提高CO_(2)封存强度的多层协同抽注技术

Improvement of CO_(2) Sequestration Intension with Collaborative Pumping-injection Technologies in Multi-formations

中国已提出2030年碳达峰、2060年碳中和的碳减排目标,提高CO_(2)捕集、地质利用与封存(CCUS)技术发展水平与商业化规模,是实现中国碳减排目标的关键所在。“十四五”规划已明确提出要开展碳捕集利用与封存(CCUS)重大项目示范。然而,由于中国大多数CO_(2)储层的低渗透、非均质等特征,导致单一储层的CO_(2)封存能力有限,无法满足CCUS重大项目示范所需的CO_(2)地质封存量。本文提出将CO_(2)封存强度(单位土地面积的CO_(2)封存量)作为评价CCUS项目储层封存能力的关键指标,并计算了中国主要CO_(2)咸水层封存和CO_(2)强化驱油场地的CO_(2)封存强度,结果表明,现有CO_(2)咸水层封存和CO_(2)强化驱油项目的封存强度大多在105 t/km^(2)以下,无法满足中国双碳目标的需要。为显著提高CO_(2)封存强度,提出CO_(2)多层协同抽注技术的概念,通过注入井在多个储层射孔注入CO_(2),并利用采水井从多个储层中采出咸水,实现储层可用孔隙和储层压力的最优化调控,最终实现CO_(2)封存强度的大幅度提高。为验证CO_(2)多层协同抽注技术的效果,利用T_(2)Well模拟软件,构建3种CO_(2)多层统注及协同抽注的数值模型,模拟了CO_(2)定压注入过程,分析了注入60 d后的储层压力分布、储层内CO_(2)饱和度分布及CO_(2)累计注入量。结果表明:在多层协同抽注条件下,储层压力聚集现象有明显缓解,从而降低了封存区域因压力聚集导致的力学不稳定性。通过分析CO_(2)饱和度可知,注入CO_(2)后,在抽注井间压力差的驱使下,羽流将向采出井偏移;此外,受岩石性质的影响,羽流形状和范围略有差异。根据3种条件下的模拟结果计算CO_(2)封存强度可知,各向异性砂岩条件下多层协同抽注的封存强度最高达到1.115×10^(6)t/km^(2),远大于现在已实施项目的封存强度。因此,多层协同抽注技术将较大地提高CO_(2)封存强度,有利于节约中国国土资源,促进CO_(2)封存技术的推广。

China has put forward a carbon emission reduction target to reach CO_(2) emission peak in 2030 and carbon neutrality in 2060.It is vital for China to improve the development and commercialization scale of carbon capture,utilization and storage(CCUS)technology,to achieve the carbon emission reduction target.According to the 14th Five-Year Plan,large-scale demonstration CCUS projects will be carried out in China.However,due to the low permeability and heterogeneity of most CO_(2) storage formations in China,the capacity of CO_(2) storage is limited,which cannot provide enough subsurface CO_(2) storage space for the operation of large-scale CCUS projects.In this study,the concept of CO_(2) storage intensity(the amount of CO_(2) storage per unit area)was proposed to evaluate the CO_(2) storage capacity of China’s ongoing CCUS projects as the key indicator.The CO_(2) storage intensity indicator was calculated in both deep saline aquifer CO_(2) storage and CO_(2)–EOR projects.The results showed that the CO_(2) storage intensities of all the listed projects were lower than 105 t/km^(2),which was unable to meet the needs of China’s dual carbon tar-get.To substantially improve the CO_(2) storage intensity,a multi-layer coordinative injection and pumping technology was proposed in this study.This technology can substantially improve the CO_(2) storage intensity by injecting CO_(2) through multiple perforation tunnels and extracting saline water from multiple formations.The available pore spaces are increased and the formation pressure is optimized with this technology,which fa-vors improvement of the CO_(2) storage intensity.To validate the performance of this technology,a multi-layer CO_(2) injection model was built by T2Well code for the numerical simulations of three different scenarios.CO_(2) injection was set as a constant pressure process during the 60 days in-jection.By looking at the pressure and CO_(2) saturation distributions,it was noted that the accumulation of pressure was reduced by the coopera-tion of injection and pumping,which decreased geomechanically instability.Based on the CO_(2) saturation distribution maps,migration of CO_(2) was driven by the pressure difference between the injection and pumping wells,which made the plume move toward the pumping wells.In addition,rock properties changed the shape and migration range of the plume during CO_(2) injection.The CO_(2) storage intensities were calculated under the three simulated conditions.Among them,the CO_(2) storage intensity for the heterogeneous sandstone was the highest,which reached 1.115×10^(6) t/km^(2).This value was far larger than China’s existing CCUS projects.In summary,the multi-layer injection and pumping technology can greatly increase the amount of CO_(2) injection,which is beneficial for the conservation of land in China and promotes the deployment of large-scale CCUS projects in China.