FLAC3D井壁稳定模拟

1、基于FLAC-3D的水合物井壁稳定性数值模拟研究天然提水合物是一种混合了水、气等的混合物，主要组成部分为甲烷。其他比例较小的 组分有CO2、H2S，以及极少量的乙烷和高价烃类。水合物在深海或者永冻土地带高压低温 的下状态很稳定。随着化学试剂的注入，引起温度升高压强降低会导致水合物的分解。水合 物的分解如同冰的融化，会伴有强烈的吸热，并释放出气体和水。考虑到水合物的巨大储量， 在将来极有可能称为一种替代能源。然而水合物分解造成的严重温室效应也可能导致极大的地质灾难，威胁到海洋甚至是陆地型 油气田，因此深海水合物钻探有着很大风险。钻探水合物沉积物时，压力和温度的改变可能会导 致水合物大规模分解。通

2、常水合物沉积物在海床表层，甚至比表层套管还要浅，因此安装防喷器 就无从说起。钻进过程中，温压控制不当造成的水合物分解也极有可能造成井身结构的破坏。如果是没有隔水板的钻进，气体会进入到开放的环空空间，不断上升，并由于吸热造成钻杆 柱附近的钻具结冰。如果有隔水板钻进，气体进入回路环空，与钻井液混合到一起升到表层。不 管哪种情况，都会有爆炸和火灾的危险，气体中可能含有的硫化氢更是无法控制。同时，随着大 量气体进入，钻井液的密度也会降低。而随着钻井液密度的降低导致液柱压力降低又将导致新一 轮的水合物分解，如此恶性循环。液柱压力降低还有另一个副作用，那就是对井壁的支撑作用削 弱，因此而导致井壁坍塌，钻孔

3、超径等问题。钻井液流变性能的改变会还影响孔内清洁，在加上 地层强度以及空隙压力的改变，很可能就会导致缩径从而卡钻。更有甚者，当水合物分解时，沉积物储层的力学和物理性质都会发生改变，空隙流体压力也 会增大。伴随水合物分解造成的储层物性变化包括：渗透率上升；热力学性质的改变；弹性模量 降低以及固井强度低；沉积物强度降低会加剧井壁的不稳定性。随着水合物分解造成固井强度降 低以及空隙压力增加会造成更多的机械故障。Despite these possible risks HBS have been drilledsuccessfully in the past with few reportable i

4、ncidents(eg. Ohara et al., 2000; Collett and Dallimore, 2002 ,Minerals Management Service 2004), see /homepg/offshore/safety/ wtrflow.html.尽管有这么多风险，过去的水合物沉积物钻进案例还是很成功的，只出现了极少的问题。作为将来一种可能的深海钻进技术，对天然气水合物钻进的风险形成良好的认识并在问题发 生前及时预报并采取措施是十分重要的。数字模型是模拟研究水合物沉积物机理的一个有效手段，并可以由此估算钻井参数(例如可 用的泥浆密度，组分以及温度)，这些目前都还缺

5、少一个安全推荐值。数值模拟中需要被考虑到 的主要因素有：Numerical modelling can be an effective tool thatenables the simulation of mechanisms leading towellbore instability in HBS, and to assess drillingparameters such as mud weight, composition andtemperature that can be used, while still remainingwithin a safe operational en

6、velope. Some of the factorsthat need to be evaluated are:effect of drilling fluid on heating the formation andchanging the stresses and pore pressure;impact of the selected constitutive model;effect of heating the formation on thermodynamicstability of the hydrates and wellbore stability; and effect

7、 of reduction in the sediment strength (i.e. particularly,loss of cohesion) due to hydrate dissociation.模型建立水深1310m,海底365m处，为简化计算只取半径0.5m高1m圆柱，钻杆直径0.09m。建立网格如图:Minneapolis, MN USA模型参数比奥系数1沉积层体 积模量7.0 GPa钻井泥浆 温度20 C (293 K)初始沉积层孔隙率0.49沉积层剪 切模量0.69 GPa固有渗透 率1x10-15m2水合物形成后沉积层孔隙率0.25泊松比0.45气体常数8.31441J

8、K-1M0I-1导热率1.4 Wm-1K-1原位孔隙 水压力17 MPa水合物晶 体体积1.728x10-27m3比热容1.9x103K-ikg-i各向同性 应力32 MPa阿伏加德 罗常数6.02205x1023水合物线性膨胀 系数7.7x10-5 K-1垂直应力21 MPa内聚力1.8 MPa孔隙流体的线性膨胀系数30 x10-5 K-1泥浆压力20 MPa内摩擦角35沉积层饱和密度2.200 kgm-3原位温度15 C(288 K)抗拉强度1.5 MPa模型一此模型只考虑力学变形，地层无渗透性。竖向应力经过重新分布，变化较小，初始应力21MPa，重新分布后最大压应力为20.987MPa，

9、井壁周围应力较小；径向初始应力32MPa，经过应力重分布，最大压应力 为47.635MPa，分布在井壁周围较小范围内。井壁周围曾经因剪切到达过屈服面，现在已处于弹性变形阶段，范围很小。FLAC3D 3.00Step 653 Model Perspective 12:35:04 Fri Jan 14 2011Center:Rotation: TOC o 1-5 h z X: 0.000e+000X:0.000Y: 5.000e-001Y:0.000Z: 0.000e+000Z:0.000Dist: 3.265e+000 Mag.: 1Ang.: 22.500Plane Origin:X: 0.0

10、00e+000Y: 5.000e-001Z: 0.000e+000Plane Normal:X: 0.000e+000Y: 1.000e+000Z: 0.000e+000Contour of SZZPlane: onMagfac = 0.000e+000 gradient Calculation -4.6695e+007 to -4.5000e+007. -4.5000e+007 to -4.0000e+007-4.0000e+007 to -3.5000e+007-3.5000e+007 to -3.0000e+007-3.0000e+007 to -2.5000e+007-2.5000e+

11、007 to -2.0000e+007-2.0000e+007 to -1.5000e+007-1.5000e+007 to -1.1912e+007Interval = 5.0e+006Historyx10A41.81.61.41.21.00.80.60.40.22.04.06.01 Max. Unbalanced ForceItasca Consulting Group, Inc.Minneapolis MN USAPlane Origin:X: 0.000e+000Y: 5.000e-001Z: 0.000e+000Contour of SXXPlane: onMagfac = 0.00

12、0e+000Interval = 5.0e+006Plane Origin:X: 0.000e+000Y: 5.000e-001Z: 0.000e+000FLAC3D 3.00Step 653 Model Perspective 12:35:32 Fri Jan 14 2011Center:Rotation: TOC o 1-5 h z X: 0.000e+000X:0.000Y: 5.000e-001Y:0.000Z: 0.000e+000Z:0.000Dist: 3.265e+000 Mag.: 1 Ang.: 22.500Plane Normal:X: 0.000e+000Y: 1.00

13、0e+000Z: 0.000e+000radient Calculation-4.7635e+007 to -4.5000e+007-4.5000e+007 to -4.0000e+007-4.0000e+007 to -3.5000e+007-3.5000e+007 to -3.0000e+007-3.0000e+007 to -2.5000e+007-2.5000e+007 to -2.0000e+007-2.0000e+007 to -1.5000e+007-1.5000e+007 to -1.1856e+007Itasca Consulting Group, Inc. Minneapo

14、lis, MN USA _FLAC3D 3.00Step 653 Model Perspective 12:35:49 Fri Jan 14 2011Center:Rotation: TOC o 1-5 h z X: 0.000e+000X:0.000Y: 5.000e-001Y:0.000Z: 0.000e+000Z:0.000Dist: 3.265e+000 Mag.: 1 Ang.: 22.500Plane Normal:X: 0.000e+000Y: 1.000e+000Z: 0.000e+000Contour of SYYPlane: onMagfac = 0.000e+000.ra

15、dient Calculation -2.0987e+007 to -2.0750e+007. -2.0750e+007 to -2.0500e+007-2.0500e+007 to -2.0250e+007-2.0250e+007 to -2.0000e+007-2.0000e+007 to -1.9750e+007-1.9750e+007 to -1.9500e+007-1.9500e+007 to -1.9250e+007-1.9250e+007 to -1.9000e+007-1.9000e+007 to -1.8809e+007Interval = 2.5e+005FLAC3D 3.

16、00Step 653 Model Perspective 12:36:06 Fri Jan 14 2011Center:X: 0.000e+000Y: 5.000e-001Z: 0.000e+000Dist: 3.265e+000Rotation:X: 0.000Y: 0.000Z: 0.000Mag.:1Ang.: 22.500Plane Origin:Plane Normal:X: 0.000e+000X: 0.000e+000Y: 5.000e-001Y: 1.000e+000Z: 0.000e+000Z: 0.000e+000PJane: on None shear-pMN USAIt

17、asca Consulting Group, Inc.模型二考虑钻井液渗透进入水合物地层。第一步，在钻开水合物地层，钻井液尚未侵入时，应力重新分布，X、Y、Z向最大压应 力分别为 38.898MPa、21.141MPa 和 41.392MPa。井壁周围很小范围内应力为拉应力，在模型1中没有出现这种情况，放大查看，范围相 当小，猜测可能与固定边界的孔隙水压力有关，具体原因不知。钻孔周围较大范围曾因剪切到达屈服面，很小范围内因拉伸到达过屈服面，且目前均处 于弹性变形阶段。FLAC3D 3.00 x10A4Step 1276 Model Perspective 13:19:01 Fri Jan 14

18、 2011Center:Rotation:X: 0.000e+000X:0.000Y: 5.000e-001Y:0.000Z: 0.000e+000Z:0.000Dist: 3.265e+000 Mag.: 1 Ang.: 22.500Plane Origin:X: 0.000e+000Y: 5.000e-001Z: 0.000e+000Plane Normal:X: 0.000e+000Y: 1.000e+000Z: 0.000e+000Contour of SZZPlane: onMagfac = 0.000e+000radient Calculation-I -3.8898e+007 t

19、o -3.5000e+007 -3.5000e+007 to -3.0000e+007. -3.0000e+007 to -2.5000e+007-2.5000e+007 to -2.0000e+007-2.0000e+007 to -1.5000e+007-1.5000e+007 to -1.0000e+007-1.0000e+007 to -5.0000e+006-5.0000e+006 to0.0000e+000 to5.0000e+006 to1.0000e+007 toI1 1.5000e+007 to0.0000e+0005.0000e+0061.0000e+0071.5000e+

20、0071.9645e+0071.81.61.41.21.00.80.60.40.2Itasca Consulting Group, Inc.0.20.40.60.81.01.2Minneapolis, MN USAx10A3FLAC3D 3.00Center:Rotation:X: 0.000e+000X: 0.000Y: 5.000e-001Y: 0.000Z: 0.000e+000Z: 0.000Dist: 3.265e+000Mag.:1Ang.: 22.500Plane Origin:Plane Normal:X: 0.000e+000X: 0.000e+000Y: 5.000e-00

21、1Y: 1.000e+000Z: 0.000e+000Z: 0.000e+000Step 1276 Model Perspective 12:39:41 Fri Jan 14 2011Contour of SXXPlane: onMagfac = 0.000e+000radient Calculation-4.1392e+007 to -4.0000e+007-4.0000e+007 to -3.0000e+007-3.0000e+007 to -2.0000e+007-2.0000e+007 to -1.0000e+007-1.0000e+007 to 0.0000e+0000.0000e+

22、000 to 1.0000e+0071.0000e+007 to 2.0000e+0072.0000e+007 to 2.1409e+007Interval = 1.0e+007FLAC3D 3.00Step 1276 Model Perspective 12:39:52 Fri Jan 14 2011Center:Rotation:X: 0.000e+000X:0.000Y: 5.000e-001Y:0.000Z: 0.000e+000Z:0.000Dist: 3.265e+000 Mag.: 1 Ang.: 22.500Plane Origin:X: 0.000e+000Y: 5.000e

23、-001Z: 0.000e+000Plane Normal:X: 0.000e+000Y: 1.000e+000Z: 0.000e+000Contour of SYYPlane: onMagfac = 0.000e+000radient Calculation-2.1141e+007 to -2.0000e+007-2.0000e+007 to -1.5000e+007-1.5000e+007 to -1.0000e+007-1.0000e+007 to -5.0000e+006-5.0000e+006 to 0.0000e+0000.0000e+000 to 5.0000e+0065.000

24、0e+006 to 9.8822e+006Interval = 5.0e+006Itasca Consulting Group, Inc.Minneapolis, MN USA _FLAC3D 3.00Step 1276 Model Perspective12:41:33 Fri Jan 14 2011Center:Rotation:X: 0.000e+000X:0.000Y: 5.000e-001Y:0.000Z: 0.000e+000Z:0.000Dist: 3.265e+000 Mag.: 11.6 Ang.: 22.500Plane Origin:X: 0.000e+000Y: 5.0

25、00e-001Z: 0.000e+000Plane Normal:X: 0.000e+000Y: 1.000e+000Z: 0.000e+000Contour of SXXPlane: onMagfac = 0.000e+000radient Calculation-3.0175e+007 to -3.0000e+007-3.0000e+007 to -2.0000e+007-2.0000e+007 to -1.0000e+007-1.0000e+007 to 0.0000e+0000.0000e+000 to 1.0000e+0071.0000e+007 to 2.0000e+0072.00

26、00e+007 to 2.1409e+007Interval = 1.0e+007Plane Origin:X: 0.000e+000Y: 5.000e-001Z: 0.000e+000FLAC3D 3.00Step 1276 Model Perspective 12:42:06 Fri Jan 14 2011Center:Rotation: TOC o 1-5 h z X: 0.000e+000X:0.000Y: 5.000e-001Y:0.000Z: 0.000e+000Z:0.000Dist: 3.265e+000 Mag.: 1 Ang.: 22.500Plane Normal:X:

27、0.000e+000Y: 1.000e+000Z: 0.000e+000Block StatePJane: on Noneshear-pshear-p tension-pItasca Consulting Group, Inc.Minneapolis, MN USA第二步，钻井液侵入水合物地层，进行流固耦合计算。进行的计算无法很好的收敛。图 为耦合计算2000步得到的应力场孔隙场云图。井壁周围约10cm处应力过大。井壁各处的 弹塑性状态如图。FLAC3D 3.00Step 3276 Model Perspective 13:20:00 Fri Jan 14 2011Center:X: 0.00

28、0e+000Y: 5.000e-001Z: 0.000e+000Dist: 3.265e+000Rotation:X: 0.000Y: 0.000Z: 0.000Mag.:1Ang.: 22.500Plane Origin:X: 0.000e+000Y: 5.000e-001Z: 0.000e+000Plane Normal:X: 0.000e+000Y: 1.000e+000Z: 0.000e+000Contour of SZZPlane: onMagfac = 0.000e+000Gradient Calculation-9.7275e+007 to -8.0000e+007-8.0000

29、e+007 to -6.0000e+007-6.0000e+007 to -4.0000e+007-4.0000e+007 to -2.0000e+007-2.0000e+007 to0.0000e+000 to2.0000e+007 to4.0000e+007 to0.0000e+0002.0000e+0074.0000e+0075.4941e+007Interval = 2.0e+007History1 Max. Unbalanced Force1.02.03.0Itasca Consulting Group, Inc.Minneapolis MN USAFLAC3D 3.00Step 3

30、276 Model Perspective 12:44:43 Fri Jan 14 2011Center:Rotation:X: 0.000e+000X:0.000Y: 5.000e-001Y:0.000Z: 0.000e+000Z:0.000Dist: 3.265e+000 Mag.: 1 Ang.: 22.500Plane Origin:X: 0.000e+000Y: 5.000e-001Z: 0.000e+000Plane Normal:X: 0.000e+000Y: 1.000e+000Z: 0.000e+000Contour of SXXPlane: onMagfac = 0.000

31、e+000radient Calculation-9.2561e+007 to -8.0000e+007-8.0000e+007 to -6.0000e+007-6.0000e+007 to -4.0000e+007-4.0000e+007 to -2.0000e+007-2.0000e+007 to 0.0000e+0000.0000e+000 to 2.0000e+0072.0000e+007 to 4.0000e+0074.0000e+007 to 5.2730e+007Interval = 2.0e+007Itasca Consulting Group, Inc.Minneapolis

32、, MN USA _FLAC3D 3.00Step 3276 Model Perspective 12:44:52 Fri Jan 14 2011Center:X: 0.000e+000Y: 5.000e-001Z: 0.000e+000Dist: 3.265e+000Rotation:X: 0.000Y: 0.000Z: 0.000Mag.:1Ang.: 22.500Plane Origin:X: 0.000e+000Y: 5.000e-001Z: 0.000e+000Plane Normal:X: 0.000e+000Y: 1.000e+000Z: 0.000e+000Contour of

33、 SYYPlane: onMagfac = 0.000e+000Gradient Calculation-9.7609e+007 to -8.0000e+007-8.0000e+007 to -6.0000e+007-6.0000e+007 to -4.0000e+007-4.0000e+007 to -2.0000e+007-2.0000e+007 to0.0000e+000 to2.0000e+007 to4.0000e+007 to0.0000e+0002.0000e+0074.0000e+0075.7148e+007Interval = 2.0e+007FLAC3D 3.00Step 3276 Model Perspective 12:45:03 Fri Jan 14 2011Center:Rotation: TOC o 1-5 h z X: 0.000e+000X:0.000Y: 5.000e-001Y:0.000Z: 0.000e+000Z:0.000Dist: 3.265e+000 Mag.: 1 Ang.: 22.500Plane Origin:X: 0.000e+000Y: 5.000e-0