【作者】 张涛；

【导师】 王德民；

【作者基本信息】 大庆石油学院 ， 油气田开发工程， 2009， 博士

【摘要】 低渗透砂岩储层具有巨大的资源潜力和相对较大的勘探与开发难度。储层渗透率低,自然能量不充足,靠自然能量开采,弹性能量衰竭快,开发水平低。为提高低渗透油田的开发水平,注入气、水向地层补充能量驱替开采是一种自然的思路。但注水压力较高,有些渗透率低的地层注水压力甚至超过地层破裂压力,注水困难;而且注水成本高,渗透率降低严重。注气与注水相比,气体粘度低,与原油粘度相差更大,在地层中更容易发生窜槽等现象。因此本文研究了适合低渗透油藏开发的一种新型驱替方法,即气驱的同时点滴注入水、表面活性水,通过控制气驱点滴体系的气液比以达到形成不同的渗流阻力。不同的渗流阻力注入体系,可以针对不同的低渗透率地层进行注入开发,这种新型驱替方法可以弥补气驱注入波及体积小,指进现象严重,发生气窜现象,阶段采收率低等缺点;可以弥补水驱注入压力高,注入困难等缺点。本文的研究成果不仅加深了解低渗透油藏的开发理论、渗流力学理论,而且对于实际指导低渗透油藏开发、提高低渗透油藏采收率有重大的的学术理论意义和工程实际应用意义。全文的研究共分四个部分,下面分别作简要叙述:1、气驱驱油机理和气驱驱替压力梯度低于水驱的原因研究本部分进行了气驱的驱油机理理论研究。对CO₂,N₂,烃类气体的提高采收率机理进行了剖析,分析了这几种气体在油藏中发生的物理化学变化,并分析气体在油藏中发生混相或非混相的原因和对提高采收率贡献的结果。这部分还对水气交替注入的特点和开采机理作了介绍。结果指出:气体注入不发生混相驱替机理是:有限量的蒸发和抽提、降低原油粘度、原油膨胀、压力下降造成溶解气驱和降低界面张力等;发生混相的气驱主要机理是体积膨胀、粘度降低、溶解气驱、相间界面张力降低、相对渗透率的改善、和井周围地层渗透率的改善等。从气体的粘度、气体与原油的界面张力、两相渗透率的角度分析了气体驱替压力梯度小的原因。研究表明:实际油藏中N₂、CH₄、CO₂气体的粘度范围在100⁹00×10^-4mPS之间,驱替不发生混相时,N₂、CH₄、CO₂气驱流度比M远大于1,会发生粘性指进现象,使得波及系数比水驱低,因此气驱宏观压力梯度小与水驱的压力梯度;气体与原油的界面张力小于水与原油的界面张力,相同油藏,气体驱替的压力梯度更低;虽然相同饱和度下气驱的气相相对渗透率低于水驱中水相的相对渗透率,但由于水的粘度比气体粘度大10倍以上,而相对渗透率相差不过2倍左右,相同饱和度下气体比水更容易通过岩心孔道。因此气体驱替时较水驱驱替阻力更小。2、气驱点滴水/活性水改变渗流阻力室内实验以及机理研究室内研究证明:在无油岩心上,N₂驱替的同时,点滴注入水,可以增加注入相的渗流阻力。气驱点滴注入的过程中,增加点滴注入的频率,可以增加驱替相的宏观压力梯度。采用无量纲压力梯度来衡量渗流阻力的增加值时,本次实验结论:压力上升无量纲最小值在气液比为584:1时为0.103,无量纲最大上升值在气液比为102:1时为0.607;随气液比的降低,压力上升无量纲值增加。点滴频率越快,压力上升无量纲值越大,即渗流阻力越大。点滴注入活性水体系,有同样的规律,但压力上升无量纲值更大。相同点滴频率下,压力上升无量纲值为,点滴水体系小于点滴0.05wt%活性剂溶液体系,小于点滴0.1wt%活性剂溶液体系,小于点滴0.2wt%活性剂溶液体系;相同点滴浓度的体系,气液比越小,压力上升无量纲值越大。本次实验结论:在饱和油的岩心上的气驱点滴实验证明,在渗透率为15¹9×10^-3μm²的岩心上,单独注水的渗流阻力在气驱点滴0.2wt%活性剂溶液气液比为38:1和气液比32:1之间。气驱点滴水/活性水体系,通过控制气液比可以改变驱替的压力梯度,不同的压力梯度有不同的阶段采出程度,压力梯度越高,阶段采出程度越大。气驱点滴体系增加渗流阻力的机理研究表明,低渗透岩心中,气驱点滴水体系有以下特点:由于毛管力的作用产生的指向岩石壁的压力p_I所造成的摩擦力和薄膜所造成的摩擦力;非混相气体有更大气水表面张力而产生更大的阻力;当毛管中液体要运动时,会产生一个附加阻力p_II;当液珠进入到狭窄喉道时,产生第三种毛管效应附加阻力p_III。气体点滴活性水体系,同样可以产生p_II, p_III附加阻力,增大体系的渗流阻力。3、低渗透油层聚合物驱可行性研究在聚合物溶液的驱油机理研究基础上,开展了渗透率为10⁵0×10^-3μm²的岩心流动实验。实验结果证明:随着聚合物相对分子质量、聚合物浓度的增大,阻力系数和残余阻力系数增大。选择的400万和600万分子量的聚合物,浓度为600mg/L和800mg/L在10、30、50×10^-3μm²的岩心上均为发生堵塞,说明实际油藏开发时,在地层压力允许的条件下,低渗透油藏可以采用聚合物驱进行开发。4、不同驱替方法下的渗流阻力计算匹配研究从低渗透岩心的启动压力梯度方向研究表明:由水油、气油两相驱替的最大启动压力梯度,结合地层破裂压力、井距可以确定水驱、气驱适合的最低渗透率地层。适合气驱、水驱的最低渗透率范围内,确定为适合气驱点滴水/活性水驱的渗透率范围;确定方法为:通过气驱点滴不同配方的实验确定点滴体系与油的最大启动压力梯度,根据压力梯度来确定不同配方对应的渗透率范围。验证聚合物驱是否适合的方法为:根据孔隙半径与聚合物分子回旋半径的比值关系,选取适合聚合物种类;开展流动实验,选取不发生堵塞的聚合物;在上面结果上,开展不同分子量聚合物驱油启动压力实验,最后确定聚合物的种类和浓度。更多还原

【Abstract】 Low permeable sandstone reservoir has enormous reserves ,but it is more difficult to be explored and developed than nonmal reservoir. Because the low permeable sandstone reservoir has some features as follows: low permeability, lacking of natural power in reservoir, elastic energy decreasing fast when developing with natural power, low oil recovery. For enhance oil recovery of low permeable reservoir, gas or water is injected to layer to make up power of reservoir.Pressure of waterflooding is higher than breakdown pressure of stone in some lower permeable reservoir, it is not only expensive but hard to carry out water flooding. And after injection of water, the permeability went down sharply in low permeable reservoir. Compare with water flooding, it was lower viscosity of gas than water, the viscosity of gas was far from oil, so phenomenon of bypass channel happen often.This paper make a research of a new displacement technique which is gas flooding with liquid（water or surfactant solution） droping ,and it will apply to low permeable reservoir. This flooding system can chance filtrational resistance at will by adjusting gas fluid ratio. The different filtrational resistance flooding system can apply to develop different permeability reservoir, and the system can improve problems, which were small swepting volume and finger advance and lower period oil recovery, of gas flooding; it can make up both higt pressure and difficult of water flooding as well. The research result of this paper is not only to make deeply understanding of low permeable reservoirs develop theory and filtration theory, but also to have a enormous meaning of both technicality and engineering with conducting oilfield developing and enhanve oil recovery in low permeable reservoirs.There are four parts in this dissertation, brief introduce as follows:1.The mechanism of gas flooding and why pressure gradient of gas flooding is low than water flooding.This part conduct a gas flooding mechanism research. The research is about recovery of CO₂,N₂,gaseous hydrocarbon flooding, analyse physical and chemic changing of some kind gas above injecting to reservoir, and the reason and effect in oil recovery of miscible phase happen or not happen between gas and oil. This part have introduced the feature and mechanism of WAG yet. It is shown that: the mechanisms of non-miscible phase gas flooding are that limited gas evaporating and extracting from oil, decreasing oil viscosity, oil expanding, gas extracting from oil after pressure low than bubble point pressure, decreasing interfacial tension force etc. the mechanisms of miscible phase gas flooding are that volume swelling, decreasing oil viscosity, gas extracting from oil after pressure low than bubble point pressure, decreasing interfacial tension force, improving relative permeability and imprving permealility near around well etc.The gas flooding pressure gradient is low than water flooding was analysed from gas viscosity, the IFT between gas and oil, two-phase permeability. It is shown that: the viscosity spectrum of N₂、CH₄、CO₂ is 100⁹00×10^-4mPS, N₂、CH₄、CO₂ gas flooding’s mobility ratio is more than 1 when non-miscible phase happened, because of that, the sweep efficiency of gas flooding is less than water flooding, so at same reservior, the pressure gradient of gas flooding is more lower. Gas-phase’s relative permeability in gas flooding is lower than water-phase’s relative permeability in water flooding at same oil saturation, but gas is easy to go through porous channel than water at same oil saturation, because the viscosity of water is 10 times bigger than that of gas, and gas relative permeability is only 2 times smaller than that of water.2.The experiment and mechanism research on gas flooding with water/surfactant solution dropping changing filtrational resistanceThe finished experimental results, which was completed once, of non-oil saturated experiment research in room are that: N₂ gas flooding with water dropping system can increase filtrational resistance. The injecting system pressure gardient went up when increase frequency of dropping water. Use zero dimention pressure gradient to measure filtrational resistance, the least zero dimention pressure gradient is 0.103 when gas fluid ratio is 584:1, the biggest zero dimention pressure gradient is 0.607 when gas fluid ratio is 102:1. The least zero dimention pressure gradient increase by gas fluid ratio decreasing. The faster frequence of dropping, the bigger zero dimention pressure gradient increasing value. That mean more filtrational resistance were produced. It were same rules when gas flooding with dropping surfactant soultion. Moreover, it is more bigger zero dimention pressure gradient increasing value. At same dropping frequence, the zero dimention pressure gradient increasing values sorted form samll to big were that dropping water, dropping 0.05wt% surfactant solution, dropping 0.1wt% surfactant solution, dropping 0.2wt% surfactant solution. There is a rule that the samller gas fluid ratio, the bigger zero dimention pressure gradient increasing value.The results of oil saturated experiment research in room are that: experiments were taken on 15¹9×10^-3μm² artificial core. The filtrational resistance of water flooding is near same to gas flooding dropping 0.2wt% surfactant solution at gas fluid ratio between 38:1 to 32:1. The dropping system can chance filtrational resistance at will by control gas fluid ratio. There are different period oil recovery when different pressrue gradient flooding. The bigger pressure gradient, the bigger period oil recovery. The results of mechanism research of dropping system are that: at low permeable reservoir, gas flooding droping system have some feature as follows: there is a force p_I point to wall of pore,which caused by capillary force.The p_I and film of bubble can bring a friction force. Non-miscible phase gas meet water have bigger IFT, it can produce bigger resistance force. When the liquid is going to move, there is a new resistance force p_II pop up. When liquid dropping move to narrow throat, a new resistance force p_III was shown. It is same that when gas flooding with dropping surfactant solution, there are also p_II, p_III.3.Research on incresing filtrational resistance of Polymer floodingBase on flooding oil mechanism of HPAM, there are some flooding experiment on 10⁵0×10^-3μm² were carried on. It is shown that: coefficient of resistance and residual resistance factor increase by incresing polymer molecular weight or concentration. It did not block when inject 400×104 and 600×10⁴ polymer molecular weight at concentration of 600mg/L and 800mg/L to 10、30、50×10^-3μm² artificial core. So some low permeable reservoirs can flooding by HPAM.4.Research on filtrational resistance of different way flooding calculate corresponding to different permeablitity.Results of research on threshold pressure gradient of low permeability are that: Base on the biggest water-oil and gas-oil threshold pressure, breakdown pressure and distance between wells, it can be calculated that the least permeability fitting for gas or water flooding. Between gas and water flooding fitting permeability area, it fit for gas flooding with drop water or surfactant solution. The way of connect different dropping system to different permeability: To make it clear that the biggest threshold pressure gradient dropping system and oil, base on threshold pressure gradient, figure out this dropping system fit what permeability.To prove it is fitting or not that polymer flooding in different permeable reservoir: calculate the ratio of pore body radius and molecule circle round of polymer, make sure the ratio is rational, base on that to slect polymer; conduct flowing experiments, screen out non-block polymer system; after that, carry on different concentration threshold pressure gradient experiment, final figure out which polyer at how many concentration is suitable.更多还原