian Petroleum Safety Authority article echoed her assertion, stating, "increased knowledge of the interaction between technical and organizational elements - and the people using these - is crucial in understanding the underlying causes of incidents."2 Although safety in the oil and gas industry is driven by multiple factors, it is clear from industry experts and incident data that the key factor influencing an organization's safety performance is people and the culture they operate in. To move the needle with a company's safety performance, you have to affect the hearts of its people through its safety culture. At the core, organizational culture is enhanced by the way its key assets (people) are engaged, led, communicated with, and incentivized – in other words, by affecting the human experience. An organization's safety culture is a microcosm of the overall culture, with a more heightened and critical lens because of the direct impact on people's health, well-being and lives. Statoil's Development & Production USA Business Area (DPUSA) came to this realization during a review of their safety program in early 2017. The organization had grown through acquisitions over the past several years and had the challenge of ensuring safety excellence while integrating the employee and contractor workforce into the broader organization.
Offshore East Africa is a new frontier in terms of deepwater exploration. One of the new projects in ultradeepwater offshore Tanzania was located in Block 2 with water depths ranging from 1000 to 3000 m. Seismic data had shown the potential presence of shallow gas, shallow water flow, and gas hydrates while drilling the riserless section. Lack of local oilfield infrastructure, and the lack of pump and displace (PAD) mud availability made the project challenging because the surface section was to be completed within a matter of several days. Statoil decided to drill the Tangawizi-1 U1 pilot hole to confirm the absence of shallow hazards and avoid the need for overbalance drilling the riserless section with PAD mud. The 8 ½-in. pilot hole penetrated 600 m through the critical zone below the seabed, drilled with sea water, was then plugged back by filling the open hole with cement. The decision was made to perform the cement job through the 8 ½-in. Bottomhole assembly (BHA) containing measurement while drilling (MWD) and logging while drilling (LWD) tools. The combination of deepwater, riserless, potential shallow hazards and pumping through a BHA with significant restrictions made successfully setting balanced plugs extremely challenging. The slurry was designed following industry standards to prevent fluid influx or destabilizing the hydrates during the setting process by the use of an optimized particle size distribution (OSPD) slurry system. In addition, to successfully be placed through the BHA and avoid plugging the nozzles, this system needed to be stable and have low rheology. The pilot hole was successfully abandoned by setting two cement plugs. Cement returns were observed at the seabed by a remote operated vehicle (ROV) and no visual flow after placement was observed.
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