低渗透油田注水井压裂数值模拟研究

收稿日期:2002203218作者简介:张　磊(1973-),男,河北张家口人,工程师,在读硕士,从事油田开发研究。

文章编号:100023754(2003)022*******低渗透油田注水井压裂数值模拟研究张　磊1,王文军2,张红军3(11大庆油田有限责任公司第三采油厂,黑龙江大庆　163113;21大庆油田有限责任公司开发部,黑龙江大庆　163453;31大庆油田有限责任公司井下作业分公司,黑龙江大庆　163455)摘要:在改进的黑油模型基础上,建立了一种油、水两相三维油藏裂缝数值模型,可以对垂直裂缝油藏不同井网条件下注水井压裂效果进行数值模拟。

以朝阳沟油田为例,在反九点法井网条件下,裂缝处于有利方位和不利方位时,对注水井压裂后的注入动态以及对应油井的生产动态的影响进行了分析,并与油田的实际生产动态进行了对比。

研究结果为注水井压裂效果评价提供了一种手段,对于经济有效地进行低渗透油田注水开发具有实际意义。

关键词:注水井;压裂;数值模拟;朝阳沟油田中图分类号:TE319 文献标识码:A 实践证明,区块整体压裂是开发低渗透油田的有效方法,合理的水力裂缝方位和裂缝参数对经济有效地开发低渗透油田是非常重要的[1]。

以往的研究主要是针对油井进行的,但注水井压裂同样会影响整体开发的效果。

因此,有必要建立一种油、水两相三维油藏裂缝数值模型,对垂直裂缝油藏不同井网条件下注水井压裂效果进行数值模拟并提供评价手段。

1　三维两相油藏数值模型及求解方法在改进的黑油模型基础上,建立了两相三维油藏裂缝数值模型,可以对五点法井网(裂缝方位分别为0°和45°)和反九点法井网(裂缝方位分别为0°和45°)条件下,注水井压裂对井组单元内油水井生产动态的影响进行模拟研究[2]。

111　模型的基本假设针对实际情况,对模型提出的基本假设是:(1)油藏均质,各向同性,渗流为等温渗流;(2)油藏内仅有油、水两相渗流,地层压力大于饱和压力;(3)油、水不混溶;(4)地层流体和岩石微可压缩;(5)忽略毛管力作用;(6)裂缝为两翼对称垂直缝,井眼和裂缝穿过压裂层,多井压裂裂缝方向一致。

112　数学模型流动方程考虑了重力项和垂向的流动ρo o KK ro μoΦo +q o =55t (ρoo φS o )(1)ρww KK rw μwΦw +q w =55t (ρww φS w )(2)Φo =p o +ρo gz (3)Φw =p w +ρw gz(4) 分别考虑五点井网、反九点井网注采井都压裂的情况,边界条件和初始条件为p (x ,y ,z ,t )|Ω1=p w f(5)p (x ,y ,z ,t )|Ω2=p inj(6)5pΣ|6∈f (x ,y ,z )=0(7)p (x ,y ,z ,t )|t =0=p i (8)S w (x ,y ,z )|t =0=S wi(9) 上述模型中的一些辅助关系为S o +S w =1(10)K ro =K ro (S w )(11)K rw =K rw (S w )(12)μ=μ(p )(13)ρ=ρ(p )(14)113　网格划分及差分求解采用不均匀网格,裂缝单独作为一排网格,裂缝附近网格由小到大逐渐变化,纵向上按均匀网格划分,裂缝处理用二维(y 方向放大缝宽,相应减小缝内渗透率)方式。

使用I MPES 法求解,计算过程中,方程左端达西项系数均取上一时间步的值,即做常数处理,等式右边按泰勒级数展开,取一级小量,通过方程合并,得到压力和饱和度方程,用隐式求解压力方程,解出压力分布后带入饱和度方程,求解每一层的注入量和采出量,累加后可得单井的注采量。

在上述理论模型的基础上,编制了注水井压裂后油水井动・14・第22卷 第2期 大庆石油地质与开发　P 1G 1O 1D 1D 1 2003年4月态数值模拟程序。

2　应用实例朝阳沟油田是1986年投入开发的大庆外围低渗透油田,1987年进入注水开发阶段,采用300m 井距反九点法井网注水。

为了强化注水,弥补地下亏空,1990年以来开始对部分注水井进行压裂改造,见到了一定的增注效果。

针对朝阳沟油田的开发特点和油藏参数,应用垂直缝条件下油水井压裂数值模拟软件,在裂缝处于有利方位和不利方位的条件下,注水井压裂的不同裂缝参数对压裂后注入动态以及对应油井生产动态的影响进行了数值模拟研究,模拟过程中,油井的裂缝参数不变(穿透比为013)。

在整体裂缝参数研究的基础上,还针对单井的具体地层条件和裂缝参数,对注水井压前压后的注入动态进行了模拟,并与实际生产动态进行了拟合对比[3-5]。

211反九点法井网裂缝方位与井排夹角为45°的模拟结果对于反九点法井网,当人工裂缝夹角与井排夹角为45°时,裂缝处于有利的方向。

不同裂缝穿透比下注水井注入动态变化的模拟结果见图1和图2。

从图中可以看出,当裂缝穿透比为011时,压后日注入量就明显增加,从整个井组生产全过程考虑,计算到油井含水98%时,累计注水达199000m 3,生产时间由9500d 缩短到7670d 。

因此,注水井压裂以后,可以明显的提高日注水量,从而增加了水驱强度。

另外,从图中还可以看出,随着裂缝穿透比的增大,压裂增注的效果越来越接近,当穿透比超过012以后,模拟的注入动态曲线基本重合,说明继续增大压裂施工规模无益于增注效果提高。

因此,对于注水井压裂,应以短缝为宜,裂缝穿透比应控制在012以内。

图3、图4给出了注水井压裂后,井组单元内连通油井计算到含水98%时,生产动态变化的模拟结果。

可以看出,当注水井不压裂时,注水见效后边井稳定产能516t/d ,角井稳定产能617t/d ,计算到含水98%,生产天数为9500d ,采收率达28112%。

当注水井压裂穿透比为013时,注水见效后边井稳定产能915t/d ,角井稳定产能913t/d ,计算到含水98%,生产天数为7510d ,采收率达28153%。

由此可见,由于注水井压裂后,增加了水驱强度,从而提高了油井的采油速度。

另外,从图中还可以看出,注水井压裂后,对边井和角井的影响程度不同,角井见水后油井产能下降较大。

这主要是由于角井与裂缝在一条直线上,见水后含水上升较快引起的。

212　反九点法井网裂缝方位与井排夹角为0°的模拟结果当人工裂缝与井排夹角为0°时,未压裂和压裂后的注水井注入动态变化见图5和图6。

・24・大庆石油地质与开发　P 1G 1O 1D 1D 1 第22卷　第2期 与反九点法井网裂缝方位与井排夹角为45°时的情况相似,当裂缝穿透比为011时,压后日注入量就明显增加,从整个井组生产全过程考虑,计算到油井含水98%时,累计注水达178000m3,生产时间由9010d缩短到6980d。

但随着裂缝穿透比的增大,压裂增注的效果越来越接近。

注水井压裂时也应以短缝为益,裂缝穿透比应控制在012以内。

对于井组单元内连通油井,计算到含水98%时,从生产动态变化的模拟结果可以看出,当注水井压裂时,边井角井的产能都比不压裂的情况增加,但各井增产的幅度有所不同,生产天数由9010d缩短到6980d,采收率为27114%,比反九点法井网裂缝方位与井排夹角为45°时的情况低。

由此可以看出,对于反九点井网油水井压裂,井组的采收率与裂缝方位和井排夹角的大小有关,方位角为45°时采收率最高。

这是因为当裂缝与井排夹角为0°时,注水井裂缝与两口边井裂缝的压力梯度很大,而与其它井的压力梯度小,因而注水井波及的面积减少;当裂缝与井排夹角为45°时,注水井与边井、角井裂缝间的距离相当,注水井裂缝影响的范围大,波及面积增加,因而采收率增大。

213　单井预测与拟合根据朝阳沟油田裂缝形态监测的结果,裂缝方位与井排夹角在3715°～45°,为了计算方便,按45°考虑,应用数值模拟软件对朝阳沟油田已压裂的注水井的压前压后注入动态进行了预测,并与实际动态进行了对比。

以朝124-72井为例,该井有效厚度为1016m,平均有效渗透率为916×10-3μm2,稳定注水压力为1318MPa,地层流体参数借鉴油田数据,该井1988年投注,1994年全井压裂改造,共加014～018mm砂2518m3,应用压裂设计软件预测平均支撑缝长90m,平均缝宽115mm。

在此基础上,应用数值模拟软件对注水井压前压后动态进行了预测。

结果表明压前压后程序预测注入动态与实际注水情况符合较好。

现场应用该方法模拟预测38口井,平均符合程度达25%,可以满足生产中优化注水井压裂参数,预测注水井压后的注入动态的要求。

3　结　论(1)注水井压裂可以有效的提高注水井的注入能力,降低启动压力,增大驱替压力梯度,从而增加油井产能,提高低渗透油田的采油速度和开发效益。

(2)对于注水井压裂,应以短缝为益,裂缝穿透比应控制在012以内。

(3)对于反九点井网油水井压裂的情况下,井组的采收率与裂缝方位和井排夹角的大小有关,裂缝方位角为45°时采收率最高。

(4)经现场实际资料验证,该方法可以用来预测注水井压后的注入动态,为注水井压裂参数优化提供依据。

符号注释:ρ°o———地下油相密度,kg/m3;μo———地下油粘度,mPa・s;φ———孔隙度,%;K ro———油相相对渗透率;S o———含油饱和度,%;g———重力加速度,m/ s2;p w f———油井井底流压,MPa;p i———原始地层压力,MPa;ρw w———地下水相密度,kg/m3;μw———地下水粘度,mPa・s;K———地层有效渗透率,μm2; K rw———水相相对渗透率;S w———含水饱和度,%; z———垂向深度,m;p inj———注水井井底流压,MPa; S wi———原始地层含水饱和度,%。

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Chaoyangg ou OilfieldArticle I D:100023754(2003)022*******Execution and Evalu ation for Fracturing Pre2P ad Stimulation K OU Y ong2qiang,H UANGQiu2bing(D ownhole Operating C om2 pany of Shengli Petroleum Administrative Bureau,D ongying257077, China)Abstract:Fracturing pay zone differ from each other in their geologic characteristics,physical conditions and production cases1T o take s ome necessary measures such as pre2pad stimulation is im portant for s ome fracturing stimulations,Which can ensure fracturing process and im2 prove fracturing result1In this paper,acid pre2pad,liquid nitrogen pre2pad and diesel2mutual s olvent pre2pad were introduced,included in their executing process;application conditions and oilfield applica2 tion results,conventional execution and evaluation methods for these pre2pads were discussed als o1K ey w ords:fracturing;pre2pad;technical property;application condition;application resultArticle I D:100023754(2003)022*******The Method of I ncreasing PCP Work LifeH UANG Y ou2quan,HE Y an,LI U He(Oil Production T ech2 nique Research Institute of Daqing Oilfield C om pany Ltd1,Daqing 163453,China)Abstract:Beam pum ping units and electrical submersible pum ping ar2 tifical lift techniques haven’t been full played in scale formation and abrasive application of ASP drive wells,the wells produce s ome am ount of sand and the wells for heavy oil cold recovery1Sur face drive PCP will become an economy and high efficiency artifical lift technique for scale formation and abrasive applications by the structural parame2 ters adjustment,technique optimization1In this paper,the optimum design method for PCP’s structural parameters is created by analyzing the target function in scale formation and abrasive applications;the methods to achieve the best scale resistance and wear per formance,to prolong the w orking life by selecting proper materials of construction and optimization w orking conditions are discussed1K ey w ords:PCP(progressing cavity pum p);stator pitch;rotor ec2 centricity;scale formation;wearArticle I D:100023754(2003)022*******The I nfluence of Acid Solution on Oil R eservoir to Complex Pro2 tective T echniqueC AO Wei2zheng1,H AN Zhi2chang2,S UN X iao2ming2,X U Y un2 long1,XI AO Lu2chuan1(11Exploration and Development Research Institute of Daqing Oilfield C om pany Ltd1,Daqing163712,China;21 N o15Oil Production C om pany of Daqing Oilfield C om pany Ltd1, Daqing163513,China)Abstract:T o the problem of low abs orbed2water thickness of new wa2 ter2injection wells in N o119T ai block of X ingnan Oilfield,according to the experience of injecting protection reagent before wells are injected, on the basis of simulation2experiment estimation,through combining three kind techniques of the oil layer washing,acidifying and clay2ex2 pand inhibitor,the com plex protection reagent of oil reserv oir was de2 velopd1Experiment indicates that the match degree of acid s olution of com plex protection reagent to reserv oir decides applied results1I f acid s olution is selected properly,it can im prove the capability of seepage flow in oil layer effectively1This technique was applied to4wells,the start2up pressure was reduced effectively and water abs orbability was V ol122N o12 Petroleum G eology&Oilfield Development in Daqing Apr12003 [3]。