Downhole annular pressure is becoming a standard measurement in all drilling environments. When monitored in the context of other drilling parameters, and with a fundamental understanding of hydraulics principles it is possible to identify undesirable drilling conditions, suggest remedial procedures, and help prevent serious problems from developing. For wells with only a small difference between fracture gradient and pore pressure, drilling without realtime downhole annular pressure information may not be possible. Indeed, this is particularly true for extended reach wells, for high temperature / high pressure (HTHP) wells, and in deep water environments where large flowing friction pressure losses or very narrow pressure margins can exist. Previous publications have discussed how with realtime downhole annular pressure measurements a driller can more effectively maintain the equivalent circulating density (ECD) and equivalent static density (ESD- when not circulating) within a desired range in order to prevent lost circulation and maintain borehole integrity (including managing swab, surge and gel breakdown effects). Annular pressure data are used to evaluate the effects of flow and pipe rotation on the ECD, and to evaluate formation integrity tests. With accurate downhole data the driller can apply conventional drilling practices more effectively to reduce both rig time and potentially also the number of required casing strings. In order to interpret annular pressure measurements it is important to first understand the physical hydrodynamic principles. It is also important to analyze pressure data in the context of all downhole and surface drilling parameters. Recent experiences with downhole pressure data have demonstrated how ECD trends can be used to anticipate drilling problems before they develop into serious events. Even with the ECD within its desired range, drilling problems not apparent from conventional procedures can be anticipated. We present three case histories. The first is from an extended reach drilling project where the annular pressure data gave advanced warning of high cuttings loading, and helped avoid a potential lost circulation or stuck pipe event. This example also illustrates the significant flowing pressure losses that can occur along an extended reach wellbore. A second case history demonstrates the importance of using annular pressure measurements in deep water environments both to establish and maintain safe pressure margins. Downhole pressure data can also be used to evaluate kill procedures. The final example was from an extended reach well where the drilling fluid had sagged during a bit trip, and shows how by evaluating downhole annular pressure measurements, safer and more efficient tripping practices can be developed. P. 535

Major problems are often encountered in relaxed basins when extended reach wells are drilled through depleted reservoirs. As wellbore inclination increases, the imbalance between vertical and horizontal stresses can cause formation breakouts leading to increased cuttings and increasing the potential for stuck pipe. Higher mud densities can stabilize the imbalance and facilitate cuttings transport, but increase the risk of differential sticking and lost circulation. Additionally, higher mud densities can create fractures that take mud while drilling and return mud during connections. This ‘ballooning’ or ‘weeping’ complicates the correct diagnosis and increases the risk of losing the well. Early identification of these competing mechanisms can be critical to successful drilling. Real-time resistivity-at-the-bit images are now possible to aid diagnosis, but are currently limited to water-based muds, and a limited range of conductive oil-based muds (OBMs). Nevertheless, conventional resistivity measurements can still be used in wells drilled with OBM. A case study is described of a highly deviated Gulf Coast well drilled with synthetic OBM that penetrated a severely depleted reservoir. Based on the data collected the original assumption that depleted sands were the only source of lost return zones was in error. The losses were found to be in the bounding shales as well. After losing two wellbores, the project was abandoned due to wellbore instabilities and limited reserves. Investigations into the lessons learnt highlight how multiple passes with both resistivity and annular pressure measurements could have been used to diagnose the location and mechanism of borehole failure, and hence suggest appropriate action. Indeed, the resistivity measurements were found to be responding to induced fractures hours before any changes in equivalent circulating density (ECD) or significant drilling observation. A methodology is given for diagnosing drilling induced fractures from the real-time measurements, so that remedial actions can be promptly taken. Success in future operations will come from including these new methods into the drilling plan. Introduction The use of resistivity images to distinguish between natural and drilling-induced fractures has been described by Rezmer-Cooper et al.1,2 While drilling, it is important to distinguish natural features from those induced by the drilling process so that the drilling program can be modified to minimize the impact of the induced fractures. A geological analysis of borehole images includes the search for open natural fractures. Wrongly identifying drilling-induced fractures as natural fractures results in an optimistic forecast, and could lead to incorrect remedial procedures being recommended for the drilling program. However, even though real-time images are now possible, and can now complement existing conventional real-time logging-while-drilling (LWD) measurements, their use is limited to water-base muds or conductive oil-base muds, which are still in their infancy, and have yet to gain wide acceptance.

fax 01-972-952-9435. AbstractBecause of shallow water flow concerns in deepwater wells with narrow stability margins, pressure differences of a few tenths of a lbm/gal can make the difference between straightforward drilling and the need for an extra string of casing to protect shallow intervals. Accurate leak off tests (LOTs) / formation integrity tests (FITs) are essential to enable efficient management of the equivalent circulating density (ECD) within the safe pressure window. • Removing the uncertainties in the compressibility of the drilling fluid; this is particularly true of synthetic muds. • Avoiding the need for additional circulation(s) to condition the mud. • Increasing the accuracy of the LOT/FIT, allowing more precise casing point determination.

The cost of well construction can exceed budget dramatically if drilling operations are plagued by wellbore-instability problems and excessive time and resources are needed to free stuck pipe, regain circulation, or clean the hole efficiently. Annular pressure while drilling has been recognized recently as one of the key downhole measurements for aiding real-time diagnosis of the condition of the wellbore and drilling fluids. In addition to conventional drilling-mechanics measurements, time-lapse logging-whiledrilling (LWD) documents the dynamic change in measured properties during well construction. This can be essential in diagnosing wellbore failure, and the mechanism of failure, in addition to dynamic processes such as cuttings buildup.An example from a horizontal well in the North Sea is used to illustrate how LWD resistivity images can be used in conjunction with annular-pressure-while-drilling measurements to detect the onset of drilling-induced fractures. Although the majority of azimuthal images have been acquired to understand the geology and petrophysics of reservoirs, the images usually contain features resulting from geomechanical processes.Analysis of these features reveals important information for optimizing drilling and understanding the geomechanics of the well. Coupling resistivity images to the pressure measurement enables problem identification and correct remedial actions to optimize the drilling operation, for example, ensuring that swab and surge pressures are kept to a minimum, and correct hole-cleaning procedures are used to prevent irreversible formation breakdown.

Visualization: What value does it bring today, and what can it potentially bring to well construction? Many in the industry today regard it as a gimmick that looks nice and may be good in the Geoscience domain but has no real place in the well construction arena. However, that perspective is rapidly changing. In varying environments outside the petroleum industry three-dimensional visualization has demonstrated many diverse benefits. This paper discusses the gains realised so far and future potentially rich areas to exploit, in the framework of well construction. Visualization allows complicated geometric and computational models to be simply represented; wells can more easily be linked to the larger picture of the field. No longer is there a need to use terms that confuse all but the individual discipline experts, a picture is now available. This speeds and facilitates the communication and mutual understanding of problems and potential solutions. Discipline experts can look for creative solutions to be suggested from their extra-discipline peers, small and subtle changes are much more easily dealt with, and the exercise becomes a shared-learning experience. Teams start to appreciate what is involved in the collaborators disciplines, thereby facilitating future work in the team. Visualization enables a common language to be established for future communication amongst a multi disciplinary team. Mutual understanding and appreciation of problems can greatly enhance team performance. Once a model of a field is created, that includes offset well data from the drilling of the wells, we have, an intuitive repository of knowledge for future well construction projects that can be used by rig-site engineers for real-time decision-making, directional drillers for assessing anti-collision risks, and a simple and effective tool for current or future peer reviews to interrogate and more easily understand historical information in the form of knowledge. Perhaps the most powerful benefit of all for the technique is the draw that it provides to bring people together. Introduction Large-scale visualization has only recently started to come of age, and for most people in the oil industry it is associated with the Geological and Geophysical (G&G) side of the business. Extensive mapping of fields and key geological surfaces, viewed simply and easily in an integrated environment has become commonplace. In the world of drilling, viewing of complex directional plans in a multi well environment is more routine than ever. In some cases the progress of the wells can even be monitored in real-time1.