Khalid, Ali (Weatherford International Ltd) | Ashraf, Qasim (Weatherford International Ltd) | Luqman, Khurram (Weatherford International Ltd) | Moussa, Ayoub Hadji (Weatherford International Ltd) | Nabi, Agha Ghulam (Pakistan Petroleum Limited) | Baig, Umair (Pakistan Petroleum Limited) | Mahmood, Amer (Pakistan Petroleum Limited)
Carbonate platforms are one of the most common reservoirs on earth, and as such are one of the most frequently explored.
Sulaiman fold belt in Pakistan is known to contain multiple hydrocarbon bearing carbonate formations. One such formation is the Sui Main Limestone formation. The formation when first discovered was known to contain over 9.5 Tcf of gas in Sui field, and up to 5.0 Tcf of gas in the neighboring Zin field. Over the years due to extensive field development and production, the Sui Main Limestone reservoir has been driven to depletion. Operators are now looking to explore deeper horizons in the same fields.
The challenge in deeper exploration of the subject fields is now a depleted pressure of about 2.1 ppg EMW of the Sui Main Limestone formation. In addition to the low pressure, the SML formation is highly fractured in nature. These two factors resulted in massive circulation losses when an attempt to drill a well was made through the approximately 650 m width of the SML formation. To cure losses, operators resorted to heavy LCM pills, and numerous cement plugs. Losses in the hydrocarbon bearing SML formation also led to well control and stuck pipe events on multiple occasions. Successful drilling through the whole width of SML formation would sometimes take up to almost 3 months. Drilling time and lost circulation materials thus generated excessive well costs.
The operator sought a solution which would eliminate circulation losses in the SML formation, and cut down drilling time substantially. An underbalanced system was first considered for achieving these objectives but as the SML formation bore sour gas and excessive equipment would be required for a safe underbalanced operation, the option was ruled out. A nearbalanced nitrified foam system was thus designed to be able to drill the SML formation delivering the same benefits of an underbalanced operation without its perils.
By applying a nearbalanced nitrified drilling technique, operators in the subject fields were able to cut down the drilling time to about 3-5 days, achieve a substantial increase in drilling performance, and practically reduce the NPT to 0.
This paper studies the planning & design of a nearbalanced nitrified foam system for two different wells with hole sections of size 17", and 8-1/2". The paper also discusses the equipment selection, the wellsite execution, and the results achieved by applying nearbalanced nitrified foam drilling in the subject fields.
Ashraf, Qasim (Weatherford International Ltd) | Khalid, Ali (Weatherford International Ltd) | Ali, Farhad (Weatherford International Ltd) | Luqman, Khurram (Weatherford International Ltd) | Mousa, Ayoub (Weatherford International Ltd) | Babar, Zaheer Uddin (Pakistan Petroleum Limited) | Hussam Uddin, Muhammad (Pakistan Petroleum Limited) | Ullah, Safi (Pakistan Petroleum Limited)
An operator has drilled more than 32 wells to date in Adhi field, a gas and condensate field in northern Pakistan. The majority of these wells produce from depleted sands and some also produce from limestone reservoirs. The wells range in depth between 8,366 and 11,483 ft (2,550 and 3,500 m).
The operator was in the process of drilling the 8 1/2-in. hole section with the least possible mud weight to minimize the overbalance across the lost-circulation-prone limestone formation. While drilling the section, an unexpected gas pocket was encountered and subsequently required an increase in mud weight. To further add to already challenging drilling conditions, a fault was expected in the middle of the section. This fault was expected to produce total losses. The resulting loss of hydrostatic head would have caused a troublesome well-control scenario.
The above conditions led to an inherently tight drilling window. The operator thus made precise management of wellbore pressures a prime objective. However in conventional drilling, relying on the mud weight and pumping rate for accurate management of wellbore pressures proves highly inefficient, if not impossible.
A managed pressure drilling (MPD) and underbalanced drilling (UBD) hybridized system was devised to enable drilling the 8 1/2-in. hole section. An MPD system that applies constant bottom hole pressure would enable drilling the section with the least possible mud weight and as close as possible to the pore pressure line. In the event that heavy to total losses were encountered because of the predicted fault, the system could be switched over to UBD flow drilling. By switching over to UBD, the equivalent circulating density (ECD) would be reduced further and allow the well to flow while drilling and mitigating losses.
An MPD and UBD system was also expected to offer numerous benefits in drilling, including reduced chances of differential sticking, reduced formation damage, increased rate of penetration and bit life, less washouts in the drillstring and pumps, reduced nonproductive time, and enhanced abilities to execute well control with the pipe in motion without fear of getting stuck.
The MPD and UBD hybrid system was deployed to the location. The operator was able to drill the 8 1/2- in. section to the target depth. The operator commenced drilling with an MPD system but, as expected, heavy losses were encountered. Drilling then proceeded with UB flow drilling until reaching target depth. The hybrid system enabled the operator to achieve target depth, eliminate an entire casing string, and substantially reduce NPT. This paper discusses the planning, design, and execution of the MPD and UBD hybrid system.
This case study highlights the field-trial of a pump-out stage tool, pump-out float collar, and the annular casing packer. These technologies were integral to drilling and completing wells in the Santos coal-seam gas (CSG) development of the Roma field in the Surat Basin of southeast Queensland.
Pump-out systems—which allow a primary cementing job to be performed above a slotted casing string using a pump-out stage tool, annular casing packer, and pump-out float equipment—eliminate the need for drill out operations. Once the casing is landed, a ball is deployed from surface to actuate the inflation of an annular casing packer below the stage tool and above the slotted casing. A second ball is deployed to shear and shift a sleeve to open the stage tool and begin the primary cement job. Once complete, a cementing wiper plug is released from surface and pumped behind the cement slurry to shift the stage tool into the closed position. The internal pump-out casing components are displaced to the bottom of the well and require no further intervention.
This case history includes results of the initial field-trial runs and technical details on well configurations, slotted liner placement across the coal-bed intervals, pressure charts, cement-job data, shear information on the ball seat, detail on the stage-tool operation, pumping out the float collar, and displacement of the internal equipment downhole. These jobs planned to eliminate the need to run a dedicated drillout trip during initial completion and also the need to change out the pipe rams in the blowout preventer (BOP).
Ultimately, the pump-out system provides a full-bore casing geometry with no internal restrictions and is expected to reduce completion costs by 15%.
The adoption of segregated drilling campaigns is commonplace in an effort to harness economies of scale and reduce well construction costs. In an attempt to increase the financial efficiency of drilling campaigns, the division of the well construction and completions operations can be segregated into two distinct phases. A drilling and casing phase leaving a cased well in a Temporary Abandonment (TA) status, followed by a phase consisting of clean-up, completion and stimulation operations resulting in the handover of the well to production to bring hydrocarbon production online. As such an Intervention and Completion Unit (ICU) with the capability to perform perforation, multi-zone completion installation, stimulation, clean-up operations and well testing has significant advantages when deployed in the later phase of a segregated multi-phase drilling campaign.
This paper describes the collaborative development of an ICU that facilitates the installation of multi-zone and smart well completions, conveyance for well servicing operations, well bore clean-up (WBC) activities, well testing and stimulation activities. The challenge of undertaking traditional drilling phase activities with a technically capable, yet cost effective ICU is discussed, particularly the core areas where the reduction in specification through it being redundant for the phased operations.
The key parameters driving the ICU development and design are presented from the operator's perspective, based on prior campaign experience utilizing this approach with alternative technology. The process identifying the key requirements of the completion and well servicing operations is described with the selection of implementing new technology solutions in the design. The avoidance of Non-Productive Time (NPT) is a core aspiration in making incremental cost efficiencies. The identification of operations not on the critical path that can be performed simultaneously or as an offline activity, have the potential to make high cost impacts.
Through innovative design and the implementation of novel and field tested technology, allied to extensive use of offline activities as concurrent operations, the ICU has the potential to make significant cost savings in a segregated well construction project. Collaboration between the operator and service provider drives a design which provides a technically pragmatic and capable ICU and as such attracting project cost savings allied to lower support equipment costs. Further, the deployment flexibility of the ICU allows it to perform operations ranging from well construction activities such as well slot preparation, completions and intervention, to well deconstruction activities such as heavy workover, Permanent Abandonment (PA) phases and slot recovery. The ability to perform multi-phase operations whilst mobilized to a platform brings further cost benefits and operational flexibility.