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Collaborating Authors
Naganathan, Sivaraman
Abstract Exploration and development of Heavy oil fields in Muglad Basin in Northern Africa started with conventional vertical wells and as time progressed this matured into drilling of horizontal and high angle wells. Typically drilling challenges in this area include drilling of very reactive shale's, shallow kick off depths and high build rates. Unconsolidated sandstones and interbedded shale's are sensitive to mud weight and are prone to lost circulation. First few horizontal wells were drilled with traditional technology of positive displacement motor with Silicate mud. Many of these wells faced hole cleaning challenges leading to pack off -excessive back reaming and stuck pipe incidences, uneven build rates via sliding in interbedded formation leading to high borehole tortuosity. It is significant to note that due to these difficulties one of the planned horizontal wells was sidetracked thrice after stuck pipe incidences and finally completed as a 30 deg deviated well with an AFE over run of 300%. Taking leaf from experience of horizontal drilling in Muglad basin, rotary steerable system (RSS) has been deployed to drill horizontal well in Umm Bareira field. This field is shallow, highly unconsolidated and heavy oil with viscosity nearly 350 cp. This methodology of drilling has resulted into significant improvement in drilling performance, saving days and cost and eliminating stuck pipe incidences. Well has been completed openhole with sand control strategy using standalone screen with two swell packers for addressing the future reservoir management requirements like intervention for isolating the high water cut intervals in the horizontal section and better productivity and avoiding life cycle risks. Well produced 1300 bopd which is 5 times higher than vertical well and more so make production significant from the field. This paper highlights the learning curve of horizontal well drilling, completion and production of viscous oil field in Muglad basin. Introduction Umm Bareira is a small heavy oil field in Muglad basin. Three exploratory and appraisal wells have been drilled in the field. Three hydrocarbon bearing layers have been encountered at the shallower depth. Viscosity of the crude oil in field is very high. Reservoir is highly permeable and unconsolidated. All the wells were tested through swabbing due to its viscous nature and productivity was very poor. Exploitation of the field by vertical wells only is not a feasible concept. Therefore, it has been decided to drill horizontal well and complete openhole which will provide maximum reservoir contact and also enable to delay the water production and control the sand incursion problem. Geological Setting The development of oil-bearing basins in Sudan is closely associated with the global phenomenon of plate tectonics and particularly with the separation of Africa from South America trend. This west and central African Rift System extends from the Benue Trough in Nigeria to Cameron, Chad, Central African Republic and Sudan. The evidence for further southeast extension has been destroyed by Tertiary uplift associated with recent rifts in East Africa. The shear zone was identified by geophysical means, and has been demonstrated to experience right lateral movement in the Cretaceous. All the basins of the Sudanese rift-related system, such as the Muglad, White Nile, Blue Nile, Khartoum and the Atbara basins, terminate northwards at the Central African Shear Zone. The development of the rift basins of southern Sudan is related to the processes that operated not only within central Africa, but also along the western and eastern continental margins. The Sudanese interior basins are interpreted to be Mesozoic to Tertiary in age. Thus the Late Jurassic to Early Cretaceous Muglad Basin formed part of the West and Central African Rift-System. The deep drilling coupled with geophysical data suggested the presence of sedimentary sequences of some 15000 m in the Muglad basin. The subsurface continental sedimentation is structurally controlled and resulted in favourable juxtaposition of source, reservoir and seal. Abu Gabra and Bentiu formations deposited during rift Phase 1. Darfur Group and Amal formations deposited during rift Phase 2 and Nayil, Tendi, Adok and Zeraf deposited during rift-Phase 3. Most of the oil is accumulated in the Lower Cretaceous Abu Gabra and Bentiu formations and the Upper Cretaceous Darfur Group.
- Africa > South Sudan > Northern Liech > Bentiu (0.49)
- Africa > Sudan > Khartoum (0.44)
- Phanerozoic > Mesozoic > Cretaceous > Lower Cretaceous (0.54)
- Phanerozoic > Mesozoic > Cretaceous > Upper Cretaceous (0.34)
- Geology > Petroleum Play Type > Unconventional Play > Heavy Oil Play (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.57)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.35)
- Geophysics > Seismic Surveying (0.46)
- Geophysics > Borehole Geophysics (0.46)
- Africa > Sudan > Muglad Basin (0.99)
- Africa > South Sudan > Unity > Muglad Basin > Fula Basin > Bentiu Formation (0.99)
- Africa > South Sudan > Unity > Muglad Basin > Fula Basin > Aradeiba Formation (0.99)
- (3 more...)
Developing Heavy Oil Fields By Horizontal Well Placement - A Case Study
Naganathan, Sivaraman (Schlumberger) | Li, Pan You (CNPCIS,Sudan) | Hong, Luo Hui (CNPCIS,Sudan) | Sharara, Abdul Mageed (CNPCIS,Sudan)
Abstract Fula is a heavy oil field located in Muglad basin in Sudan. Aradeiba reservoir in the field consists of highly heterogeneous sandstone that is thinly bedded, unconsolidated, bearing typical heavy oil. Bentiu reservoir is composed of massive sandstone, unconsolidated and traped very high viscous oil. Production performance of vertical wells indicates that the reservoirs are facing problems of low productivity, bottom water conning and sand production. In his circumstance CNPCIS set itself a daunting task of tripling the production in less than a year. Horizontal wells were considered as best option for improving the productivity in this small to medium sized heavy oil field, and controlling the sand production due to low drawdown pressure and increased exposure the reservoir. This paper discusses about comprehensive geological study , identification of target oil pools, well design, selection of fit for purpose technologies and the complete well placement cycle including detailed analysis on the drilling and steering challenges while placing horizontal well through reactive shales and channel sand environment. The paper also discusses about various completion strategies , the results of well placement, value of using new technology , lessons learnt and cost /production analysis. Team work, communication, knowledge sharing and deployment of fit for purpose technologies has resulted in a five fold increase in production through horizontal wells compared to vertical wells with no sand production. The paper illustrates how integration of different disciplines led to successful well placement, enhanced production with sand and water management in heavy oil environment. Introduction Fula Oilfield is located on central structutre belt of Fula depression in Muglad Basin which consists 3 main blocks -Fula-1, Fula Central and Fula North. Three reservoirs have been found by the exploratory and appraisal wells in the area. Bentiu formation is the main reservoir in Fula Oilfield with massive lose sand and average viscosity is about 1536.39 cp at 500C. Aradeiba is the second reservoir with stratified unconsolidated paysand and average viscosity around 450 cp at 500C. Bentiu reveroir is prone to sand production and water break through very quickly and Aradeiba reservoir is prone to serious sand production and very low output rate in conventional vertical wells. In order to prevent sand production from both reservoirs, to delay water production from Bentiu formation and increase productivity and enhace the reservoir recovery factor operator decided to drill horizontal wells. Another important driving force behind drilling horizontal wells is to improve the light oil production from Aradeiba reservoir that is crucial for blending and transporting the heavy oil from Bentiu reservoir through the pipeline. Seven horizontals have been drilled, out of which four of them are in Aradeiba formation and three are placed in Bentiu fiormation. The production performances of all the wells are extremely good year to date. Geological Setting and Stratigraphy Being a rift and Cretaceous sedimentary basin, Muglad basin is located south of Republic of Sudan. Tectonics was complicated by faulting and continuous fault movement and several sub-basins formed result in this large numbers of tensional faults. Structures within these depressions show significant variations in age of formation, complexity and size. The result of regional stratigraphy study indicates a major East Africa rift basin appeared and developed in the Late Jurassic to early Cretaceous. Early rift sediments interbedded with coarse rift clastics derived from surrounding uplifted basement source rocks. Several types of continental depositional environment may had existed in different areas including fluvial and lacustrine during the Cretaceous and younger period. Fula Sub-basin is located in north part of Muglad Basin and consists of 5 structure belts namely south step-faulted belt, south depression, central structure belt, north depression and north step-faulted belt. Several oilfields like Moga, Keyi and Jake have been discovered after Fula field in Fula Sub-basin recent years. Located in Central Structure Belt of the sub-basin, Fula is one of the earliest oilfield put into production.
- Africa > South Sudan > Northern Liech > Bentiu (1.00)
- Africa > Sudan > West Kordofan State (0.76)
- Africa > Sudan > Southern Darfur (0.76)
- Phanerozoic > Mesozoic > Cretaceous > Lower Cretaceous (0.48)
- Phanerozoic > Mesozoic > Cretaceous > Upper Cretaceous (0.46)
- Geology > Sedimentary Geology > Depositional Environment (1.00)
- Geology > Petroleum Play Type > Unconventional Play > Heavy Oil Play (1.00)
- Geology > Geological Subdiscipline (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.37)
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- Asia > Middle East > Qatar > Arabian Gulf > Rub' al Khali Basin > North Field > Laffan Formation (0.99)
- Asia > Kazakhstan > Aktobe Oblast > Precaspian Basin > North Block (0.99)
- Africa > Sudan > Western Korfofan > Muglad Basin > Fula Basin > Block 6 > Fula Field (0.99)
- (6 more...)
- Well Drilling > Well Planning (1.00)
- Well Drilling > Drilling Operations > Directional drilling (1.00)
- Well Completion > Sand Control (1.00)
- (5 more...)
Abstract Exploration and development of Heavy oil fields with high water cut and sand production in Muglad basin in Northern Africa started with vertical wells and as time progressed matured into drilling Horizontal wells. Typically drilling challenges in this area include drilling very reactive shales , shallow kick off depths and high build rates, unconsolidated sand stones interbedded with shales which are sensitive to mud weight and are prone to lost circulation. First few horizontal wells were drilled with conventional technology of positive displacement motor with silicate mud. Many of these wells faced hole cleaning issues leading to pack off , excessive back reaming and stuck pipe incidences. Uneven build rates via sliding in interbedded formation leading to high borehole tortuosity . It is significant to note that due to these difficulties one of the planned horizontal wells was side tracked three times after stuck pipe incidences and finally completed as a 30 degree deviated well with a total cost over run of 300% above AFE. Since then Rotary steerable system has been deployed to drill these challenging wells with significant improvement in drilling performance , saving days and cost and eliminating stuck pipe incidences. This paper compares the performances of drilling with PDM Vs RSS in the same reservoir and presents the lessons learnt. A cost benefit analysis has also been performed and it clearly shows that RSS is both technically and economically a sound approach to drilling horizontal wells in Muglad basin. Introduction Horizontal well drilling campaign in Sudan was started in 2004 with the following objectives:Increase well bore exposure to reservoir and hence increase the rate of production of heavy oil. Decrease the near well turbulence and hence decrease sand production. Decrease of Draw down pressure which will eventually lead to decrease in water cut. The candidate wells were chosen in very well developed fields targeting by passed oil. Presence of good number of close by vertical offset wells offered good geological control for well placement. On the drilling front there were lots of challenges that were encountered while drilling the horizontal wells. In this paper we will look into the evolution of drilling techniques from the first well to the recent wells and see how continuous adoption of new and fit for purpose technology has minimized drilling risks and lead to economical drilling of horizontal wells. Drilling Challenges in Muglad basin Drilling of horizontal wells require in depth knowledge about the formations in the basin. Clear understanding of problems posed by the formations will go a long way in mitigating the drilling risks. Figure 1 shows the formation stratigraphy of muglad basin Tendi and Nayil Formations are predominantly made up of water sensitive shale formations, which at times lead to bit and stabilizer balling. The next formation below is the Amal massive sandstone. Amal sand can be abrasive in some areas and usually have issues of lost circulation; build up of well bore deviation. Below Amal sand stone is Ghazal and Zarqa formations. These are made of consolidated sand shale intercalations and do not pose any major drilling problems. Aradeiba formation that lies beneath Zarqa can be sub divided into two major bodies, the upper and the lower Aradeiba shales. Both these formations are strong water sensitive and result in borehole instability, tight spots, pack off even while drilling vertical wells. The lower Aradeiba also has some sand stone reservoirs embedded between the shale bodies which contain some promising reserves. Bentiu reservoir is primarily a sandstone reservoir, which has very low pore pressure gradient. Differential sticking is one of the major concerns in this formation.
- Africa > Sudan (1.00)
- Europe > Norway > Norwegian Sea (0.44)
- Africa > South Sudan > Northern Liech > Bentiu (0.25)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (1.00)
- Geology > Geological Subdiscipline (1.00)
- Africa > Sudan > Western Korfofan > Muglad Basin > Block 4 > Heglig Field (0.99)
- Africa > Sudan > Western Korfofan > Muglad Basin > Block 2 > Heglig Field (0.99)
- Africa > Sudan > Western Korfofan > Muglad Basin > Block 2A > Bamboo Field (0.99)
- (3 more...)
Abstract Maximization of recovery from anisotropic small and medium size oil fields is a daunting task for operators. Development strategies and concepts implemented in large fields generally are not appropriate for small and medium size fields. Inappropriate strategies and methodologies of exploitation affect the overall recoveries and economics of the project. This is further complicated in tight, viscous and sand incursion prone formations. This paper discusses about number of small fields located in Muglad basin wherein oil accumulation is found in multiple layers of late cretaceous deposits. The formations are heterogeneous, unconsolidated with higher viscosity and strong aquifer support. Some formations are tighter too. Field performance is marred by exponential rise of water cut due to adverse mobility and lifting through ESP. Production is affected due to poor influx in tighter formations through conventional wells. This behavior is limiting the producing life of existing wells, resulting into decline in production and causing significant bypassed and undrained oil. Horizontal wells with state-of-art completion both in openhole and cased holed with suitable artificial lift techniques were considered as one of the IOR option for maximizing well productivity in these thinly bedded heavy oil field with objective for tapping the bypassed oil and delaying the water production while controlling the sand production. This paper discusses about the challenges in planning and executing cycles of real time well site well placement, completion, perforation and artificial lift selection. Lessons learnt and results of the well placement along with cost/production analysis will be presented. Production results to date have been remarkable with productivity improvement factor varying 3โ4 folds compared to vertical wells. The paper illustrates how integration of different disciplines with focused efforts led to successful well placement, sand and water management in heavy oil environment and also oil production from tight formations. Introduction Oil continues to be the world's major energy resource, accounting nearly 40% of primary energy demand. Its occurrence is widespread in all the continents. Commercial oil discoveries have been made in quite large number of countries but these reserves are unevenly distributed and bulk of reserves is located in Middle East countries. They hold nearly half of the world's known reserves. Oil industry has progressed tremendously since its inception. Technological development has impacted all gamut of activities viz exploration and production in substantial manner. General technological development in all walks of life resulting in continuous increase in oil demand, rise in oil prices, and geopolitical reasons have necessitated the technological breakthrough's in understanding of the reservoir complexities and behaviour and this has resulted into a more integrated approach to the management of the existing hydrocarbon resources and producing assets. Continual advancement/improvement in oil & gas exploration and exploitation practices and better reservoir management has led the industry in maximization of the recovery from producing fields and from new oil discoveries too. Most important is continuous reduction of lifting cost by introducing new technologies. These technologies have reduced the finding cost through better exploration and appraisal techniques, better drilling and completion practices and have also helped in accelerating the production from mature fields.
- Africa > South Sudan (0.91)
- Africa > Sudan (0.68)
- North America > United States > Texas (0.47)
- Europe > Norway > Norwegian Sea (0.45)
- Research Report (0.54)
- Overview > Innovation (0.34)
- Geology > Petroleum Play Type > Unconventional Play > Heavy Oil Play (1.00)
- Geology > Mineral (1.00)
- Geology > Geological Subdiscipline > Stratigraphy (1.00)
- (2 more...)
- Geophysics > Borehole Geophysics (1.00)
- Geophysics > Seismic Surveying > Surface Seismic Acquisition (0.68)
- Africa > Sudan > Muglad Basin (0.99)
- Africa > South Sudan > Unity > Muglad Basin > Unity Basin > Block 5A > Unity Field (0.99)
- Africa > South Sudan > Unity > Muglad Basin > Fula Basin > Bentiu Formation (0.99)
- (3 more...)
- Well Drilling > Well Planning (1.00)
- Well Drilling > Drilling Operations > Directional drilling (1.00)
- Well Completion > Sand Control (1.00)
- (12 more...)
- Information Technology > Architecture > Real Time Systems (0.67)
- Information Technology > Communications > Networks (0.46)
Rotary Steerable System Applications in the Middle East
Pratten, Charlie (Schlumberger) | El Kholy, Khamel (Schlumberger) | Naganathan, Sivaraman (Schlumberger) | Sharaf, Ehab (Schlumberger)
Abstract Rotary Steerable drilling systems have led to a step change in drilling performance in many areas of the world. However their use in the Middle East has generally been slower to develop than in other drilling provinces around the world such as The North Sea where the value of rotary steerable drilling has been documented since 1998. Commercial as well as technical issues have limited widespread deployment of these systems in the region. This paper reviews successful rotary steering applications in the Middle East to date and explores areas for potential increased use. Using case studies the paper looks a range of specific applications where the change from steerable motor to rotary steerable system has been both technically and commercially successful in the Middle East. Through these case histories the paper will demonstrate both tangible and intangible benefits resulting from the use of rotary steerable systems that have led to a step change in overall drilling performance in the Middle East. Introduction The stratigraphy of the Middle East is relatively uniform over a wide area bringing a commonality to drilling issues and performance across the region. For the last decade or so steerable positive displacement motors have been used for the majority of directional drilling work. Steerable motor drilling is a relatively inefficient process, with associated problems in the Middle East area ranging from trajectory control in unstable shales, pipe sticking in lost circulation zones and slide drilling in carbonate reservoirs. Rotary steerable systems are in many cases able to overcome these difficulties through continuous drillstring rotation and optimized bit and drilling parameter selection. Rotary steerable systems are now in use in all common hole sizes from 6" to 17 1/2" allowing problems to be addressed throughout the well. Steerable Motor Drilling Steerable motor drilling is inefficient. With a requirement to slide the bottom hole assembly in order to steer the well path drilling becomes slower and potentially more problematical. ROP is impacted as a result of wellbore friction and BHA and drillstring components hanging up. Hole cleaning, without drillstring rotation, is adversely affected, as cuttings will drop out of suspension to the low side of the hole. The transition from slide back to rotate requires rotating the motor bend through the section steered. This can result in hole spiraling. Steering a steerable motor requires maintaining the orientation of the bend in the desired tool face setting. Reactive torque from the motor itself works against good tool face control with the force turning the string in a counterclockwise direction. The magnitude of reactive torque will depend on the torque being generated at the bit which itself is a function of bit aggressivity, motor torque output and the formation being drilled. Tool face control using a light set PDC bit with large cutter diameter run on a low speed high torque motor can be extremely difficult. As a result a compromise on bit selection is frequently made for steerable motor drilling. It is not unusual for a roller cone bit to be run for a critical directional section of the well due to problems controlling toolface with a PDC bit. Orienting a PDC bit can be time consuming with frequent time spent off-bottom in order to control reactive torque. Significant progress has been made using depth-of-cut control technology whereby steerability and ROP improvements have been documented and indeed these new bit designs have proven excellent for medium radius applications. However the basic inefficiencies of steerable motor drilling remain. The rotary sections with a steerable motor can also result in inefficient drilling. As with a rotary bottom hole assembly the directional behavior of a steerable motor assembly will be a function of stabilizer gauge and spacing as well as drilling parameters used. As a result the drilling parameters will be set to control the directional tendency of the assembly as opposed to maximizing ROP. Micro-tortuosity associated with a slide rotate sequence is of particular significance in many regional reservoirs. Coiled tubing accessibility can be severely impacted by a tortuous well path in the reservoir. In 6" hole, today's extended power motors are susceptible to formation effects and can be difficult to stabilize and highly tortuous well path can result in the reservoir, often masked by a survey interval of every stand.
- Europe > Middle East (1.00)
- Asia > Middle East > Saudi Arabia (1.00)
- Africa > Middle East (1.00)
- Geology > Geological Subdiscipline > Stratigraphy (0.54)
- Geology > Rock Type > Sedimentary Rock (0.36)
- Asia > Middle East > UAE > Arab Formation (0.99)
- Asia > Middle East > Oman > Central Oman > South Oman Salt Basin > Nahr Umr Formation (0.99)
- Asia > Middle East > Kuwait > Jahra Governorate > Arabian Basin > Widyan Basin > Hith Formation (0.99)
- Asia > Middle East > Saudi Arabia > Thamama Group Formation (0.94)