Enhanced recovery of tight reservoirs after fracturing by natural gas huff-n-puff: Underlying mechanisms and influential factors  

作　　者：Chuan-Jin Yao Ya-Qian Liu Bai-Shuo Liu Zheng-Dong Lei Jia Zhao Lei Li 

机构地区：[1]National Key Laboratory of Deep Oil and Gas,China University of Petroleum(East China),Qingdao 266580,Shandong,China [2]Key Laboratory of Unconventional Oil&Gas Development(China University of Petroleum(East China)),Ministry of Education,Qingdao,266580,Shandong,China [3]School of Petroleum Engineering,China University of Petroleum(East China),Qingdao,266580,Shandong,China [4]Research Institute of Petroleum Exploration&Development,PetroChina,Beijing,100083,China

出　　处：《Petroleum Science》2023年第6期3498-3515,共18页石油科学（英文版）

基　　金：supported by the National Natural Science Foundation of China(Grant No.U22B6004,51974341,51904324);the Fundamental Research Funds for the Central Universities(No.20CX06070A);the Science and Technology Support Plan for Youth Innovation of University in Shandong Province(Grant No.2019KJH002).

摘　　要：Tight oil resources are abundant in the world.It is very important to strengthen the research on the development theory and technology of tight oil reservoirs for ensuring national energy security.Natural gas huff-n-puff can effectively improve the oil recovery of tight oil reservoirs.However,the pore-scale oil production characteristics and the mechanisms of natural gas huff-n-puff in matrix-fracture cores are poorly understood.The influence degree of important factors on oil recovery is not clear and the interactions between factors are rarely considered.In this paper,the oil production characteristics and mechanisms of natural gas huff-n-puff in tight cores with different fracture lengths were quantitatively analyzed by combining nuclear magnetic resonance(NMR)with numerical simulation technology.The influencing factors and their interactions were evaluated by the response surface method(RSM).The results show that tight cores mainly consist of medium pores(0.1–1μm)and small pores(0.01–0.1μm).The fracture mainly increases the proportion of macro-pores(1–10μm)and medium pores.In the natural gas huff-n-puff process,crude oil from macro-pores(1–10μm)and medium pores is mainly developed,and the contribution percentage of crude oil in medium pores to oil recovery is the largest,up to 98.28%.The position of gas–oil contact(GOC)moves deeper as the number of huff-n-puff cycles increases.The contents of CH_(4) and CO_(2) in the oil phase remain at a high level within the GOC,while between the GOC and the component sweep front,the contents of CH_(4) and CO_(2) in the oil phase decrease with the increase in dimensionless distance.The gas component sweep volume is increasing with the increase in fracture length.Moreover,the injected natural gas mainly extracts C_(3)–C_(10) components from crude oil.The reduction law of crude oil viscosity is consistent with the migration laws of CH_(4) components along the path.Compared with soaking time and gas diffusion coefficient,the injection pressure is the most signi

关 键 词：Natural gas huff-n-puff Matrix-fracture cores Nuclear magnetic resonance(NMR) Numerical simulation Response surface method(RSM) 

分 类 号：TE357.1[石油与天然气工程—油气田开发工程]