Syntheses and properties of associative acrylamide copolymers containing short hydrophobic chains used in a friction reducer for slick-water fracturing

Two allyldimethylalkyl quaternary ammonium salt(AQAS)monomers,N,N-dimethylallylphenylpropylammonium bromide(AQAS1)and N,N-dimethylallylnonylammonium bromide(AQAS2),were synthesized and used to prepare modified polyacrylamide materials.Two new drag reducers were synthesized from acrylamide(AM),sodium acrylate(Na AA)and a cationic modified monomer(AQAS1 or AQAS2)via aqueous solution polymerization,and the copolymers were named P(AM/Na AA/AQAS1)and P(AM/Na AA/AQAS2),respectively.The structures of the drag reduction agents were confirmed by IR and1H NMR spectroscopies.The molecular weight(Mw)of P(AM/Na AA/AQAS1)was 1.79×10^(6)g/mol.When the copolymer concentration was 1000 mg/L and the flow rate was 45 L/min,in fresh water the highest drag reduction rate was 75.8%,in 10,000 mg/L Na Cl solution the drag reduction rate decreased to 72.9%.The molecular weight of P(AM/Na AA/AQAS2)was 3.17×10^(6)g/mol.When the copolymer concentration was500 mg/L and the flow rate was 45 L/min,the drag reduction rate reached 75.2%,and in 10,000 mg/L Na Cl solution the drag reduction rate was 73.3%,decreased by approximately 1.9%.The drag reduction rate for partially hydrolyzed polyacrylamide(HPAM)was also investigated,and the results showed that the drag reduction rates for 500 and 1000 mg/L HPAM solutions were merely 43.2%and 49.0%in brine,respectively.Compared with HPAM,both of the above copolymers presented better drag reduction capacities.

Research and Application of an Environmental-Friendly Low-Damage and High Salt-Resistance Slick Water Fracturing Fluid System

The Sulige gas field is a typical low-pressure low-permeability tight sandstone gas reservoir. The reservoir has poor seepage capacity, strong heterogeneity, high mineralization of formation water and extremely scarce water resources on the site. These unfavorable factors have brought great difficulties to the on-site mining process. Now, a nano-composite green environmental protection slick water fracturing fluid system CQFR can be quickly dissolved because of the larger specific surface area, and the small molecular size makes the damage to the reservoir less than 5%, and the average drag reduction effect can reach more than 73%. It can quickly and well dissolve and maintain performance under high salinity conditions and fracturing flowback fluids. It responds well to the complex reservoir conditions on the construction site and makes the flowback fluid recyable, which greatly reduces the consumption of water resources on the construction site and effectively improves the construction efficiency and economic benefits.

Adsorption damage and control measures of slick-water fracturing fluid in shale reservoirs

The slick-water polymer adsorption damage and control measures in shale were examined using a shale pack model of the Ordovician Wufeng Formation–Silurian Longmaxi Formation in the Changning block of the Sichuan Basin. The adsorption law of slick water under different displacement time, concentrations, p H values and temperatures of polymer were tested by traditional displacement experiment and UV-Vis spectrophotometer. The adsorption equilibrium time was 150 min, the amount of adsorption was proportional to the concentration of the polymer, and the maximum adsorption concentration was 1 800 mg/L. With the increase of p H value, the adsorption capacity decreased gradually, the adsorption capacity increased first and then decreased with the increase of temperature, and the adsorption capacity was the largest at 45 ?C. The adsorption patterns of polymers on shale were described by scanning electron microscopy and magnetic resonance imaging. It is proved that the adsorption of polymer on shale led to the destruction of the network structure of anionic polyacrylamide molecules, and the shale adsorption conformation was characterized qualitatively. Finally, according to the adsorption law and adsorption mechanism, it is proposed to reduce the adsorption quantity of polymer on shale surface by using hydrogen bond destruction agent. The effects of hydrogen bond destruction on four kinds of strong electronegative small molecules were compared, the hydrogen bond destroyer c was the best, which lowered the adsorption capacity by 5.49 mg/g and recovered permeability to 73.2%. The research results provide a reference for the optimization of construction parameters and the improvement of slickwater liquid system.

Numerical Study of Oil Pollution on Sea Waters

This paper adopted an upstream FEM of 2-D unsteady flow to calculate the tidal flow in Zhoushan sea area. Based on the verification of the tidal current and environmental situation, the effects of the oily waste discharged from the oil berths on water quality have been calculated with a similar method. The isodilutions of oil pollutant are drawn from different sewage discharges. The moving loci of the slick centrepoint of oil spill have been calculated. The spreading area of the oil spill has also been forecasted. The results indicate that the set of models can predict the transport of oil spill in the sea area with reasonable accuracy.

压裂复杂裂缝中支撑剂输送数值模拟研究

在非常规储层水力压裂施工过程中,水力裂缝容易与天然裂缝交汇形成复杂裂缝,支撑剂的运移和铺置形态直接决定了储层的增产效果。为了研究支撑剂在复杂裂缝中的铺置规律,基于欧拉-欧拉方法建立了支撑剂-压裂液两相流数学模型,并利用复杂裂缝室内实验装置与数值模拟的砂堤铺置形态对比的方式进行了模型验证,结果表明,选取的模型可用于研究滑溜水在复杂裂缝内的携带支撑剂的运移铺置规律。以相似准则为基础,建立了简化的复杂裂缝平板模型,并将砂堤形态参数、砂堤面积进行归一化处理,获得了压裂液排量、黏度、支撑剂粒径、裂缝宽度以及裂缝形态对支撑剂在复杂裂缝中铺置的影响规律。结果表明:增大排量、黏度和减小粒径均有利于支撑剂向裂缝深处运移,并且排量对支缝中的砂堤形态影响最明显,但增大排量不利于支撑剂填充近井地带。缝宽的影响体现在壁面效应,在注入时间相同的情况下,当压裂液黏度从1 mPa·s增加到5 mPa·s时,主缝砂堤的归一化长度平均增加了37.9%,归一化高度平均降低了61.4%。裂缝结构越复杂,所有支缝中的支撑剂铺置面积占比越高,分流作用越大。随着复杂裂缝的支缝数量、级数以及支缝延伸长度的增大,支缝中的砂堤高度与长度均有所降低;相对于T1型裂缝,T3和T5型裂缝中的砂堤长度、高度减小最多。

一种具有超长侧链的疏水缔合型聚合物的合成及减阻性能评价

采用曲拉通和丙烯酰氯醇解合成一种水溶性可聚合单体,仅使用水作为溶剂合成一种具有超长侧链的疏水缔合型聚丙烯酰胺(HAPAM)作为减阻剂,通过分子动力学模拟方法对比了聚丙烯酰胺、部分水解聚丙烯酰胺和合成的具有超长侧链的HAPAM与水的相互作用,并分别以去离子水和盐水配液改变HAPAM含量,测量不同HAPAM含量的滑溜水在不同流速下的摩阻,并计算相应的减阻率。实验结果表明,具有超长侧链的HAPAM与水的相互作用最强;减阻率随流速的增加而增大,HAPAM含量越高,减阻率达到70%所需的流速越高,减阻率最高可达80%以上;盐对滑溜水的减阻率和黏度有显著负面影响,需提高HAPAM含量才能获得理想的减阻率;SEM表征结果显示,HAPAM在清水和盐水中的分布形态均为网状结构。

深部煤层气水平井大规模极限体积压裂技术--以鄂尔多斯盆地东缘临兴区块为例

针对深煤层渗透性差、弹性模量较低、泊松比较高、塑性强、破裂压力高、裂缝扩展难度大、加砂困难等特点,提出缝网改造规模化、缝网扩展均衡化、缝网支撑有效化的压裂设计理念,形成以高排量大规模注入、高强度加砂、等孔径限流射孔、暂堵转向、一体化可变黏滑溜水、多粒径组合支撑剂为核心的深煤层水平井大规模极限体积压裂技术。将该技术应用于鄂尔多斯盆地东缘临兴区块首口深煤层多级压裂水平井先导性试验,施工排量18 m^(3)/min、加砂强度2.1 m^(3)/m、用液强度16.5 m^(3)/m,压裂后形成了复杂裂缝网络,平均缝长为205 m,储层改造体积为1987×10^(4)m^(3),最高产气量达6×10^(4)m^(3)/d,实现了深部煤层气的高效开发。

Extreme massive hydraulic fracturing in deep coalbed methane horizontal wells:A case study of the Linxing Block,eastern Ordos Basin,NW China

Deep coal seams show low permeability,low elastic modulus,high Poisson’s ratio,strong plasticity,high fracture initiation pressure,difficulty in fracture extension,and difficulty in proppants addition.We proposed the concept of large-scale stimulation by fracture network,balanced propagation and effective support of fracture network in fracturing design and developed the extreme massive hydraulic fracturing technique for deep coalbed methane(CBM)horizontal wells.This technique involves massive injection with high pumping rate+high-intensity proppant injection+perforation with equal apertures and limited flow+temporary plugging and diverting fractures+slick water with integrated variable viscosity+graded proppants with multiple sizes.The technique was applied in the pioneering test of a multi-stage fracturing horizontal well in deep CBM of Linxing Block,eastern margin of the Ordos Basin.The injection flow rate is 18 m^(3)/min,proppant intensity is 2.1 m^(3)/m,and fracturing fluid intensity is 16.5 m^(3)/m.After fracturing,a complex fracture network was formed,with an average fracture length of 205 m.The stimulated reservoir volume was 1987×10^(4)m^(3),and the peak gas production rate reached 6.0×10^(4)m^(3)/d,which achieved efficient development of deep CBM.

低渗页岩储层压裂及一体化压裂液研究现状

常规石油气资源日益减产,能源资源争夺越发激烈,分布广泛、储量丰富的页岩油气等非常规油气藏成为了化石能源开发的焦点。页岩储层具有低孔、低渗、难以造缝的特征,需采用大规模压裂沟通天然微裂缝,扩宽油气通道,方能形成稳定工业气流实现增产。传统现场粉剂配液模式逐渐无法满足压裂作业要求。因此,本文围绕一体化滑溜水压裂液的优缺点、运用等结合页岩油气开采,概述了国内外一体化悬浮体系压裂液使用状况及相关特点,并综合讨论了在低伤害、环境友好等热点趋势下非常规压裂液的发展方向和特点。

解吸附可降解乳液型降阻剂研究

针对浅层常压页岩气吸附气含量高,难以提高产量实现有效开采及常规聚合物降阻剂难以实现自然降解的问题,通过水相分散聚合合成无油相乳液型降阻剂。通过摩阻仪、磁悬浮天平等对降阻剂及其形成的降阻水体系进行性能评价,实验结果表明,利用该降阻剂配制的0.6%~1.0%降阻水体系实验室降阻率均达到70%以上,现场降阻率84%,解吸附实验结果表明产品解吸率达到85%,远超常规乳液降阻剂产品,具有较高的工程实用性,可以满足施工的要求;使用特性黏数法评价了降阻剂的自然降解能力,其在95℃下330 h能够实现自然降解,降解率达到86%,岩心伤害率远低于胍胶体系,IC50测试结果表明该降阻剂在使用浓度下无毒环保。为开发浅层常压页岩气提供了技术借鉴和新的产品思路。

页岩气体积压裂滑溜水的研究及应用

页岩储层需要采用大排量、大液量体积压裂才能获得工业气流,体积压裂要求压裂液具有可连续混配、低摩阻和高返排率性能。根据四川页岩储层特征和实验结果,研制了降阻性能高的聚丙烯酰胺降阻剂、高效复合防膨剂及微乳助排剂,研制了适于四川页岩气体积压裂的滑溜水。该配方在四川W、C区块直井8井次现场试验表明,降阻率为65.5%～68.3%;W区块平均返排率为46.19%,C区块返排率27.93%;累计增加井口测试产量6.24×104～11.35×104 m3/d。

滑溜水压裂主裂缝内支撑剂输送规律实验及数值模拟

滑溜水压裂时通过泵送大排量压裂液在储层中形成主裂缝为主干的裂缝网络,主裂缝内支撑剂的铺置状况直接影响油气井的产能。采用自主设计的大型可视化平板裂缝装置来研究大排量泵送时主裂缝内支撑剂的输送规律,建立了相应的数值模型模拟了砂堤在不同时刻的铺置形态,并分析了湍流对支撑剂铺置的影响规律,为滑溜水压裂时主裂缝内支撑剂的有效铺置提供一定的理论指导。研究表明,滑溜水压裂时支撑剂在主裂缝内的铺置规律与小排量压裂时不同:支撑剂首先在主裂缝入口处形成一个较低的砂堤,而在距入口较远处形成一个较高的砂堤,之后才一层一层周期性的覆盖在两处砂堤之上,直到达到最终的平衡高度;大排量压裂时易引起湍流,将主裂缝进口端暂时沉降的支撑剂重新卷入裂缝深处,形成类似"卷云状"的沉降结构;数值模拟与物理实验模拟得到的支撑剂铺置结果相似,证明了研究的数值模型具有一定的实用性。

耐盐减阻剂的制备及性能评价

研发了一种高耐盐性的减阻剂,用高矿化度产出水直接配制滑溜水再次使用,降低环境污染和处理费用。以丙烯酰胺与2-丙烯酰胺-2-甲基丙磺酸为单体,采用分散聚合的方法制备一种耐盐减阻剂,考察合成条件对悬浮乳液减阻剂的稳定性影响,并测试该减阻剂的耐盐性能。结果表明,当pH值在7.5左右,硫酸铵加量为36%,稳定剂用量为0.75%时,能得到稳定的减阻剂,其重均分子质量达到1.61×10~7 g/mol。在清水中,0.2%的该减阻剂具有良好的溶解性,102s就能完全伸展并水化。在40L/min的体积流速时能达到80%的减阻率,并且在100g/L的K^+、Ca^(2+)、Fe^(3+)溶液中分别都保持60%以上的减阻率。另外,在高矿化度水中直接配制滑溜水时,该减阻剂在107s就完全溶胀,表观黏度达到2.15mPa·s,仍然具有很好的减阻性能。采用分散聚合方法制备的耐盐减阻剂成功在高矿化度水配制出滑溜水,对产出水的重复利用有很大的促进作用。

滑溜水压裂液中减阻剂的制备及特性研究

采用反相微乳液法制备了一种用于滑溜水压裂液中的水溶性减阻剂,对减阻剂的粒径大小分布、重均分子量、降阻率和悬砂能力进行了测试。结果表明,减阻剂粒径小,分布窄,分子量高[Mw=(2.08±0.65)×107g/mol],具备高分子减阻的特性;向清水中加入0.05%的减阻率,减阻率可达55%,并且具有一定的携砂能力。因此,该减阻剂的应用能很好的降低压裂施工摩阻、减小泵功、适当提高砂比,有助于非常规低渗储层的开采。

滑溜水携砂性能动态实验

为了研究支撑剂密度对滑溜水携砂性能的影响,自主设计了大型可视平板裂缝模拟系统,使支撑剂在裂缝中的动态沉降、砂堤形态可视化。运用该装置研究了不同支撑剂密度下滑溜水的携砂性能及支撑剂在裂缝中的沉降运移规律。实验结果表明,随着实验时间延长,砂堤高度逐渐增加,但增幅减缓;随着支撑剂密度减小,砂堤变平缓,砂堤的高度降低,堤峰向深处运移,且砂堤向裂缝深部推进速度增大,更多的支撑剂沉降在裂缝深部;支撑剂密度增大对沉降速度影响较大,对水平运移速度影响较小。研究结果可为支撑剂沉降运移动态研究及支撑剂优选提供参考。

减阻水压裂液用黏土稳定剂的合成与应用

针对现有减阻水压裂液用黏土稳定剂配伍性差、用量大、防膨率低、固体形态不便于现场配液等问题,研制了一种阳离子型液体黏土稳定剂SRCS-1。SRCS-1的分子链上分布阳离子基团,又含有小分子阳离子化合物,2者协同作用达到稳定黏土的效果。其分子量较低,既能保证所含的阳离子基团能够提供较高的防膨率,又能避免过长的分子链和过多的阳离子与阴离子聚合物减阻剂发生相互作用而产生沉淀或絮凝,与减阻水中阴离子聚合物减阻剂配伍性良好,加量0.3%条件下防膨率达到68.2%,优于收集到的现场应用过的同类产品。通过表面张力、ζ电位、粒度测试分析了该黏土稳定剂的防膨机理。SRCS-1在新疆孔探1井进行减阻水压裂液进行了现场应用,配液方便、快捷,表现出优良的配伍性和防膨性,减阻水性能稳定,施工顺利。

滑溜水用减阻剂室内性能测试与现场摩阻预测

经验预估滑溜水压裂现场的减阻效果具有差异较大的不足,而以往的减阻剂减阻性能评价实验多侧重于相关产品的对比优选,对其测试结果如何应用于现场实际的说明并不多见。针对以上问题,搭建了室内环路摩阻测试系统,依据Prandtl-Karman定律,通过清水湍流率定出测试用的3条直管管径分别为10.46,7.59和5.86 mm。对不同管径,在一定泵送排量梯度下对5种不同浓度的DR-800减阻剂溶液的摩阻压降进行了测定。对于0.07%和0.10%浓度的减阻剂溶液,将测试压降换算成摩阻系数,与考虑黏度项计算出的雷诺数相对应,可以很好地拟合于Virk渐近线,证明了DR-800减阻剂的优良减阻性能。在定量测试减阻性能后,采用摩阻放大法中的阻力速度法,将室内实验测得的降阻比与阻力速度进行回归得出表达式,确定出各阻力速度所对应的具体减阻率大小。运用该式,通过迭代计算,可以得到每种工况下相对确定的减阻率,比起经验预测,精度明显提高。因此,上述的室内研究方法对减阻剂的现场应用具有指导意义。

页岩气藏压裂改造难点与技术关键

我国的页岩气资源储量非常可观,国外成功开发的经验表明,压裂改造是实现页岩气高效、经济开发的重要技术步骤。为此,在详细调研和总结国内外相关成果的基础上,从压裂改造的角度分析了页岩气储层基本特征,阐述了页岩气藏压裂理论、材料和工艺3个方面所面临的难题和挑战,进而提出了页岩气藏改造技术关键。结论认为:剪切作用有利于形成复杂裂缝网络;页岩中的气体以吸附、游离和溶解状态存在,在非达西流动状态下,气体渗流机理更为复杂;以微地震数据为基础,通过离散裂缝网络模型描述缝网是目前计算页岩气产能的主流方法;滑溜水压裂应根据储层条件研制和筛选支撑剂和添加剂,开发井下工具,并优化泵注程序和压裂工艺,以形成高导流能力的大型复杂裂缝网络为改造作业目标。

致密砂岩储层CO_2压裂裂缝扩展实验研究

为提高天然裂缝和层理不发育致密储层压裂裂缝的复杂性,基于真三轴压裂模拟实验系统,开展了致密砂岩储层CO_2压裂实验研究,分析了水平应力差、压裂液类型和排量对压裂裂缝扩展规律的影响。研究表明,超临界CO_2压裂形成的水力裂缝形态最复杂,液态CO_2次之,滑溜水压裂产生的水力裂缝形态简单;采用液态CO_2压裂时,低水平应力差(≤3 MPa)有利于提高水力裂缝的复杂程度;液态CO_2压裂的起裂压力相比于滑溜水压裂降低22.1%,超临界CO_2压裂的起裂压力相比于滑溜水压裂降低28.2%;提高排量会加快井筒内流体增压速率,起裂压力升高。实验证明超临界CO_2压裂能够有效提高裂缝复杂性。

国内外水力压裂减阻剂研究进展及展望

减阻水体系是基于页岩储层发展起来的一种新型压裂液体系,凭借其优异的性能,在国外得到广泛研究和应用,但国内的研究与应用较少,所用减阻剂主要依赖国外进口。探讨了国外减阻剂的研究进展,同时对几种常见的减阻剂类型及其机理进行了概述,并对减阻剂未来的研究和发展进行了展望,可为国内减阻剂研发提供一定的指导意义。本文认为,通过在常规W/O反相聚合物减阻剂中引入表面活性剂,提高其转相速度和对聚合物分子改性的方式,可提高其抗盐性能;对减阻剂中聚合物的降解易采用化学氧化法,通过对减阻剂水化速度和自动破胶能力进行改进,促进无害化减阻剂的发展;对于高含盐量和高矿化度的油层产出水和压裂液返排液,易采用分散聚合物减阻剂,该减阻剂具有独特的分散机理(不需要转相),应用范围更加广泛,必将成为减阻剂的又一热门研究领域。