石油开采外文翻译---北福克兰盆地石油地质.doc

oil, including oil exploration, is the next big subject for the falkland islands. we have pleasure in publishing this very full and detailed study of the oil prospects in the north falkland basin. dr ian duncan is ceo of desire petroleum plc, which is a leading operator in this field, and his article is an authoritative account of the current situation.petroleum geology of the north falkland basinby dr ian duncan, ceo of desire petroleum plcwithin the falkland islands designated area there are three major basins: north falkland basin, falkland plateau basin and south falkland basin. the subject of this article is the north falkland basin, where desire petroleum has been exploring for hydrocarbons since 1997.the north falkland basin is a failed rift, which formed during the break-up of the ancient landmass of gondwana. plate tectonic reconstruction suggests that the entire falklands area prior to the break-up was originally located to the south-east of south africa and moved to its present position during the opening of the south atlantic during the jurassic to the cretaceous. the north falkland basin can be further subdivided into a northern, or main, basin in which tranches a to fare located and a southern basin in the area of tranches i and l. the southern basin is undrilled and comprises an older suite of rocks than that found in the main basin to the north. this article concentrates on the main area in tranches c and d where the next drilling campaign will take place.exploration historythe first phase of exploration was in the early 1990s when spectrum acquired the first detailed 2d seismic across the area. these data defined the outlines of the n-s trending north falkland basin, approximately 180 kms long by 30 kms wide and formed the basis for the evaluation which led to the first round of licensing in 1996. seven licences were awarded in 1997 to shell, amerada, lasmo, international petroleum corporation (ipc) and desire. these companies acquired more 2d seismic over their licences and in addition shell acquired a small 3d survey. shell, amerada, lasmo and ipc formed fosa (falklands offshore sharing agreement) jointly to conduct a drilling campaign in 1998. the semi-submersible drilling rig the borgny dolphin was contracted and drilling began in april 1998. amerada drilled two wells: 14/9-1 and 14/9-2; shell drilled two wells: 14/5-1 and 14/10-1; lasmo and ipc drilled one well each: 14/13-1 and 14/24-l.drilling ended in november 1998.of the six wells, five recorded good oil and or gas shows but the presence of hydrocarbons in commercial quantities was not established. over the next few years amerada, shell and lasmo withdrew from the falklands and as a result desire petroleum became the operator of tranches c and d and argos evergreen became the operator of tranche a. following the acquisition of further seismic in 2000, ipc were acquired by talisman who became the operator of tranche f.continuing low oil prices stifled all activity in the area until 2004 when desire acquired 800km2 of 3d seismic over tranches c and d. in the same year rockhopper exploration was awarded new licences in the area.at the beginning of 2005, desire raised sufficient money to fund further drilling in the north falkland basin and rockhopper farmed-in to tranches c and d. at the time of writing (december 2005) desire is seeking a rig to commence drilling as soon as one becomes available. during 2005 desire assumed a 100% interest in tranche f and rockhopper acquired further licences in the area. the latest licence position is shown in fig.l.geologythe north falkland basin has a predominantly nonmarine jurassic to lower cretaceous fill overlying devonian basement. these non-marine sediments are overlain by a marine sequence of upper cretaceous to recent age. in the deepest part of the basin in tranche d the total section is over 5 kms in thickness.the non-marine rocks were deposited in a large lake, into which flowed several large rivers which formed sandstone deltas and fans as shown schematically in fig 2. this lake was of a size similar to the present day lakes of east africa. the lake filled slowly with fine- grained claystones, which at times were deposited in oxygen-free conditions resulting in rocks with very high organic carbon content. these rocks are the source of the oil generated in the basin. eventually in the upper cretaceous as a result of a significant sea level rise marine conditions became established in the basin.the north falkland basin contains all the ingredients necessary for the discovery of hydrocarbons, namely source rocks, reservoir rocks, seals and traps.source rocksthe 1998 drilling campaign established the presence of a thick (over 1,000 metres) non-marine, oil source rock, believed to be one of the richest in the world. these source rocks were immature in five of the six wells drilled but attained maturity in one of them; live oil of 27 degree api was recorded at the surface from well 14/ 10-1.the source rocks are mature in the deeper parts of the basin where the temperatures and pressures are sufficiently high to generate and expel oil. the location of this area of mature source rocks the kitchen is shown in fig.3. only the basal part of the source rock is mature with the majority of the source rock being immature.richards (british geological survey) and hillier (shell) in 2000 in which they estimated that up to 60 billion barrels of oil had been generated and expelled from this source rock. there is also a deeper separate source rock, mature for the generation of gas, as demonstrated by the good gas shows at this deeper level in well 14/5-1.sealsthe abundant claystones throughout the section including the immature upper part of the source itself provide good sealing potential.reservoirsdesire believes that finding effective reservoir rocks is the largest risk associated with the discovery of hydrocarbons in commercial quantities in this area; i.e. sandstones of sufficient quality to produce oil at rates high enough to be commercial. however the seismic character of prospects such as the liz prospect provide good indications that good quality reservoir rocks may be present.trapsthe 2d and, in particular, the 3d seismic data show a number of structural and stratigraphic trapping mechanisms.play conceptthe 1,000 metres thick source rock is mature only at the base in the deeper parts of the basin. the overlying, immature, source rock is a very effective regional seal, see fig 4, and it is believed this has prevented the upward migration of oil into the overlying horizons. these shallower horizons were the main target in the first drilling campaign and the failure to find commercial hydrocarbons may be the result of the difficulty in charging these horizons.desire now believes that the major potential of the basin may be in the untested flanks of the basin at the level of the mature oil source rock as shown in fig 4. at this level the oil would have only a short distance to migrate from the mature oil source rock to the predicted reservoir rocks. in addition the best reservoir development may be on the flanks of the basin. the 3d seismic data acquired in 2005 was designed specifically to test this new model.prospectsnine prospects have been identified (see fig.1), most of which have multiple targets. only two of these will be described in detail to illustrate the variety of prospect types found in the basin.liz prospectthis is the largest prospect and is likely to be the first one drilled in the next campaign. it is a stratigraphic trap and based on seismic amplitude mapping has geometry suggestive of a fan-delta deposited by a large river flowing into the lake see fig 5. this fan-delta is detached by faulting from the up dip feeder channel and lateral sealing is provided by the rich oil source rock, which is mature at the distal end of the fan. the feeder channel shows drape on the seismic data and this is possible evidence for the presence of coarse sandstones, which are likely to provide good reservoirs. in addition to testing the liz fan at the well location the edge of the beth fan will also be drilled. the water depth is around 350 metres and the total depth of the well will be circa 3,000 metres.ninky prospectthis is an example of a structural trap. at a number of levels immediately above the mature oil source rock the structural contours are closed against a fault. unlike the liz prospect vertical migration up a fault is required to fill the traps but on the seismic a fault is clearly defined reaching from the mature source rock to the overlying traps.as this prospect is near the centre of the basin, thinner poorer quality reservoirs might be expected but again seismic amplitude geometrics suggest that thicker distal fan sandstones might be present. this prospect is located in a water depth around 400 metres with a planned total depth of circa 3,100 metres.environmentdesire recognises the international importance of the environment of the falkland islands and is committed to doing everything possible to minimise any impact on the environment its operations may have. all of the operations will be carried out in accordance with uk north sea standards and only water-based drilling muds and low toxicity chemicals will be used.to identify all the possible impacts of the three well operation, desire commissioned rps, one of the leading environmental consultancies in europe, to undertake an environmental impact assessment (eia). rps suggested a number of measures to minimise environmental impact and concluded that the proposed operations can be carried out without a significant impact on the environment. full details of the eia can be found on the desire website at www.desireplc.co.uk.drillingdrilling in the north falkland basin is relatively straightforward. the first drilling campaign established that there were no serious drilling hazards and that a 3,000 metre well could be drilled injust over twenty days. in addition the water depths (350-410 metres) are not considered deep in todays terms and the weather conditions are similar to the central north sea.as a result a heavy duty deep water drilling rig is not required and, as in the previous campaign, desire intends to use a third generation semi-submersible rig as shown in fig 6.developmentin the event of a commercial oil discovery the most likely development scenario is one now widely employed throughout the world and particularly in the north sea. it would involve completing the producing wells on the seabed and tying them back to a fpso (floating production, storage and offloading) facility. oil would be transported to a refmery located anywhere in the world by shuttle tankers. minimal onshore facilities would be required in the islands.economicsbased on the above assumptions, a number of economic models have been run. as a result of the favourable fiscal regime in the falklands, relatively small oil fields are likely to be commercial. for example, based on a $30/barrel oil price and a 10% discount factor, oil fields containing 40 million barrels would be commercial. oil prices have risen considerably during 2005 and, although costs have also risen, it is believed the overall commerciality of a discovery has been considerably enhanced.conclusions1. a working hydrocarbon system in the north falkland basin has been established.2. the area has the potential to become a major hydrocarbon province, but further drilling can only prove this.3. desire has identified nine prospects for drilling and preparations are well underway for resumption in drilling as soon as a suitable rig can be contracted.4. an environmental impact assessment has determined that a three well exploration-drilling programme will not have a significant impact on the environment.further explanatory diagrams can be found on desire website at www.desireplc.co.uk.c. copyright retained by desire petroleum plc.references: richards, p. c. and hillier, b. v., 2000 post- drilling analysis of the north falklands basin - part 2:petroleum system and future prospects. journal of petroleum geology, vol23 (3),pp273-292.acknowledgements: i would like to thank dr colin phipps for his helpful suggestions in the presentation of this article.石油,包括石油勘探,是福克兰群岛下一个大的主题。我们很高兴地出版这非常充实详细的北方福兰克群岛石油前景研究。伊恩邓肯博士是desire petroleum plc的首席执行官，这个领域的领头者，在现状下，他的文章是权威的。北福克兰盆地石油地质伊恩邓肯博士，desire petroleum plc的首席执行官在福兰克群岛指定区域有三个主要盆地：北福克兰盆地，福克兰高原盆地，南福克兰盆地。这篇文章以北福克兰盆地为主，自1997年开始desire petroleum已在此勘探烃类物质。北福克兰盆地是冈瓦纳古陆解体时形成的衰退峡谷。板块构造重组学说指出整个福兰克地区在解体之前侏罗纪与白垩纪南大西洋板块开放之时，从南非东南部移动到现在位置。北福克兰盆地可进一步细分为南北两部分，北部也就是主要的包括a区到f区，南部盆地为i区和l区。南部盆地未被钻探，并含有一套比北部盆地老的岩层。这篇文章把重点放在将要开始钻探的c区和d区。勘探历史第一阶段的探索是在90年代初由频谱获得整个地区第一个详细的二维地震数据。这些数据指出了福兰克北部盆地轮廓,大约有180公里宽长和30公里宽,形成了1996年第一轮评价的基础。在1997年7个许可证被授予shell, amerada, lasmo, international petroleum corporation(ipc) 和desire公司。这些公司获得了超过许可证更多的二维地震数据，另外，shell公司获得了小部三维调查许可。1998年，shell, amerada, lasmo 和 ipc组成了fosa组织（福克兰群岛海岸共享协议）来共同管理钻井工程。在1998年4月，borgny dolphin半潜式钻探签约并开始钻探。amerada公司钻了两口井：14/9-1 和14/9-2井；shell公司钻了两口井：14/5-1 和 14/10-1井; lasmo公司和ipc公司各钻了一口井：14/13-1 和14/24-1井。钻探于1998年11月结束。在这6口井中，5口有良好的油气显示，但是烃类物质的商业储量并不足够。在以后的几年里，amerada, shell 和lasmo公司将从福克兰地区退出，这导致desire petroleum公司成为c区和d区经营者，argos evergreen公司成为a区经营者。通过2000年更深的地震测井，talisman获得了ipc成为f区的经营者。持续低迷的油价抑制了该地区的所有活动直到2004年获得了c区和d区800km2的地震数据。在这一年，洛克霍普勘探公司获得了这一地区的开发许可。2005年初，desire公司斥巨资投资北福克兰盆地深部钻井，rockhopper加入到c区和d区。在本文攥写时（2005年12月）desire公司正在寻找钻机尽快开钻。在2005年desire公司承担了f区100%的产权，rockhopper获得了该地区更多的开发许可。最近的开发许可位置如图1所示。图1.北福克兰盆地目前许可和前景图地质北福克兰盆地拥有一套以陆相侏罗纪到下白垩纪为主下附泥盆纪的地层。这些陆相沉积物上附晚白垩纪到新近纪海相沉积序列。在盆地d区最深部分总截面厚度要超过5千米。这些陆相岩层在一个大的湖泊中沉积，几条大型河流汇入形成砂岩三角洲和扇形沉积，如图2所示。这个湖和现在东非的湖泊大小相近，湖中慢慢沉积细粒粘土矿物，这些物质在缺氧环境下沉积导致岩石有机碳含量很高，这些岩石是石油主要来源。最终在早白垩纪，海平面上升造成盆地海相条件确立。北福克兰群岛盆地含有寻找烃类物质的所有条件，即烃源岩，储集层，盖层和圈闭。图2.北福克兰盆地下白垩纪地质图烃源岩1998年钻井确定了厚的（超过1000米）被认为是世界上最富集的陆相石油烃源岩，6口井中5口烃源岩是不成熟的，只有一口是成熟的。从井14/10-1中开采出来的石油api值为27已标记在表面。烃源岩在盆地更深部分已经成熟，那里的温度和压力已经足够高到产生和排泄石油。这一地区的成熟烃源岩“厨房”位置如图3所示。只有基部烃源岩是有大部成熟源岩组成。2000年richards（英国地质调查）和hiller(shell公司)估计在这些源岩中曾产生和排泄石油600亿桶。还有一个更深的独立成熟源岩可生成天然气，就像在井14/5-1中深部良好的天然气显示一样。盖层整个地区丰富的粘土矿物含有未成熟的顶部，这提供了良好的潜在封闭条件。储层desire公司认为有效储集层的发现是该地区发现烃类物质商业储量的关键。例如，优质砂岩可产生较高的产油率可以成为商用。然而预期的地震特性如利兹预测提供的良好预测表明良好的优质储积岩会显现出来。图3.北福克兰盆地烃源岩分布图圈闭二维，特别是三维地震数据显示了大量的结构和地层圈闭机制。play concept1000米厚的烃源岩只有在深部盆地的基底是成熟的。上附未成熟源岩是一种有效的局部圈闭，见图4，这被认为阻挡了石油向上附岩层的运移。这些较浅地层是第一次钻井工程的主要目标，把握这些地层的困难可能是导致商业烃化物发现失败的原因。图4. 未检测区域desire公司认为主潜力盆地可能位于与图4所示烃源岩同一