水平井开发技术的成本与效益分析.doc

水平井开发技术的成本与效益分析Cost/Benefits of Horizontal Wells S.D.Joshi,SPE,Joshi Technologies International,Inc.Abstract This is asummary of state of the art horizontal well technology and areview of the economic benefits of horizontal wells.The paper describes various reservoir applications of horizontal wells from primary recovery to EOR applications.The paper includes field examples of different applications.Although horizontal wells have been drilled as early as 1927,the major thrust of drilling horizontal wells started in 1980.Initial wells were short length wells(about 250 ft.long wells).In 1985,the first medium radius horizontal well was drilled using adown-hole mud motor.Since then,using horizontal wells has become acommon practice.Today,the medium radius drilling technique is the most commonly used drilling method.In the U.S.,the majority of applications are in low permeability,naturally fractured,carbonate reservoirs.However,in California,Alaska and Gulf of Mexico most of the wells are drilled in clastic reservoirs.Similarly,outside the U.S.,most of the horizontal wells are drilled in clastic reservoirs.Horizontal wells have been used to produce thin zones,fractured reservoirs,formations with water and gas coning problems,waterflooding,heavy oil reservoirs,gas reservoirs,and in EOR methods such as thermal and CO2 flooding.The paper includes field examples with cost benefit analysis for various applications.选自SPE83621：水平井开发技术的成本与效益分析(S.D.Joshi等)摘要：这是一篇关于水平井开发技术现状总结和经济效益回顾的文章。这篇文章描述了水平井在各种油藏中的应用，从最初的提高采收率到EOR应用。这篇文章同时也包含了不同应用下的矿场实例。尽管水平井最早起源于1927年，但是其大规模的应用却是从1980年开始的。最初的水平井是长度较短的(大约250英尺)。在1985年，第一口的中半径水平井采用井下泥浆马达技术钻成。从那以后，水平井的应用变的十分普遍。现在，中半径水平井钻井技术是最常用的水平井钻井技术。在美国，大多数的水平井应用于低渗透油藏、天然裂缝油藏、碳酸盐油藏。然而，在加利福尼亚、阿拉斯加以及墨西哥湾大多数的水平井用于常规油藏的开发。同样，在全球范围内，水平井也主要用于常规油藏的开发。水平井的开发一直以来主要用于薄油层、裂缝性油藏以及有底水锥进和气体锥进的储层，水淹层、重质油藏、气藏、以及提高采收率的热力采油和CO2驱等。本文同时列举了包含成本和效益分析的各种油藏应用下的水平井开发实例。introduction Some of the early horizontal well efforts date back to 1930.After World War II,with the advent of jet perforation,major industry efforts were focused on casing the drilled hole and perforating in the desired zones.The field implementation of this perforation technique was agreat success and at least fora while horizontal drilling took aback seat.In the late 70s and early 80s,with oil prices around abarrel,interest in horizontal wells was reignited.The purpose of the horizontal wells was to enhance well productivity,reduce water and gas coning,intersect natural fractures and to improve well economics.In the early 80s,Elf Aquitaine,a French company,introduced horizontal wells to the oil industry to produce aheavy oil carbonate reservoir in the Rospo Mare Field,offshore Italy,in the Adriatic Sea.At the same time,in the U.S.,several companies were using horizontal wells to reduce gas coning in the Abo Reef in New Mexico.They were also using horizontal wells to intersect fractures in the fractured carbonate reservoirs in Oklahoma,Kansas and Texas.The drilling technique used by Elf Aquaitain was very different from that used in the U.S.The Elf technology involved drilling long radius(1000 ft.turn radius,see Fig.1)and long length(a few thousand ft.)wells.3 They were also using down-hole motors to turn the bit and drill wells.To date,this long radius drilling technology remains suitable todevelop offshore fields around the world.In the U.S.,initial efforts were with theshort radiusdrilling technique where turn radius was around 30 ft.The wells were drilled using stabilizers,knuckle joint and flexible collars.A mushroom type,helical collar joint was used to provide necessary flexibility to the drill pipe to turn from the vertical to the horizontal direction in ashort distance.Well completion was either open-hole or with aslotted liner.The typical well length was 100 to 300 ft.The major disadvantage of this drilling technology was its limited completion options andhigh cost of drilling.In the mid-eighties,the cost of drilling the 30 ft.radius well was of the order of00 to00 per ft.To minimize this drilling cost,and to drill long length wells,a medium radius drilling technology was developed.The first medium radius horizontal well was drilled in 1985.4 Turn radius for the medium radius wells was about 300 ft.to 600 ft.and it utilized down-hole motors.To date,medium radius technology remains the most common method to drill horizontal wells.This drilling method provides various completion as well as artificial lift options.It is quite common to see well lengths varying from 1000 ft.to 5000 ft.Short radius technology has also evolved over time and there has been significant cost reduction.This,however,remains aniche market mostly in low productivity wells in the U.S.and parts of China.In the U.S.,small independentswith marginal wells(production rate less than 10 BOPD)uselow cost,short radius technology to enhance well production.背景介绍：最早的水平井开发见效的实例可以追溯到1930年。在第二次世界大战结束以后，随着射孔技术的出现，石油工业逐渐把重心放到用套管完井并射开目的储层的操作上来。这一射孔技术的实现是一个石油工业界巨大的进步，至于在一定程度上为水平井技术的发展起到了奠定技术的作用。在70年代模80年代初，油价达到35美元一桶，巨大的利益重新促使人们重新对待水平井技术。水平井的目的在于提高油井的产能，降低水气的锥进，沟通储层裂缝从而提高经济效益。在80年代初，ELF Aquitaine,一个法国的公司，讲水平井技术引入了石油工业。这一应用是在意大利Adriatic海的一个近海重质碳酸盐油藏。同时，在美国也有很多公司在墨西哥湾的Abo reef油田采用水平井技术来减少汽水锥进。同时他们也利用水平井沟通储层裂缝来开发Oklahoma、kansas、以及Texas地区的碳酸盐裂缝油藏。ELF公司采用的钻井技术和美国公司采用的技术十分不同。Elf公司的技术包括长半径以及长水平段技术(见图1)。他们同时应用井下马达来控制钻头和钻进。在今天，这种长半径钻井技术在开发海上油田仍然十分流行和实用。而在美国，最初的钻井技术采用的却是短半径技术(大约30ft)。这些井是利用稳定柱、转向节以及灵活的接箍组成。一个新型的技术，helical collar技术可以提供足够的灵活性可以使井在一个很短的距离范围内从垂直变成水平。完井技术可以是裸眼完井或者射孔完井。典型的水平段长为100到300英尺。这种技术的主要缺点是他有限的完井选择和较高的成本。在80年代中叶，钻一口30ft短半径水平井的成本是2000到3000美元每英尺。为了最小化钻井成本，长水平井一种中半径水平井技术开始发展起来。第一口中半径水平井钻于1985年。转向半径对于中半径水平井在300ft到600ft之间。同时采用井下马达技术。现在，中半径水平井钻井技术仍然是最流行的水平井技术。这种方法可以支持多中完井措施，包括人工举升选择。通常的水平段长度在1000到5000ft之间。短半径技术随着时间也不断的演化目前其成本已经大大降低。但是，这项技术在美国和中国的部分地区对于低产井仍然有广阔的前景。目前在在美国，一些单独的边缘井(产量小于10BoPD)通常采用短半径水平井技术来提高产能。Recent Developments In the last few years,several technical advances have been made.Some of these advances include LWD and MWD(logging while drilling)and geo-steering.Technologies are available to drill and complete multi-lateral wells,drill with coiled tubing,drill under-balance,and use rotary steerable assembly to drill straight holes.For completion,one can cement and stimulate horizontal wells in low permeability formations and gravel pack long horizontal wells in high permeability formations.These new technologies are briefly described below.Technologies have been developed to drill multi-lateral wells.These wells have various shapes and offer the possibility of different types of completions to isolate and control production from different branches of multi-laterals(see Figure 2).Nevertheless,through the year 2002,the large scale multi-lateral applications are seen in heavy oil reservoirs(where wells are completed with slotted liners)and in carbonate reservoirs using open ho le completions.A large scale of applications of multi-laterals is found in the heavy oil reservoirs in Canada and Venezuela and in the carbonate reservoirs in the Middle East.5,6 Another development is under balance drilling of horizontal wells to minimize formation damage,especially in low permeability formations.7 The technique has been very popular in Canada.In addition to low permeability formations,under-balance drilling is also important in depleted gas reservoirs where current reservoir pressure is significantly less than the hydrostatic pressure.If one uses liquid drilling fluids,it would result in an excessive mud loss,resulting in reduced well productivity and possibly anon-commercial well.Under-balance drilling allows us to drill and complete horizontal wells in depleted gas reservoirs.8 Typically,horizontal well productivity is two to five times larger than the vertical well productivity.Thus,for the given economic gas rate limit,horizontal wells could be produced with up to 1/2 to 1/3 reservoir pressure as compared to the reservoir pressure required for economic production from avertical well.This results in alarge enhancement of producible reserves from discovered,depleted gas fields.Horizontal wells are drilled in the depleted gas reservoirs in Texas,Oklahoma and also in Canada.Typically,drilling are-entry well is less expensive than drilling agrass roots horizontal well from the surface.There-entry well costs could be further reduced by using the Coiled tubing drilling technique.This is especially importantin Alaska where drilling costs are high.9 Significant advances have also been made in drilling technology to drill straight horizontal holes.The straight horizontal holes are necessary to obtain reliable gravel pack completions and to eliminate acid accumulation in the low spots along the length of the horizontal well.The corrosive acid effects can significantly reduce liner life in offshore,expensive,high production rate wells in deep waters.Progressi vely,steerable rotary assembly is used to drill horizontal wells,especially in deep water reservoirs to achieve fairly straight drilled holes.10 Most of the horizontal wells drilled in North America are completed as open hole or with slotted liners.The stimulation of horizontal wells is found to be necessary in many low permeability formations.Stimulation techniques are available for open hole horizontal wells using liquid fracs(eitherwater fracs or acid fracs).In afew cases in onshore U.S.,horizontal wells are cemented and fracture stimulated in the low permeability formations,such as Devonian formation in West Texas 11(12000 ft deep,k=0.05 md),Diatomite 12 formation in Belridge Field in California,and Kuparek Field in Alaska.13 Open-hole gravel packing has also been an important development,especially for deep water reservoirs,which are typically high permeability,unconsolidated reservoirs.14 Open hole gravel packing is used quite commonly in horizontal wells in the Gulf of Mexico.15目前的研究现状：在过去的几年，又有几项技术创新。包括LWD和MWD(随钻测井和随钻测量)以及地质导向技术。这些技术可以应用于多层油层的开发，同时采用连续油管技术以及在欠平衡条件下采用采用旋转导向设备来钻直井段。对于完井，可以采用水泥固井并针对低渗透油藏采取各种措施以及对高渗储层采取防沙工艺。这些技术的介绍如下：多层油藏的钻井技术一直在不断发展。这些井拥有不同的形状并且可以采用不同的完井方式来隔离和控制和各个分支的生产(见图2)。然而，自从2002年以来，大规模的多层油藏开发多用于重质油藏的开发(通常用割缝衬管完井)以及碳酸岩开发(裸眼完井)。主要应用的范围在加拿大的Venezuela以及中东的碳酸盐油藏。另一个主要技术的发展是欠平衡压力钻井技术的发展。这项技术可以大大降低对储层的伤害，尤其对于低渗透油藏。这在加拿大十分流行。除了在低渗透储层，欠平衡压力钻井对于油层压力大大低于静液柱压力的衰竭气藏也十分重要。如果利用液体钻井流体，将会导致大量的泥浆漏失，导致井的产量大幅下降并有可能成为无经济效益井。欠平衡压力技术可以用来开发衰竭气藏。典型的，水平井的产能是直井的2到5倍。因此，对于给定的临界气体产量限制，水平井可以在直井开发极限油藏压力的1/2或者1/3条件下开采并有经济效益。这可以大大提高已经开发的衰竭气藏的开发效果。水平井开发衰竭气藏已经用于Texas，Oklahoma以及加拿大。通常条件下，对老井的测钻要比从地面重新钻一口井的成本要低的多。这种老井测钻的成本可以用过采用连续油管技术使成本进一步降低。这对与Alaska地区的高成本钻井现状有重要的意义。对于直线水平段的钻井技术也有了长足的发展。直线水平段对于确保砾石充填完井的效果以及消除沿着水平段酸液的积累都有重要的影响。腐蚀酸的影响对于海上深水高产井的寿命是十分重要的。渐渐的，旋转导向设备应用与水平段的钻井，尤其是深水油藏的开发来确保得到相对比较直的水平段。大多数的北美地区的水平井是采用裸眼完井和割缝衬管完井的。水平井的措施处理对于低渗透油藏来讲是十分重要的。井底处理技术可以用于(水相或者酸相)的裸眼水平井的措施处理。在美国的一些陆上低渗透油藏实例中，水平井是采用固井并压裂处理的。比如Devonian储层(West Texas)以及加利福尼亚的Belridge油田等。裸眼砾石充填完井同样是一项重要的进步，尤其对于深水油藏(通常高渗，固结性不好)。这一技术主要应用于墨西哥湾油藏的水平井开发。Cost/Benefits Of Horizontal Wells Disadvantages of horizontal wells are：1.High cost as compared to avertical well.In the U.S.,a new horizontal well drilled from the surface,costs 1.5 to 2.5 times more than avertical well.A re-entry horizontal well costs about 0.4 to 1.3 times avertical well cost.2.Generally only one zone at atime can be produced using ahorizontal well.If the reservoir has multiple pay-zones,especially with large differences in vertical depth,or large differences in permeabilities,it is not easy to drain all the layers using asingle horizontal well.3.The overall current commercial success rate of horizontal wells in the U.S.appears to be 65%.(This success ratio improves as more horizontal wells are drilled in the given formation in aparticular area.)This means,initially it is probable that only 2out of 3drilled wells will be commercially successful.This creates extra initial risk for the project.Benefits of horizontal wells are：1.Higher rates and res erves as compared to vertical wells.This results in less finding cost and less operating cost per barrel of oil produced.In the U.S.,as shown in the example in this paper,in places where vertical well operating costs are to per barrel of oil,the horizontal well operating costs are to per barrel.2.For many horizontal well projects,the finding(developing)cost,defined as well cost divided by well re