超前注水提高特低渗透油田开发效果

作者简介:车起君(1961-),男,甘肃定西人,工程师,从事石油开发研究。

　　文章编号:100023754(2003)0120020203

超前注水提高特低渗透油田开发效果

车起君1,雷均安2,冉玉霞1,贺治勇2

(11长庆油田分公司勘探开发研究院,西安　710021;21大庆油田有限责任公司第一采油厂,黑龙江大庆　163001)

摘要:安塞油田是鄂尔多斯盆地石油地质储量最大的整装级大油田,也是世界著名的特低渗透油田。

因此,进一步提高开发效果和经济效益及最终采收率是油田开发首要任务。安塞油田在大面积同步注

水开发取得较好效果的同时,不断探索开发的新途径。通过对超前注水机理的研究及现场试验,建立了有效的驱替压力系统,使地层压力始终保持较高的水平,降低了因地层压力下降造成的地层伤害,抑制了油井的初始含水率,从而提高了投产初期油田的产量,使得油田能够保持较长的稳产期,减缓了递减,提高最终采收率。

关键词:超前注水;理论依据;特低渗透油田;开发试验效果中图分类号:TE35716　　　文献标识码:A 　　低渗透油田由于岩性致密、渗流阻力大、压力传导能力差,一般天然气能量都不足、油井自然产能低,如果仅仅依靠天然能量开发,油井投产后,地层压力下降快,产量递减大,一次采收率很低,而且压力、产量降低之后,恢复起来十分困难[1]。

因此,低渗透油田为了提高开发效果,必须采取保持压力的开发方式,实行早期注水。安塞油田油藏评价、水驱油试验和开发结果,实施早期注水,水驱采收率为20%～25%,较自然能量开采提高215～310倍。

在同步注水采油保持压力水平开发取得良好效果的前提下。经过室内研究和试验,生产实践中部分超前注水井的分析总结,得出超前注水是提高低渗透油田最终采收率的又一重要途径。

1　超前注水提高单井产量机理及作用

(1)超前注水建立了有效的压力驱替系统

根据渗流流体的理论,在极限供油半径内,可动原油的动用程度与渗透率、压力梯度的关系为[2]

F =1-51714K -1

2[A /(Δp/L )n ]+81613K

-1

[A 2/(Δp/L )2n ]

式中　F ———可动油动用程度;K ———渗透率;

Δp/L ———压力梯度。

从图1可以看出,可动油的动用程度与驱动压力梯度成正比,驱动压力梯度越大,则可动油的动用程度亦越大。

　　低渗透油层由于孔道半径很小,原油边界层的影响显著,在流动过程中出现压力梯度。大量研究资料表明,启动压力梯度与渗透率成反比,渗透率越低,启动压力梯度越大。安塞特低渗透油田的渗流特征为非达西渗流,流体流动需要一定的启动压差,超前注水提高了地层压力,使油层更多孔道内的压力梯度大于启动压力梯度。因此超前注水,可以使地层具有较高的压力梯度及较大的生产压差,即建立了有效的压力驱替系统。

(2)超前注水降低了因地层压力下降造成的地层伤害

国内外研究认为,裂缝性低渗透油藏,地层压力大幅度下降后,油层孔隙度将会减小,裂缝闭合,渗透率降低。试验表明,安塞低渗透油藏地层压力下降,渗透率下降,再恢复地层压力,渗透率只能恢复到6015%～8712%。

(3)超前注水降低了油井的初始含水率

根据实验研究结果,油水两相在低渗透地层中作拟稳定渗流时,它们各自的流动符合有启动压力梯度

・02・第22卷　　第1期　　大庆石油地质与开发　P 1G 1O 1D 1D 1　　2003年2月

f w={1+(K ro/K rw)×

{1-{[φ/(2K)]12τo}/(Δp/L)}}-1

式中　f w———含水率;K ro、K rw———油、水的相对渗透率;K———绝对渗透率;φ———孔隙度;τo———原油极限剪切应力;Δp/L———启动压力梯度。

从上式中可看到,影响含水率的因素诸多。当启动压力梯度为零时,则变为一般的达西定律条件含水率计算公式。在低渗透率条件下,渗流的过程存在启动压力梯度,地层的渗流特征为非达西渗流,这时影响含水率的因素较多,除了油水粘度比外,渗透率和原油极限剪切应力的影响就不可忽视。在其它相同条件下,启动压力梯度越大,含水率越小;原油极限剪切应力越小,含水率越低;渗透率越低,含水率越高;超前注水提高了地层压力,减小了地层压力下降对地层孔隙度、渗透率的伤害,因此降低了含水。

(4)超前注水始终保持了较高地层压力,有利于提高最终采收率

安塞油田水驱油试验表明,随着驱替压力梯度的增大,水驱油效率逐渐增大,提高和保持了较高的地层压力,即提高了驱替压力,增大了生产压差,克服了毛管力及其它阻力的作用,可以使更细小孔道的原油被驱出。

2　安塞油田概况

安塞油田区域构造为倾角不足半度的西倾单斜,其上发育着差异压实的鼻状隆起。沉积环境主要为湖泊三角洲前缘沉积体系,产油层位有长6、长4+5、长3、长2等4套层系。主要开发层系为长6油藏,孔喉组合以小孔细喉型为主,平均喉道半径为0143μm,属小孔喉高密度分布。空气渗透率1129×10-3μm2。原始地层压力813～1011MPa,饱和压力4165～6179MPa,是一个“低渗、低压、低产”的油藏。

为了安塞特低渗透油田的高效开发,针对低压、低渗、低产油藏的特点,逐步扩大试验,为经济有效的投入开发提供了实践依据。经过了探井试采、井组自然能量及注水开发试采、先导性开发试验和工业化开发试验滞后注水,到1990年采用反九点正方形井网大面积注水开发,基本上采取了注采同步的开发原则,油田达到了较好的开发效果。

渗透率主要由粗喉道提供,致使大部分孔隙被性喉道所控制,造成退汞效率低,难采体积大。平均退汞效率为2813%。

油藏水驱效率为4613%,水驱效率随着渗透率增大而增加,渗透率小于1×10-3μm2,水驱效率为3617%;渗透率大于1×10-3μm2,水驱效率为4818%,水驱油特征受不同沉积相带的影响,其水驱油效率差异较大。

3　开发效果

安塞油田长6油藏的注水开发,经历了井组滞后注水,先导性和工业化试验区晚注水,全面注水开发后的同步投产投注,以及不同建产时间的个别井见到的超前注水效果。

(1)自然能量开发阶段,产量递减快

塞6井组长6油层9口试采井,初期平均单井日产油4114t,一年后下降到11t,年递减达5413%。

塞5井组4口井初期平均单井日产油3162t,一年后下降到1158t,年递减达5614%。

两井组经过4年的自然能量开发,产量递减到018～110t,并在低水平下基本稳产。

(2)滞后注水开发阶段,注水见效缓慢

1988年开辟的先导性开发试验区,19年进行的工业化开发试验区,滞后注水8～12个月,投产后日产油由初期的5118t下降到一年后的3131t,年递减达3611%,注水6～8个月后油井见效,见效后平均单井产能(315t)仅为初期产能的6716%。

(3)同步注水开发初期递减幅度减小、注水见效较快,见效后产量亦较高

1991年同步投产投注的采油井,产量由初期的4193t/d下降到5个月后的3165t/d,递减率2519%。注水5个月后开始见效,见效稳产期产量(318t)达初期产量的7711%,较滞后注水产量幅度提高。

(4)超前注水井开发效果明显好于同步和滞后注水

不同建产期部分井超前注水开发效果分析说明,超前注水油井产量高,递减小,见效稳产期长。初产、见效稳产期及整个生产时间,单井日产能均高于同步和滞后注水井区。

4　超前注水开发试验实施效果

2001年安塞油田实施超前注水井组12个,对应采油井57口。根据生产时间较长、具有可对比资料的44口井分析看出,2001年超前注水试验取得了较好的开发效果。

(1)超前注水区压裂排液产量明显高于非超前注水区

・

1

2

・

　2003年2月　　　　　　　　车起君等:超前注水提高特低渗透油田开发效果超前注水区先注水一定时间采油井再进行压裂排液,其排液产量高。

(2)超前注水初期日产油量明显提高,含水降低

从投产的初期产量看,超前注水区与非超前邻井地层物性基本相同的状况下,超前注水井日产液、日产油均较高,含水较低,初期递减率较小。

(3)超前注水地层压力保持在原始地层压力的110%左右为好

从压力监测资料分析,在一定时间内,注水量一定时,超前注水采油井地层压力持续上升,但上升到一定值后,压力值不在上升。因此,从地层压力上升角度分析,超前注水时间在2～3个月后,地层压力上升速度缓慢,或者趋于平稳。要想保持更高的压力水平,须提高注水量或延长注水时间。

(4)受地层各向异性的影响,不同的水驱方向,压力传导速度不同

超前注水压力监测资料说明,双向水驱及轴向水驱井压力上升快,压力值高,为原始压力的10711%;侧向水驱井则低,为原始压力的10115%。

(5)超前注水时间越长,压力值越高,试油及初期日产油亦高

超前注水时间达4～5年的4口井,产量及初始压力值高。投产时压力值为原始压力的11817%。试油日产油高出40～60t/d。投产初期日产油高出4～6t/d。

(6)超前注水时机以3～6个月较佳

超前注水不同注水时机试验结果表明,在目前试验范围,即一年左右,注水时间越长产量相对较高。但从最佳的经济效益角度考虑,相对合理的超前注水时间应为3～6个月。

从地层压力上升值及保持水平分析,在一定的注水强度下,超前注水2个月后,压力上升速度变缓,以后又注水1个月,压力值趋于稳定。压力保持水平基本在105%～110%。

(7)地层物性好、超前注水时间长,油井初期产能高;物性相近超前注水时间长的井产量亦较高超前注水8个井组,由于油层物性及超前注水时间的差异,每个试验井组的初期产能相差亦较大。

(8)超前注水井注水压力正常

按注采比及注水强度所需正常注水量条件下,超前与同步注水井注水压力基本接近。超前注水井注水3个月后注水压力仅高015～018MPa。

(9)在满足地层注水量的情况下吸水指示曲线正常

从视吸水指数曲线可看出,王窑、杏河基本上均在日注水量达到80m3时,曲线出现拐点,但拐点后的结果截然相反。王窑区随着注水压力的提高日注水量上升幅度减小;杏河区随着注水压力的提高日注水量上升幅度增大。分析认为与投注前的措施规模有关,王窑区采取挤活性水或爆燃压裂措施,而杏河区采取加石英砂水力压裂。安塞油田长6油藏正常日注水量一般为40m3。

5　结束语

(1)在压裂投产方式上,建议采取注水井先注水一定时间(3～6个月),再进行压裂改造,效果会更好。

(2)超前注水使地层保持了较高的压力水平,建立了有效的压力驱替系统,使油井产量较高,含水较低,初期递减较小。

(3)超前注水保持较高的地层压力,可降低因地层压力下降造成的地层伤害。

(4)安塞油田不同区块试验说明,油层物性越好,超前注水效果亦越好。

(5)对于安塞油田低电阻油藏,可以通过超前注水提高单井产能。

(6)试验结果表明,当油藏含水较高时,超前注水对提高单井日产油效果不大。

(7)超前注水在地质上取得了较好的效果,但新区或较大规模地实施,就得先期进行地面注水系统建设,先钻注水井或采油井不投产,在资金和产量紧张的情况下,实际操作起来问题较多。

参考文献:

[1]李道品1低渗透砂岩油田开发[M]1北京:石油工业出版社,

19971

[2]黄延章1低渗透油层渗流机理[M]1北京:石油工业出版社,

19981

编辑:邵宪志

・

2

2

・大庆石油地质与开发　P1G1O1D1D1　　　　　　　　第22卷　第1期the West B lock of B eiyiqudu andong in the S azhong Oilf ield ZHAN G Y ong2qing,QU Y ong2hong,XU Luo2bin(Explo2 ration and Development Research Institute of Daqing Oilfield Com2 pany Ltd.,Daqing163712,China)

Abstract:Now the Daqing oilfield is faced with severe situation of deep development,and multiple subjects are needed to go along to2 gether in order to enhance recovery factor.Reality of oilfield devel2 opment still needs forecasting interior heterogeneity and space dis2 tribution laws of three dimensions of all kinds of sandbody between wells carefully,exactly,quantitatively.This paper takes the ex2 ample of Pu I formation of the west block of Beiyiquduandong in the Sazhong oilfield,with the application of the methods of fine contrast of high resolution sequence,quantitative token of flow u2 nits,reservoir modeling controlled by the sedimentary microfacies, reservoir numerical simulation to carry out the comprehensive study.The paper opens out quantitative heterogeneity of river2delta facies reservoir,thus the distribution of remaining oil in sandbody inside is showed from the point of view of macroscopic,and reser2 voir comprehensive models are set up.The study of multiple sub2 jects the practical means for fine reservoir description and predic2 tion,and improve prediction level,it has practical significance for the same reservoir fine of oilfield.

K ey w ords:multiple subjects;reservoir simulation;geological modeling;numerical simulation;forecast

Article ID:100023754(2003)0120020203

E ffects of Advanced W aterflooding in Extra2permeability Oilf ield Development

CHE Qi2jun1,L EI J un2an2,RAN Yu2xia1,HE Zhi2yong2 (1.Exploration and Development Research Institute of Changqing Oilfield Company Ltd.,Xian710021,China; 2.No11Oil Pro2 duction Company of Daqing Oilfield Company Ltd.,Daqing 163001,China)

Abstract:Ansai oilfield has the largest oil geological reserves in Or2 dos Basin,and the most well2know extra2permeability oilfield in the world,too.Therefore,to enhance the development effects,e2 conomical benefit,and ultimate recovery of it is the most important task of engineers.New approaches are being continually searched after,while better effects have been made by conventional water2 flooding over a large area in Ansai oilfield.Advanced waterflooding keeps formation pressure in high level,reduces formation damage caused by formation pressure decline and controlls the initial water cut,thus enhancing the initial individual2well producing rate,keep2 ing oil well long stable production period,slowing down the degres2 sion,and beneficial to enhancing ultimate recovery by establishing the effective driving pressure.

K ey w ords:advanced waterflooding;theoretical foudation;extra2 permeability oilfield;development test effect

Article ID:100023754(2003)0120023203

U tilizing R eservoir B asic G eological P arameters to Establish Weng Cycle Model

L IAN GJ un2bin(Shengli Oil Production Company of Shengli Oilfiled Company Ltd.,Dongying257051,China)

Abstract:On the basis of rational exploitation,the regularity of oil yield is depended on the oil geological property.The regional equa2 tion of the coefficient B of the Weng cycle model2a kind of oil annu2 al yield predicting method has been established by utilizing reservoir basic geological parameters,such as proven oil reserves,recover2 able oil reserves,porosity of reservoir,crude oil density at ground and so on.Together with the coefficient c and n,according to the astringency of the Weng cycle predicting model and taking the least fitting error of the recoverable oil reserves and the initial oil produc2 ing rate as the restriction condition,can be solved out making use of the iterative method,the Weng cycle model of the reservoir can be established at early stage.The research by21oilfields in Jiyang de2 pression and10oilfields on the world proves that this method is practicable and the predicting accuracy of the equations is accept2 able.It can be applied to calculate the economic recoverable oil re2 serves,evaluating the commerical value of the proven reserves, and laying down the rational development index at initial exploita2 tion stage.

K ey w ords:Weng cycle;oil yield;prediction;model;reservoir;economic evaluation

Article ID:100023754(2003)0120026203

R esearch on Improved Production and the Optimizing Cost2benef it Arrangement Method

DON G Zhi2lin1,L IU Wei2wen1,L I Rong2(1.Planning De2 partment of Daqing Oilfield Company Ltd.,Daqing163453,Chi2 na; 2.Exploration and Development Research Institute of Daqing Oilfield Company Ltd.,Daqing163712,China)

Abstract:At the late period of high water cut stage during oilfield development stimulation treatments must be applied to make up production decline and maintain oil production.The stimulation production for different treatments varies,and the costs for differ2 ent treatments in the same block and those for the same treatment in different blocks are not the same at all.According to the analysis to the influential factors during oilfield stimulation and based on the theory of iso2marginal cost and present value approach this paper es2 tablishes reasonable distribution models of stimulation treatments in different blocks,and provides reasonable distribution methods to the improved production in different blocks.The stimulation treat2 ments after reasonable distribution can not only coincide with the production in oilfield development but also improve the economical benefit greatly and provide decision evidence for oilfield develop2 ment planning.

K ey w ords:stimulation;treatment;theory of iso2marginal cost; present value approach

Article ID:100023754(2003)0120029203

The Fluid2Solid2H eat Coupled Math’s Model in the Multiphase Flow Porous Media of E lastic R eservoir

WAN G Z i2ming,DU Zhi2min(S outhwest Petroleum In2 stitue,Nanchong637001,China)

Abstract:A new fluid2solid2heat coupled mathematical model about the multiphase flow in porous media of elastic reservoir has been founded on the base of system analysis of the three physical field, which include fluid mechanic field,solid mechanic field and tem2 perature field,and comprehensive utilization of flow mechanics, rock mechanics,heat mechanics theories.The model provided that rock matrix were variable,heat in reservoir could be trans2 ferred freely abiding by law of thermodynamics and process.The fluid pressure was able to make rock matrix deformation.On the other hand,rock matrix deformation could also make reservoir flowing properties and fluid pressure in porous changed.S o,safely coupled fluid flow equation,rock deformation equation and temper2 ature field equation have been founded.These equations coupled, and only can be soluted simultaneously.The direction to solute the equations have been provided in article.The model really make flow in porous media,deformation and temperature variation coupled, and can be better reflect the properties of the reservoir than those models existing before,which developed reservoir traditional flow the ories and fluid2solid coupled mechanics theory and can be used in petroleum engineering.

K ey w ords:reservoir;elastic medium;temperature field;flow in porous media;fluid2solid2heat couple;math’s model

Article ID:100023754(2003)0120032203

H ydrodynamic C ause for R esidu al Oil Stagnated in the R eservior Micro2structure

GUO De2zhi,WAN G Huai2min,L I Cui2ling(Exploration and Development Research Institute of Daqing Oilfield Company Ltd.,Daqing163712,China)

Abstract:Reservior micro2structure is a small subclass on the oil2 field structure because of fine distinction of the layers depth.This paper analyzes the cause for residul oil stagnated in the reservior mi2 cro2stucture that used the hydrodynamic method then oilfield injec2 tion water exploration.It pointed out that residual oil stagnated in the reservior micro2structure is a hydrodynamic trip,we may use potential energy theory of Hubbert for exploration and jugement. The result analyzed has indicated that residual oil forms when po2 tential energy gradient of oil phase point to inside of reservior micro2 structure because the direction of potential energy gradient is differ2 ent from oil and water.The knowledge of exploiting this kind of residul oil is given in the paper also.

[2]　　　Vol122No11　　　Petroleum G eology&Oilfield Development in Daqing　　　Feb12003