IPA03-G-141
PROCEEDINGS, INDONESIAN PETROLEUM ASSOCIATION Twenty-Ninth Annual Convention & Exhibition, October 2003
THE ABADI GAS FIELD
H. Nagura* H. MP Bandjarnahor*
I. Suzuki* K. Kihara*
T. Teramoto* T. Swiecicki**
Y. Hayashi* R. Bird***
T. Yoshida*
ABSTRACT
The Abadi field is Indonesia’s first discovery in the Middle Jurassic Plover Formation. This potentially giant gas discovery is located some 350 km east of Timor Island and 350 km north of Darwin, Australia.
It lies just north of the international boundary with Australia, in 400-800 m water depth. The Masela Production Sharing Contract (PSC) was awarded to Inpex as Operator with 100% interest in November 1998. The discovery well Abadi-1 was drilled and completed in late 2000. Following discovery, a 2,060 km2 3D seismic survey was acquired in 2001 and two successful appraisal wells were drilled in 2002.
Geologically, the field comprises relatively undeformed Australian continental margin that extends into Indonesian waters. It lies on the eastern extremity of the Sahul Platform and occupies a large tilted fault block bounded to the east and south by the Calder-Malita Grabens. The accumulation contains a significant gas column, reservoired within shallow marine, highly mature, quartzose sandstone of the Middle Jurassic Plover Formation. Close analogues are to be found in the giant Greater Sunrise and Bayu- Undan fields. Reservoir quality, at a depth of ~3,900 m, varies from surprisingly good to poor, reflecting a complex interaction of primary depositional controls and later diagenetic influences. A preliminary estimate of reserves size is about 5 TCF.
Inpex has undertaken a variety of exploration projects and studies, including high-resolution sequence stratigraphy and seismic -driven paleofacies reconstructions to model the reservoir architecture.
* Inpex Masela, Ltd.
** Cerberus Consultants
*** P.T. Paradigm Geophysical Indonesia
Utilizing this framework, a full-field 3D model is currently being developed to better characterize the likely range of reserves and to provide the basis for a more accurate understanding of the economic value of Abadi.
INTRODUCTION
The Abadi gas field was discovered in late 2000 with the successful drilling of the Abadi-1 well. The field is located within the Masela PSC block in the eastern part of the Timor Sea, Eastern Indonesia, along the Indonesia -Australia international boundary (Figure 1).
Approximately 100 km north of the block, the Babar Islands and Tanimbar Islands follow an east-west trend along the outer ridge of the Banda Arc. The block name of Masela originates from one of these islands. The deep Timor Trough with more than 1,500 m water depth lies between the island arc and the block. The Masela Block is on the upper slope area of the Australian Continental Shelf with associated water depths ranging from 300 m to 1,000 m.
Active exploration work was conducted on the Australian side of the Timor Sea from the mid 1960s, and the discovery wells of the Sunrise-Troubadour gas fie ld were drilled in the early stages (Troubadour- 1 in 1974, Sunrise-1 in 1975). Although exploration efforts were halted in the Timor Gap area in the late 1970s and 1980s by the boundary dispute between Indonesia and Australia, the discoveries of the Evans Shoal gas field (Evans Shoal-1 in 1988) and the Bayu Undan gas field (Bayu-1 in 1995) were eventually added to the area’s commercial reserves. Some of these fields are now on track for development. On the other hand, no exploration work was conducted on the Indonesian side of the Timor Sea until Geco-Prakla
© IPA, 2006 - 29th Annual Convention Proceedings, 2003
shot a 2,594 km 2D spec seismic survey in 1996 under an arrangement with MIGAS.
Following Geco-Prakla ’s spec survey, Pertamina opened the Masela Block PSC tender on October 19, 1997, together with the adjacent Leti Block. Inpex conducted a regional evaluation using the Geco- Prakla data together with open file seismic and well data from the Australian side. The prospectivity was assessed, and a bid was submitted to Pertamina for the Masela PSC on April 3, 1998. The Masela PSC was awarded to Inpex and the PSC was signed on November 16, 1998, between Inpex and Pertamina with the witness and approval of MIGAS.
Inpex Masela, Ltd. was established as the project company to execute the exploration program with financial support from the Japan National Oil Corporation. This paper summarizes the exploration activities conducted in the Masela Block to date.
REGIONAL SETTING
The Abadi field lies within the Northern Bonaparte Basin, on the Sahul Platform at the eastern end of the Sunrise-Troubadour High (Figure 2). It is bounded to the east by the Masela Deep, which is the northern extension of the Calder Graben. The Malita Graben lies further to the southwest and accommodates thick Cretaceous-Tertiary sediments. The northwest trending Goulburn Graben, with thick Paleozoic sediments, is located to the southeast. The Timor Trough lies to the north.
Approximately 250 km west of Abadi, the Sunrise- Troubadour gas field (proved & probable recoverable reserves: 8.4 TCF; public information from Northern Territory Government of Australia) occupies the axis of the Sunrise-Troubadour High. The Evans Shoal gas field (proved & probable recoverable reserves:
6.6 TCF; public information from Northern Territory Government of Australia) is approximately 150 km southwest of Abadi between the Sunrise-Troubadour High and Malita Graben.
Development of the Northern Bonaparte Basin was influenced by rifting and continental separation in middle Jurassic to early Cretaceous times along the northwestern Australian margin, and later modified by the collision between the Indo-Australian and Sunda plates from the Miocene to the present (Whittam et al. 1996).
The lithostratigraphy of the Abadi field area is shown in Figure 3. Fluvio-deltaic to shallow marine deposits of the Middle Jurassic Plover Formation accumulated in a pre-rift to early syn-rift tectonic regime. This formation is the main reservoir objective in the area.
Marine claystone of the lower Cretaceous Echuca Shoals Formation unconformably overlies the Plover Formation. Overlying the Echuca Shoals Formation is the predominantly carbonate Jamieson Formation, followed by thick prograding shelf and slope sediments of the Cretaceous Wangarlu Formation.
The Tertiary section consists of drift phase deposits, predominantly thick shelf carbonates. The late Miocene collision between the Indo-Australian and Sunda plates initiated the final tectonic phase in this area and continues to the present day. Left-lateral transtension and plate flexure rejuvenated Jurassic normal faults and produced a new set of normal faults with a dominant north-easterly strike.
EXPLORATION HISTORY
Pre Bid Evaluation
In 1997/98, the Masela Block was evaluated based on approximately 2,600 km of Geco-Prakla spec seismic data (GPARI-96 series) shot during 1996 in Indonesian waters. Available Australian open file 2D seismic (3,500 km) and well data (13 wells) were also incorporated for the evaluation. These well data included Troubadour-1, Sunrise-1, Loxton Shoals-1, Evans Shoal-1, Lynedoch-1, Tuatara-1 and others.
The primary reservoir rocks of these discoveries were Jurassic sandstone similar to many other North West Shelf discoveries. No exploratory wells had been drilled in Indonesian waters of this area up to that time.
Line spacing of the available 2D seismic data within the Masela Block was roughly 10 km x 25 km. The Albian carbonate marker above the Jurassic sandstone level provided a readily mappable horizon on seismic data throughout the area, and this became the key horizon for our interpretation. Time mapping and simple depth conversion of the Albian marker identified two structural leads. One of these structures, located just west of the Masela Deep, was in a favourable positio n to trap hydrocarbons migrating from the Masela Deep with a closed area of more than 1,000 km2. Basin modeling suggested the generation and migration of hydrocarbons from the Masela Deep to this adjacent area.
This primary lead, named Abadi, was located in the central part of the block in water depths ranging from 400 m to 800 m. It was initially expected to hold hydrocarbon reserves of more than 2 TCF with an upside potential of 5 TCF in the Jurassic reservoir.
Inpex submitted a bid to Pertamina to obtain the Masela Block on April 3, 1998, and the Masela PSC was awarded to Inpex on November 16, 1998.
Additional Evaluation after Signature of PSC
After signing the PSC, a 2,948 km 2D seismic survey (IM99 dataset) was conducted utilizing M/V Geco Rho (PT Geco-Prakla) in February to March 1999 to evaluate in detail the structure and stratigraphy of identified leads and to continue exploration over the entire block. The seismic program was designed to infill the existing GPARI-96 grid, reducing the block- wide line spacing to 2 km x 4 km. The GPARI-96 lines in the Masela Block area were also reprocessed to have seismic images consistent with the new acquisition. To develop a more detailed regional understanding, seismic data were exchanged with Shell, operator of the adjacent NT/P49 block in Australian waters just south of the Masela Block. A pre-drilling well data trade was also agreed with Shell, and well data from Lynedoch-2 and Tyche -1 were added to our database. These data trades were conducted with MIGAS approval.
Regional maps and prospect interpretations were updated and refined utilizing these data . The seismic time interpretation was converted to a depth map using a two-layer model to remove the water depth effect. The Abadi structure was defined as a drillable prospect and the location of an exploration well was selected to test it.
The Abadi prospect has three-way dip closure, bounded to the east by the north-south trending eastward dipping normal fault that marks the western boundary of the Masela Deep. The prospect was interpreted to be a paleo-high structure during the Mesozoic syn-rift phase, and structural closure was enhanced by compression in the Miocene collision phase. The major risks were presence of effective reservoir rock within the Plover Formation and the presence of source rocks in the Masela Deep. The risk related to the trap and the seal were considered to be low.
Abadi-1
Abadi-1, the first exploration well in the Masela Block, was located 760 km east of Kupang, or 350 km north from Darwin , Australia. The drill ship Energy Searcher arrived on location on September 29, 2000, and Abadi-1 spudded in 457 m of water on October 1, 2000. The objective of the well was to test the hydrocarbon potential of sandstones in the Middle Jurassic Plover Formation. The well was drilled without a riser using seawater until reaching the 13- 3/8” casing point at 2,139 m, in the uppermost part of the Wangarlu Formation. After Setting 9-5/8” casing at 3,795 m in the Echuca Shoals Formation, the objective Jurassic Plover sandstone was intersected and 18 m of conventional core was cut with 100%
recovery. TD was called at 4,230 m, after ‘hot-shot’
palynological analyses confirmed a Bajocian age (Middle Jurassic) for the bottom sample and a VSP showed that Abadi-1 had penetrated the objective seismic reflections. Comprehensive wireline logging confirmed the presence of gas-filled sandstone in the upper part of the Plover Formation, with 73 m of gross hydrocarbon column including 21 m of extremely good quality reservoir. Though not readily recognizable from log data, the gas water contact was established at 3,900 mSS from MDT pressure measurements (Figure 4).
One production test was conducted in the Plover Formation over the interval 3,867 m - 3,887 m. This flowed gas, condensate and water at the sustained rate of 25 mmscfgpd, 260 bcpd (52.5o API) and 178 bwpd through a 40/64” choke. The water condensed from water vapour within the gas. The gas contained 9.6 % CO2 as determined by laboratory test. After completing the testing program, the well was plugged and abandoned as a gas and condensate discovery, and the rig was released on December 11, 2000. This success was the first Plover discovery in Indonesian waters.
3D Seismic Acquisition and Interpretation
The available map and drilling results indicated that the Abadi structure could hold significant gas reserves, hence exploration continued with plans for 3D seismic acquisition and processing. A 3D seismic survey of 2,060 km2 was conducted from July to September 2001, utilizing the PGS M/V Ramform Challenger with 8 streamers and a 4,200 m cable length. A 700 km2 “fast track area” was selected to
expedite interpretation over the main part of the Abadi structure and allow delineation drilling from the 1st quarter of 2002. On-board processing was completed for this “fast track area,” and the migration cube was available for interpretation by the middle of September 2001. Processing for the full cube continued in the onshore processing center and was completed by the end of 2001.
3D seismic interpretation of the “fast track area”
focused on determining optimal delineation well locations. A clearer image of the Abadi structure emerged as time interpretation maps were converted to depth, showing the structure to consist of northern and southern blocks separated by an east-west trending normal fault (Figure 5). Seismic facies analyses and paleogeographic modeling were conducted at the reservoir level, integrating the 3D seismic and Abadi-1 well data. Based on these interpretation results, two delineation well locations were selected. One was in the northern fault block, 13.5 km northeast of Abadi-1, and the other was in the southern fault block, 16.5 km southwest of Abadi- 1. The predicted depths of the Top Plover level at both wells were estimated to be approximately 20 m deeper than that of Abadi-1 and approximately 50 m shallower than the indicated gas water contact.
Abadi-2/2ST
Inpex began delineation drilling at Abadi-2, situated in 580 m of water, using the drill ship Energy Searcher. The rig arrived at the location on March 19, 2002, and spudded Abadi-2 on March 20, 2002.
The well reached the principle reservoir objective at 3,756 m, 113 m shallower than prognosis. Two conventional cores were cut from 3,783 m to 3,837 m (54 m) within the Plover Formation, though total recovery was only 9.6 m (17.8%). Intermediate check shot data revealed that interval velocit ies in the Abadi-2 area are much slower than estimated from seismic velocity analysis. This velocity difference contributed to the significant error in the depth prediction.
The well encountered a problem with 9-5/8” casing just after cutting #2 core, which caused us to plug back the original hole and sidetrack from 3,556 m as Abadi-2ST. Because of this casing trouble, no wireline logs were run for the coring interval of Abadi-2. After setting a 7” liner at 3,756 m in the
sidetracked hole, a 6” hole was drilled to 3,986 m and then wireline logging was conducted. As no shows were detected in the bottom part of the section and penetration into the lower reservoir section of the Plover Formation was confirmed by the PEX log suite, this depth (3,986 m) was selected as TD of Abadi- 2ST.
The wireline logging data and MDT pressure plot confirmed the presence of the gas reservoir in the upper reservoir section of the Plover Formation (Figure 4). The gas pressure data of Abadi-2ST fall almost on the same trend line as Abadi-1 suggesting the gas to be in pressure equilibrium between Abadi-1 and Abadi-2ST. The pressure data of the possible water sandstone was obtained below the shale zone of the verrucosa maximum flooding surface, which is described in the reservoir section below. The pressure of this zone is slightly higher than the water pressure in the Abadi-1, and if we assume this sandstone is in the same reservoir unit with the gas reservoir above the verrucosa zone, the GWC is estimated to be approximately 3,890 mSS in Abadi- 2ST.
After wireline logging was completed, one production test was carried out in the Plover Formation over the intervals of 3,829 m - 3,839 m and 3,845.5 m - 3,850.5 m. The test flowed gas, condensate and water at the rate of 18.6 mmscfgpd, 150 bcpd (51o API) and 127 bwpd through a 44/64” choke. The gas contained 9.5 % CO2 by laboratory test, and 5 ppm H2S were detected in wellsite measurements.
Abadi-3
After completion of Abadi-2/2ST drilling, the rig was towed to the Abadi-3 location and the well was spudded on July 29, 2002. The well was situated in 423 m of water.
Abadi-3 intersected the objective Jurassic Plover sandstone at 3,832 m, 19 m shallower than prognosis.
Four conventional cores were cut within the upper part of the Plover Formation, resulting in the recovery of 58.16 m of core. The 8-1/2” hole was drilled to 4,032 m, which was considered deep enough to evaluate the upper Plover reservoir section.
The wireline logging data and MDT pressure plot confirmed the presence of gas in the upper reservoir section of the Plover Formation (Figure 4). The gas
pressure data of Abadi-3 lies on exactly the same line as the gas pressure data of Abadi-1. These data confirm that the gas is in pressure equilibrium between the two wells. The GWC was not observed on the wireline logs. No reliable formation pressure data was acquired in the water bearing zone below the gas column because of super-charging and/or seal- failure of the MDT tool. However, the highest interpreted water based on PEX log response is at 3,896 mSS.
Given these results from Abadi-3 and pressure data from Abadi-1 and Abadi-2ST, the GWC appears to be different for each of these three wells. This difference may be due to hydrodynamic flow across the basin from the Timor Trough area as discussed by Nowell (1999).
Two production tests were conducted in the Plover Formation. The interval of 3,899 m - 3,906 m was perforated for DST #1, which resulted in no flow due to a tight reservoir. DST #2 was conducted over the interval 3,855 m - 3,867 m and flowed gas and condensate through 44/64” choke at a rate of 13.8 mmscfgpd, 266 bcpd (51-56o API) and 57 bwpd. The gas contained 9.2 % CO2 by laboratory test, and 6.66 ppm H2S were detected in wellsite measurements.
PETROLEUM GEOLOGY Source and Migration
The source for the Abadi gas is postulated to be laterally equivalent marine shales deposited contemporaneous with the Plover Formation.
Thermal maturity studies indicate such source rocks should be mature for gas in the Calder-Malita Grabens, Masela Deep, and directly down-dip from the Abadi field towards the Timor Trough. The Grains containing Oil Inclusion (GOITM) technique of Eadington et al (1996) did not detect oil inclusions on quartz grains in the gas filled sandstone (GOI values are less than 0.2%), indicating no liquid hydrocarbon migration before the gas trap.
Trap and Seal
The Abadi structure is a paleo high that has been reactivated and modified by subsequent rifting both in the latest Jurassic/earliest Cretaceous and in the Neogene. The Abadi field is fault bounded to the east, and divided into two parts, a northern block and a
southern block, by an east-west trending normal fault (Figure 5). Multiple conjugate fault sets cut the field, but to date there is no clear evidence of fault compartmentalization. A structural spill point to the west separates Abadi field from the Sunrise- Troubadour accumulations updip.
Movement along the bounding faults to the south and east juxtaposed the Plover reservoir succession against early Cretaceous shales of the Echuca Shoals Formation, providing the primary side-seal. Topseal is also provided by the regional Echuca Shoals Formation.
Reservoir Stratigraphy
A high resolution, reservoir-scale stratigraphic framework has been developed drawing on evidence from wireline log data, conventional core, CST (sidewall core) and MSCT (rotary sidewall core) samples, biostratigraphy and ichnofacies. A total of 86 m of conventional core was cut in the 3 wells.
Palynological zonation with an age resolution of between one and four million years (Helby et al. 1987, and Laurie and Foster, 2001) provides the main chronostratigraphic framework for the correlation.
Stratigraphic correlation of the 3 Abadi wells is shown in Figure 6.
The stratigraphic succession can be readily divided into a series of genetically related zones based on the presence of bounding surfaces related to periods of rapid marine flooding. These have been named by reference to the palynological interval containing them. The deepest sediments penetrated in Abadi-1 appear to occur just above the caddaense flooding event recognized within the Sunrise-Troubadour field (Seggie et al. 2000). The Zone 4 sediments overlying this comprise a 220 m thick succession of stacked, progradational to aggradational deltaic sediments with limited reservoir potential encountered to date. This deltaic succession is capped by a thin shale associated with a flooding event, the verrucosa maximum flooding surface (mfs). The Abadi gas reservoir confirmed so far lies above this maximum flooding surface. This lower deltaic unit, however, lies above the GWC in higher structural positions that remain undrilled.
The verrucosa mfs is well defined on log, palynology and seismic data and is a key surface for mapping.
Overlying this is an 80-100 m thick, laterally
persistent coarsening upward succession comprising Zone 3. This zone passes from a lower interval of offshore shales with thin storm sands, into lower shoreface silts and fine sands and eventually into fine to medium grained, planar and cross-bedded, extensively bioturbated upper shoreface sands. On seismic data, this interval shows well-developed progradational geometries that, together with the well data, are indicative of shoreline progradation (Figure 7). No evidence of emergence has been seen to date, though sedimentary structures and ichnofabrics indicate a strong tidal influence. Zone 3 sands were tested in the Abadi-2ST well and flowed at over 18 mmscfgpd. This zone is capped by a thin flooding event, the base indotata mfs.
The base indotata mfs is well defined by log, palynological and seismic data and is another key surface for mapping. Overlying this is a 50 m thick, laterally persistent coarsening upward succession comprising Zone 2. This zone passes from a lower interval of offshore shales with thin storm sands, into lower shoreface silts and fine sands and eventually into fine to medium grained, planar and cross-bedded, extensively bioturbated upper shoreface sands. No evidence of emergence has been seen to date.
Capping this zone are massive, extensively bioturbated, predominantly medium grained sands that display a characteristically blocky log profile and excellent reservoir properties. Relict sedimentary structures and ichnofabrics indicate a strong tidal influence, and these sands are interpreted to have been deposited in a tidal delta setting. These sands were tested in the Abadi-1 and 3 wells and flowed at rates of up to 25 mmscfgpd. The sediments of Zone 2 are capped by a thin flooding event, the base aemula mfs.
The base aemula mfs can be defined on log and palynological data. Sediments of Zone 1, above the base aemula mfs, comprise a thin succession of non- reservoir quality sands possibly representing deposits of an offshore bar in Abadi-1, whilst in Abadi-3 the interval compr ises offshore marine shales. In Abadi- 2ST, Zone 1 sediments are absent due to erosion.
Reservoir Quality
Reservoir quality within quartzarenite sandstones of the Plover Formation is dependant on a complex interaction of primary depositional setting and diagenesis. In the Abadi field the cleanest sands
preserve excellent reservoir quality despite burial depths in excess of 3,400 m below the seabed.
Although the burial depth of the Plover sandstone is nearly 1,500 m deeper than in the Sunrise-Troubadour field, the sandstones in the Abadi field still possess reservoir properties capable of commercial flow rates.
A crossplot of porosity vs. permeability from core plug data shows three clear trends indicative of different litho-facies within the Plover reservoir section of the Abadi field (Figure 8).
Facies 1 shows high porosity and permeability values and corresponds to tidal delta deposits. The data points for the sandstones of core #1 of Abadi-1 and core #1 of Abadi-3 fall in this facies group. The sandstones of core #1 in Abadi-1 comprise medium to coarse-grained quartzarenite with excellent visible porosity (Figure 9). The framework grains are composed mostly of quartz (72-75 %), with very minor amounts of K-feldspar (<0.4 %), chert (<1 %), metaquarzite (<0.4 %), bioclasts (<0.4 %) and other grains (Figure 10). Quartz grains are monocrystalline quartz with a grain size from 100 to 900 µm. The rocks are medium-well sorted to well sorted. Porosity is mainly intergranular. The detrital clay volume is very low (<0.4 %) and occurs as dispersed matrix, associated with burrow linings. Porosity ranges from 7-13 % and the volume of quartz overgrowth is 10- 16 %. The kaolinite content is less than 1 %. Other diagenetic minerals including pyrite or illite are also minor. The very low clay and feldspar contents indicate the well winnowed and texturally highly mature nature of these sandstones. The sandstone of core #1 of Abadi-3 has almost the same characteristics except the grain size is predominantly fine to medium.
For a given porosity, the permeability of Facies 2 (Figure 8) is an order of magnitude worse than Facies 1. However, Facies 2 sands still retains good reservoir properties. This facies is represented by sandstone in core #1 of Abadi-2. These sands are fine to medium grained, moderately to well sorted quartzarenite to subarkose/sublitharenite. In contrast to Facies 1 sandstones, the percentage of quartz grains is lower at 55-60 %, while the contents of other framework grains like K-feldspar (1-3 %) and chert (1-2 %) are higher. The clay content is still minimal (0.4-2 %) and kaolinite cement content is 5-10%. The porosity is 10-15 % and the volume of quartz overgrowth is 10-18 %.
Facies 3 is represented by the middle part of Core #4 of Abadi-3. This interval is below the gas water contact and diagenetic calcite cement is dominant.
This sandstone is predominantly medium-grained, moderately to well sorted, clean quartzarenite.
CONCLUSIONS AND FUTURE PLANS
The Abadi gas field is the single largest discovery made in the Indonesian waters for several years.
Predictions of a gas reservoir within the Plover Formation made dur ing the fast track exploration program were confirmed by Abadi-1, 2/2ST and 3 wells. High-resolution sequence stratigraphic correlations provide the framework for a practical reservoir subdivision. Pressure data indicate the existence of a single tank system, although pressure plots indicate the possibility of small differences in gas-water contacts within the field.
Work is now ongoing to accurately model the reservoir. Establishing a stochastic 3D geological model and reservoir simulation are seen as essential steps to provide an accurate assessment of reserves range. Determining the size of the prize on offer, which is preliminarily estimated as about 5 TCF, will then allow future delineation planning and a more focused marketing effort to be undertaken. The present major tasks are addressing the depth conversion uncertainty and reservoir facies mapping, which together control much of the net reservoir volume. In addition to this subsurface work, Inpex is now conducting preliminary screening of development concepts and commercial/marketing evaluations in order to expedite commercialization of Abadi field. Development options include Floating LNG, GTL (Gas to Liquids), DME (Dimethyl Ether), and raw gas sales via pipeline.
ACKNOWLEDGEMENTS
The authors would like to thank BP Migas and Inpex Masela, Ltd. for allowing this paper to be published.
REFERENCES
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Haq, B.U., Hardenbol, J. and Vail, P.R., 1988.
Mesozoic and Cenozoic chronostratigraphy and cycles of sea-level change, SEPM Special Publication, 42, p. 71-108.
Laurie, J.R. and Foster, C.B., (ed) 2001. Studies in Australian Mesozoic palynology II, Association of Australasian Palaeontologists Memoir 24.
Helby, R., Morgan, R., and Partridge, A.D., 1987. A palynological zonation of the Australian Mesozoic, in Jell, P.A. (ed), Studies in Australian Mesozoic Palynology, Association of Australasian Palaeontolo gists Memoir 4, p. 1-94.
Nowell, N.A., 1999. Water Washing in the Northern Bonaparte Basin, APPEA Journal 39 (1), p. 227-247.
Seggie, R.J., Ainsworth, R.B., Johnson, D.A., Koninx, J.P.M., Spaargaren, B., and Stephenson, P.M., 2000.
Awakening of a sleeping giant: Sunrise-Troubadour Gas-Condensate Field, APPEA Journal 40 (1), p.
417-436.
Whittam, D.B., Norvick, M.S., and McIntyre, C.L., 1996. Mesozoic and Cainozoic tectonostratigraphy of Western ZOCA and adjacent areas, APPEA Journal 36 (1), p. 209-232.
Figure 1 - Location map of the Abadi gas field. Contour lines indicate water depths in meters. The Abadi gas field is located within the Masela PSC block in the eastern part of the Timor Sea, Eastern Indonesia, along the Indonesia -Australia international boundary. The deep Timor Trough of more than 1,500 m water depth lies between the outer ridge of the Banda Arc and the Masela Block. The Masela Block is on the upper slope area of the Australian Continental Shelf with associated water depths ranging from 300 m to 1,000 m.
Figure 2 - Tectonic elements map of the Northern Bonaparte Basin. The Abadi field lies at the eastern end of the Sunrise-Troubadour High on the Sahul Platform. It is bounded to the east by the Masela Deep, which is the northern extension of the Calder Graben. The Malita Graben lies further to the southwest and accommodates thick Cretaceous-Tertiary sediments. The northwest trending Goulbourn Graben, with thick Paleozoic sediments, is located to the southeast. Timor Trough lies to the north. Well locations referenced in this paper are indicated. Approximately 250 km west of Abadi, the Sunrise-Troubadour gas field (proved & probable recoverable reserves:
8.4 TCF; public information from Northern Territory Government of Australia) occupies the axis of the Sunrise-Troubadour High.
The Evans Shoal gas field (proved & probable recoverable reserves: 6.6 TCF; public information from Northern Territory Government of Australia) is approximately 150 km southwest of Abadi between the Sunrise-Troubadour High and Malita Graben.
Figure 3 - Generalized stratigraphic column of the Abadi field area (age scale based on Haq et al. 1988, and palynological zonation based on Helby et al. 1987 and Laurie and Foster, 2001). Fluvio- deltaic to shallow marine deposits of the Middle Jurassic Plover Formation accumulated in a pre-rift to early syn-rift tectonic regime. This formation is the main reservoir objective in the area. Marine claystone of the lower Cretaceous Echuca Shoals Formation unconformably overlies the Plover Formation. Overlying the Echuca Shoals Formation is the predominantly carbonate Jamieson Formation, followed by thick prograding shelf and slope sediments of the Cretaceous Wangarlu Formation. The Tertiary section consists of drift phase deposits, predominantly thick shelf carbonates.
Figure 4 - Formation pressure versus Depth plot of Abadi-1, 2ST and 3 wells. The GR curves of three wells are also shown for reference. The gas pressure data for 3 wells fall almost on the same line, suggesting the gas to be in pressure equilibrium. GWC was established at 3,900 mSS in Abadi-1. In Abadi-2ST, GWC is estimated to be approximately 3,890 mSS. In Abadi-3, no reliable formation pressure data was acquired in the water-bearing zone below the gas column, however, the highest water is interpreted at 3,896 mSS from the PEX log suite. Pressure data indicate the existence of a single tank system, although pressure plots indicate the possibility of small differences in gas-water contacts within the field.
Figure 5 - Depth map of Albian seismic marker. Contour lines indicate depths in meters. The Abadi field is fault bounded to the east and divided into two parts, a northern block and a southern block, by an east-west trending normal fault. Location of seismic line in Figure 7 is shown. A 700 km2 “fast track area” is also shown which was selected to expedite interpretation over the main part of the Abadi structure and to allow early delineation drilling.
Figure 6 - Correlation section of the reservoir sequences in Abadi-1, 2ST and 3. The succession can be readily divided into a series of genetically related zones based on the presence of bounding surfaces related to periods of rapid marine flooding. These have been named by reference to the palynological interval in which they lie. DST intervals and cored intervals in three wells are indicated.
Figure 7 - Seismic inline 4996 through Abadi-1 (Location shown on Figure 5). Seismic polarity is SEG normal with red as peak and black as trough. Yellow line indicates the Albian marker which corresponds to the base of the Jamieson Formation. This marker provided a readily mappable hor izon on seismic data throughout the area, and this became the key horizon for our interpretation.
GR curve of Abadi-1 is shown as reference. Well-developed progradational geometries are observed in the seismic interval correlatable to the upper part of the Plover Formation in the well that, together with the well data, are indicative of shoreline progradation.
Figure 8 - Porosity versus permeability for core plugs from Abadi-1, 2 and 3, showing clear trends indicative of different litho-facies within the Plover reservoir section. Facies 1 shows high porosity and permeability values and corresponds to tidal delta deposits.
The data points for the sandstones of core #1 of Abadi-1 and core #1 of Abadi-3 fall in this facies group. Facies 2 is represented by sandstone in core #1 of Abadi-2 and still retains good reservoir properties. Facies 3 is represented by the middle part of core #4 of Abadi-3. This interval is below the gas water contact and diagenetic calcite cement is dominant.
Figure 9 - Thin section photomicrograph of the sandstone of the Plover Formation at 3,872.12 m in Abadi-1. Medium grained, well sorted quartzarenite containing common quartz overgrowths that have reduced intergranular porosity. Visible porosity is moderate (13%, shown in blue) and is mainly of intergranular type. Measured permeability is 610 mD.
Figure 10 - Porosity, permeability and thin section point count data from conventional core of Abadi-1, 2 and 3. GR curves from wireline logs and core GR measurement are also shown as reference. The sandstones of core #1 in Abadi-1 comprise quartzarenite and framework grains are composed mostly of quartz, with very minor amount of other framework grains like K-feldspar, chert, metaquartzite and bioclasts. The clay volume is also low and these indicate the well winnowed and texturally highly mature of these sandstones. The sandstones of core #1 in Abadi 3 have almost the same characteristics, and these sandstones are categorized as Facies 1 in the porosity versus permeability plot in Figure 8. In the sandstones of core #1 in Abadi-2 that are categorized as Facies 2, the percentage of quartz grains is lower while the contents of other framework grains are higher compared with sandstones of Facies 1.
