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普光气田上二叠统长兴组与下三叠统飞仙关组碳酸盐岩埋深较大，天然裂缝、溶洞等大尺度结构发育特征突出，是典型的破碎性储层[1]，常规酸化、酸压[2]等改造措施进一步扩展通道尺度[3]。区域内深部气层地层压力系数下降后，井筒液柱压力与地层压力形成压差，引发漏失[4]。漏失控制不当时，井底硫化氢上窜增大作业风险[5]，地层暂堵势在必行。目前，包括超细纤维[6]、冻胶[7]、绒囊修井液[8]等多种堵剂可用于封堵低压气井。其中，绒囊修井液堆积封堵机制[9~10]，解决了堵剂尺度与地层漏失通道匹配的难题[11]，先后于煤层钻井封堵[12]、低压气井修井暂堵[13]、致密气转向压裂暂堵[14]等多个领域成功应用。
对于普光气田深部低压气层，垂深大导致暂堵后承压要求高，此时，漏失通道尺度较大，绒囊修井液封堵可行但用量过大，增加作业成本，且大量流体进入地层不利于作业后产量恢复[15]。
利用颗粒、纤维等固态堵剂通过堆积、架桥[16]等方式将大尺度漏失空间切割成多个小尺度漏失单元，可降低绒囊修井液封堵用量。暂堵后，解除绒囊暂堵结构，恢复地层产气能力，兼容封堵性与经济性目标可行。为此，实验对比绒囊修井液复合固相堵剂前后封堵所需流体体积以及封堵解除后通道渗流能力恢复效果，结合现场试验，评价技术效果。
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室内串联4枚直径38 mm、长60 mm的人造岩心，内含30 mm×5 mm贯穿裂缝模拟地层大尺度漏失通道。选择80~120目碳酸钙颗粒和直径10~20 μm、长度5~6 mm纤维作为复合固相。配制绒囊修井液：0.2%囊核剂+2.5%囊层剂+0.8%囊膜剂+1.2%绒毛剂+0.1%氢氧化钠。实验流程见图1。
图 1 封堵实验流程图
Figure 1. Flow chart of plugging experiment
恒流速5 mL/min注入绒囊修井液及与质量浓度0.1%、0.2%、0.5%、1.0%、1.5%碳酸钙颗粒、纤维的复合体系，记录裂缝入口驱压达20 MPa时累计注入体积。封堵后，注入质量分数1%的亚硫酸铵破胶剂，静置30 min进行破胶。考虑室内大尺度裂缝中高压气体稳定驱替控制困难，选择清水反向驱替并间隔5 min测定出口流速，评价裂缝渗流能力恢复效果。
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累计完成绒囊修井液及其复合体系封堵实验共13组，实验数据见表1，可以看出，单一绒囊体系累计注入139~146 mL，均值142 mL；绒囊复合颗粒、纤维体系累计注入流体体积范围49~123 mL、34~118 mL。绒囊流体用量随固态堵剂加量增加而下降。
表 1 不同体系封堵实验测试数据
Table 1. Test data of different systems in the plugging experiment
序号 固相 加量/% 绒囊流体累计注入量/mL 1 无 0 146 2 无 0 139 3 无 0 141 4 颗粒 0.1 123 5 颗粒 0.2 114 6 颗粒 0.5 86 7 颗粒 1.0 63 8 颗粒 1.5 49 9 纤维 0.1 118 10 纤维 0.2 103 11 纤维 0.5 77 12 纤维 1.0 54 13 纤维 1.5 34 -
封堵体系返排后裂缝渗流能力恢复效果评价实验共13组，实验数据见表2。可以看出，注入绒囊修井液，清水驱替15 min时流速完全恢复；复合体系中，颗粒加量0.1%升至1.0%，清水流速完全恢复时间延长至25 min，加量1.5%时，流速存在0.1 mL/min损失；纤维加量0.1%升至0.5%，清水流速完全恢复时间延长至30 min，加量超过1.0%后，流速存在0.2 mL/min损失。实验表明，裂缝渗流能力恢复速度随固态堵剂加量升高而小幅度降低，同时，最终恢复效果存在微弱的损失。
表 2 封堵返排后裂缝出口清水流速分布
Table 2. Flow velocity distribution of clear water at the fracture outlet after the flowback of plugging agent
固相 加量/% 不同驱替时间出口流速/(mL · min−1) 5 min 10 min 15 min 20 min 25 min 30 min 无 0 3.1 4.8 5.0 5.0 5.0 5.0 无 0 3.5 5.0 5.0 5.0 5.0 5.0 无 0 3.2 5.0 5.0 5.0 5.0 5.0 颗粒 0.1 2.6 3.6 5.0 5.0 5.0 5.0 颗粒 0.2 2.4 3.2 4.8 5.0 5.0 5.0 颗粒 0.5 1.7 2.8 4.3 5.0 5.0 5.0 颗粒 1.0 1.4 2.3 3.8 4.9 5.0 5.0 颗粒 1.5 0.9 2.1 3.5 4.5 4.9 4.9 纤维 0.1 2.3 3.5 5.0 5.0 5.0 5.0 纤维 0.2 2.2 3.1 4.5 4.9 5.0 5.0 纤维 0.5 1.3 2.5 3.9 4.3 4.9 5.0 纤维 1.0 1.1 2.0 3.4 4.6 4.8 4.9 纤维 1.5 0.5 1.8 3.1 4.3 4.6 4.8 -
S-3X井位于鄂尔多斯盆地伊陕斜坡构造，产层马家沟组碳酸盐岩气层垂深近4 000 m，且气层天然裂缝、溶洞发育，钻井打开储层后井筒流体累计漏失量超过2 000 m3。酸化后，试气无阻流量超过200×104 m3/d，产气能力较高。
S-3X井投产至今，地层压力系数0.40，为打捞断脱油管计划修井作业。首次压井时，累计注入绒囊修井液约500 m3，井口泵压升至3 MPa，但无法建立循环。二次压井时，以160 m3绒囊修井液复合0.5%纤维注入后，不间断跟注130 m3绒囊修井液，泵压升至7.9 MPa且顺利建立循环，达到预期目标。
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P2-Y井位于普光气田，完钻层位长兴组底部垂深达6 000 m，酸压改造后测试无阻流量350×104 m3/d。修井作业前地层压力系数0.35。考虑邻近D5-Z井使用120 m3绒囊修井液封堵起效，但有效封堵周期较短，试验复合封堵技术。先以60 m3清水携带4 m3规格100目粉陶砂注入地层后，跟进80 m3绒囊修井液，井口泵压增幅达5 MPa，顺利建立循环，达到预期目标。
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根据室内实验与现场施工数据，分析绒囊修井液复合固态堵剂暂堵技术，应用于普光气田深部低压气层大尺度漏失通道封堵效果。
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室内实验中，绒囊修井液复合体系注入裂缝后，入口驱压均升至20 MPa，封堵性能稳定。颗粒、纤维加量从0.1%升至1.5%，绒囊修井液体积下降93 mL、108 mL，相对单一体系平均用量142 mL，分别下降65.49%和76.06%。由图2可以看出，流体体积降幅随颗粒、纤维加量增大而升高。两者之间拟合定量关系为
$$ {S_{\rm{f}}} = 0.198\;3\ln{\theta _1} + 1.467\;1 $$ (1) $$ {S_{\rm{f}}} = 0.214\;9\ln{\theta _2} + 1.626\;3 $$ (2) 式中，Sf为绒囊修井液体积降幅，%。
图 2 流体用量降幅随固相堵剂加量变化趋势
Figure 2. Change trend of the decrease amplitude of fluid consumption with the dosage of solid plugging agent
式(1)和式(2)中，固态堵剂加量越高，所需绒囊修井液体积降幅越大。研究表明，小加量的固体堵剂将大尺度漏失空间分割成多个小尺度单元后，显著提高绒囊修井液封堵效率。
现场S-3X井与P2-Y井计算复合体系提高地层承压能力达34 MPa、39 MPa，封堵强度足够。S-3X井相对首次压井的流体体积降幅达42%，P2-Y井相对邻井压井的流体体积降幅33.33%。试验表明，绒囊修井液复合固相堵剂暂堵技术降低绒囊流体用量有效。
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实验对比裂缝中封堵结构破胶后，反向驱替清水流速恢复效果见图3。可以看出，随着固态堵剂加量升高，恢复速度小幅度放缓。其中，单一体系破胶后清水稳定流速可完全恢复；复合体系中，颗粒与纤维加量分别小于1.0%、0.5%时，清水流速可完全恢复；当颗粒、纤维加量分别达1.5%、1.0%时，清水流速存在0.1~0.2 mL/min的微弱损失，但整体恢复效果理想。
图 3 裂缝出口清水稳定流速恢复趋势
Figure 3. Recovery trend of the stable flow velocity of clear water at the fracture outlet
对于普光气田深部低压气井，地层流体漏失通道尺度较大，初始渗流能力较高。此时，复合少量固相堵剂后，漏失通道主体仍由绒囊修井液充填，保证作业后通道渗流能力快速恢复，维持绒囊流体储层伤害控制的优势。
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(1)绒囊修井液复合固态堵剂暂堵技术，满足普光气田深部低压气层大尺度漏失通道封堵要求的同时，有效降低流体用量，兼容封堵技术性与经济性。
(2)固态堵剂注入地层后，将大尺度漏失空间分割为多个小尺度漏失单元，改善了绒囊修井液封堵效率。作业后，小尺度漏失单元内绒囊修井液暂堵解除后，地层渗流能力可快速恢复，储层伤害较低。但是溶洞型漏失可能效果不佳，需要进一步试验。
(3)绒囊修井液与固态堵剂复合暂堵技术，是多种封堵材料的融合，为深部油气层封堵技术经济性开发提供了可借鉴的思路。建议多与一些材料融合，如凝胶、水泥等。
Application of fuzzy-ball workover fluid combined with solid plugging agent to the temporary plugging of deep low-pressure gas layers in Puguang Gas Field
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摘要: 普光气田深部碳酸盐岩地层天然裂缝、溶洞与改造后人工裂缝结构共存，井筒液柱与地层形成压差时成为漏失通道，需实施暂堵。绒囊修井液封堵低压气层可行，但封堵大尺度通道用量过大，为此，引入固态堵剂辅助绒囊修井液降低流体用量。室内串联直径38 mm、长60 mm，含缝宽5.0 mm贯穿裂缝的人造岩心，模拟大尺度漏失通道。绒囊修井液复合质量分数0.1%~1.5%的碳酸钙颗粒和纤维，对比单一体系与复合体系注入裂缝至驱压达20 MPa时流体用量；封堵后，注入破胶液解除暂堵，重复测定清水流速恢复效果。实验结果表明，相同承压所需绒囊修井液体积随固态堵剂加量增大而下降12.3%~60.5%，与固态堵剂加量正比关系较明显；破胶后，裂缝中清水流速恢复率达98%，伤害程度较低。S-3X井、P-2Y井分别试验绒囊修井液与纤维、绒囊修井液与颗粒复合封堵技术，计算提高地层承压26 MPa、32 MPa，复合体系用量相对单一体系降幅超过30%。绒囊修井液复合固相堵剂满足普光气田深部气层大尺度漏失通道中封堵性与经济性双重要求，扩展了绒囊流体应用领域。Abstract: In Puguang Gas Field, natural fractures, vugs and hydraulic fractures coexist in the deep carbonate formation and they will become leakage channels when there is pressure difference between wellbore fluid column and formation. Therefore, temporary plugging is needed. It is feasible to apply the fuzzy-ball workover fluid to plug low-pressure gas layers, but its consumption is too high while plugging large-scaled channels. The solid plugging agent was introduced to assist fuzzy-ball workover fluid, so as to decrease the fluid consumption. In the laboratory, the artificial cores (diameter 38 mm and length 60 mm) containing through-going fractures of 5.0 mm wide are connected in series to simulate large-scaled channels. After the fuzzy-ball workover fluid was added with calcium carbonate grains and fibers with the mass fraction of 0.1%-1.5%, the fluid consumption of single system in the fracture to reach the displacement pressure of 20 MPa was compared with that of complex system. After plugging, gel breaker was injected to remove the temporary plugging and then the recovery effect of the flow velocity of clear water was measured repeatedly. It is experimentally indicated that under the same pressure, the needed volume of fuzzy-ball workover fluid decreases by 12.3%-60.5% with the increase of the dosage of solid plugging agent and it is obviously in a direct proportion to the dosage of solid plugging agent. After gel breaking, the recovery rate of the flow velocity of clear water in fractures reaches 98%, indicating lower damage degree. The complex plugging technology of fuzzy-ball workover fluid and fiber and that of fuzzy-ball workover fluid and grain were tested in Well S-3X and Well P-2Y, respectively. According to the calculation results, the formation pressure was increased by 26 MPa and 32 MPa, respectively and the consumption of complex system is 30% less than that of single system. In conclusion, the fuzzy-ball workover fluid combined with solid plugging agent can meets the plugging and economic requirements of large-scaled leakage channels in Puguang Gas Field and it expands the application fields of fuzzy-ball fluid.
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Key words:
- deep gas reservoir /
- low pressure /
- temporary plugging /
- fuzzy-ball fluid /
- solid plugging agent /
- reservoir damage
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图 2 流体用量降幅随固相堵剂加量变化趋势
Figure 2. Change trend of the decrease amplitude of fluid consumption with the dosage of solid plugging agent
图 3 裂缝出口清水稳定流速恢复趋势
Figure 3. Recovery trend of the stable flow velocity of clear water at the fracture outlet
表 1 不同体系封堵实验测试数据
Table 1. Test data of different systems in the plugging experiment
序号 固相 加量/% 绒囊流体累计注入量/mL 1 无 0 146 2 无 0 139 3 无 0 141 4 颗粒 0.1 123 5 颗粒 0.2 114 6 颗粒 0.5 86 7 颗粒 1.0 63 8 颗粒 1.5 49 9 纤维 0.1 118 10 纤维 0.2 103 11 纤维 0.5 77 12 纤维 1.0 54 13 纤维 1.5 34 
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表 2 封堵返排后裂缝出口清水流速分布
Table 2. Flow velocity distribution of clear water at the fracture outlet after the flowback of plugging agent
固相 加量/% 不同驱替时间出口流速/(mL · min−1) 5 min 10 min 15 min 20 min 25 min 30 min 无 0 3.1 4.8 5.0 5.0 5.0 5.0 无 0 3.5 5.0 5.0 5.0 5.0 5.0 无 0 3.2 5.0 5.0 5.0 5.0 5.0 颗粒 0.1 2.6 3.6 5.0 5.0 5.0 5.0 颗粒 0.2 2.4 3.2 4.8 5.0 5.0 5.0 颗粒 0.5 1.7 2.8 4.3 5.0 5.0 5.0 颗粒 1.0 1.4 2.3 3.8 4.9 5.0 5.0 颗粒 1.5 0.9 2.1 3.5 4.5 4.9 4.9 纤维 0.1 2.3 3.5 5.0 5.0 5.0 5.0 纤维 0.2 2.2 3.1 4.5 4.9 5.0 5.0 纤维 0.5 1.3 2.5 3.9 4.3 4.9 5.0 纤维 1.0 1.1 2.0 3.4 4.6 4.8 4.9 纤维 1.5 0.5 1.8 3.1 4.3 4.6 4.8
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