Challenges and Opportunities for Development of Marginal Fields through Cluster system: A case study from Western Offshore Basin, India

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1 Paper ID : Challenges and Opportunities for Development of Marginal Fields through Cluster system: A case study from Western Offshore Basin, India A K Maji, B Mudiar & Narayana Swamy ONGC, Mumbai, India akmaji@gmail.com Abstract: Development of marginal fields in recent time is gaining momentum in view of increasing crude oil prices and declining production from existing mature fields. The discoveries of large fields in mature basins world over are increasingly rare with time. Crude oil production in India is mainly contributed by Western Offshore Basin fields and is undergoing steady decline. To support and sustain the production, smaller fields which have been discovered and left undeveloped for economical reasons at the time of discovery are being taken up for development utilizing existing nearby facilities. With improved infrastructure and innovation in technologies like Sub-sea completion, minimum facility well platform, availability of Floating Production Storage & Offloading, Mobile Offshore Production Unit, multi phase pumps, host of other new ideas available and utilization of various lift technologies will make these smaller discoveries economically viable. A cluster of five marginal fields (BHE, B-59, B-127, B-157 and B-15) located east of Mumbai High field is the case study for adoption of innovative technologies for development vis-à-vis early monetization. BHE field was discovered in the year 1976 and other fields in early nineties, lying in the bathymetry range of 40-60m. Hydrocarbon accumulations are proved in multilayered reservoirs within Paleocene Clastics and Oligocene carbonates. These are generally thin, heterogeneous carbonates, clastics and silty sandstone having in-place volume of the order of MM bbl. O+OEG. Inter distances of the fields are in the range of km. Development of these fields are uneconomical on standalone basis, however, they may become economical if developed through cluster system with innovative technologies under the prevailing geological set up. This paper presents the technical and business challenges that are critical for profitable development of these smaller prospects. Innovative alternatives are discussed from both technological and commercial standpoints that can benefit the economical development of marginal fields in cluster system. Introduction: Marginal Fields are, by definition, fields with limited production potential. Primarily, they are small pool reservoirs capable of sustained productivity only for a limited period. Being small pools, they rarely support more than 2 to 3 wells in each structure. On account of low productivity, stand alone development of these fields is never justified on techno-economic considerations. This is more so, when product pricing is not very favorable in the market. Within normal business viability considerations, production from these structures can be attempted only when market supports a comparatively higher product price. In context of fields in Western Offshore, ONGC, India, such structures are in BHE, B-59, B-127, B-157 and B-15 fields. The recoverable hydrocarbon potential in these structures was assessed individually. Several discoveries in Western Offshore, India which were not considered economic at the time of discovery started to produce in the past few years. This change happened due to the (i) clustering together the isolated smaller fields (ii) utilizing existing processing facilities and/or pipeline as well as exporting facilities e.g., single buoy mooring (SBM) to minimize capital expenditure. (iii) Construction of several new pipelines and production facilities, besides the use of some new approaches like utilization of Mobile Offshore Production Unit (MOPU), Floating Production, Storage and Offloading (FPSO) in order to put the discoveries on production. 1

2 A cluster of four marginal fields (B-15, B-59, B-157 and B-127) located North of Mukta field (Fig. 1) and another field BHE east of Mumbai High are planned for cluster development. BHE field was discovered in the year 1976 and the remaining fields were in early nineties in the bathymetry range of m. Hydrocarbon accumulations are proved in multilayered reservoirs within Bassein and Panna formations. In the recent past Q-marine 3D data was acquired in the North of Mukta field, covering some of the fields as mentioned. Reassessment of hydrocarbon volume in B-59, B-127 and BHE fields recently has enhanced potential of these three fields. The total in-place hydrocarbon of the cluster is only MMt (O+OEG) in PB category, of which about 29.9 MMt (O+OEG) could be considered in the initial phase of development. Accumulations are mainly in Panna formation for B-15 & B-127 fields, Bassein & Panna formations for B-59 & B-157 fields and Mukta & Panna formations for BHE fields. Discovery & Delineation: 1. B-15 field B-15 is a complex structure consisting of three culminations over a basement ridge trending in NNE- SSW direction. The structure is bounded by faults on the Eastern and Western limbs and is also affected by cross faults of a later generation trending NE-SW. The discovery of hydrocarbons in B-15-2 well (1994) led to further exploration of B-15 structure A total of six exploratory wells have been drilled over this field, out of which only B-15-2 have proved to be oil bearing in Panna Formation The in-place hydrocarbon of the field is MMt oil and 44.6 MMm 3 solution gas in PB category. 2. B-59 field B-59 structure is located 135 km NW of Mumbai City, in the Heera-Panna Block of the Western Offshore Basin. B-59 field consists of a NNE-SSW trending anticlinal closure formed at the levels of Panna and Bassein formations. The Eastern limb of the anticline is partly affected by a small NW-SE trending fault at Panna level, but at the shallower Bassein level it remains unaffected. The field was discovered in The bathymetry is about 50m. As of now, six exploratory wells have been drilled, out of which 3 wells have encountered hydrocarbons in Bassein and Panna formations. Well B-59-1 is oil bearing in Bassein Upper and Panna formations. B-59-2 is gas bearing in Panna Formation. B-59-3 has shown oil indications in Panna formation. The remaining three wells are found to be dry. The total estimated in-place hydrocarbon includes 3.77 MMt oil, MMm 3 solution gas and MMm 3 free gas in PB category. 3. B-127 field B-127 field is located to the North of Mukta field at a water depth range of 40 to 55m. The structure comprises of a couple of E-W trending closures bounded by a major NNE-SSW trending fault in the West and a NE-SW trending low in the South. The field was discovered in the year A total of five exploratory wells have been drilled till Out of these B-127-1, B are oil and gas bearing, B and B are gas bearing, while B is found to be devoid of any hydrocarbon. The total estimated in-place hydrocarbon includes 9.40 MMt oil, MMm 3 solution gas, MMm 3 gas cap gas and MMm 3 free gas in PB category. These reserves are distributed in Panna formation through six different blocks namely, B127-1 SU-I, B127-2/5 SU-II, B127-2 SU-III, B127-5 SU-IV, B127-2 SU-IV and B127-3 SU-IV in the depth interval m MSL. 4. B-157 field 2

3 B-157 is a small oil and gas field, situated 18 km East of Mumbai High Field at a water depth of m. It is an anticline structure with saturated oil in Lower Bassein and free gas in Upper Bassein formations. B-157 structure is an oval shaped, four way closures trending in N-S to NNW-SSE direction. The areal extent of the structure is about 11 sq. km at Bassein level. Discovery of hydrocarbons in the first exploratory well B (1990) led to drilling of another four delineation wells over the structure. Out of these wells, B and 4 are oil and gas bearing. Oil and gas pools are located within Panna (Depth 2560 m MSL) and Bassein formations (Depth range: m MSL). Panna Formation is oil bearing, while Bassein Formation is oil and gas bearing. The total estimated in-place hydrocarbon includes MMt oil and MMm 3 solution gas, MMm 3 gas cap gas and MMm 3 free gas in PB category. 5. BHE The Bombay High East field is located on the down thrown side of the NNW-SSE trending Bombay High East fault, which is a major, down to the basement, normal fault affecting the Eastern limb of the Bombay High field. A series of small culminations have formed along the fault zone. One such culmination constitutes the main Bombay High East field. Two other minor culminations, over which wells BHE-4 and BHE-5 drilled, are located to the North and South of the main field. The field lies at a water depth of 70 to 75 m The main Bombay High East field, consisting of wells BHE-1, BHE-2, BHE-A-1, BHE-A-2 and BHE-A- 3 forms a small, NE-SW trending closure, partly dissected by a North-South trending fault in the Western part of the structure. Five exploratory wells have so far been drilled in the main Bombay High East field out of these four are oil bearing. The exploratory wells BHE-1, BHE-A-1 and the inclined wells BHE-A-2 and BHE-A-3 drilled in close proximity of each other proved to be oil bearing. Well BHE-2 drilled on the flank of the structure was however found to be devoid of hydrocarbon. In addition to the above wells, BHE-4, drilled on a separate culmination in the Northern part of the block, proved to be gas bearing from Mukta formation. Bassein formation, which could not be tested due to paucity of rig time, also gave hydrocarbon indications in cutting and core samples. Well BHE-5, drilled on a small culmination in the Southern part, showed oil indications. The in-place hydrocarbon of the field is 5.51 MMt oil and MMm 3 solution gas and 76.3 MMm 3 free gas in PB category. These reserves are distributed in two reservoirs viz. Mukta (Depth ~ 2125 m MSL) and Panna (Depth ~ 2270 m MSL) Development Strategy: By virtue of geographical closeness, the structures (BHE, B-59, B-127, B-157 and B-15) can be grouped in definite clusters (Fig. 2). Without cluster consideration, as it can be seen, the total productivity of each field is not high enough to support stand-alone exploitation, in spite of comparatively more favorable market scenario with reference to what it was when these structures were discovered. Present era probably provides the most favourable market scenario in foreseeable future and development of these structures can be most sensible in business terms in today s market scenario. However, in spite of favorable market scenario, unless certain fundamental issues are addressed suitably, such type of field development may still not be practicable. This paper analyses the case studies of the above mentioned Marginal field development process in ONGC to identify these issues. For any offshore field development, the two critical components which call for capital expenditure are surface facilities and drilling. This paper looks into the issues related with surface facilities alone. To facilitate drilling, it may require a dry-well-head approach or sub-sea completion approach. Nevertheless, requirement of well is fundamental and mandatory for any field development. Through a study by an external agency, it has been found that sub-sea completion may not be a cost effective option over dry type well head considerations when length of umbilical required for operations of subsea completion equipments becomes more than the threshold value of 9 Kms. Further, sub-sea 3

4 completion will lead to increased operational expenditure if frequent revisits are requirement for production from these wells. Primarily, based on these two issues, it is decided whether wells will be of sub-sea completion type or dry-well-head completion from deck of a well platform. The analysis presented herein considers well platform. In B-59 field, 3.77 MMt oil is distributed in two reservoirs (Panna and Bassein) having good petrophysical properties (Permeability ranges from md & PI ranges from 2.0 to 2.2 b/d/psi) and production potential as seen in the exploratory well testing. Two wells are required for sequential exploitation of both the reservoirs. After exploitation of deeper Eocene pay, the upper layer will be exploited through zone transfer. In order to increase the productivity, the reservoir section will be penetrated at high angle (say about 45 0 ). For exploiting the small free gas accumulations in the northern down dip, one separate well need to be considered for simultaneous gas production from the B-59 field. The B-15 structure is well brought out in 3D seismic. It is a four way closure. The in-place being negligible (0.267 MMt), the present development scheme does not consider its development. In BHE field, the discovery well penetrated two reservoirs in Eocene and late Oligocene. However, three delineation wells had encountered only Oligocene pools indicating limited area extent of Eocene pool. Therefore the present development scheme envisages exploitation of Late Oligocene reservoir (Mukta pay) only. A high angle producer is planned near the delineation well where the reservoir development found to be good(k= md, PI=13.66 b/d/psi). Further development of the field would be based on the performance of this well. However, for exploitation of Panna zone which is relatively tight (permeability range: md), another horizontal well is warranted for higher oil recovery. In B-127 field, Panna reservoir is well developed through out the field and good to very good permeable in nature and PI is estimated in the range of b/d/psi. Panna pay in block of B127-1 SU-I is an extensive sand body having oil in-place of about 4.0 MMt and very good petro-physical rock properties (K=803 md). The well PI during exploratory well testing estimated of the order of 2.4 b/d/psi. For optimum development of this reservoir two wells are required to be drilled and after complete exploitation, the gas cap gas has to be produced through zone transfer at later date. For initial development for Panna formation in block of B127-2 SU-III, 1 well is required to be drilled which also may be utilized for exploiting the free gas zone of Panna in B127-2/5 SU-II block through zone transfer at later stage. Similarly another well is required for development of Panna reservoir in block of B127-5 SU-IV having estimated oil in-place of 2.52 MMt. In B-157 field, all the zones (Panna, B-Lower & B-Upper) are less extensive but overlapping one above another. B-upper reservoir contains Free Gas having AOFP of 6.40 lakh m3/d & permeability of 15.2 md, B-Lower zone contains both MMt in-place oil and MMm3 gas cap gas. The well PI and permeability in this sand estimated as 6.2 b/d/psi & md respectively. The Panna pay (sub hydrostatic reservoir pressure) is having less in place oil of about 0.23 MMt and Free gas of 567 MMm3. In view of above the oil zones needs to be exploited first. Subsequently the gas zones of all the reservoirs may be exploited simultaneously through commingle completion. Hence two wells are needed in the geologically suitable areas for effective exploitation of all the zones. The nearest processing facility at NQO complex & Well Head Platform LE are located around 18 km and 13 km respectively. As far as facilities are concerned, there are four unmanned well platforms are needed in the cluster of four fields. The platforms are to be inter-connected through oil and gas pipeline. Subsequently, the combined oil and gas from the cluster fields will go to either SH Process Platform or NQ Process Platform for processing and onward transmission to unloading terminal. 4

5 Conclusion: There are a great need to study and find unconventional solutions to develop more and more small sized fields, especially that these types of fields are expected to be abundant in the Western Offshore fields, India In Marginal Field Development, processing cost is required to be reduced by using available existing facilities in existing platforms and the denser pipeline network is of great value. Apparently nothing much can be achieved towards making any extra effort for improvised technology on this issue. Minimizing cost of well platform structures rather than any costly improvisation of processing technology may be the primary variables, which need attention for surface facility in any Marginal Field Development project This study is basically a conceptual study for development of the B-59 cluster of Marginal fields in Western Offshore Basin, ONGC, India. References: 1. Well Completion Reports of B-59, BHE, B-127, B-157 and B-15 fields (Internal ONGC report). 2. Reservoir Study Reports of B-59, BHE, B-127 and B-157 fields (Internal ONGC report). 3. Tewari R D et.al. Stepping on Development of Small and Medium size oilfields through Horizontal Wells- The way ahead SPE , Agiza M. N et.al. Marginal Oil Fields, Profitable Oil at Low Reserves: How? SPE-30035, 1995 Acknowledgement: The authors are highly grateful to Mr. J G Chaturvedi, ED-Chief NMFD, ONGC, Mumbai, India for his continuous encouragement, support and valuable guidance during the study. Thanks are due to the ONGC Management for the permission to publish this paper in Petrotech-2010 International Conference. Table- 1: Inter-distances of the Cluster Fields and Process Complex From To Distance, km B-59-1 B B-59-1 BHE-A B-59-1 B B B B NQG 17.0 BHE-A-1 SHP 11.0 Table- 2: Distances of Cluster fields Platforms along with Flow lines and Water Depths Field Platform No. of Flow lines, Water Depth, Remarks Wells km m B Exploited mainly as gas with less oil B Simultaneous oil & gas flow BHE Simultaneous oil & gas flow B Simultaneous oil & gas flow B Not considered (less in-place) Total Fig.-1: Location Map of Cluster fields (B-59, B-127, B-157, BHE & B-15) 5

6 Fig.-2: Schematic diagram of Flow lines and Platforms of Cluster fields B-105 B-15 B-188B-48 B-46 NQO B-157 SBM B-59 B-127 BHN MUMBAI HIGH 14" OIL WO-24 ICW BHS 12" GAS BHE-1 Mukta Field (JV) Panna B-45 SH Field (JV) D-33 D-1 B-121/119 B-55 16"X 77kmB-55toSHG VASAI EAST B-149 BPA (BSE) B-147 BS-13 BS-16 B-192 B-22 BPB 28"X78kmSH-BPBLine BS-12 36" X 231kmGastrunklineBasseintoHazira 42" X 244kmGastrun klinebpbtohazira BASSEIN 26" Gas t runklinetouran 30" X 203kmOiltrunklinetoUran B-172 B-80 B-178 WO-5 B-173A B-23A WO-15 B-28 B-193 B-179 WO-16 B " " X kmshp-heeraline kmshp-heeraline INDEX B-28A OIL LINE GAS LINE B-37 OIL FIELD B-134 GAS FIELD NEELAM OIL & GAS FIELD Marginal Fields around Mumbai High SOUR FIELD D-18 and Bassein Fields HIGHLY SOUR FIELD SCALE SWEET OIL/GAS HEERA 0 km 10 km 20 km 30 km 40 km 24"Oil trunklinetouran 18" oil and gas line 26"GastrunklinetoUran B-15-2, 40 m NQG B-157-4, 50 m 17 Km gas line 18.2 Km 21.4 Km Facilities: 4 well platforms 11 wells ~ 85 km flow lines Developable volume: Oil = MMt, Gas = BCM Oil line 27.4 Km B-59-1, 50 m 6.8 Km 9 July 2010 SHP 11 Km BHE-A-1 70 m - B-127-1, 55 m 6