气田污水处理回注系统腐蚀机理与防护对策研究

1、长庆油田分公司科技攻关项目汇报材料气田污水处理回注系统腐蚀机理与防护对策研究2007年12月编写：校对： 审核： 参加人员： 2007年12月目 录前 言·····································&

2、#183;·················································&

3、#183;·······························1第一章 靖边气田污水处理系统存在的主要故障··············

4、83;··································21 靖边气田回注污水的处理工艺及现状············&#

5、183;··············································2 1.1 净化厂回注污水的处理工艺及现

6、状··················································

7、;········2 1.2 北二区、南二区回注污水的处理工艺及现状·····································

8、3;······32 污水的处理系统存在的主要故障·········································

9、;··························4 2.1 污水处理和回注系统存在严重的腐蚀现象····················

10、;··························4 2.2 污水处理和回注系统存在严重的结垢现象····················

11、;··························6 2.3 污水中微生物的大量繁殖·····················

12、··················································

13、···6 2.4 污水处理系统出水水质不合格············································

14、;······················63 小结···························

15、··················································

16、······································6第二章 气田污水处理系统回注污水的腐蚀机理及影响因素分析·······&

17、#183;·············81 气田采气工艺特点及污水的水质特点·································

18、··························8 1.1 采气工艺流程······················

19、··················································

20、······················8 1.2 第一采气厂天然气气体组成·························

21、·············································8 1.3 气田污水的组成性质分析··&

22、#183;·················································&

23、#183;·····················8 1.3.1 水质分析··························&

24、#183;·················································&

25、#183;······················8 1.3.2 污水处理系统出水（回注污水）中悬浮物粒径分布······················&

26、#183;······102 第二净化厂回注污水管线附着物组成分析·······································

27、83;·········113 腐蚀倾向的判断······································

28、3;·················································

29、3;····124 污水处理系统腐蚀因素及腐蚀机理··········································

30、83;··················12 4.1 H2S和CO2的腐蚀作用····························&#

31、183;·················································&#

32、183;12 4.1.1 硫化氢腐蚀···············································

33、··············································12 4.1.2 二氧化碳的腐蚀·&#

34、183;·················································&#

35、183;·································14 4.2 溶解氧的腐蚀作用··············

36、;··················································

37、;····················15 4.3 细菌的腐蚀作用···························

38、83;·················································

39、83;··········15 4.4 溶解氧引起的腐蚀·····································

40、···············································165 气田污水处理及回注污水的腐蚀

41、影响因素的研究·····································17 5.1 矿化度对不含醇污水的腐蚀影响········&#

42、183;·················································&#

43、183;·17 5.2 pH值对不含醇污水的腐蚀影响·············································

44、;·················18 5.3 H2S含量对不含醇污水的腐蚀影响·····························

45、·····························19 5.4 CO2含量对不含醇污水的腐蚀影响·················&

46、#183;·······································21 5.5 四种回注污水的腐蚀规律研究·······

47、;··················································

48、;·······216 小结··········································

49、;··················································

50、;·····················23第三章 第一采气厂污水处理及回注系统腐蚀控制方法及耐蚀金属材料、缓蚀 剂的的选择与性能评价·····················

51、··················································

52、····24第一部分 控制腐蚀的方法···········································

53、3;·······································241 控制腐蚀的关键环节········

54、83;·················································

55、83;··························242 腐蚀的控制技术·····················

56、3;·················································

57、3;·····················25 2.1 合理的设计··························

58、3;·················································

59、3;···················25 2.2 正确选用金属材料····························&

60、#183;·················································&

61、#183;·····25 2.3 改变腐蚀环境··········································

62、··················································

63、25 2.4 电化学保护················································

64、················································26 2.5 用耐腐蚀非

65、金属材料代替金属材料················································&#

66、183;·······26 2.6 采用耐腐蚀覆盖层········································

67、;············································26 2.7 使用化学药剂···

68、3;·················································

69、3;······································273 小结··········

70、3;·················································

71、3;·················································

72、3;··27第二部分 气田污水处理及回注系统耐蚀金属材料的选择与性能评价···········271 气田回注系统耐腐蚀材质的选择····························&#

73、183;····································27 1.1 超高强度油井管···········

74、··················································

75、···························27 1.2 高压套管·····················&

76、#183;·················································&

77、#183;····························28 1.3 防腐蚀套管···················&

78、#183;·················································&

79、#183;······················28 1.4 特殊螺纹油井管·························

80、;··················································

81、;·············28 1.5 连续管···································&

82、#183;·················································&

83、#183;··················28 1.6 膨胀管·····························

84、83;·················································

85、83;························29 1.7 抗CO2腐蚀油井管·······················

86、;··················································

87、;············29 1.8 不锈钢系列····································

88、;··················································

89、;··········292 气田回注污水耐腐蚀材质的性能评价····································

90、83;····················303 小结····························

91、83;·················································

92、83;··································30第三部分 缓蚀剂的筛选及性能评价············

93、83;·················································

94、83;····311 缓蚀剂的选择及作用机理···········································

95、··································312 缓蚀剂的筛选及性能评价·············

96、83;·················································

97、83;·············32 2.1 静态挂片缓蚀试验··································

98、··················································

99、32 2.2 静态酸性缓蚀试验···············································

100、83;····································33 2.3 动态挂片缓蚀试验···········

101、··················································

102、·······················34 2.4 缓蚀剂加药量与缓蚀率的关系·······················

103、3;········································34 2.5 缓蚀剂不同温度下的缓蚀性能······&#

104、183;·················································&#

105、183;·······34 2.6 模拟现场动态腐蚀试验·······································

106、83;····································353 细菌腐蚀的控制···········

107、3;·················································

108、3;·······························36 3.1 油田细菌腐蚀的危害················

109、··················································

110、··············36 3.2 杀菌剂评价方法·································

111、3;·················································

112、3;····36 3.2.1 镜检法···········································

113、3;·················································

114、3;·······36 3.2.2 标准平皿计数法········································

115、·············································36 3.2.3 液体稀释法··

116、3;·················································

117、3;········································36 3.3 杀菌剂WT-809的杀菌效果······&

118、#183;·················································&

119、#183;·············374 缓蚀剂、杀菌剂的配伍性能·································

120、83;·········································375 小结·······

121、83;·················································

122、83;·················································

123、83;·····38第四章 气田回注污水处理系统的防腐处理方法和工艺流程研究···················391 气田回注污水处理系统防腐处理方法的确定················

124、3;····························392 气田回注污水处理系统工艺流程的确定··················&

125、#183;··································40第五章 结论··············

126、;··················································

127、;···········································41前 言随着靖边气田的逐步开发，局部区块开始产出地层水，气田污水总量在逐渐增大，

128、不含醇污水量也越来越大，造成目前的污水处理工艺和处理能力已不能满足生产需要，严重影响了气田的正常生产和富水区中的储量动用，增加了气田生产组织难度。随着开发规模的扩大及富水区块的全面开发，产水井、产水量会不断增加，产水井的合理开发和污水拉运、处理之间的矛盾将更加突出。靖边气田的主力气层为下古奥陶系马家沟组，该产层在局部区块产出地层水。通过长期动态监测，结合静态分析，认为目前整个气田范围内存在北二区、陕5井区、陕93井区和陕181井区四个产水区，另外还有32个产水井点。目前水体面积738.05km2，投产井中有48口产出地层水，占靖边气田投产井总数的20.48%，所产污水约占气田污水总量的60%以

129、上。目前采气一厂建成的气田污水（设计）处理能力为700 m3/d，分为含醇污水处理和不含醇污水处理两种工艺，其中气田含醇污水设计处理能力300 m3/d，气田不含醇污水设计处理能力400 m3/d。含醇污水处理系统包括污水预处理、甲醇回收、污水回灌等处理单元，第一采气厂含醇污水处理装置主要建在三座天然气净化厂内，其中甲醇再生装置是含醇污水处理的关键设备，目前共有4套装置。不含醇污水处理系统主要建在靖边气田两个较大的富水区，即南二区和北二区。产出污水，连同生产污水、检修污水、循环水排污水等经过处理后，回注地下， 由于天然气产出污水中溶解有高浓度的CO2、H2S等腐蚀性气体，而且常含有大量的矿物质

130、、悬浮物、机械性杂质及乳化油、烃类气体等。使污水具有较强腐蚀性和较易结垢倾向性。靖边气田污水的水质特点决定了其对金属设备和管线具有很强的腐蚀性。使污水处理和回注系统长时间存在腐蚀、细菌滋生、出水固悬物超标等问题，导致污水处理及回注系统管线及油套管多处腐蚀穿孔，影响了生产的正常进行。 为解决这一长期存在的问题，经过大量的实验室研究，并根据我们对同类系统研究和处理的经验，确定出了适宜的污水处理方案和配套的化学助剂。第一章 靖边气田污水处理系统存在的主要故障靖边气田含油含醇污水由于吸收天然气中的CO2、H2S等组分而显酸性，而且常含有大量的矿物质、悬浮物、机械性杂质及乳化油等，再加上在天然气开采过程

131、中为了减缓腐蚀及防止水合物的生成，人们在井筒和地面管线中定期注入一定量的组成较为复杂的化学药剂和甲醇，这就使得采出污水成为一个含醇、含盐、含油、含大量机械杂质、呈酸性的具有较强腐蚀性和较易结垢的复杂且稳定的体系。根据结垢理论分析和预测，这种水系统在常温常压下已有结垢趋势存在，在甲醇回收过程中，随着温度的增加，其结垢趋势将进一步增加。所以气田含油含醇污水在高温下有严重的结垢趋势存在，在甲醇回收处理过程中会产生大量结垢，从而使甲醇回收装置中换热器管程和精馏塔陶瓷波纹板填料中产生严重的结垢堵塞，同时水中大量的机杂和乳化油的沉积会进一步加剧管程和精馏塔陶瓷波纹板填料堵塞，影响甲醇回收装置处理效率和处理

132、能力。另外，由于气田污水矿化度和Cl-离子含量很高、且pH值较低，同时还溶解有一定量的CO2、H2S等腐蚀性气体和大量的乳化油存在，使这种气田含醇污水对管线和设备等具有很强的腐蚀性。1. 靖边气田回注污水的处理工艺及现状1.1净化厂回注污水的处理工艺及现状净化厂的回注污水主要包括生产污水、检修污水、循环水排污、锅炉房排污、甲醇回收单元塔底水及生活污水；生活污水、生产污水和检修污水经核桃壳过滤器处理，循环水排污、锅炉房排污及甲醇回收单元塔底水（又称混合污水）经纤维球过滤器处理；处理后的各种污水在调节罐混合，然后由回注泵回注到地层。图1 第一净化厂回注污水处理工艺流程图2 第二净化厂回注污水处理工

133、艺流程1.2 北二区、南二区回注污水的处理工艺及现状北二区共有产水井数21口，目前正常生产产水井数18口，井筒积液井数3口。随着井网的不断完善，2004年后该井区水气比降低并趋于稳定，平均日产气量3.5863×104m3 ，平均日产水量9.891m3，累计产气10.0079×108m3，累计产水18.664 ×108m3。北二区在运行过程中，日均处理水量84m3，回注压力为9.80Mpa。其污水回注处理工艺流程为：来水 à 大罐沉淀 à 组合过滤器 à 回注地层。南二区共有产水井数14口，目前正常生产产水井数9口，井筒积液井数5口。到

134、2003年后该井区内井网逐渐完善，产水气井增多，水气比趋于稳定，目前平均日产气量3.3674×104m3 ，平均日产水量6.732m3，累计产气量8.8378×108m3 ，累计产水量7.090 ×104m3。南二区在运行过程中，日均处理水量245m3，回注压力为9.30MPa。其污水回注处理工艺流程为：来水 à 大罐沉淀 à 组合过滤器 à 回注地层。第一净化厂的污水处理单元及处理量见表1。表1 第一采气厂气田污水处理系统建设情况2000150199710024020005020011002001100408200350200350

135、2004200/2402003200/2402 污水处理系统存在的主要故障2.1 污水处理和回注系统存在严重的腐蚀现象图3 第一净化厂回注井油管腐蚀情况图4 第二净化厂回注井油管腐蚀情况无论是一净、二净，还是北二区、南二区污水处理系统，均存在着严重的腐蚀现象，其中一净污水处理系统回注管线腐蚀相对较轻，金属表面覆盖一层黄色的铁锈（见图3所示）；二净污水处理系统腐蚀严重，管线局部出现腐蚀穿孔的现象，金属表面覆盖厚厚一层黑色腐蚀产物（见图4所示）。图5 北二区回注井油管腐蚀情况图6 南二区回注井油管腐蚀情况北二区污水处理和回注系统存在严重腐蚀现象，有些污水回注管线中出现了腐蚀孔洞现象，管壁表面覆盖一

136、层均匀、黑色的腐蚀产物（北二区污水处理及回注系统腐蚀情况见图5所示）；南二区污水处理及回注系统腐蚀现象相对较轻，未出现腐蚀穿孔（洞）现象，管线表面覆盖一层黄色、均匀铁锈（南二区污水处理及回注系统腐蚀情况见图6所示）。2.2 污水处理和回注系统存在严重的结垢现象 污水对金属管线的严重腐蚀，使金属表面附着厚厚一层腐蚀产物形成的锈垢。这些锈垢在金属表面的附着，一方面容易产生垢下腐蚀（局部腐蚀）、为硫酸盐还原菌的繁殖提供了场所，进一步促进局部腐蚀的发生；另一方面，锈垢的严重附着，使得污水回注管线的有效管径缩小，降低了污水回注时的有限通量。2.3 污水中微生物的大量繁殖 气田产出水中含有大量的有机质、硫

137、酸根、硫等杂质，并处于无氧的水质环境，为硫酸盐还原菌提供了良好的孳生环境和充足的营养源。使污水中硫酸盐还原菌大量孳生。2.4 污水处理系统出水水质不合格 一净、二净污水处理系统采用了较为完善的净化处理工艺，出水（回注污水）中悬浮物相对较低、水较清只是腐蚀严重，再加上含油量较高（尤其一净污水），在回注水中含有一些黑色的悬浮物；北二区、南二区污水处理系统由于只采用了相对简单的处理工艺，出水（回注污水）水质相对较差，悬浮物、浊度较高，水呈半透明或不透明，其中南二区呈土黄色。 污水中溶解高浓度的H2S气体，有明显的硫化氢气味。这种气体的存在，大大增加了污水对金属的腐蚀。3 小结污水处理系统中主要存在以

138、下故障：1）严重的腐蚀。在一净、二净及北二区、南二区污水处理及回注系统中主要存在金属腐蚀故障，严重的部位出现了腐蚀穿孔、洞的现象。妨碍了泵系统正常运行。2）腐蚀产物的严重附着，在污水回注管线上附着一层厚厚的锈垢。3）污水水质的特殊性及特殊的水质环境，为硫酸盐还原菌的大量孳生提供了所需的营养和繁殖场所，使污水中硫酸盐还原菌大量孳生。第二章 气田污水处理系统回注污水的腐蚀机理及影响因素分析1 气田采气工艺特点及气田污水的水质特点1.1 采气工艺流程靖边气田开发初期，总体认为是无水气藏、丰度较低，气田采取的是高压集气、集中注醇、污水集中处理等配套工艺。随着气田的大面积开发和产能的大幅度提高，气田产出

139、污水总量逐渐增大，不含醇污水量也越来越大。天然气中常伴有CO2、H2S等腐蚀性气体，这些伴生气溶解在产出污水中，使产出污水水质更加复杂，呈严重腐蚀性水质。1.2 第一采气厂天然气气体组成 表2 第一采气厂天然气的组成从表中天然气气体组成可以看出：天然气中含有大量的H2S和CO2气体，使得采气产出水中含有高浓度H2S和CO2气体等溶解性气体。这是污水处理系统腐蚀的主要原因。1.3 气田污水的组成性质分析 水质分析经过现场取样进行详细分析测试，得出一净、二净、南二区、北二区回注污水中各种离子含量的分析结果见表3。从表中四种水样的离子组成性质可以看出：1）净化厂污水中有溶解状的CO2、H2S气体，散

140、发出明显的硫化氢气味；污水pH值较低污水，呈微酸性。2）净化厂回注污水中钡、锶离子含量较高，钙、镁、铁、HCO3-离子含量相对较低；北二区、南二区中钡、锶离子含量更高，钙、镁、铁、HCO3-离子含量相对较高。 3）于气田污水矿化度和Cl-离子含量很高。4）一净污水中含有少量黑色悬浮固体（FeS），二净污水中含有大量黑色悬浮固体（FeS）；南二区回注污水发黄（Fe3+），不透明；北二区滤后回注水较清；另外，回注污水中含有较高浓度的悬浮物和油污，其中，北二区和南二区污水中悬浮物很高，而一净和北二区回注污水中油污含量很高。 5）四种污水均属于氯化钙型。表3 气田回注污水的离子含量分析结果分析项目一净

141、二净南二区北二区含量(mg/L)含量(mg/L)含量(mg/L)含量(mg/L)阳离子K+ + Na+4072.915358.2834776.7416154.61Ca2+835.01957.801601.482357.67Mg2+268.13208.541191.68491.57Ba+Sr13843.5113464.8158571.9448894.10Fe13.1612.98459.22633.79阴离子Cl-15421.2817379.5455565.57115537.22SO42-0.00.00.00.0CO32-0.00.00.00.0HCO3-455.49234.65215.32325

142、.74OH-0.00.00.00.0其他总矿化度34909.4937606.60151981.96183859.18悬浮固体21.7527160.5292含油量57.84.555.261640气味硫化氢味硫化氢味硫化氢味硫化氢味水型CaCl2型CaCl2型CaCl2型CaCl2型透明度半透明半透明不透明半透明外观水较清，有少量黑色悬浮物水较清，有大量黑色悬浮物水发黄水清pH值6.06.55.55.5根据对四种回注污水的水质分析和理论计算，这些污水具有很强的腐蚀倾向；在处理及回注过程中，会对金属设备和管线产生严重的腐蚀；这些污水中暂硬成垢离子（CO32-、HCO3-等）较高，而永硬成垢离子（SO

143、42-等）低，在微酸性水质条件下产生硬垢的结垢倾向很小。但由于腐蚀产物、油污、悬浮物等的存在，会在污水处理和回注系统的金属管线上产生一层厚厚的附着物，促进微生物的大量繁殖和垢下腐蚀的产生。 污水处理系统出水（回注污水）中悬浮物粒径分布图7 第一净化厂回注污水中悬浮颗粒物的粒径分布曲线图8 第二净化厂回注污水中悬浮颗粒物的粒径分布曲线图9 南二区回注污水中悬浮颗粒物的粒径分布曲线图10 北二区回注污水中悬浮颗粒物的粒径分布曲线通过对回注污水中悬浮物粒径分布（分布图见图7-图10所示）可以看出：1）一净、二净污水中悬浮固体的粒径相对较大，大于10m的占绝大多数（体积百分含量70%），说明这种污水中

144、的悬浮颗粒易于去除，不会对地层造成伤害。2）南二区、北二区污水中悬浮固体的粒径相对较小，小于10m的占绝大多数（体积百分含量70%），说明这种污水中的悬浮颗粒不易去除，必须借助其他的方法进行去除，如果不经过处理就直接回注地层，可定会堵筛地层喉道，造成注水压力升高，增加污水回注难度和成本。2 第二净化厂回注污水管线附着物组成分析第二净化厂的回注污水管线外壁黏附一层厚厚的黑色物，并且从上到下有5根管线外壁都有。对5根管线上的黑色附着物通过化学容量法进行垢样的离子组成分析，并通过-衍射分析垢样的类型。垢样的离子组成分析结果见表4，垢样的垢型分析结果见表5。表4 二净回注管线垢样离子组成分析结果分析项

145、目井筒1井筒2井筒3井筒4井筒5110减量4.635.655.155.234.88550灼烧减量22.6825.0325.927.0336.38930灼烧减量25.7829.2327.7830.339.78酸不溶物4.234.153.952.722.53铁离子的含量42.5248.9140.8744.3745.20钙离子的含量2.761.664.422.210.0镁离子的含量1.560.630.300.740.60硫酸根离子的含量0.700.863.271.302.65硫酸钡的含量0.00.00.00.1250.14表5 二净回注管线垢样垢型分析结果分析项目井筒1井筒2井筒3井筒4井筒5CaC

146、O322.018.2126.3421.80SiO26.129.457.119.675.59Fe9S837.3748.13417.6739.7661.68FeCO330.839.82FeFe2O49.48Fe2O38.2416.0117.49FeO(OH)13.6724.7330.8312.7515.25从表中分析结果可以得出：1）附着物中含有大量多硫化物、碳酸铁、碳酸钙（合量大于50）；2）附着物中含有硫化亚铁，用酸处理时有硫化氢气味；3）垢样中硫酸盐含量较少；4）附着中钙、镁离子含量较少，铁离子含量较多；5）垢样中几乎不含硫酸钡。通过对污水回注管线表面附着物组成的分析，可以看出净化厂污水处理和回注系统中主要存在着H2S-CO2-H2O体系对金属材质的腐蚀，附着物以腐蚀产物为主，成垢离子结晶析出形成的硬垢较少，这与对污水水质的分析及过相吻合。3 腐蚀倾向的判定 对靖边气田污