Reducing Formation Damage to Low-Porosity and Low-Permeability CBM Reservoirs Using Calcium Carbonate Nanoparticles
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摘要: 传统暂堵剂难以封堵低孔低渗煤层气储层中的大量纳米级别孔隙.通过煤岩显微观测、钻井液基本性能测试、泥饼清除实验、煤岩孔隙分布实验和气体渗透率实验,探讨了纳米碳酸钙降低低孔低渗煤层气储层伤害的效果.结果表明:纳米碳酸钙材料只有在水溶液中保持纳米级的分散状态,才可能对低渗煤岩起到暂堵作用;基于纳米碳酸钙的可降解钻井液既能封堵低孔低渗煤岩中微米级别孔隙,也能封堵其中的纳米级别孔隙;经过生物酶和稀盐酸双重解堵后,煤岩渗透率恢复值达77.17%~97.98%,储层保护效果好;煤岩孔隙分布实验可以在纳米尺度上研究纳米材料对低孔低渗储层的暂堵效果.研究成果可为纳米碳酸钙在低孔低渗煤层和页岩钻完井过程中的应用奠定良好技术基础.Abstract: It's difficult to block a mass of nanoscale pores in the low-porosity and low-permeability coalbed methane (CBM) reservoirs using traditional temporary plugging additives. The performances of reducing formation damage to low-porosity and low-permeability CBM reservoirs using calcium carbonate nanoparticles (nCaCO3) are evaluated in this study through microscope investigation of coal rocks, the basic performance tests of drilling fluid, mud cake removal tests, pore size distribution tests and gas permeability tests of coal rocks. It is found that only when nCaCO3 are dispersed to nano-scaled state in water solution could it temporally plug the low permeability coal rocks. However, nCaCO3 based degradable drilling fluid not only blocks the microscale pores in low-porosity and low-permeability coal rock, but also blocks the nanoscale pores. With the double unplugging technology of biological enzyme plus low concentration hydrochloric acid on the nCaCO3 based drilling fluid, the permeability recovery rate of coal rocks ranges from 77.17% to 97.98%. The reservoir protective effect on reservoir proves good. It is shown that the pore size distribution test could be used in the investigation on temporally plugging performance of nanoparticles to low-porosity and low-permeability reservoirs on nanoscale. This study may offer a technical support to facilitate future applications of nCaCO3 in drilling and completion process of low porosity and low permeability coal seams and shale formation.
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表 1 基于纳米碳酸钙的可降解钻井液基本性能
Table 1. Basic properties of nCaCO3-based degradable drilling fluid
密度(g·cm-3) 表观黏度(mPa·s) 滤失量(mL) 滤饼(mm) pH 1.02 23.00 13.40 0.20 7.00 表 2 基于纳米碳酸钙的可降解钻井液的破胶效果
Table 2. Gel breaking efficiency of nCaCO3-based degradable drilling fluid
时间(h) 表观黏度(mPa·s) 破胶率(%) 0 23.00 - 1 4.70 79.57 2 3.70 83.91 3 3.50 84.78 12 3.30 85.65 表 3 纳米碳酸钙分散液暂堵过程中的煤岩气体渗透率变化
Table 3. Coal rock permeability fluctuation in temporary plugging process of nCaCO3 dispersion
煤样编号 上流压力(MPa) 气体渗透率(0.986 9×10-15 m2) 渗透率恢复率(%) K0 K1 K2 1# 0.40 2.46 1.18 3.21 130.49 0.50 2.67 1.40 2.94 110.11 0.60 3.10 1.79 3.57 115.16 2# 0.50 0.61 0.46 0.72 118.03 0.55 0.68 0.50 0.77 113.24 0.60 0.72 0.57 0.91 126.39 表 4 纳米碳酸钙钻井液暂堵过程中的煤岩气体渗透率变化
Table 4. The coal rock permeability change in the process of temporary plugging in contact with nCaCO3 drilling fluid
煤样编号 上流压力(MPa) 渗透率(0.986 9×10-15 m2) 渗透率恢复率(%) K0-1 K1-1 K2-1 K3-1 3# 0.45 0.82 0.33 0.50 0.68 82.93 0.50 0.92 0.41 0.54 0.71 77.17 0.60 1.24 0.53 0.80 0.96 77.42 4# 0.45 0.99 0.53 0.79 0.97 97.98 0.50 1.02 0.64 0.88 0.98 96.08 0.60 1.21 0.66 0.89 1.10 90.91 -
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