Summary Typical shale well completions involve massive, multistage fracturing in horizontal wells. Aggressive trajectories (with up to 20°/ 100 ft doglegs), multistage high-rate fracturing (up to 20 stages, 100 bbl/min), and increasing temperature and pressure of shale reservoirs result in large thermal and bending stresses that are critical in the design of production casing. In addition, when cement voids are present and the production casing is not restrained during fracturing, thermal effects can result in magnified load conditions. The resulting loads can be well in excess of those deemed allowable by regular casing design techniques. These loads are often ignored in standard well design, exposing casing to the risk of failure during multistage fracturing. In this work, the major factors influencing normal and special loads on production casing in shale wells are discussed. A method for optimization of shale well production casing design is then introduced. The constraints on the applicability of different design options are discussed. Load-magnification effects of cement voids are described, and a method for their evaluation is developed. Thermal effects during cooling are shown to create both bending stress magnification and annular pressure reduction caused by fluid contraction in trapped cement voids. This can result in significant loads and new modes of failure that must be considered in design. The performance of connections under these loads is also discussed. Examples are provided to illustrate the key concepts described. Finally, acceptable design options for shale well production casing are discussed. The results presented here are expected to improve the reliability of shale well designs. They provide operators with insight into load effects that must be considered in the design of production casing for such wells. By understanding the causes and magnitude of load-augmentation effects, operators can manage their design and practices to ensure well integrity.

Managed Pressures Drilling (MPD) offers the capability to detect very small influxes when compared to using conventional rig equipment. Furthermore, the potential exists to control and circulate out the influx with the MPD equipment, without shutting in and performing conventional well control. When executed appropriately, this approach to managing an influx represents a higher degree of safety and enormous cost savings. However, managing an influx with MPD, particularly when a subsea BOP is in place, is quite different to conventional well control. A critical part of implementing MPD is to ensure that there is a clearly defined procedure for determining when MPD influx management must cease, and well control be initiated. A typical approach, regulated in some regions and voluntarily followed in others, is to create an MPD Operations Matrix before the operation begins, which outlines procedures that should be followed based on identifiable parameters following an influx. This matrix clearly identifies when it is appropriate to carry on with normal MPD operations, perform specific MPD influx control strategies, or shift to conventional well control. Forming the MPD Operations Matrix, however, can be challenging and has frequently been created inappropriately for the situations in which its use is intended. Development of a good understanding of how the well pressures and flow rates behave during MPD influx management is critical to ensuring a seamless handover between MPD influx management and Well Control. In this work, extensive transient multiphase simulation is used to demonstrate the sensitivity of surface pressures to well, drilling and influx characteristics and their resulting importance in the development of an operations protocol. Particular attention is given to influx volume, intensity and dispersion within a water based drilling fluid. Also considered are multiple wellbore geometries with primary focus on deepwater applications, oil based drilling fluid, pump rate and drilling fluid density and rheology. Where possible, findings are validated using recorded field data. This paper discusses and defines the transition between MPD influx management and conventional well control. The key parameters for calculating the boundaries of MPD influx management are determined and a protocol developed for smooth handover to well control operations. The protocol enables guidance to varying levels of influx management ranging from full influx detection and removal using the MPD equipment, to assisted shut in.

A Petrobras deep water exploration well is planned to be drilled in over 2438 m (8000 ft) of water offshore Brazil. As is typical of deep water wells, it has a narrow drilling window between pore pressure and fracture gradient requiring many casing strings to reach TD. Because pressure related problems are often extremely costly when drilling conventionally in deep water, initial design assumptions were conservative, assuming the maximum pore pressure and minimum fracture gradient for casing point and pipe selection. As with all conventional casing designs, the resulting pipe has limited capacity to withstand increased burst and collapse loads associated with extending hole sections if the opportunity arises. Managed Pressure Drilling (MPD) enables the development of an adaptive well design by providing three key advantages over conventional drilling; 1) The ability to detect kicks and losses extremely accurately (in gallons, rather than barrels); 2) The ability to rapidly respond to and dynamically control detected kicks and losses by adjusting backpressure on the annulus, keeping their volumes small; and 3) The ability to perform dynamic pore pressure and formation integrity tests. Detecting and responding to kicks rapidly allows for the well to be designed with smaller kick tolerances. Furthermore, by keeping the kicks small they can be circulated out quickly without requiring conventional time consuming well control operations which often lead to further hole problems. When this advantage is coupled with dynamic pore pressure and dynamic formation integrity tests, real time optimization of casing points can be achieved safely with reduced risk of costly well control incidents. The method presented here, applicable to any deep water well, uses low, expected and high pore pressure / fracture gradient estimates to develop an adaptive casing design for the well. In this paper, kick tolerance calculations for selecting casing points using MPD are defined. The effect of reduced kick tolerance requirements due to the application of MPD is demonstrated and finally, an adaptive procedure for real time design optimization of the well is presented. The method results in decision criteria that identify key depths where casing strings can be eliminated without compromising the ability to reach objective TD. The resulting adaptive casing design will most likely eliminate at least one and has the potential to eliminate two casing strings, representing significant cost savings.

Managed Pressure Drilling (MPD) dynamic influx control techniques offer substantial advantages over conventional well control, including reduced influx size, and the ability to control and circulate an allowable influx without requiring conventional methods. With careful planning and execution, MPD dynamic influx control can yield considerable increases in safety and efficiency.Many issues with conventional well control, particularly in deepwater operations, can be mitigated or even eliminated using dynamic influx control. Notably, conventional methods passively rely on the influx to increase wellbore pressure sufficiently to balance reservoir pressure, resulting in needlessly large influx volumes. In contrast, MPD methods quickly detect and actively apply pressure to control an influx in a fraction of the volume.Furthermore, conventional influx removal methods are typically slow, leading to drawn out well control events with high likelihood of further complication, such as stuck pipe and secondary influxes. Conversely, using dynamic influx control, an allowable influx may be controlled and removed from the wellbore in a few hours, not days.In this work, methods that address concerns with current well control practices through application of dynamic influx control are outlined. In addition, transient, multiphase simulation is used to demonstrate comparison between dynamic influx control and conventional well control, clearly quantifying potential benefits of adopting these new methods.

A Petrobras deepwater exploration well is planned to be drilled in water depth greater than 2438 m (8,000 ft) offshore Brazil. As is typical of deepwater wells, it has a narrow drilling window between pore pressure and fracture gradient, requiring many casing strings to reach total depth (TD). Because pressure-related problems are often extremely costly when drilling conventionally in deep water, initial design assumptions were conservative, assuming the maximum pore pressure and minimum fracture gradient for casing-point and pipe selection. As with all conventional casing designs, the resulting pipe has limited capacity to withstand increased burst and collapse loads associated with extending hole sections if the opportunity arises.Managed-pressure drilling (MPD) enables the development of an adaptive well design by providing three key advantages over conventional drilling: the ability to detect kicks and losses extremely accurately (in gallons, rather than barrels); the ability to rapidly respond to and dynamically control detected kicks and losses by adjusting backpressure on the annulus, keeping kick volumes small; and the ability to perform dynamic pore-pressure and formation-integrity tests. Detecting and responding rapidly to kicks allows for the well to be designed with smaller kick tolerances. Furthermore, by keeping the kicks small, they can be circulated out quickly without requiring conventional, time-consuming well-control operations, which often lead to further hole problems. When this advantage is coupled with dynamic pore-pressure tests and dynamic formation-integrity tests, real-time optimization of casing points can be achieved safely with reduced risk of costly well-control incidents.The method presented here, applicable to any deepwater well, uses low, expected, and high pore-pressure and fracture-gradient estimates to develop an adaptive casing design for the well. In this paper, kick-tolerance calculations for selecting casing points by use of MPD are defined. The effect of reduced kick-tolerance requirements because of the application of MPD is demonstrated, and an adaptive procedure for real-time design optimization of the well is presented. The method results in decision criteria that identify key depths where casing strings can be eliminated without compromising the ability to reach objective TD. The resulting adaptive casing design will most likely eliminate at least one, and has the potential to eliminate two, casing strings, representing significant cost savings.