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Basement reservoirs in Asia China Yaerxia Field, Yumen The Yaerxia oil field in the Jiuxi Basin (western part of Jiuquan Basin) was the first basement reservoir in China (Guangming & Quanheng, 1982; P'An, 1982). Oil is produced from fractures in Palaeozoic metamorphic rocks. Oil production was up to 1,050 bbl/day at that time. Discovered in 1959, the Yaerxia basement oil field produces from the Quannaogou Formation, which consists of phyllite, slate, and meta-sandstone. The rock is hard and compact. Because the joints, faults, and fractures are well developed, production from some wells is quite high. Highly productive wells (such as 114, 514, and 519) are all situated in the vicinity of a fracture zone or at fault intersections. During the period 1959 to 1979, 24 wells penetrated the Silurian (which is more than 19,700 ft thick) 21 of which indicated oil and gas. The depth of the wells ranged from 8,530 ft to 10,500 ft (2,600 m to 3,200 m). Twelve wells had commercial value, six of which had initial production of less than 70 bbl/day, and three wells produced 70 bbl/day to 350 bbl/day of oil. Only two wells had initial production of 700 bbl/day to 1,050 bbl/day. Xinglongtai Oil and Gas Field The Xinglongtai oil and gas reservoir is located in the middle of the west trough in the Lower Liaohe depression. The 26,300 ft (8,000 m) deep Qingshui syncline is present to the south. The reservoir rock is composed of Archeozoic slightly metamorphosed granite, Mesozoic granitic breccia and extrusive rocks (andesite and basalt). Only the Archeozoic granite is considered to be a basement rock here (P'An, 1982). By the end of 1976, 8 productive wells had been drilled in the Xinglongtai oil field. A single well drilled to the Mesozoic volcanic rocks was producing approximately 756 bbl/day. Oil production from one particular well, which had been drilled into the granite and granitic breccia, was between 210 bbl/day and 420 bbl/day. The Xinglongtai basement reservoir is a high pressure, highly saturated reservoir with a hydrocarbon column of 2,300 ft (700 m). The gas column is about 590 ft (180 m) with an oil column not less than 1,640 ft (500 m). Dong Sheng Pu Buried Hill Field The Dong Sheng Pu Buried Hill reservoir located in Xin Min County, Liaoning Province is a fractured, metamorphic basement rock. The structural location of the Buried Hill reservoir is the centre of the Da Ming Tun Depression with a minimum burial depth of 2,600 m (Ullah et al, 1988). Exploratory drilling began in October 1982 based on seismic data. In January 1983, Well 3, located above the crest of the Buried Hill, tested oil at a rate of 183.8 tons/day. By December 1987, there were 14 active producers and one observation well with cumulative volumes of oil and gas of 1,050,000 tons and 65,500,000 m3 respectively. Water injection was initiated in October 1986 through four injectors with a cumulative volume of 290,000 m3 (Ullah et al, 1988). During late 1985 and early 1986, a detailed reservoir study was conducted to determine the most appropriate method of developing and operating the field. Ullah et al state that a water flooding scheme would produce the most efficient method of oil recovery compared to natural depletion and gas injection. With water injection, oil production rates varied between 1,163 m3/day and 1,838 m3/day which relates to an estimated cumulative oil production, at the end of the field's production life, of 25,390,000 m3. Production from granites has also been reported at Bohai Bay field. Other Production has also been reported from fractured basement consisting of PreCambrian gneiss at Wangzhuang field in China. Also from volcanics at Dujiatai, Qija, Shijutuo and Shuguang (Lee, 1989), and from metamorphics at Jinganpa. India An appraisal well was drilled in 1997 (Well PY-1-12) to confirm the significance of a 1980 gas discovery reported by India's Oil & Natural Gas Commission (ONGC) (see J.Pet.Tech., Sept. 2001). The discovery, named PY-1, is in the Cauvery basin about 100 miles south of Madras in the Bay of Bengal. The reservoir, which is hosted in heterogeneous, PreCambrian, weathered granite and sealed by Cretaceous to Eocene shales, lies on the crest of a northeast-southwest basement ridge known as the Portonovo high (Anon, 1995). The field lies beneath approximately 250 ft of water (see Oil & Gas J., Nov. 1995). It was estimated that PY-1 could yield as much as 116 BCF of gas and 1.16 M bbl of condensate in primary production. Process facilities were designed on flow rate criteria of 53 MM scf gas and 600 bbl condensate (see J.Pet.Tech., Sept. 2001). In 1980, the ONGC logged four productive gas wells in the PY-1 field, including the PY-1-1 discovery well. Production tests of the wells reportedly ranged as high as 13 MMCF/day. The PY-1 field pay zone occurs in sections as thick as 200 ft and at depths of 5,000 ft to 5,500 ft. PY-1 is within, and surrounded by, Block CY-OS/2, a 3.8 million acre tract formerly known as Block 17 (Anon, 1995). Indonesia Sumatra - Beruk Northeast The Beruk Northeast oil field of Central Sumatra was discovered in 1976 with the drilling of the Beruk Northeast Well No. 1 into a Pre-Tertiary basement. The oil field is located within the Central Sumatra BackArc Basin, one of a series of Tertiary basins oriented along the western and southern margin of the Sudan Craton. In addition to Beruk Northeast, only four other fields have been reported as producing from Pre-Tertiary basement in Indonesia. Koning & Darmono (1984) state that oil production from Pre-Tertiary rocks is exceptional in Southeast Asia. The Beruk Northeast field is situated within a group of oil fields in the central area of the Pertamina-Calasiatic-Topoco Coastal Plains-Pekanaru Production Sharing Block. The basement rocks, which tested oil, consist of fractured metaquartzites, weathered argillites and weathered granite. Beruk Northeast Well No. 1 was drilled to a total depth of 1,634 ft into the basement. An openhole test of the basement flowed at 1,680 bbl/day. A thin Telisa sand located approximately 100 ft above the basement was tested and flowed at 480 bbl/day. By 1984, Beruk Northeast Well No. 1 had produced in excess of 1,100,000 barrels of oil, 640,000 barrels of water and 42 MMCF of associated gas. All production from the well has been obtained through the naturally occurring fracture system in the Pre-Tertiary basement metaquartzites (negligible matrix porosity exists from core studies). Subsequent development wells have been less productive, possibly due to the poor characteristics of the weathered argillite and granite reservoirs (Koning & Darmono, 1984). In the Sei Teras field, South Sumatra, 15,000 barrels of oil and 1 BCF of gas has been produced since 1977 from two wells in basement limestone and quartzite. Approximately 21 million barrels of oil and 14 BCF of gas has been produced from Pre-Tertiary rocks in the Tanjung field, South Kalimantan (Koning & Darmono, 1984, after Tiwar & Taruno, 1979). The basement rocks in this field consist of porphyritic extrusives (lava) and volcanics as well as metamorphosed sandstones, shales and claystones. In both the Sei Teras and Tanjung fields, the basement is locally deeply weathered and fractured (Koning & Darmono, 1984). Java - Jatibarang Field The Jatibarang field is located in Northwest Java, approximately 200 km to the east of Jakarta. The field produces from eight shallow sedimentary zones, but major production zones are in naturally fractured volcanic formations (Soewono & Setyoko, 1987). The Jatibarang volcanic formation consists of lava flows (andesite/basalt), tuff and agglomerate/ volcanic breccia. Oil was first discovered in the volcanic reservoir in November 1969 with the drilling of Well JTB-44, at a depth of 2,011 m (Sembodo,1973) and has been developed since 1973. Initial production from 20 wells was approximately 40,000 bbls/day. Since then, many wells have been drilled, the production of which varies from 250 bbls/day to 3,000 bbls/day. The depth of wells varied between 2,000 m and 2,300 m, with hydrocarbons found between 1,900 m and 2,200 m (Sembodo, 1973). By April 1987, the cumulative recovery of the Jatibarang volcanic reservoir was 83.9 M bbls of net oil from 136 wells (Soewono & Setyoko, 1987). Kalan et al (1994) present the results of a geological investigation of the Jatibarang Field performed in 1991/1992 by Elf Aquitaine Indonesia. The investigation was part of a feasibility study into the utilisation of horizontal drilling to improve production from the Jatibarang volcanics. The feasibility study concluded that the drilling of horizontal wells would provide increased recovery from the volcanic reservoir (actual production figures were not provided). Fracturing in the volcanics is believed to be the most intensive in the tight folds of the Central and Western Blocks which accounts for the good production (previously discussed above). Kalan et al (1994) proposed the use of a horizontal well in the Eastern Block of the Jatibarang Field where the volcanic reservoir has produced less than expected due to lower intensity of folding and fracturing. Japan In western Japan gas is produced from granite at a depth of about 4300 m. The best well is said to produce about 800 bbl of condensate per day (Russell and Warren Hunt, pers. comm., 2000) and an unspecified, but large, gas flow. In the Nagaoka and Niigata fields 5400 bopd oil and 14 bcf gas is produced from green tuff and volcanic formations (Kitchka, pers. comm., 2000). Korea Oil has been recovered from fractured granite. Thailand Sirikit Oil Field The Sirikit field lies in the Phitsanulok Basin, one of a series of Tertiary rift-related structures in central and northern Thailand. The tectonic history of the area is complex: the original, extensional, half graben was deformed during deposition of the upper reservoir sequence by left-lateral strike-slip faulting (Knox & Wakefield, 1983). During the Mesozoic, most of central and western Thailand was affected by large, left lateral wrench faults and compressional tectonics. More recently, most of the Thai region was rotated clockwise developing large extensional (growth) faults and minor divergent wrench movement. These extensional tectonics lasted throughout the Tertiary and caused the formation of the many relatively small sedimentary basins in central and southwest Thailand. The pre-Tertiary structures in the Sirikit field consist of block faulted and tilted basement rock in an upthrown position. Basement in this field consists mainly of metamorphic clastic red beds The Field has produced about 1.17 M bls of oil from basement so far (November 1998). About 14 wells had been drilled into the pre-Tertiary basement (to 1995) many of which had oil shows and two have been placed under production. Using the seismic data of the area, a model was created of the Central Sirikit High. This part of the field has the only producing well. 3 wells were drilled in this area, one has been in production since 1991, one was shut in after it rapidly watered out and one only produced water. This proved the assumption that hydrocarbon distribution was directly related to the fracture pattern. A fracture simulation model using software packages (Frame and Poly3D) has come up with a prediction of the fracture pattern of this field (Smitt, 1998). Vietnam Ongoing exploration activities (initiated in the 1970's) have proved the existence of oil and gas in basement reservoirs in the offshore area of South Vietnam. This has resulted in the discovery of several oil and gas fields (Dmitriyevskiy et al, 1993; Areshev et al, 1992) including White Tiger (Bach Ho), Dragon (Rong) and Rang Dong fields. The oil company Vietsovpetro started working in offshore South Vietnam in 1981 and started to produce oil in 1986. By the end of 1991, about 100 wells had been drilled (85% of them by Vietsovpetro). Half the wells penetrated the basement with basement cores recovered from 26 wells. The majority of these cores came from the White Tiger field. By the mid-1990's, the company was producing 180,000 bbl/day. This production rate is likely to increase as White Tiger and Dragon fields are improved (both fields producing from basement reservoirs). Dragon field's basement was producing at 8,000 bbl/day (George, 1995). Vietnam's chief offshore asset is the White Tiger field which generated over 50 MM bbl in 1996 (Anon, 1997). The volume in place and, hence, the field's lifespan, remains unknown. In 1988, while testing in the White Tiger field (Well MSP-1-1), an oil flow of 1,500 m3/day was achieved. The basement was then identified as an oil reservoir of significant importance. Further drilling into the basement was undertaken, especially in the northern and central blocks of White Tiger. The White Tiger area is divided into three fault-bounded blocks; northern, central and southern. The basement was not penetrated in the southern block. Traces of oil were also found in the basements of the Big Bear (South Con Son basin), Dragon and Bavi (Areshev et al, 1992). Granites constitute the basement in the central part of White Tiger and predominate in the basement of the Dragon field. They also occur in the basement of the White Tiger northern block, together with microcline, hornblende-biotite and biotite-granodiorites. Microcline, hornblende-biotite and biotite-granodiorites also occur in the basement of the Bavi and Big Bear structures. The basement rocks of the southern Vietnamese shelf contain very large oil accumulations. The White Tiger oil field is at a depth of 5,000 m, of which 4,000 m is fractured basement granite with a pay zone interval of 1,000 m (Russell, 1997) and with 1992 oil production at a rate of more than 2,000 m3/day (Areshev et al, 1992). Well 17-VT-1XR (Vau Thieu), located in Block 17 offshore Vietnam (southwest of the White Tiger and Dragon oil fields), was originally drilled as an exploration well. The well was the fourth exploration well to be drilled by Enterprise Oil in Block 17 (Anon, 1996a). The first 3 wells proved to be disappointing, especially when considering their proximity to the White Tiger and Dragon oilfields (Anon, 1996a). Well 17-VT-1XR was drilled to a TD of 2,389 m and was tested at 750 bbl/day of oil. The well penetrated 430 m into the basement granite in the Cuu Long Basin (Enterprise Oil, 1996; Anon, 1996b). However, the well has since been abandoned as an oil discovery (Tang, 1996). Navigation Back to main textEurope North America South America Africa CIS and Russia Middle East Oceania |