超临界二氧化碳压裂裂缝研究现状与展望

Current Status and Prospects of Research on Supercritical CarbonDioxide Fracturing Cracks

超临界二氧化碳压裂是一种新型无水压裂技术,即可封存二氧化碳又可节约水资源,具有易起裂、缝网复杂、返排快、保护地层等特点。在压裂研究中裂缝起裂与形态至关重要,因此对超临界二氧化碳压裂裂缝起裂与形态展开调研,发现:超临界二氧化碳压裂的起裂压力很低,仅约为水力压裂起裂压力的70%,优势十分明显,目前对起裂主导机理,外界影响因素以及起裂后压力快速下降过程的研究尚存不明之处,未来需重点研究;超临界二氧化碳压裂产生裂缝非常复杂,比水力压裂裂缝具有更好的沟通性,学者们从黏度、温度、水平应力差、层理等多个角度讨论裂缝形态影响因素,未来可从滤失性、时间效应以及返排速率等参数入手,继续完善超临界二氧化碳压裂裂缝形态研究;超临界二氧化碳压裂产生的裂缝非常小,有效性难以评定,在研究配套增黏剂和支撑剂的同时,也可利用裂缝面粗糙特性,形成裂缝自支撑以增强裂缝有效性。

Supercritical carbon dioxide fracturing is a new type of waterless fracturing technology,which can store carbon dioxide and save water resources,and it has the characteristics of easy cracking,complicated sewing net,fast return,and protection of strata.The crack initiation and morphology of supercritical carbon dioxide fracture cracks were reviewed as two important characteristics in fracture study.More evidence show the advantage of supercritical carbon dioxide fracturing has a very low cracking pressure,only about 70%of the hydraulic fracturing cracking pressure.So far,the dominant mechanism of crack initiation,external influence factors and the rapid decline of pressure after cracking are still unclear,future works will focus on these aspects.The cracks formed by supercritical carbon dioxide fracturing are very complex,however,they have better connectivity than hydraulic fracturing cracks.Scholars discussed the factors affecting crack morphology from different views such as viscosity,temperature,horizontal stress difference and mat.In the future,more affords will be made to improve the shape of supercritical carbon dioxide cracks by taking parameters such as fluid loss,time effect and return rate.The cracks generated by supercritical carbon dioxide fracturing are very small,so that the effectiveness is difficult to assess.Therefore,studying on the tackifier and proppant,the crack surface roughness characteristics can be utilized to form crack self-supporting to enhance crack effectiveness.