【作者】 刘洋；

【导师】 郭小阳；

【作者基本信息】 西南石油大学 ， 油气井工程， 2012， 博士

【摘要】 气窜是几乎所有天然气井都要面临的棘手难题。固井后的环空气窜不仅破坏层间封隔,而且影响油气田的安全勘探开发。水泥浆防气窜能力是影响早期气窜的一个重要因素。研究表明,早期气窜的实质是气体在时变性塑态多孔介质渗流的物理过程,最终导致环空带压或层间窜流。目前并没有任何经典理论描述这一时期气体在水泥浆基体内的运移规律。因此国内外学者在水泥浆防气窜能力评价研究方面遭遇瓶颈,仍停留在对水泥浆防气窜能力作粗略的定性对比分析,进行事后评估。为了形成科学的水泥浆防气窜能力综合评价方法,本文针对早期气窜,从水泥材料特性入手,提出气侵危险时间内水泥浆渗透率、静胶凝强度过渡时间、初凝前体积收缩率这三个水泥浆防气窜关键性能,并通过气窜试验、静胶凝强度试验、体积收缩试验,分析各防窜关键性能发展规律。在此基础上,考虑了气侵危险时间内水泥浆渗透率、孔隙度及顶部边界的时变性,修正了连续方程与运动方程,建立了气体层间窜流数学模型及气体窜至井口数学模型,提出了水泥浆体积收缩评价方法。最终形成了水泥浆防气窜能力综合评价方法,并在DN2-5井和DN2-7井Φ177.8mm尾管固井实践中检验了其准确性。通过室内研究与现场固井实践,得到以下结论：(1)气侵危险时间内水泥浆渗透率反映了水泥浆抗窜能力强弱,静胶凝强度过渡时间关系着气窜发生可能性及危害程度,水泥浆初凝前体积收缩将造成孔隙压力下降,它们是影响水泥浆防气窜能力的关键性能。(2)水灰比和降失水剂类型都将影响水泥浆抗窜能力。随着水灰比增加,水泥浆视渗透率上升,但启动压力变化不大。在静胶凝强度等于48Pa时,成膜类降失水剂表现出优良的抗窜能力,启动压力明显,聚合物胶粒类降失水剂次之,三元共聚物降失水剂和纤维素类降失水剂抗窜能力最差。而在静胶凝强度达到240Pa后,水泥浆抗窜能力相差不大。膨胀水泥浆主要在终凝后发生体积膨胀,对早期气窜影响很小。液硅与胶乳水泥浆体系能降低滤饼渗透性,显著提高水泥浆抗窜能力。(3)水灰比和缓凝剂是影响水泥浆静胶凝强度过渡时间的重要因素。水灰比越高,静胶凝强度过渡时间越长。缓凝剂对对静胶凝强度过渡时间也存在一定负面影响,其中以羟基羧酸类强螯合作用高温缓凝剂影响最显著。缓凝剂对静胶凝强度影响的本质原因在于缓凝剂延缓诱导后期及加速水化阶段水泥水化速率,延长水泥浆塑态时间。稠化过渡时间是水泥浆动态性能,静胶凝强度过渡时间是水泥浆静态性能,并且二者反映的不是同一水化时期水泥浆胶凝结构增长速率,没有必然联系。(4)在国内外典型水泥石体积收缩膨胀仪基础上,解决了“连续测量水泥浆(石)体积变化”、“检测水泥浆初终凝时间”、“连续测量凝结过程水泥浆孔隙压力变化”三个技术难题,研制了高温高压水泥石体积收缩膨胀仪。仪器精度较高,具备了连续测量体积收缩,检测水化放热,测量孔隙压力下降三个主要功能。(5)水灰比和膨胀剂是影响初凝前体积收缩率的重要因素。随着水灰比增大,塑性阶段时间延长,初终凝时间延迟,初凝时体积收缩率增加。晶格型膨胀剂主要通过后期的结晶作用产生结晶压,推动水泥石宏观体积膨胀,而对水泥浆早期塑性体积收缩没有明显改善作用。发气剂KQ-B在水泥浆处于塑性阶段时,通过化学发气能起到补偿水泥浆体积损耗,延缓孔隙压力下降的作用。即使在50MPa高压条件下,当发气剂KQ-B加量达到2%时依然能明显减小初凝前体积收缩,提高水泥浆防气窜能力。(6)水泥浆防气窜能力综合评价方法从气窜临界距离角度定量分析气窜危险程度,能直观反映水泥浆防气窜能力强弱。在迪那气田两口典型高压气井DN2-5井和DN2-7井Φ177.8mm尾管固井的应用表明,水泥浆防气窜能力的评价结果与固井质量解释成果、气窜检测结果一致,评价方法具备较高的准确度。更多还原

【Abstract】 Gas migration is a difficult problem with which all natural gas wells will confront. Gas migration after cementing not only leads to zonal isolation failure, but also affects safe exploration and development of oil and gas field. Gas block ability of slurry is an important factor that affects early gas channeling. Studies show that the essence of early gas migration is the the physical process of gas percolation through time-variable-plastic porous media. There is not any classical theory to describe the law of gas migration through slurry matrix. Domestic and foreign scholars encounter bottlenecks in evaluating gas block ability. The evaluation level still remains using a rough qualitative comparison to analysis gas block ability.In order to form a scientific evaluation method, basing early gas migration, studying from material properties of cement, proposed three key gas blocking properties of slurry: slurry permeability in gas kick dangerous time, SGS transition time, volume shrinkage before initial setting. Then the development of the three key gas blocking properties was analyzed by gas migration experiment, SGS experiment, volume shrinkage experiment. Basing on these analyses, gas migration model was established and slurry volume shrinkage evaluation method was proposed. At last, the accuracy of the evaluation method was examined in Φ177.8mm liner cementing in DN2-5well and DN2-7well.After laboratory research and cementing practice, following conclusions and understanding were drawn:(1) Slurry permeability in gas kick dangerous time reflects the gas blocking ability; SGS transition time affects gas kick probability; volume shrinkage causes the decrease of pore pressure. So they are the key gas blocking properties of slurry.(2) Water to cement ration and the type of fluid loss additive affect the gas blocking ability of slurry. With the increasing w/c, slurry permeability increases, but threshold pressure decreases. When the SGS is equal to48Pa, the threshold pressure of film forming fluid loss additive is the highest of all, the polymeric colloid fluid loss additive is the second, terpolymer loss additive and cellulose fluid loss additive are the lowest. But when the SGS is equal to240Pa, the gas blocking ability of6type fluid loss additive has a little difference. The volume expansion of expanding cement happens after final set, which has little relation with early gas migration. The liquid silicone and latex slurry system can reduce the cake permeability and significantly improve the gas blocking ability of slurry.(3) Water to cement ratio and retarder are important factors which affcet the SGS transition time. The higher the water-cement ratio is, the longer the SGS transition time will be. Retarder has some negative impact on SGS transition time. The hydroxycarboxylic acid high temperature retarder has more significant negative impact on SGS transition time. The nature reason of the impact of retarder on SGS time is that the retarder slows the cement hydrationrate which extends the plastic state time of slurry. Thickening time is a dynamic property of slurry, while SGS transition time is static property of slurry. The two do not rmeflect the SGS increasing in same hydrating time and have no direct relation.(4) Basing on the home and abroad cement shrinkage/expansion device, three problem "continuous measurement of the cement volume change","test of cement initial set and final set","continuous measurement of cement pore pressure change" were solved, the high temperature high pressure cement shrinkage/expansion device was developed. The high accuracy device has functions of continuous measurement of the cement volume change, test of hydrating thermal discharge, test of cement pore pressure change.(5) Water to cement ratio and expanding agent are important factors which affect the volume shrinkage before initial set. With the increase of water to cement ratio, the plastic stage time extends, the initial set and final set prolongs, the volume shrinkage before initial set increase. Lattice type expanding agent promotes cement to expand by crystallization pressure through later stage crystallization, which can’t improve early cement shrinkage. Gassing agent KQ-B can compensate cement volume decrease by chemical gassing, delay pore pressure decrease, when the slurry is in plastic stage. Even pressure is50MPa, Gassing agent KQ-B can significantly reduce the cement volume shrinkage before initial set and increase the gas blocking ability, when the dosage of KQ-B is more than2%.(6) Cement practice in two typical high pressure gas DN2-5well and DN2-7well Φ177.8mm liner cementing showed that the forecast results of slurry gas blocking ability coincided with the log interpretation and gas leakage test. The accuracy of comprehensive gas blocking ability evaluation method is high.更多还原