Study On Suitability And Oil-increasing Effect Of CO₂ Huff And Puff In Low-efficiency Horizontal Wells In JS Oilfield

The K2t1 reservoir of B1 fault block in JS oilfield belongs to the heavy oil reservoir with small block structure.Due to insufficient energy of formation,low displacement efficiency and flooding,more and more horizontal wells are in low-yield,low-efficiency and high-water-cut status.Poor water quality of the stratum is difficult to form or can not form an effective water injection well network,the formation energy is seriously insufficient,resulting in a large decline in the output of single wells in inefficient horizontal wells,and long-term low-yield state of insufficient liquid supply.For such low-yield and low-yield horizontal wells,conventional measures are difficult to tap the potential.However,the use of single-well throughput can supplement the formation energy,which is currently a better single-well stimulation technology.This paper is mainly aimed at the actual problems faced in the current development process of JS oilfield.Based on the investigation of relevant literatures at home and abroad,this paper evaluates the suitability of CO2 injection in target reservoirs,and uses indoor experiments and numerical simulation techniques.In-depth analysis of the influencing factors and mechanism of enhanced oil recovery,getting the following recognition:(1)After investigating a large number of domestic and foreign literatures,and statistically analyzing the various influencing param eters,the main considerations are fluid characteristics,reservoir characteristics,reservoir characteristics and other parameters.The evaluation criteria and weights of the inefficient low-level well injection CO2 throughput were obtained,and the fuzzy comprehensive evaluation method was used to evaluate the suitability of the inefficient horizontal wells.It was found that not any well was suitable for CO2 injection.(2)Through the comparison of the results of gas injection expansion experiments of crude oil samples,when CO2 is injected into the formation fluid,it will lead to an increase in the expansion coefficient,saturation pressure and dissolved gas-oil ratio of the crude oil sample,and the viscosity-reducing effect on the formation crude oil is also significant.Both of them are beneficial to improve the efficiency of oil displacement.With the increase of CO2 injection volume,the volume expansion capacity of formation oil and CO2 increases,and the relative volume increases obviously,indicating that the elastic energy plays a leading role in the process of CO2 displacement.(3)Through the indoor combined long core injection CO2 throughput test results,it is recognized that the injection pressure,injection volume,injection speed,soak time and throughput cycle have different effects on the recovery rate,of which the injection pressure and injection volume have the greatest influence,the injection pressure is 22.5MPa.The degree of recovery is 4.74%higher than the injection pressure of 14.5MPa,followed by the number of cycles,followed by the injection speed,and finally the well time.(4)Numerical simulation was used to study the mechanism of CO2 flooding in low-efficiency horizontal wells and the parameters were optimized.The results showed that there were some optimization values for the parameters such as injection volume and injection speed,and the effects of different parameters were also found to be different,but the results were basically consistent with the experimental results.The reasonable injection volume for optimizing and screening a single well is 800t,the gas injection rate is 80t/d,the well time is 10d,the liquid sampling speed is 30m3/d,and the throughput cycle is 2 cycles.Through the above research,it provides a new idea and a new method for increasing production and efficiency of inefficient horizontal wells in JS oilfield,it is helpful to the sustainable and stable production of oilfields.