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Thibodeaux, H. (Chevron) | Williams, J. (Chevron) | Duhe, N. (Chevron) | Milazzo, J. (Chevron) | Kvalo, M. (Schlumberger) | Deplaude, O. (Schlumberger) | Vargas, N. (Schlumberger) | Hobin, J. (Schlumberger) | Jesudas, J. (Schlumberger) | Clements, J. (Schlumberger)
The Permian basin has been one of the main drivers leading the recovery of recent drilling activity on U.S. land. It has been a focus for drilling activity that has targeted conventional reservoirs since the first well was drilled in 1925. Through the depletion of conventional reservoirs, fracture pressure in these zones has decreased due to the reduction in pore pressure. Some of these previously drilled reservoirs throughout the Permian Basin have been selected for the reinjection of produced water which has caused abnormal pore pressures to occur. The combination of having both loss and injection zones exposed in the same drilling interval has resulted in challenges for operators as they have to navigate the resulting mud weight windows of highly developed fields of the Midland and Delaware Basins. As development throughout the Permian basin continues, these mud weight windows will only become more difficult to manage.
In one of Chevron's highly developed Midland Basin fields, managing the exposed injection and loss zones in the intermediate hole section proved to be challenging. This hole section had routinely experienced severe to complete losses upon entering the Upper Spraberry formation as a result of trying to manage higher pressures inflicted by the San Andres formation, a shallower injection zone. The mud weight could not be reduced to mitigate these losses without inducing an influx from the San Andres. Circulation could often not be reestablished upon entering the Spraberry formations which resulted in mud cap or blind drilling in order to reach section total depth (TD). These losses and overall wellbore conditions introduced higher risk and consequences in the form of well control events, wellbore instability, and mechanically or differentially sticking 9-5/8" casing prior to reaching planned set point. The immediate solution to isolate the wellbore problems was to implement a contingency liner, which comes at a premium and decreases drilling and completions efficiencies of the production hole section.
Managed pressure drilling techniques were identified as a solution to simultaneously navigate a shallow injection zone and a deeper loss zone within the same hole section. The necessary equivalent mud weight profile was established through the reduction of MW and the addition of surface back pressure. This enabled a higher equivalent mud weight to be held at the shallow injection zone and a lower equivalent mud weight to be held across the loss zones. Additionally, managed pressure cementing techniques were used to achieve a similar pressure profile during cementing operations in order to increase the likelihood of maintaining returns while placing cement across the loss zones.
Managed pressure drilling and cementing techniques implemented in this field contributed to the elimination of contingency liners and significant non-productive time in hole sections where both injection zones and loss zones were exposed. As laterals are extending beyond 10,000’ across the Permian Basin, the team has collectively proven the concept that the MPD system is part of an equipment package that can eliminate contingency liners and deliver the preferred sizes of production hole and production casing that is crucial to successfully reaching TD and efficiently placing hydraulic fracturing jobs at optimal rates.
A reentry drilling campaign of six highly deviated wells was successfully drilled from a fixed offshore platform through depleted reservoirs by utilizing managed pressure drilling in eight hole sections. The main challenge was the narrow drilling window of 0.05 to 0.60 ppg between wellbore stability mud weight, driven by unstable shales, and reduced fracture gradient of the reservoir sands, driven by depleted pore pressure. The necessity to balance risk of lost circulation, hole cleaning, and wellbore stability drove the team to employ new technology in order to achieve success. Managed Pressure Drilling (MPD) is one of several technologies for optimizing drilling operations and reducing Non-Productive Time (NPT) while drilling narrow windows. The Surface Back Pressure (SBP) variant of MPD can be used not only on exploration wells with pore pressure uncertainties to identify and control influxes, but also can be employed in severely depleted reservoirs to enable drilling operations which are conventionally unattainable due to constricting drilling window. This case study discusses the main objectives and requirements for MPD, along with the planning, equipment, and execution strategies used to drill and make connections with a mud weight statically underbalanced to wellbore stability gradient. Furthermore, the paper discusses the use of novel pressure testing techniques and automated fluid displacements with the MPD system to maintain a constant anchor point pressure prior to tripping and avoid losses and wellbore collapse. Finally, this study provides results, achievements, and recommendations on SBP application in a brownfield reservoir.
Copyright 2013, Unconventional Resources Technology Conference (URTeC) This paper was prepared for presentation at the Unconventional Resources Technology Conference held in Denver, Colorado, USA, 12-14 August 2013. The URTeC Technical Program Committee accepted this presentation on the basis of information contained in an abstract submitted by the author(s). The contents of this paper have not been reviewed by URTeC and URTeC does not warrant the accuracy, reliability, or timeliness of any information herein. All information is the responsibility of, and, is subject to corrections by the author(s). Any person or entity that relies on any information obtained from this paper does so at their own risk. The information herein does not necessarily reflect any position of URTeC. Any reproduction, distribution, or storage of any part of this paper without the written consent of URTeC is prohibited. Abstract When operators face complex pressure regimes that make conventional drilling in horizontal applications difficult, the implementation of managed pressure drilling (MPD) techniques has proven successful in achieving planned well objectives while minimizing nonproductive time (NPT) from pressure and stability related events. When properly planned and executed, MPD techniques can ultimately reduce overall time and cost of even the most complex wells by managing the challenges from narrow pressure profiles. MPD, where a constant bottomhole pressure (BHP) dynamic target is at, or just above, reservoir/pore pressure for drilling, during connections and tripping, and also while running casing and during cementing operations, offers solutions for many of today's challenges in horizontal applications. This dynamic target BHP for horizontal applications, whether controlling at the curve, the heel, or the toe (an exclusive technology), can be dialed into ―on demand‖ according to current conditions and situations encountered using these automated techniques.
The naturally fractured Buda formation, which underlies the Eagle Ford shale play across central and south Texas, is experiencing resurgence in exploration and production activity as a result of improvements in horizontal and underbalanced drilling techniques. Formed during the Cretaceous period, the Buda formation was produced from vertical wells for decades, leaving aside the potential of crossing all the vertical fractures and associated recoverable hydrocarbons. However, many fractures in the Buda formation are underpressured because not filled with hydrocarbons from the overlying Eagle Ford formation. The application of Underbalanced Drilling in horizontals wells to drill Buda wells is today showing excellent results.
The underpressured nature of some fractures in the Buda dictates that wells be drilled underbalanced; drilling the formation conventionally typically results in issues such as considerable circulation losses and then associated kicks when drilling through depleted and filled fractures. In certain areas, the Buda formation also presents the challenge of hydrogen sulfide gas (H2S), which poses environmental and safety issues. In some cases, the Buda's fracture systems may be vertically extensive enough to establish hydraulic continuity with underlying formations, a situation that could result in extraneous water production.
This paper examines a case study employing Underbalanced Drilling (UBD) techniques to drill a well in the Buda Limestone formation. Before embarking on the project, the operator conducted a six-county assessment of the Buda, comparing wells that were drilled using a conventional mud system with wells that were drilled using underbalanced drilling techniques. A significant concern with drilling the wells conventionally was that the weight of the drilling fluid column would create pressure against the 5.0 pounds per gallon (ppg) or less from sub pressured fractures from Buda formation, which could result in severe to total loss of drilling mud. Even drilling this formation with freshwater applies 8.33 ppg of pressure for a column of fluid. The study revealed the UBD wells mitigated the loss of drilling fluid and allowed the producing section to be drilled successfully to total depth. Using UBD techniques also yielded significant improvements in production through its ability to prevent drilling mud and chemical additives from invading the drilled formation.
With the UBD approach, the operator was able to drill the production section of eleven wells (at today) to TD (Target Depth) using an open-hole completion and effectively control low-pressure zones. The approach resulted in benefits such as reducing rig time and nonproductive time (NPT), incurring minimal fluid losses, obtaining early production of crude while drilling, and characterizing the reservoir for future developments.
As the industry continually strives to meet the ever-growing demand for hydrocarbons worldwide, new technologies are seeing expanded application not only in emerging, but in mature conventional plays with untapped potential. UBD technology was combined with advanced MWD tools, mechanically operated wellbore isolation devices, multibore wellhead system and efficient four phase separation. This has provided the operators an opportunity to have a second look at the Buda formation and overcome steep challenges to produce wells more efficiently and economically than before.
Epps, Steve (Lavaca River Operating Company) | Pellegrini, Thomas (Lavaca River Operating Company) | Valecillos, Juan C. (Weatherford International Ltd.) | Craig, Hunter (Weatherford International Ltd.) | Arnone, Maurizio (Weatherford International Ltd.)
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.