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.
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.
Shoaib, M. (Politecnico di Torino) | Qamar, M.S. (Politecnico di Torino) | Khan, M.R. (NED University of Engineering & Technology) | Khan, A. (Texas A&M University at Qatar) | Mumtaz, S. (NED University of Engineering & Technology) | Abbasi, A. (NED University of Engineering & Technology)
With the rapidly declining conventional gas reservoirs, Pakistan has been facing a severe energy crisis and it has become very important to look forward towards the unconventional resources such as tight gas reservoirs to meet the growing energy demands. Companies are looking forward for economically viable production from tight gas resources while considering new Tight Gas Policy of the country. The most important step is to correctly estimate Original Gas in Place (OGIP) and Estimated Ultimate Recovery (EUR) in case of tight gas reservoir before declaring the reservoir to be economical or uneconomical on the basis of detailed simulation and economic modeling.
Techniques to estimate OGIP and EUR are different from conventional techniques since conventional techniques can lead to erroneous results. Flowing material balance is one of the methods which uses stabilized flowing pressure-rate data to estimate OGIP and EUR in case of tight gas reservoirs. Blasingame Type Curve, Super Hyperbolic Decline (assuming b>1) and mathematical model based Power Law proves to be more accurate in case of tight gas reservoirs as compared to conventional techniques like, Arp's Decline Curve, conventional material balance, etc. Paper presents practical application of above methods on the anonymous field data. Results from above methods are also validated from numerical reservoir simulation model. Economic model is made using Tight Gas Policy applicable in Pakistan and from sector modeling results, value of post-tax NPV is estimated for different cases to see whether development of tight gas reservoir is economically feasible or not.
Super hyperbolic decline over predicts the reserves while Power law, flowing material balance and production type curves are most suitable for OGIP or EUR estimation of tight gas reservoir. OGIP and EUR of tight gas reservoir from these methods are approximately 7Bscf and 5.5Bscf respectively. Different cases were performed on a sector model of tight gas reservoir to optimize post-tax NPV. Most of the cases were not economically feasible but horizontal well having lateral of 570ft, multifrac (9 frac) having fracture half-length equals 222.5ft and fracture width equals 0.02ft is economically feasible due to maximum post-tax NPV and IRR value.
It is recommended to use above mentioned methods for in place or EUR estimation in case of tight gas reservoir to avoid erroneous results. Along with that, tight gas reservoirs are economically feasible to produce in Pakistan with improved technology and by utilizing the incentives given by Government in new Tight Gas Policy.
The name “Sui” has become synonymous with natural gas in Pakistan on discovery of the first well in 1952. Sui is Pakistan Petroleum Limited’s (PPL) flagship gas field and is one of the major contributors in meeting the energy demands of the country since its inception. Two major reservoirs of this field are the Sui Main Limestone (SML) and Sui Upper Limestone (SUL); both of which have become highly depleted over time.
Pakistan is striving to meet its growing energy needs and is making all possible efforts to enhance production. Operator successfully drilled one horizontal well in the Sui Main Limestone in underbalanced conditions and planned to drill the FIRST HORIZONTAL WELL in the SUL reservoir to enhance production of the field. Drilling a horizontal well in this formation with conventional drilling techniques was a high risk task due to depleted reservoir with shale interbedding, complete loss of circulation, hole instability and reservoir damage issues which altogether made it almost impossible to complete the well.
The operator took this challenge to implement innovative technologies to mitigate all hazards and meet objectives. Drilling and reservoir related problems were identified in detail. A comprehensive Geo-Mechanics Study was conducted to define the safe drilling window of the SUL Reservoir. To maintain bottom hole pressure within the defined drilling window, further integration of Multiphase Fluid Drilling (Membrane Nitrogen & Water Based Mud) and Electromagnetic Measurement While Drilling tools along with real time ECD (Equivalent Circulating Density) and Gamma Ray monitoring Sensors were selected. A major challenge for the operator was to complete the well in the same reservoir conditions which was accomplished by applying Downhole Deployment Valve Technology with 9-5/8” casing.
This paper will elaborate the details of planning and execution strategies to complete this challenging project. The application of these innovative technologies represents a step change in improving Operator’s ability to exploit mature reservoirs, especially those that are severely depleted like the Sui Gas Field and also for the Oil & Gas Sector in Pakistan.
Overview of Application
Sui Upper Limestone is secondary reservoir in Sui Gas Field of Pakistan. It is a depleted reservoir with a reservoir pressure range of 774 - 970 psi (3.65 ppg – 4.58 ppg EMW). Operator planned horizontal well inside the Sui Upper Limestone covering a lateral distance of ±384m with a vertical thickness of 53m from 1208m (TVD) to 1261m (TVD). This was the first horizontal well planned and drilled in this reservoir.
Drilling horizontal well in this depleted formation was very difficult with conventional overbalanced drilling methods. This could have jeopardized the well objectives. Drilling hazards like complete loss of circulation, differential pipe stuck, low drilling performance and severe formation damage were identified as primary potential risks leading to substantial NPT and associated cost. Operator had faced all such problems while drilling vertical wells in SUL Formation in the same field.
The formation also has interbedded shale strings of 3-4 m thickness. This could consequence wellbore stability concerns while drilling horizontal well in the subject formation. This was identified as secondary potential risk.
Saleem, Saad (Pakistan Petroleum Limited) | Sattar, Suhail (Pakistan Petroleum Limited) | Shahzad, Atif (Weatherford Oil Tools M.E. Limited) | Ziadat, Wael (Weatherford Oil Tools M.E. Limited) | Sabir, Shahid Majeed (Weatherford Oil Tools M.E. Limited)
The name "Sui?? has become synonymous with natural gas in Pakistan. Sui is Pakistan Petroleum Limited's (PPL) flagship gas field. Commercial exploitation of this field began in 1955.
Two major reservoirs of this field are Sui Main Limestone (SML) and Sui Upper Limestone (SUL). Both the reservoirs have become highly depleted by time. Conventional drilling technologies in these formations result in complete loss of drilling fluid, stuck pipe and severe formation damage issues.
Pakistan Petroleum Limited (PPL) planned to drill a horizontal well Sui-93(M), where target reservoir was Sui Main Limestone (SML). Drilling a horizontal well with conventional drilling techniques can cause a complete loss of drilling fluid. Underbalanced Drilling integrated with electromagnetic telemetry transmission was successfully used to drill this well to a target depth of 2200m MD with complete directional controls. Electromagnetic transmission modeling was performed on the resistivity data of offset wells to determine signal attenuation for Sui-93(M) Well. Based on modeling results it was decided to run an extended range set-up with a downhole antenna.
The main reason for using EM-MWD was to provide real time data for annular pressure (APWD sensor) and directional controls in UBD environment. The APWD (annular pressure while drilling-real time ECD) sensor was considered mandatory to monitor and ensure underbalanced condition while drilling, thereby avoiding significant problems such as lost circulation and stuck pipe.
This paper discusses the planning, results, problems and lessons learned during the first application of the Extended Range EM-MWD (Electromagnetic-Measurement while drilling) technology in Sui-93(M) well.
The application of EM-MWD along with UB technology represents a stepwise progression for improving PPL's ability to exploit mature reservoirs, especially those that are severely depleted like in Sui Gas Field, Pakistan.
The explosive growth of shale gas production in the US has sparked a global race to determine which other regions from around the world have the potential to replicate this success. One of the main areas of focus is the Asia Pacific region, specifically Pakistan.
In this paper, real results from seven different US shale basins- Marcellus, Eagle Ford, Haynesville, Barnett, Woodford (West-Central Oklahoma), Fayetteville and Bakken- have been used to develop a comprehensive sequence of shale exploitation strategy for emerging shale plays. The study involves integration of shale gas exploitation knowledge reinforced by a decade of experience across most of the North American shale gas basins, with published data. Different reservoir properties have been compared to develop a comprehensive logic of the effective techniques to produce from shale-gas reservoirs. We have validated the sequence with real results from US shale production ventures, published case histories, and by global experts who have been directly involved in shale reserves evaluation and production.
Subsequently, several different reservoir attributes of Pakistan shale plays have been compared with US basins, in an attempt to identify analogues.
It is the intent of this paper to diminish the difficult and often expensive learning cycle time associated with a commercially successful shale project, as well as to attempt to illustrate the most influential factors that determine optimum production. A very few papers in the petroleum literature that provide an extensive and systematic approach towards shale exploitation strategy for given shale-reservoir conditions
Encouraged by the U.S. successful experience with shale plays, many Asia Pacific countries including China and India - having 1275 & 63 TCF of technically recoverable Shale gas respectively - have already started off with aggressive plans to exploit their vast shale reserves.
Pakistan is currently suffering an energy shortfall of 2.3 BCF and the energy demand is expected to increase further by 245% until 2022, as compared to 2008. As its conventional reserves deplete, there is a need to work on new frontiers of energy sources. Unconventional gas resources, such as shale gas, tight gas and coal bed methane, are the avenues that should be focused on, in the current scenario.
According to EIA estimates, Pakistan's total Risked Gas in Place is 206 TCF, while its Technically Producible Shale Reserves are 51 TCF. It is interesting to compare these postulations with the Sui gas field serving the energy needs of Pakistan for decades, and having an estimated original recoverable reserve of 12 TCF. However, efforts to develop this potential resource have been lacking perhaps due to the economic and technological challenges.
Adhi gas-condensate field is located near Islamabad, Pakistan. Pakistan Petroleum Limited started fluid processing and recovery of Liquefied Petroleum Gas and Condensate around in 1990. The liquid stream was processed with no solids deposition in the past. Recently, the liquid processing circuit of the plant has experienced an increasing amount of black solid deposition, which is trapped into the liquid filters located in the plant.
To identify the root causes of the problem of these solids depositional systematic approach was applied including taking various solid, liquid and gas samples from the plant inlet and various locations inside the processing plant and analyzing them for diagnostics.
Based on the outcome of the root-cause analysis, a chemical mitigation strategy has been developed, tested and implemented, resulting in significant reduction in problems related with solid depositions in processing plant.
Adhi gas condensate field is located near Islamabad, Pakistan. The fluid in Adhi is processed in two liquefied Petroleum Gas (LPG)/Natural Gas Liquid (NGL) plants (plants I and II) and Oil Stabilization Facility (OSF). The condensate was processed without solid deposition in these plants from 1990 to 2007.
The black solid deposits started to accumulate on the process equipment and plants' filters (Figure-1)leading to a high filter change frequency and consequent production loss.
Due to the continuous increase of the severity of the problem, a full Flow Assurance (FA) review of the field was carried out in order to mitigate the solid precipitation and problem of its depositions in plant. The first phase of the FA review was to conduct a Root Cause Analysis (RCA) where the main causes were identified including fluid compositional changes, temperature and pressure changes across the system, and incompatibility of mixing well streams with different compositions were identified to be the main causes for the asphaltenes dropout.
The RCA was based on the historical plant production data, fluid sampling, analysis results and asphaltene thermodynamic modeling.
The outcomes were:
This article details the methodology followed in solving the solid deposition problem at Adhi.
Hussain, Sajjad (Pakistan Petroleum Limited) | Saleem, Saad (Pakistan Petroleum Limited) | Sabir, Shahid Majeed (Weatherford Oil Tools M.E. Limited, Pakistan) | Asrar, Muhammad (Weatherford Oil Tools M.E. Limited, Pakistan)