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Khalid, Ali (Weatherford International) | Ashraf, Qasim (Weatherford International) | Luqman, Khurram (Weatherford International) | Hadj-Moussa, Ayoub (Weatherford International) | Ghulam Nabi, Agha (Pakistan Petroleum Limited) | Bari Khan, Faizan (Pakistan Petroleum Limited) | Azhar Khan, Muhammad (Pakistan Petroleum Limited)
Abstract As oil and gas reserves mature the world over, operators are looking towards advanced methods of increasing the ultimate recovery from their ageing fields. An energy deficient country of Pakistan relies heavily on oil and gas imports. The country was once self sustaining in at least natural gas needs. A major portion of this gas was produced from the Field-X which was discovered in the 1950’s. The primary reservoir in Field-X is the YZ-Limestone reservoir which bears sour gas. Due to extensive production from the YZ-Limestone formation, the reservoir pressure has depleted to a mere 2.0 PPG in equivalent mud weight, and it being a naturally fractured limestone formation presents numerous drilling challenges. The operator has evaluated a potential higher pressured formation in the deeper horizons of sui field but that requires drilling through approximately 650-690 meters of the YZ-Limestone formation. This feat when attempted conventionally is plagued with numerous problems like, total lost circulation, differential sticking, influxes due to the loss of a sufficient hydrostatic head, and stuck pipe following well control events. To mitigate these challenges the operator, need an effective method to drill through this depleted formation without pumping heavy LCM pills, and multiple cement plugs across the massive cavernous thief zones in the YZ-Limestone formation which could have been detrimental to the production of nearby wells. Moreover, such remedies with specialized LCM’s and acid soluble plugs would have resulted in excessive material cost and non-productive time, which in some instances extended to a period of more than a month. To address the aforementioned challenges in drilling the YZ-Limestone formation, a multiphase managed pressure drilling system was suggested to drill the formation with minimal non-productive time and cost. Multiphase hydraulics were performed to assess appropriate pumping parameters for a near-balanced condition across the YZ-Limestone formation. A closed loop MPD equipment system was designed to help maintain near-balanced conditions in pumping and static (non-circulating) periods. The designed equipment system would also ensure that the risk of H2S exposure to the atmosphere was eliminated. The application of a closed loop nitrified mpd system on a recently drilled well proved to be highly successful and reduced the drilling time to just 28 hours by not only eliminating fluid lost circulation but by also delivering an extremely high rate of penetration of 39.2 m/hr. The successful and exemplary application of nitrified MPD has opened up a new horizon for the development of deeper prospects in the Field-X and similar neighboring fields. The paper outlines the design and execution of the closed loop nitrified MPD system.
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)
Abstract 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)
Abstract 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.
Abstract 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.
Saleem, Saad (1Pakistan Petroleum Limited) | Sattar, Muhammad Suhail (1Pakistan Petroleum Limited) | Shahzad, Atif (2Weatherford Oil Tools M.E. Limited, Pakistan) | Ziadat, Wael (2Weatherford Oil Tools M.E. Limited, Pakistan) | Sabir, Shahid Majeed (2Weatherford Oil Tools M.E. Limited, Pakistan)
Abstract 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.
Hussain, Sajjad (Pakistan Petroleum Ltd.) | Saleem, Saad (Pakistan Petroleum Ltd.) | Sabir, Shahid Majeed (Weatherford Oil Tools M.E. Limited, Pakistan) | Asrar, Muhammad (Weatherford Oil Tools M.E. Limited, Pakistan)
Abstract The name "Sui" has become synonymous with natural gas in Pakistan. Located at a distance of about 650 kilometers (km) from Karachi in Balochistan Province, Sui is Pakistan Petroleum Limited’s (PPL) flagship gas field. The gas field was discovered in the late 1952 and the commercial exploitation of the field began in 1955. Two major reservoirs of this field are Sui Main Limestone (SML) & Sui Upper Limestone (SUL); both have become highly depleted over the time. Conventional drilling technologies in these formations result in complete loss of drilling fluid, stuck pipe & severe formation damage. Pakistan Petroleum Limited (PPL) planned drilling Sui93(M) as a horizontal well in Sui Main Limestone (SML) Formation. Drilling a horizontal well with conventional drilling technology in a depleted formation having 500 psi pore pressure at a depth of ~1400 m (TVD) was a real challenge. Underbalanced Drilling Technology (with DDV & ER-EM-MWD tools) was selected as an alternative drilling method. The main objectives of Underbalance Drilling Operation were to drill to target depth while eliminating fluid losses with associated problems and improve drilling performance. A multidisciplinary team of Drilling Operations experts planned and executed this challenging project. Considering the reservoir pressure of formation, stable foam was selected as drilling fluid for UBD operations. Extended Range Electromagnetic MWD tool was used for directional control along with APWD (Annular Pressure while drilling) sensor for real time Bottom Hole Pressure monitoring. Open hole section (~600 meter) was drilled successfully in Sui Main Limestone (SML) Formation. Integrated efforts of Pakistan Petroleum Limited (PPL) and associated service companies of various disciplines during planning and operation phases of the well led to this successful project. This paper highlights key factors in the underbalanced drilling design phase, operational challenges faced during execution and results of the first well drilled in Middle East region using above mentioned integrated group of technologies. These applications have opened new ventures and opportunities for depleted field developments in the region and particularly in Sui Field of Pakistan.
Summary Since 1950, Pakistan has gone through several phases of hydrocarbonexploration, but despite our geologically prospective areas, our discovery anddevelopment of substantial reserves, and our existing infrastructurefacilities, exploration has been limited. We attribute this limited explorationto the absence of long-term gas-development strategies, to the gas-priceformula, and to legislative and contractual frameworks for concessionagreements in use for most of our exploration history. This paper examines Pakistan's exploration history and reveals current gas-development strategies. It also discusses the revised pricing formula and legislation to benefit otherdeveloping countries that are in similar situations and want to accelerate thepace of their exploration activities. Introduction Pakistan has a large sedimentary area that Pakistan has a large sedimentaryarea that comprises two basinsthe Indus and the Baluchistanand covers more thanthree-fourths of the total onshore area (greater than 235,926 sq miles) andapproximately 83,404 sq miles offshore. Exploration efforts to date, however, have been relatively modest compared with the sizes of the prospective areas. The first commercial oil discovery was made in 1915 at Khaur oil field innorthern Pakistan. Indigenous oil production is Pakistan. Indigenous oilproduction is currently (May 1991) about 60,000 B/D, but the country is not yetself-sufficient. Fortunately, during the 1950's, large quantities of naturalgas reserves were discovered. The first and largest gas discovery was the Suigas field. Discovered in 1952 by the Burmah Oil Co./Pakistan Petroleum Ltd., Sui is the main source of gas supply in Pakistan. Over the years gasproduction, which currently (May 1991) stands at about 1,500 MMcf/D, has becomea major factor in Pakistan's economy. A well-developed gas Pakistan's economy. A well-developed gas transportation and distribution system has been laid andis being expanded. This paper reviews the Pakistani petroleum exploration anddevelopment petroleum exploration and development experience, especially withregard to the gas industry, for the benefit of other developing countries. Thefactors responsible for our limited past exploration activity are identifiedand recommendations are made to help accelerate this pace. Exploration History Petroleum exploration in Pakistan can be Petroleum exploration in Pakistancan be divided into three distinct phases based on the pace of explorationactivity. Phase 1 began in 1951 with the discovery of the Sui gas field. With8.624 Tcf of recoverable gas, this discovery provoked extensive explorationactivity that resulted in the discovery of six more gas fields in the 1950's: Zin (1954), Uch (1956), Khairpur (1957), Mari (1957), Mazarani (1959), and Kandhkot (1959). Sui was the first field developed to supply gas to Pakistaniindustries, which originally used imported oil and coal as their feed stock andfuel. Commercial production from Sui began in 1955. Phase 2 began in the 1960'swhen a low wellhead gas price for existing producers and low incentive levelsfor new producers caused a decline in exploration activities. A steep rise inthe gas demand, however, was observed during this phase, primarily because ofthe low gas price. Phase 2 lasted until the 1980's, with the only increase inexploration occurring in 1975 when seven wells were drilled. Explorationactivity increased again when the demand for gas exceeded the availableproducers capacity and the supply system. producers capacity and the supplysystem. The importance of natural gas was then realized, and its price, development, and utilization strategies were revived. Consequently, explorationand appraisal activities revived, and Phase 3 began with a record number ofexploratory wells being drilled 20 in 1984 and 21 each in 1988 and 1989. Fig. 1 shows Pakistan's drilling record from 1950 to 1990. Pakistan's explorationhistory indicates the importance of planning exploration activities at anoptimal level to meet a country's requirements. Our experience is also a richsource for developing countries with similar constraints on explorationactivities. Factors Affecting Exploration Activities The variety of trends cited in our exploration history, along with theircorresponding causes and effects, identity a number of factors that hinder notonly the rise but also the consistency of exploration activities. Some of thesefactors are discussed in the following sections. Long-Term Development Strategy. During the 1950's little thought was givento any future supply problems. The Sui field was large, had relatively smalloff-takes (100 MMscf/D), and gave ns a comfortable feeling of having aninexhaustible supply of gas. Although exploration activities were intense andequally fruitful during this time, no field development was carried out exceptat Sui. This lack of planning became apparent in 1964, when only the Sui fieldwas available to support a steep rise in market demands. JPT P. 1246
Abstract Sui Main Limestone (SML) is the most prolific reservoir accounting for 90% of all production from Sui Gas Field. Work carried out for obtaining estimates of reserves, future production potential and ultimate recovery from the SML reservoir is discussed. The paper presents results of well coning and reservoir simulation studies conducted. Work carried out in determining the reservoir's future compression requirements (over 75,000 HP) and debottlenecking of wells and gas gathering system is also highlighted. The paper highlights the monitoring/ control of production operations for SML. Casing/tubing corrosion, failure and resulting fluid seepages are discussed. Problems related to formation water Problems related to formation water production and its monitoring/removal are production and its monitoring/removal are presented. presented Introduction The first well drilled by Pakistan Petroleum Limited (PPL) at Sui was Petroleum Limited (PPL) at Sui was completed in 1952 and resulted in the discovery of the first, and to date the largest gas field in Pakistan. Later 5 more wells were drilled on Sui structure in order to test the east-west and north-south limits of the structure and to provide enough wells for supply of gas to provide enough wells for supply of gas to the transmission line laid from Sui to Karachi. The Sui Gas Field is located in Baluchistan, about 30 miles north-west of Kashmore town (Fig. 1). The field consists of three gas bearing formations about 3000 - 4000 feet deep, namely Sui Main Limestone (SML), Sui Upper Limestone (SUL) and Habib Rahi Limestone (HRL). SML/SUL formations have combined initial recoverable gas reserves of 8.624 trillion cubic feet (tcf) (re-estimated from earlier estimates of 4-5 tcf). SML contains the bulk of these recoverable reserves (92%) while SUL accounts for the remaining reserves (8%). The HRL gas mostly consists of inerts, hence it has not been included in the recoverable reserves. Fig. 2 shows the structure contour map on top of SML. GEOLOGY The SML is early Eocene to Paleocene in age and attains a thickness from 2050 to 2190 ft. It is generally uniform, massive, brown-grey to creamy white and probably originated as a reefal bank type probably originated as a reefal bank type deposit. The upper 50 to 60 ft is generally tight and consists of intercalating argillaceous limestone and marls. The remaining portion of the limestone is porous with minor shaly intercallations porous with minor shaly intercallations and is fairly uniform in lithology. It is finely fractured in vertical and horizontal directions. The fractures are filled with secondary calcite and asphaltic material. The lower part of the limestone consists of shaly intercallations with shales increasing towards the base and gradually passing into Ranikot (Paleocene) shales. P. 651
Abstract Removing acid gas from sour natural gas streams by contacting with monoethanolamine solutions is a tried and proven process. The process as used by Sui Gas Transmission Co. for removal of H2S and CO2 at their gas purification plant at Sui, Pakistan is different because they design for total amine solution loadings of .64 mols acid gas/mol M.E.A. This paper analyzes the system as designed and operated paper analyzes the system as designed and operated and determines if the high loading of M.E.A. is an economical approach to gas treating problems. Introduction The Sui Gas Purification Plant is located approximately 300 miles (500 km) north of Karachi in the providence of Baluchistan. Access to the plant is limited due to the remoteness of the area. Land access via dirt roads is poor at best. The majority of personnel axe flown to the site. During rare but heavy rainfall the entire area has been cut off from outside communication except for radio telephone messages. The earthen runway of the airstrip becomes a mire of mud such that airlift is impossible. Fortunately for the plant and personnel at Sui, eight to ten months a year the average rainfall is zero. C-E Natco contracted in 1976 with Sui Northern Gas Pipeline Ltd. to procure and manufacture equipment, and supervise installation and start-up of two 120 MMscfd (3.4 MM Nm3) natural gas treating facilities. These units were to be an addition to the existing facilities located at the plant operated by Sui Gas Transmission. Because of its importance to the economy of Pakistan (the Sui Field supplies over 50% of the Pakistan (the Sui Field supplies over 50% of the country's natural gas) the plant at Sui must operate with few if any interruptions. Because of somewhat limited chemicals and the production cutback necessary to convert to another process, Sui Gas elected to utilize the existing M.E.A. process with the M.E.A. loaded to unusually high ratios of acid gas. The existing facilities, which had been constructed in steps of one and two trains per unit since 1955, had a daily average production of 450 MMscfd (12.7 MM Nm3). The addition increased the number of parallel trains to nine and the average production of gas to 675 MMscfd (19MM Nm3). Two of production of gas to 675 MMscfd (19MM Nm3). Two of the existing trains had been initially designed for high loaded M.E.A. and were commissioned in 1971 by Fluor Ltd., U.K. The remaining five trains had been converted from normal M.E.A. treating to the high loaded process, and specifications for the expansion units were drawn up based on past operating experience. PROCESS DESCRIPTION PROCESS DESCRIPTION The process for treating gas at Sui is similar to many amine type gas treating facilities except for the M.E.A. solution loading. Figure 1 is a simplified process flow scheme. 120 MMscfd of 1100 psig, 140 degrees F gas, containing 7% CO2 and 0.14% psig, 140 degrees F gas, containing 7% CO2 and 0.14% H2S enters the plant through a flow control valve and is cooled by E-260 to 100 degrees F (38 degrees C). Condensed water and hydrocarbon are scrubbed out of the feed stream prior to entering the absorber V-120. 1264 gpm of 20% lean M.E.A. is pumped from the surge tank V-180 to the top tray of the absorber and flows countercurrent to the gas flow. The resulting rich amine exits the bottom of the absorber through a level control valve and flows to the flash tank V-140 where entrained hydrocarbons are flashed off. The purified gas exits the absorber and flows to downstream dehydration facilities, The rich amine flows from the flash tank through the rich/lean heat exchanger and to the reactivator still column V-160. Steam from the still reboiler strips the acid gas from the rich amine and the acid gas is separated and pumped back to the still as reflux. The reactivated amine exits the still bottom, is cooled to 100 degrees F (30 degrees C) by heat exchange, air cooling and amine/water trim exchange.