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Summary The demand for ultradeepwater scenarios invoked the frequent application of managed pressure drilling (MPD) in the last few years. In an ultradeepwater scenario, oil companies face issues such as narrow pressure windows and severe loss zones. Many wells are considered undrillable without the aid of MPD technology. MPD operations need to be correctly evaluated with consideration given to increased time and cost/benefit analysis. In this paper, we propose a probabilistic model to evaluate MPD demand by estimating the optimal number of rigs equipped with MPD and a rotating control device (RCD), and we analyze which intervention strategy is the most cost– and time–effective. Reducing uncertainty is an important factor when making decisions about drilling. We adopted a Monte Carlo simulation using loss–zone estimation, probability of prediction error, the number of rigs equipped with MPD, and several strategies. Better MPD strategies were determined on the basis of available data and the optimal number of rigs equipped with an MPD system and RCD equipment, reducing subjectivity in the decision–making process. The originality of our paper lies in the new quantitative approach to dealing with uncertainty in the prediction of fluid losses and the cost and duration of different MPD strategies, numerically simulating the possible scenarios.

Manage Pressure Drilling is not a new technology, but the transition from land operation to floaters is still recent. This created a situation where drilling contractors and operators are still learning what the true capabilities of the technology are. MPD technology adoption on floaters can be divide it in 3 different phases: Use for Early Kick Detection and wellbore stability improvement;Introduction of Hydrostatically Underbalanced fluid;Influx circulation through the MPD system; In the first phase most of the procedures and barrier concepts stay untouched. After eliminating initial skepticism, second phase commences. Hydrostatic pressure exerted by the fluid is inferior to the formation pressure. Primary barrier concept alters. The technology can be applied to drill wells with narrow operational windows, unviable conventionally. Finally, third phase starts with very limited volumes being allowed to be circulated through the MPD system. After first successful influx circulations through the MPD system, increased volumes may be encouraged to be circulated through the primary barrier.

This paper describes how Managed Pressure Drilling (MPD) techniques can be used in some workover and completion operations, such as the lower completion replacement. It also presents the first application of this kind of solution in a subsea well, which has been recently done in Lula field in the Brazilian pre-salt. Highly stimulated wells in the Brazilian pre-salt carbonate reservoirs set significant challenges for well engineers when the lower completion must be replaced in workover operations. Major fluid losses are expected as the formation cannot be isolated from the wellbore. Costly loss control operations must be performed prior to the completion retrieval, introducing LCM in the well, causing formation damage and requiring further well cleaning and stimulation. A new approach was developed, in which MPD techniques such as Mud Cap Drilling (MCD) are used to cope with the fluid losses and avoid loss control operations and its associated impacts while maintaining a safe operation. The use of two of the MPD techniques, Pressurized and Floating Mud Cap Drilling (PMCD and FMCD), in the scenario previously described allow the use of sacrifice fluid, usually treated seawater, to continuously inject underbalance or overbalance fluid into the well and avoid hydrocarbons migration during operations with highly stimulated formations still connected to the well. This also allows monitoring the well for any well control issue, as well as applying well control procedures. Even in the FMCD technique a Rotating Control Device (RCD) is used below the drilling riser slip joint to prevent any possible gas migrated into the riser to reach the rotary table. The use of this kind of solution has turned the lower completion retrieval or replacement an operation with less deviation in terms of duration and budget. Costly loss control operations are avoided and there is no need to introduce loss control materials into the well, which could lead to problems when retrieving or installing the lower completion, such as stuck pipe or equipment failure. The customization of MPD techniques and the development of specific procedures for completion and workover with MPD have led to safe and more efficient operations in challenging subsea interventions with DP rigs. This new approach has set an alternative workover philosophy for some pre-salt wells and also opened new opportunities worldwide by the application of this innovative solution. A significant amount of wells equipped with intelligent completion in pre-salt areas do not have a separated completion that could temporarily isolate the formation during heavy workover interventions. In this scenario the use of MPD techniques like presented in this paper might be a valuable solution.

In recent years, PETROBRAS has been using MPD (SBP/MCD) technology in ultradeepwater scenarios at development and exploratory wells. Although MPD techniques are an advance over conventional drilling, it also brings more complexity to the operation and, in some cases, increases the duration and costs of the interventions when compared to conventional drilling. Ideally, the rigs equipped with MPD system should only be used in wells, or in specific phases of the well, that requires MPD to conclude or where the NPT associated with fluid losses is considerable. In these scenarios, the extra costs and extra time necessary are negligible, compared to the NPT avoided, and the alternative would be not to reach target depth or drill the well. Geomechanics, pore pressure estimation and loss zone identification are not an exact science. There is always an uncertainty in predicting MPD (SBP/MCD) demand, pushing the development of techniques and strategies to optimize the allocation of MPD rigs in wells where the NPT would be so high that the use of the MPD is advantageous, or, where MPD is an enabler of well construction. This paper describes a probabilistic analysis developed to support the determination of MPD (SBP/MCD) demand, calculating the optimum number of rigs to be equipped with MPD (SBP/MCD) and RCD system, and which intervention strategy is the most cost effective for a development campaign, based on historic results.