Experimental Investigation On Effect Of Air Injection Rate And Horizontal Well Spacing During Toe-to-heel Air Injection Process

The trend of low oil price and the increasingly stringent environmental protection policy have brought great challenges to heavy oil exploitation.Among all the well pattern for Combustion Assisted Gravity Drainage(CAGD)method,the Toe-to-Heel Air Injection(THAI)method has attracted extensive attention from scholars due to the advantages of low cost,high recovery rate and oil upgrading.However,gas channeling is prone to occur in the current well pattern,and even cause engineering risk.The objective of this paper is to optimize the well network pattern from the perspective of air injection rate and horizontal well spacing.In this paper,the three-dimensional cylindrical reaction vessel devised by the research group is used to simulate the THAI process under formation conditions.The spatial distribution of the coke zone is manually measured then imported into the CAD software to reconstruct the coke zone to obtain its distribution characteristics.The temperature data was processed by Matlab software to obtain the vertical mid-plane temperature field diagram of the reaction cell at any moment.The two-dimensional distribution of the reconstructed coke zone is coupled with the vertical mid-plane temperature field to obtain a temperature region in which the coke zone is easy to generate,and the coke zone distribution at any moment can be predicted.The combustion front temperature is calculated considering the heat loss,and the propagation speed of the combustion front in the upper part and middle part are calculated to characterize the propagation characteristics in the fire chamber.In conjunction with temperature and gas concentration data,parameters such as fuel amount and fire chamber volume are processed and calculated to characterize combustion and production performance.Through 8 sets of varying well spacing and varying gas injection speed experiments,the dynamic distribution characteristics of the coke zone,combustion and production performance,and the propagation characteristics of the combustion front were studied.The effect of air injection rate and horizontal well spacing on the THAI process was analyzed.Finally,the similarity criterion is used to amplify the air injection rate and horizontal well spacing to the site scale,and an on-site scale ideal model is established in CMG to study the influence at this scale.The results of the physical model show that the propagation speed of the combustion front in the middle of the fire chamber is significantly affected by the air injection rate and the horizontal well spacing.Improper air injection rate and horizontal well spacing can cause premature oxygen breakthrough and generate erratic coke zone distribution,reducing the final recovery factor.The cumulative oil production curve and temperature field obtained by numerical simulation have certain similarities with the results of the physical model,and the effects are also validated.