Experimental Study On Synergistic CO₂ Huff And Puff Of Horizontal Well Group In Fault-block Reservoir With Side Water

As an effective option to stimulate production from single well,CO2 huff and puff has been widely implemented.CO2 synergistic huff and puff is that the effect of gas injection goes beyond more than one production well.During the development of fault-block reservoir by CO2 huff and puff,its cause,factors,optimization and mechanism still remain unclear.This paper focuses on physical simulation,which is common in reservoir engineering.First,based on the similarity criterion,a 3D physical model of fault-block reservoir with horizontal well group and side water is built.Second,experiments are carried out from the aspect of injection and production method.Injected gas volume,structural portion of gas injection,quantity of gas injection well and allocation of gas volume are selected in injection method,and order of opening well and production round of huff and puff from production method are also explored.In addition,PV properties of simulated live oil mixed with different mole portion CO2 are studied.At last,based on the PV properties of CO2-oil,numerical simulations are implemented to further analysis the synergistic results of injection and production methods,facilitating the underlying mechanism of enhanced oil recovery by horizontal well group CO2 huff and puff.Results show that with more CO2 injected,more oil production is obtained,but the linear relation changes since exchange ratio drops,and equivalent volume under 7.5MPa brings a reasonable results in oil production and water control compared to other gas injection volume.From the results of gas injection from one horizontal well,with the rise of structural portion from which CO2 is injected,and more oil is produced from the middle and high structural portion,but weaker water control.Gas injection from low portion sees the highest oil recovery and lowest water cut drop.Under the same gas injection volume,CO2 injection from the low and medium portion simultaneously does not only suppress the advance of side-bottom water,but also sweeps remaining oil of the higher portion,giving a full play of gas utilization,much obvious than that of 3 wells.Once larger gas volume is injected from low portion,less water production and larger gas sweeping volume are obtained.After soaking process,preproduction in the medium portion bring a high oil production,as a reasonable release of supplied energy.With more gas injection cycles,less oil increased and lower gas utility from the later production cycles is obtained.The huff and puff prove to be efficient over two cycles of gas injection.Except for the oil expansion,mobility improvement and energy supply,gravity segregation,water suppression and large sweeping volume are the key mechanism causing synergistic effect during CO2 huff and puff.The optimized experiments offer theoretical guidance of CO2 huff and puff from horizontal wells in fault-block reservoirs in field application.