Ashraf, Qasim (Weatherford International Ltd.) | Khalid, Ali (Weatherford International Ltd.) | Luqman, Khurram (Weatherford International Ltd.) | Hadj-Moussa, Ayoub (Weatherford International Ltd.) | Shafique, Muhammad Bilal (MOL Pakistan Oil & Gas Co. B.V.) | Abbas, Khurram (MOL Pakistan Oil & Gas Co. B.V.) | Tashfeen, Muhammad (MOL Pakistan Oil & Gas Co. B.V.) | Khan, Shahjahan (MOL Pakistan Oil & Gas Co. B.V.) | Jameel, Rizwan (MOL Pakistan Oil & Gas Co. B.V.)
The Northern Potwar Plateau of Pakistan is known for its severe geological features. Many wells have been drilled in the region, but geological correlations in neighboring fields have proven to be challenging. Excessive tectonic activity and faults have resulted in formation repetitions, abnormal in-situ stresses, and variable formation pore and fracture pressures.
One such field in the region is MDK field, where the operator was in the process of drilling a second well. Drilling of the 8 ½-in. hole section was in progress at 11,004 ft. (3,354 m) when the Bahadur Khel Salt formation was encountered. Upon drilling further into the formation, the operator encountered severe hole stability issues coupled with lost circulation. While in the salt formation, whenever circulation was stopped and annular pressure losses were eliminated, the drill string would become stuck. Upon resuming circulation, the pumping pressure would rise abruptly. The formation was highly stressed and was exhibiting a creeping behavior. Any reduction in the bottom hole pressure (BHP) would cause the formation to creep into the wellbore.
The operator spent a month attempting to drill through the highly stressed plastic salt formation, without success. The oil-based mud system was already weighted up to its maximum, and no other conventional means existed of controlling the creeping salt. The operating company had already spent ~USD 19 million dollars on the well, and was considering abandoning it after a nearby well in the same formation had been abandoned despite four unsuccessful sidetracks.
Maintaining a constant bottom hole pressure (CBHP) across the formation at all times was the only way to stabilize the salt formation and lost circulation treatment. Only managed pressure drilling (MPD) could achieve the application of CBHP. An MPD system would enable the operator to compensate for the lack of BHP by applying surface backpressure, thereby maintaining the target pressure across the formation at all times. With the help of the MPD system, the operator also sought to calculate the formation creep rate, so as to evaluate a time window for running in and out of the hole.
Besides drilling, the operator also intended to isolate the challenging section with a liner. With proper planning, the MPD system could help to achieve this objective.
A full MPD system was deployed to the wellsite and drilling resumed with a CBHP in dynamic and static periods. By CBHP MPD, the operator was able to tag bottom. Drilling and underreaming of the 8 ½-in. hole section resumed and continued until reaching the target depth of 14,745 ft. (4,494 m). After drilling, the 7-in. liner was set and cemented to the target depth using MPD.
Applying CBHP MPD enabled the operator to drill through 3,832 ft. (1,168 m) of the hole section and save the well from abandonment. This paper studies the design, execution, and lessons learned when applying MPD on the subject well.
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.
The Dhodak field is located in the eastern Sulaiman Range in Pakistan. The first well drilled there in 1975 produced gas and condensate from the Pab sandstone intervals created in the Cretaceous Age. Drilling any well in the field results in severe circulation losses because of the younger carbonate horizons of the Eocene Age, which includes the Habib Rahi and Rubbly Limestone. Operators cure these losses by spotting lost-circulation material (LCM) pills and deploying numerous cement plugs. In one particular well in the Dhodak field, an operator encountered an unexpected well-control scenario when drilling through the Rubbly Limestone, which further confirmed the potential for hydrocarbons in the horizon.
To explore the potential of the Rubbly Limestone, the operator drilled a dedicated well named Rubbly-1 using a conventional mud system and, as expected, encountered total loss of circulation. Drilling continued to the target depth, with heavy LCM pills and four cement plugs to cure losses. A prospective production interval was identified, and subsequent drill stem testing (DST) was performed. The well did not flow in the DST even after numerous attempts to kick it off. An evaluation determined that bridging materials had extensively invaded the formation when attempting to cure losses. The invading materials had clogged the pores of the reservoir formation, which resulted in no production and subsequent abandonment of the well.
Underbalanced drilling provided a feasible solution that allowed the well to flow while drilling and eliminated overbalanced pressures and invasion damage. The reservoir pressure measured just 5 lb/gal (599 kg/m3) in equivalent mud weight. The low pressure of the formation meant it could only be drilled with a foam system.
A suitable foam system provided a low equivalent circulating density that enabled drilling the Rubbly Limestone formation. By applying an underbalanced nitrified foam system, the operator drilled the horizontal to the target depth (TD) without any issues. The well started flowing while drilling, and the operator evaluated the reservoir potential by performing surface testing and openhole wireline logging, which resulted in logs with excellent resolution. This paper details the design criteria, equipment selection, and wellsite execution program used for drilling and evaluating the Rubbly Limestone formation.
Khalid, Ali (Weatherford International) | Ashraf, Qasim (Weatherford International) | Luqman, Khurram (Weatherford International) | Takla, Elie (Weatherford International) | Nabi, Agha Ghulam (Pakistan Petroleum Limited) | Ashraf, Sajjad (Pakistan Petroleum Limited) | Hasan, Naveed (Pakistan Petroleum Limited) | Ali, Muhammad (Pakistan Petroleum Limited)
Located in Sindh on the right bank of the Indus River, the Kandhkot Gas Field was discovered in 1959 and was estimated to contain up to 680 Bcf of gas reserves. The field contains three producing formations: Habib Rahi Limstone, Sui Upper Limestone, and Sui Main Limestone. The Sui Main Limestone formation has been depleted because of extensive production, and it currently exhibits a very low pressure of approximately 3.5 lb/gal (419 kg/m3) equivalent mud weight (EMW).
An operator drilling with a conventional mud system encountered total losses and resorted to heavy lost-circulation material (LCM) pills and cement plugs to cure them. All bridging materials pumped in the hole to cure losses invaded the reservoir formation. As a result, the completed well required excessive cleanup operations to bring it into production. Therefore, the operator faced costs of loss curing materials, damage to the reservoir formation, and a substantial amount of time for drilling and cleanup operations.
The operator sought a solution to not only reduce the costs associated with drilling this highly depleted reservoir formation, but also mitigate invasion damage that inevitably affects overall production volumes. Although underbalanced drilling had been used in similar situations, the operator considered the challenges of this well before execution. The horizontal well design contained a vertical section of about 1,640 ft (500 m). Challenges to account for while drilling the horizontal leg included designing appropriate directional drilling equipment for use with a multiphase fluid, cleaning the hole in the horizontal leg, maintaining underbalanced wellbore pressures in the presence of high annular pressure loss, and achieving drilling performance to offset the cost incurred by underbalanced drilling.
For the given reservoir pressure of 3.5 lb/gal (419 kg/m3) EMW, a nitrified foam system was designed to achieve an equivalent circulating density (ECD) below 3.5 lb/gal (419 kg/m3) EMW. The foam system used a specially formulated polymer system to yield a high foam quality for suspension and cutting carrying capacity. The directional drilling equipment consisted of a special mud motor and extended range electromagnetic measurement-while-drilling (MWD) system to enable drilling with a multiphase fluid system. In addition, a downhole isolation valve deployed inside the casing string enabled isolating the live well while tripping. Using the custom underbalanced system, the operator drilled the well to total depth (TD) in just 3 days and achieved an ROP average of 49 ft/hr (15 m/hr). The paper outlines the planning and design of the underbalanced drilling package, the wellsite execution, and the achieved results.
Khalid, Ali (Weatherford) | Ashraf, Qasim (Weatherford) | Nusair, Mohd. Khair (Weatherford) | Luqman, Khurram (Weatherford) | Shah, Rizwan (Weatherford) | Ghulam N, Agha (PPL) | Ali, Muhammad (PPL) | Hasan, Naveed (PPL) | Baig, Umair A. (PPL) | Sajjad, Muhammad (PPL)
This paper reviews the recently concluded first near balanced nitrified stiff foam drilling application to drill Sui Main Limestone in Sui field Pakistan. The target Sui Main Limestone formation presented numerous drilling challenges in this field. While drilling conventionally total irrecoverable losses were encountered and the resulting loss in head caused the well to kick in. Simultaneously dealing with both these problems resulted in a great amount of NPT, sometimes which extended to a period of months. To address the said problems in an effective and efficient manner, an application of a highly innovative method was considered. Thus a near balanced stiff foam system was designed and found to be highly applicable to drill the Sui Main Limestone formation.
The design of a Near-Balanced Stiff Foam Drilling system (NBD) is first discussed in the paper, which is followed by an overview of the delivered results. While drilling the entire Sui Main Limestone formation no single event of circulation loss was recorded. Also throughout the entire drilling phase "near balanced" conditions were maintained successfully and no influx from the formation was allowed to enter the wellbore. In addition to completing these objectives, another remarkable achievement was that this section was drilled in a record time of 3 days with an average ROP of 14 m/hr while maintaining excellent hole cleaning and no other related drilling problems. In comparison of offset wells where drilling of the same formation would take sometimes up to 3 months, if drilled conventionally.
To sum up, an innovative near balanced stiff foam system was designed to drill the extremely challenging Sui Main Limestone formation. All of the set objectives were delivered to expectations. The operator was able to successfully pass through a cumbersome formation in a record time for this field. This paper elaborates the process used to design a successful near balanced nitrified stiff foam system with applicability for the Sui Main Limestone formation in Sui Field, Baluchistan, Pakistan. The objective of this paper is to highlight all delivered drilling objectives and present lessons learnt while drilling the Sui Main Limestone formation. This will allow for efficient designing of a near balanced stiff foam system for forthcoming wells with similar formations and similar problems.
This paper reviews the case history of the deepest section drilled using a specially designed air/foam system in the highly fractured carbonates of "Fort Munro & "Parh" in Kup well-1 located in the Sulaiman Fold belt of Pakistan. These carbonates presented numerous drilling challenges in the well. While drilling with a conventional mud system, total incurable losses were encountered. The client attempted to cure losses by conventional means of LCM pills and cement plugs but total losses were continually encountered after drilling just a few meters with conventional drilling fluid. To address the tedious problem of lost circulation, a design of an advanced air/foam system was considered to be used for further drilling.
The paper starts off by discussing the challenges associated with drilling such a deep section with an air/foam system, and how an advanced and more sustainable foam system was designed. Numerous challenges were associated with designing a foam system for the subject well. First; the depth of the section was till 2300 m which would require a foam system to be able to bear its own hydrostatic head, second was the higher than normal formation temperature of 225 deg F which would drastically harm foam quality, and the third & last was that the designed foam system would be able to clean the hole properly at higher drilling rates compared to conventional drilling. The paper will then also present the methodology for job execution and finish off with the delivered results and conclusions.
To summarize, an advanced air/foam system was designed to mitigate total loss of circulation encountered in these carbonates of cretaceous age in Sulaiman Fold Belt of Pakistan. The advanced air/foam system allowed the operator to drill that part of the well to desired depth and successfully cased the troublesome formations. Besides curing the total losses in the subject formations, the operator was able to achieve an ROP which was five times the ROP compared to conventional drilling in the same formations. This paper will highlight the design process used to devise an advanced air/foam system that enabled to drill these carbonates of "Fort Munro" and "Parh" formations in the well. The paper will be targeted towards presenting the design objectives, the onsite execution, and the lessons learned in developing an advanced air/foam system for the well. This will aide in the efficient designing of operations for upcoming wells with similar problems even anywhere else.