Experimental Study On CO₂ Huff And Puff In Hong 87-9 Block Of Da'an Oilfield

The Hong 87-9 block in Da'an Oilfield belongs to low-permeability reservoirs.After conventional water-based fracturing,some well groups have production technology problems of insufficient formation energy and low yield and short stable production period.In order to expand the original crack volume and supplement the formation energy,the Hong 87-9 block of Da'an Oilfield has carried out CO2 waterless energy storage fracturing technology for the single well.The CO2 injection and return process of this technology is equivalent to CO2 huff and puff,the process utilizes the unique energy storage and compatibilization characteristics of CO2 to achieve the goal of increasing production in a single well.In this paper,the high pressure physical property test of CO2/crude oil system was carried out for this auxiliary flooding process.The general law of CO2 and crude oil was clarified.Through the long core CO2 huff and puff flooding experiment,the effects of various factors on CO2 throughput and oil displacement were studied,and the oil change effect of CO2 huff and puff was evaluated.This article has achieved the following results and understanding.(1)Using high temperature and high pressure sampler,CHY-? heavy oil viscometer and other experimental devices,the experimental study on high pressure physical properties of CO2/crude oil system was carried out.It is found through experiments that the crude oil in the 87-9 block of Da'an Oilfield is a typical non-Newtonian fluid,exhibiting low viscosity,low carbon and low saturation pressure,and has a large miscible potential.CO2 extraction is one of the mechanisms of-oil increase.It mainly acts on the C5?C7 component of crude oil;under high pressure conditions,the solubility of CO2 in the oil sample of this block is less sensitive to pressure;the viscosity reduction effect of CO2 on the block crude oil is not obvious.(2)Using the high temperature and high pressure core flow experimental device,the experimental research on the influencing factors of CO2 huff and puff and oil displacement(oil and gas two phases)was carried out.The results show that within a certain range,the lower the permeability,the smaller the oil saturation,and the higher the viscosity of the oil sample,the worse the CO2 huff and puff and oil displacement effect.The permeability increased from 5.12mD to 145.48mD,the recovery factor increased by 13.73%,the oil saturation increased from 26.97%to 48.0%,the recovery f-actor increased by 21.94%,and the oil sample viscosity increased from 1.26mPa s to 5.31mPa·s.The recovery factor was reduced by 5.73%.The higher the pressure,the better the effect of flooding and flooding.However,when the pressure exceeds the mixed phase pressure,the pressure increase rate is reduced.The pressure is increased from 18.02MPa to 26.01 MPa,the recovery rate is increased by 10.82%,and the pressure is increased by 26.01 MPa.To 32.15MPa,the recovery factor increased by 1.35%.The throughput can be divided into three stages.The first stage produces a smaller production pressure difference to prevent excessive gas production,and the second and third stages select a higher production pressure difference to ensure higher crude oil production..The throughput cycle increased and the overall recovery rate increased.The total recovery rate of CO2 huff and puff in the first 3 cycles was 52.72%.(3)Using the high temperature and high pressure core flow experimental device,the experiment of the CO2 huff and puff was carried out.Studies have shown that CO2 huff and puff shows a good oil-increasing effect,and a small amount of water flooding after CO2 stimulation can increase oil recovery slightly.The lower the water content,the more favorable the CO2 huff and puff effect,the more reasonable the production pressure difference is.Compared with the CO2 huff and puff effect when the water is just 98.15%,the oil recovery difference is 6.56%.Under the condition of high water content,the CO2 huff and puff is better than that of water flooding.In the first group,the CO2 huff and puff increased the recovery factor by 15.15%,the oil change rate was 0.758mL/mL,and the second group of experiments followed the water flooding recovery.The rate was 13.93%,and the oil change rate was 0.093 mL/mL.With the increase of CO2 injection,the recovery rate of CO2 is improved,but the utilization rate of CO2 is gradually reduced.The oil displacement efficiency under the condition of 0.4PV injection is the best,and the recovery factor is 18.13%.The rate of 0.232mL/mL,and the oil change rate of CO2 miscible flooding gradually decreased with the continuous displacement of the flooding.When the cumulative PV number reached 0.4PV,the oil change rate reached a maximum of 0.315mL/mL,and the cumulative PV number was injected.When the 1.2PV is reached,the oil change rate reaches a minimum of 0.133mL/mL.The research results in this paper provide a reference for the on-site application of CO2 huff and puff enhanced oil recovery technology in low-permeability reservoirs in Hong 87-9 block.It can be used as a reference for other low-permeability reservoirs to carry out CO2 flooding and flooding technology research.