Study On Rich Gas-Nitrogen Combination Flooding In Low And Ultra-Low Permeability Layer

This paper is part of National Science and Technology Major Project in 13 th Five-Year,(2017ZX05009004)"low permeability and dense reservoir high efficiency improvement of recovery technology" the task.For gas slug combination flooding to enhance recovery in low and ultra-low permeability layer,used the YS oil field as the study background.The CMG software was used to establish a slim pipe model,and the dynamic distribution of rich gas and nitrogen in the oil-gas phase was numerically simulated in the process of rich gas-nitrogen combination flooding,and the mechanism of gas-slug combination flooding was analyzed.The homogeneous and heterogeneous models are established to simulate and calculate the oil displacement effect and gas displacement efficiency under different oil layer length-thickness ratio,permeability,permeability level difference,and rich gas slug size.Two types of natural cores of low permeability and ultra-low permeability with 30 cm long were selected to conduct laboratory physical experiments on five different displacement schemes of rich gas-nitrogen combination flooding,and the reasonable front slug size and oil displacement effect of rich gas-nitrogen combination flooding were determined.The CMG software was used to predict the oil displacement effect and economic benefit of rich gas-nitrogen combination flooding under the condition of five-point well pattern.Furthermore,the co MParative analysis of oil displacement effect and economic benefit of rich gas-nitrogen combination flooding and carbon dioxide-nitrogen combination flooding was carried out.The results show that the low and ultra-low permeability layer can reduce the amount of rich gas and give full play to the advantages of both rich gas and nitrogen by using the combination flooding method with reasonable front gas rich slug and subsequent nitrogen slug.In the slim pipe model,from the distribution of the rich gas and nitrogen in the oil and gas phase,the rich gas slug should have at least 0.5 PV to effectively prevent the impact of nitrogen escape on recovery,from oil recovery curve,reasonable slug of rich gas is 0.6 PV.In the homogeneous model,there is no significant difference in the recovery rate of rich gas-nitrogen combination flooding with different permeability when the number of rich gas PV injected is less than 0.6,and the lower the permeability of the injected rich gas PV is more than 0.6,the higher the final recovery is.In the heterogeneous model,the larger the permeability level difference is,the smaller the reasonable size of the rich gas slug in the rich gas-nitrogen combination flooding is,and the lower the recovery rate is.In the physical model experiment,the slug composition of rich gas-nitrogen combination flooding is 0.6 PV rich gas slug + subsequent nitrogen.At this time,the recovery of rich gas-nitrogen combination flooding in ultra-low permeability core is 73.21%,and that of rich gas-nitrogen combination flooding in low-permeability core is 65.91%,with a difference of 7.3%.In low and ultra-low permeability five-point well pattern,limiting gas-oil ratio constraints or limiting daily oil production constraints of rich gas-nitrogen combination flooding of rich gas slug with 0.6 PV advisable.At this point,the low permeability pattern of rich gas-nitrogen combination flooding with limiting gas-oil ratio constraints recovery is 51.46%,the limit daily oil production constraints recovery is 52.80%;the ultra-low permeability pattern of rich gas-nitrogen combination flooding with limiting gas-oil ratio constraints recovery is 50.88%,the limit daily oil production constraints recovery is 51.90%.In the five-point well pattern element,low and ultra-low permeability layer reasonable rich gas-nitrogen combination flooding front slug are 0.6 PV,reasonable carbon dioxide-nitrogen combination flooding front slug are 0.4 PV.In low permeability layer rich gas-nitrogen combination flooding recovery is 6.73% lower than carbon dioxide-nitrogen combination flooding recovery,the input-output ratio of rich gas-nitrogen combination flooding is 0.38 times that of carbon-nitrogen combination flooding.In ultra-low permeability layer rich gas-nitrogen combination flooding recovery is 12.10% lower than carbon dioxide-nitrogen combination flooding recovery,the input-output ratio of rich gas-nitrogen combination flooding is 0.39 times that of carbon-nitrogen complex flooding.In general,carbon dioxide-nitrogen combination flooding has some advantages over rich gas-nitrogen combination flooding.