低渗透裂缝性油藏弱凝胶调剖实验研究

发布时间：2018-08-20 12:48

【摘要】：低渗透裂缝性油藏由于储层物性差、裂缝发育,具有基质-裂缝双重介质特征,需进行压裂改造才能获得较理想的产量和经济效益。而裂缝的存在使得水驱开发过程中,油井含水上升快、无效注水严重,甚至出现暴性水淹,水驱开发矛盾突出、油藏采出程度低。XF油田油层平均温度60℃、地层水矿化度60345 mg/L;储层裂缝发育,最大开启宽度达到2 mm,多在0.2~1.0 mm,导致油井含水上升快,出现暴性水淹现象。目前,XF油田现场已开展了大规模的弱凝胶调剖增产措施,并取得了重要成果,部分油井出水问题有所缓解。此外,还有部分层段水淹状况仍未得到明显改善,调剖效果较差。目前室内实验对调剖剂的评价模型,多采用多孔介质物理模型,或是简单人造裂缝模型。这样,模型模拟油藏的相似程度较低、裂缝参数量化困难、基质-裂缝双重介质模型调剖改善后效果不能充分体现等问题。为此,本文针对油田实际,首先对现场使用的弱凝胶调剖体系性能效果进行评价,包括剪切作用、矿化度、老化作用以及溶胀作用对弱凝胶性能影响;然后重点开展了以油藏相似性准则为基础的物理模型设计与研究,利用自主研发能够实现裂缝参数可调、裂缝与基质分流、模拟程度高、模型可重复利用、操作简便的低渗透裂缝性油藏调剖物理模型,研究了包括裂缝宽度、裂缝面积以及裂缝形状等裂缝参数对弱凝胶封堵性能影响;并通过驱油试验给出影响裂缝性油藏水驱采出程度低的主要原因和相应的改善途径。弱凝胶体系性能评价结果表明,弱凝胶体系中聚合物HPAM分子受到剪切作用后相对分子质量及视黏度均随聚合物质量浓度的增加减小幅度降低;未剪切弱凝胶体系老化180 d后视黏度仍高于28000 mPa·s,剪切后和矿化度高的弱凝胶在老化25 d后出现脱水现象,弱凝胶强度和稳定性下降;溶胀作用使胶体膨胀吸水,弱凝胶强度下降。弱凝胶在裂缝物理模型中的驱替试验结果表明,弱凝胶封堵强度随裂缝宽度的增大而减小,根据其封堵作用强弱,临界裂缝宽度为0.69 mm;弱凝胶在不同裂缝宽度条件下封堵机理不同,当裂缝宽度小于临界宽度0.69 mm时,弱凝胶封堵裂缝能力在自身黏性较大的基础上,主要是弱凝胶体系的弹性作用,提高了体系的封堵强度;而大于临界宽度时,弱凝胶封堵裂缝主要依靠自身黏性或弱凝胶内摩擦力来增加后续水流动阻力,从而提高注水压力,但压力提高幅度不大;裂缝宽度为0.43 mm时,弱凝胶封堵能力与裂缝面积呈正相关关系,单位裂缝面积内的封堵压力相同;在形状不同的裂缝中,弱凝胶对直缝的封堵能力最差,而随着裂缝形状的复杂化,弱凝胶与裂缝间的受力关系复杂化,弱凝胶封堵裂缝强度是其与裂缝间的附着力和弹力的综合表现;静态条件下有利于聚合物吸附于介质表面,形成的弱凝胶附着力高、封堵强度高,而无附着力时弱凝胶的封堵能力下降幅度高达35倍;随着裂缝宽度的增加,弱凝胶的封堵能力降低、基质中的分液量降低,同时后续注入水发生绕而流形成的死油区增大,后续注入水的波及效率由100%降低至67.84%,综合采收率由43.91%下降至29.28%,弱凝胶封堵较宽裂缝的强度低是后续注入水发生绕流导致波及效率降低的原因;弱凝胶在0.43 mm裂缝中的封堵强度较高,随着基质渗透率的增加,基质吸水量增加,岩心波及效率高接近100%,而驱油效率不同导致了渗透率为0.1~1.0×10-3μm2综合采收率不同;弱凝胶-预凝胶颗粒复合体系能够有效提高弱凝胶对较宽裂缝的封堵能力,降低了后续水发生绕流的可能性,使得裂缝宽度为0.98 mm时,综合采收率由29.28%上升至42.35%。
[Abstract]:The low permeability fractured reservoir is characterized by poor reservoir physical property, well developed fractures and dual media of matrix and fracture, so it is necessary to carry out fracturing transformation to obtain ideal production and economic benefits. The average reservoir temperature in XF oilfield is 60 C and the salinity of formation water is 60345 mg/L. The maximum opening width is 2 mm, mostly from 0.2 mm to 1.0 mm, which leads to rapid increase of water cut and sudden flooding. As a result, the water production problem of some oil wells has been alleviated. In addition, the water flooding condition of some sections has not been improved obviously, and the profile control effect is poor. For this reason, in view of the actual situation in the oilfield, this paper firstly evaluates the performance of the weak gel profile control system used in the field, including shearing, salinity, aging and swelling effects on the weak gel properties; and then focuses on the development of the weak gel properties. Physical model design and research based on reservoir similarity criterion can realize adjustable fracture parameters, fracture and matrix splitting, high degree of simulation, model reusable, easy to operate low permeability fractured reservoir profile control physical model, including fracture width, fracture area and fracture shape and other fracture parameters. The results show that the relative molecular mass and apparent viscosity of polymer HPAM in weak gel system depend on the polymer mass concentration after shearing. The apparent viscosity of the unshared weak gel system is still higher than 28000 mPa.s after 180 days of aging, and the weak gel after shearing and high salinity dehydrates after 25 days of aging, and the strength and stability of the weak gel decrease; swelling makes the gel swell and absorb water, and the strength of the weak gel decreases. The results show that the sealing strength of weak gel decreases with the increase of fracture width, and the critical fracture width is 0.69 mm according to its sealing effect. The sealing mechanism of weak gel is different under different fracture width conditions. It is mainly due to the elastic effect of weak gel system, which improves the plugging strength of the system; when the width of the fracture is larger than the critical width, weak gel plugging cracks mainly rely on its own viscosity or weak gel internal friction to increase the flow resistance of subsequent water, thus increasing the injection pressure, but the pressure increases little; when the width of the fracture is 0.43 mm, weak gel plugging capacity and Fracture area is positively correlated, and the sealing pressure is the same in the unit fracture area; among the cracks with different shapes, weak gel has the worst sealing ability to the straight crack. With the complication of fracture shape, the force relationship between weak gel and crack is complicated, and the strength of weak gel sealing crack is the combination of adhesion and elasticity between weak gel and crack. The results show that under static conditions, the weak gel formed by polymer adsorbing on the surface of the medium has high adhesion and sealing strength, but without adhesion, the sealing ability of the weak gel decreases as much as 35 times; with the increase of crack width, the sealing ability of the weak gel decreases, the amount of liquid separation in the matrix decreases, and the subsequent injection water flows around and flows. With the increase of dead zone, sweep efficiency of subsequent injection water decreased from 100% to 67.84%, and comprehensive recovery decreased from 43.91% to 29.28%. The low strength of weak gel plugging wider fractures is the reason of sweep efficiency reduction caused by flow around subsequent injection water; the sealing strength of weak gel in 0.43 mm fracture is higher, with the increase of matrix permeability. Additionally, the matrix water absorption increases, and the core sweep efficiency is nearly 100%. The different displacement efficiency results in the different comprehensive recovery of 0.1-1.0 *10-3 micron 2. Weak gel-pre-gel particle composite system can effectively improve the sealing ability of weak gel to wider fractures, reduce the possibility of subsequent water flow around, and make the fracture width 0.1-1.0 *10-3 micron 2. .98 mm, the comprehensive recovery increased from 29.28% to 42.35%.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE348

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