Multiple operators had attempted to conventionally drill wells in an area of south Texas targeting an over pressurized sand. A majority of them were unsuccessful showing a history of lost time events and poor well results related to kicks and losses. Information suggests little was known about the pore and fracture pressure gradients, and that uncertainties regarding real stratigraphic distribution were present, resulting in improper casing points and mud trends not in accordance with actual wells requirements. For these reasons, one operator decided to implement Managed Pressure Drilling (MPD) technology in order to safely and efficiently drill a well to the pay zone.The scope of the operation was a re-entry sidetrack on a vertical well that originally encountered well control and multiple mud losses events. The first interval was an 8-1/2 inch intermediate section to be cased with a 7 inch liner. The liner shoe was to be set approximately 80 feet above the over pressurized target sand. The second interval was a 6-1/8 inch production section targeting the well pay zone, to be cased with a 4-1/2 inch production casing. Both intervals were considered critical, the first one having depleted zones interbedded with gas bearing formations with a final depth immediate to abnormal gas pressures, and the second demanding accurate ECD management to avoid well control events, losses and formation damage, this of cardinal interest for the operator.The implementation of MPD enabled both intervals to be drilled to the planned target in a constant bottom hole pressure (CBHP) state safely and efficiently. The well was drilled near balanced to improve drilling efficiency and increase the ability to identify pore pressures. The annular pressure profile was adjusted instantly as the well dictated by means of MPD surface equipment avoiding kicks and losses. Continuous evaluation and monitoring of well behavior in real time allowed for pore pressure predictions, which were later used to plan proper kill mud weights, tripping/stripping procedures, and managed pressure cementing operations. Implementing MPD techniques and technology proved successful in enhancing safety and drilling efficiency on a well with many uncertainties and potential hazards. This paper will describe the planning and execution of a successful drilling operation on a high potential oil/gas producer well using MPD techniques in an area where others were unsuccessful.
Two hole sections (12-1/4Љ ϫ 14-3/4Љ and 10-5/8Љ ϫ 12-1/4Љ) were planned to be drilled through sequences of unstable shale and depleted sand packages with no drilling windows, which are defined by the shale Wellbore Stability Gradient (WBSG) delimited by the "intact wellbore wall zero failure degree" and the depleted sand fracture gradient criteria. Historically, significant non-productive time (NPT) associated with wellbore instability and lost circulation had resulted in sidetracks and other costly remediation in both hole sections. The operator and the service provider have identified the Constant Bottomhole Pressure (CBHP) variant of Managed Pressure Drilling (MPD) and wellbore strengthening as the necessary technology approach to safely drill through both challenging hole sections. Dynamic and static wellbore strengthening were applied to increase the near wellbore stresses across the depleted sands to create a drilling window, whilst the MPD CBHP was used to mitigate bottom hole pressure fluctuations and cyclic stress across the shale packages.The MPD well evaluated in this paper had just four hours of non-productive time related with downhole problems and wellbore stability, a minimal fraction when compared to the 980 hours lost in the previous conventional offset well. The MPD well did not require any back reaming operation, whereas the offset well in the area required 7 back-reaming events to get a good quality wellbore. A total of 533 hours were required to drill the 2 hole sections in MPD compared to the 2,410 hours required to drill the same sections conventionally in a previous offset well in the area. This paper summarizes the key MPD planning, engineering, results obtained and lessons learned that delivered a successful campaign of producer wells.
Challenging conditions in a HP/HT well in the UK Central North Sea, led to the deployment of a contingent expandable liner. Under-reaming tools were needed to facilitate running of the contingent liner. Under-reaming operations are associated with a degree of uncertainty on the final hole diameter. A technology was deployed to monitor cutter position, wear and vibrations. With the aim of removing the above uncertainty. An open-hole calliper run was performed to validate the technology. The monitoring system utilizes an arrangement of sensors to measure variables that are critical to under-reaming operations. The sensors are housed within the expandable cutting structure of the under-reamer and comprises of a cutter block position indicator and a PDC cutting structure wear sensor. The monitoring system can also record downhole dynamics at the under-reamer. The system can therefore determine, via memory data, the actual under-reamer extension size at any point during the run, therefore allowing the minimum hole diameter to be derived. Providing immediate feedback at the rig site once the tool is at surface. The first run globally of the 12 ¼" × 14" size is presented, the monitoring system recorded 187 hrs of data. The cutter blocks position sensor showed the cutting structure was fully expanded as required whilst pumping at drilling flow rate once the tool was activated. The wear sensors were fully active and showed no wear for the duration of the systems battery life. A combination of the positional and wear sensors indicated full gauge hole to the recorded depth. Due to the type of contingent liner the delivery of gauge hole was critical. As such, the data was validated using a dedicated open-hole calliper run on wireline. The calliper confirmed the open-hole diameter calculated based on data provided by the wear and position sensors. Based on this result the requirement for an open-hole calliper run can be reconsidered. In addition, the acceleration recorded was well correlated with the MWD recorded vibration data and allowed parameter recommendations to be generated. The ability to monitor the position and status of the under-reamer cutting structure eliminates uncertainty on the final hole size following under-reaming operations and identifies any problem areas and their probable causes prior to running casing/liner. In turn this has the potential to eliminate the need for wireline runs and therefore reduce the open-hole time in a potentially unstable formation.
Two hole sections (12-1/4Љ x 14-3/4Љ and 10-5/8Љ x 12-1/4Љ) were planned to be drilled through sequences of unstable shale and depleted sand packages with no drilling windows, which are defined by the shale Wellbore Stability Gradient (WBSG) delimited by the Љintact wellbore wall zero failure degreeЉ and the depleted sand fracture gradient criteria. Historically, significant non-productive time (NPT) associated with wellbore instability and lost circulation had resulted in sidetracks and other costly remediation in both hole sections. The operator and the service provider have identified the Constant Bottomhole Pressure (CBHP) variant of Managed Pressure Drilling (MPD) and wellbore strengthening as the necessary technology approach to safely drill through both challenging hole sections. Dynamic and static wellbore strengthening were applied to increase the near wellbore stresses across the depleted sands to create a drilling window, whilst the MPD CBHP was used to mitigate bottom hole pressure fluctuations and cyclic stress across the shale packages.The MPD well evaluated in this paper had just four hours of non-productive time related with downhole problems and wellbore stability, a minimal fraction when compared to the 980 hours lost in the previous conventional offset well. The MPD well did not require any back reaming operation, whereas the offset well in the area required 7 back-reaming events to get a good quality wellbore. A total of 533 hours were required to drill the 2 hole sections in MPD compared to the 2,410 hours required to drill the same sections conventionally in a previous offset well in the area. This paper summarizes the key MPD planning, engineering, results obtained and lessons learned that delivered a successful campaign of producer wells.
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