摘要
降黏泡沫驱结合了降黏剂乳化降黏和泡沫选择性封堵的优势,可进一步提高开发后期深层稠油油藏的采收率。通过室内实验,根据降黏泡沫剂的降黏效果、起泡性能、泡沫稳定性,优选出合适的降黏泡沫剂浓度;通过单岩心驱替实验对比不同驱替方式下降黏泡沫驱驱油特征以及开采效果,通过并联岩心实验研究不同渗透率级差下降黏泡沫的分流能力,明确降黏泡沫驱提高采收率机理。结果表明:降黏泡沫驱过程中,降黏剂可以促进稠油乳化降黏,泡沫可以有效封堵大孔喉,同时抑制氮气窜流。二者结合有效提高波及系数和洗油效率,提高驱替压差,降低含水率。降黏泡沫驱可以在降黏泡沫剂驱的基础上进一步提高13%的采收率。非均质条件下,降黏泡沫驱可以有效降低高渗透岩心窜流,迫使流体转向进入低渗透岩心发挥乳化降黏作用,扩大波及范围的同时提高了洗油效率。降黏泡沫驱技术能显著提高深层低渗透稠油油藏的采收率,其优化了油流分布,增强乳化与减少稠油黏度,为深层稠油高效开发提供了有效策略。
全球稠油资源丰富,主要分布在委内瑞拉、加拿大以及中国等地。中国作为一个拥有广阔稠油资源的国家,稠油分布较广,陆上稠油探明储量约为40×1
本次研究目标区块为昌吉油田梧桐沟组,属于中深层稠油油藏。该油藏的高部位受断层和地层尖灭控制,低部位受断层和油水控制。目标油藏的埋深为1 317~1 836 m,平均油层厚度为5 m。油藏的平均孔隙度为21.4%,平均渗透率为84.9 mD。此外,该油藏地面原油密度为0.92~0.96 g/c
降黏剂驱是一种广泛使用的稠油冷采方法,不仅可以降低开采成本,还可以减少对地层的伤
1 实验器材及步骤
1.1 实验材料
实验用油:脱水脱气原油,取自昌吉油田梧桐沟组,60 ℃下的黏度为1 682.9 mPa·s,饱和分、芳香分、胶质和沥青质的质量分数分别为48.94%,30.65%,19.48%和0.93%。实验用水:昌吉油田提供的实际地层水,总矿化度为8 344 mg/L,阴离子以HCO
驱油实验 | 渗透率级差 | 岩心长度/cm | 岩心直径/cm | 渗透率/mD | 孔隙度/% | 含油饱和度/% |
---|---|---|---|---|---|---|
并联岩心 | 4.96 | 7.97 | 2.42 | 13.96 | 21.38 | 79.92 |
7.98 | 2.49 | 69.24 | 23.98 | 81.56 | ||
单岩心 | 7.95 | 2.49 | 12.09 | 21.36 | 81.97 |
1.2 实验装置
Waring Blender搅拌器:型号为GJ-3S,山东美科仪器有限公司,转速最高可以达到11 000 r/min。旋转流变仪:型号为MCR 302,奥地利Anton Parr集团制造。基恩士超景深三维显微系统:型号为VHX-600,由基恩士(中国)有限公司生产。岩心驱替实验装置:注入系统、温度控制系统、数据采集系统以及采出液收集系统,注入系统中的柱塞泵型号为100 DX,流量精度为±0.25 µL/min,压力精度为±0.5%,美国Teledyne ISCO公司生产。使用的其他仪器包括水浴锅、电子天平、烧杯、秒表、玻璃棒等。实验流程如

图1 岩心驱替实验流程
Fig.1 Flow of core displacement experiment
1.3 实验步骤
降黏泡沫剂的泡沫性能评价实验步骤如下:①在室温下,采用实际地层水制备不同质量分数(0.1%,0.3%,0.5%,0.7%和1.0%)的降黏泡沫剂溶液,每种溶液配制100 mL,并确保搅拌均匀以充分溶解。②设置恒温水槽为所需温度,将溶解充分的溶液放入恒温箱中恒温30 min。③将搅拌均匀的100 mL降黏泡沫剂溶液快速转移至量杯中,并调整高速搅拌器的转速为8 000 r/min,搅拌降黏泡沫剂溶液持续3 min。④搅拌结束后,迅速将量杯中的泡沫倒入量筒,并启动秒表进行计时,记录泡沫体积。⑤观察量筒底部析出液体的体积,当析出液体的体积达到50 mL时,结束计时。⑥改变降黏泡沫剂溶液的浓度,然后重复步骤②—④,并记录实验数据。
降黏泡沫剂的降黏性能评价实验步骤如下:①取一定量脱气脱水的稠油,分别置于5个容量为250 mL的烧杯中。按照油水体积比为7∶3的比例,分别加入质量分数为0.1%,0.3%,0.5%,0.7%和1.0%的降黏泡沫剂溶液。②将烧杯置于预设的恒定温度水浴中,并静置10 min。随后,使用玻璃棒将烧杯中的稠油与降黏泡沫剂溶液进行均匀搅拌。取出部分降黏后的稠油样品,在超景深三维显微境下观察其微观形态。③利用旋转流变仪快速测量降黏后稠油的黏度;同时,在相同条件下测量原始稠油样品的黏度;最后,计算降黏泡沫剂对稠油的降黏率。④改变温度,重复步骤②—③,记录不同温度下降黏后的稠油黏度,并计算相应的降黏率。
岩心驱替实验步骤如下:①岩心饱和地层水,称取湿重,计算其孔隙度并测量渗透率。②以0.5 mL/min的恒定速度饱和油,计算含油饱和度。③按照
2 降黏泡沫剂性能
2.1 降黏泡沫剂的泡沫性能
2.1.1 降黏泡沫剂溶液浓度的影响
起泡体积是指一定量降黏泡沫剂经过均匀搅拌所生成的泡沫的总体积,而析液半衰期则是指泡沫释放出一半液体体积所需的时

图2 泡沫性能与降黏泡沫剂溶液质量分数关系曲线
Fig.2 Relationship between foam performance and solution mass fraction of viscosity-reducer foam agents
2.1.2 温度的影响
高温不利于泡沫的生成和稳定,因此耐温性也是评价降黏泡沫剂性能的一个重要参数。主要评估了质量分数为0.5%的降黏泡沫剂溶液在不同温度下(20,40,60和80 ℃)的起泡性能和泡沫稳定性,由实验结果(

图3 泡沫性能与储层温度关系曲线
Fig.3 Relationship curve between foam performances and reservoir temperatures
2.2 降黏泡沫剂的降黏性能
2.2.1 降黏泡沫剂溶液浓度的影响
降黏泡沫剂对稠油的降黏效果可以用降黏率来评价,定义为:
降黏泡沫剂溶液的质量分数是影响降黏效果的重要参数之一。在实验过程中,合理且适度地控制降黏泡沫剂的用量不仅可以有效降低稠油的黏度,还可以节约油田的经济成本。将实验温度固定为油藏温度60 ℃,剪切速率为170

图4 不同浓度降黏泡沫剂溶液的稠油降黏率曲线
Fig.4 Viscosity reduction rate of heavy oil by viscosity reduction foam agent solutions at different concentrations

图5 乳化后油滴微观形态
Fig.5 Microscopic morphology of oil droplets after emulsification
2.2.2 温度的影响
设置实验温度为40,50,60,70和80 ℃,剪切速率为170

图6 不同温度下的稠油降黏率曲线
Fig.6 Viscosity reduction rate curve of heavy oil at
different temperatures
3 驱油特征及提高采收率机理
3.1 单岩心驱替实验驱油特征
单岩心不同驱替方式驱油特征曲线(

图7 单岩心不同驱替方式驱油特征曲线
Fig.7 Displacement characteristic curves of different single-core displacement modes
水驱阶段结束后进行降黏泡沫剂驱。在注入量达到3.5 PV时,压差出现了约0.17 MPa的小峰值。同时,在相应的注入量下,出现了含水率下降漏斗,使得含水率降低到95.4%。此外,采出程度也快速增加。这是因为降黏泡沫剂能够将原油乳化,乳化油滴起到封堵作用,并进一步扩大波及区域,从而进一步提高采收

图8 不同驱替方式下的产出液
Fig.8 Produced liquid under different displacement modes
3.2 并联岩心驱替实验驱油特征
按照气液比为2∶1注入氮气和降黏泡沫剂,注入段塞为0.8 PV。由并联岩心驱油实验驱替压差曲线(

图9 并联岩心驱油特征曲线
Fig.9 Oil displacement characteristic curves on parallel core
在水驱阶段,高渗透岩心和低渗透岩心的采出程度、含水率存在较大差异,高渗透岩心的含水率和采出程度远高于低渗透岩心。高渗透岩心水驱阶段最终采出程度和含水率分别达到63.72%和99.08%,而低渗透岩心的分别为11.73%和60.12%。高渗透岩心和低渗透岩心的采出程度变化规律相似,先是快速增加,然后增速放缓(
在降黏泡沫驱阶段,注入过程中降黏泡沫没有立刻发挥作用。而在后续水驱阶段,降黏泡沫开始发挥作用。高渗透岩心和低渗透岩心的采出程度均有所提高,低渗透岩心采出程度的提高效果要好于高渗透岩心,综合采出程度明显提高。高渗透岩心和低渗透岩心采出程度分别提高11.67%和22.36%,综合采出程度提高16.69%。同时,高渗透岩心和低渗透岩心含水率明显下降,出现了典型的含水率下降漏斗。高渗透岩心的含水率下降程度更明显。高渗透岩心含水率最低点为94.90%,低渗透岩心含水率最低点为56.70%,综合含水率最低点为88.32%。上述现象可解释为在后续水驱阶段,泡沫在高渗透岩心中迁移,有效地封堵了水窜通道,迫使后续的驱替液发生转向进入低渗透岩心,有效提高了波及系数。且降黏泡沫与稠油发生乳化降黏作用,形成O/W乳状液,有效降低稠油黏度,提高原油流动
并联岩心分流率曲线(

图10 并联岩心分流率曲线
Fig.10 Diversion rate curves on parallel core
3.3 降黏泡沫驱提高采收率机理
根据单岩心、并联岩心驱替实验过程中的驱油特征,对降黏泡沫驱的提高采收率机理进行分析。在岩心饱和油状态,稠油占据了孔隙与喉道(

图11 降黏泡沫驱提高采收率机理
Fig.11 EOR mechanism of viscosity-reducer foam flooding
4 结论
(1)降黏泡沫剂的泡沫性能和降黏性能随着浓度的增加而逐渐提升,最优使用浓度选择出现增速拐点的0.5%。使用的降黏泡沫剂具备出色的耐温性能,在60 ℃油藏温度下依然保持优异的泡沫性能和降黏性能。
(2)降黏泡沫驱兼具降黏剂的乳化降黏作用以及泡沫的选择性封堵作用,可以有效提高驱替压差,降低含水率,扩大波及系数的同时提高洗油效率。降黏泡沫驱比单一降黏泡沫剂驱的最终采出程度提高了13%。
(3)非均质条件下,降黏泡沫驱可以有效降低高渗透岩心窜流,迫使流体转向进入低渗透岩心发挥乳化降黏作用,扩大波及范围的同时提高了洗油效率。
符号解释
µ0——原始稠油黏度,mPa·s;
µ1——加入降黏剂后原油的黏度,mPa·s;
η——降黏率,%。
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