Investigation On Allied In-situ Injection And Production With Horizontal Well For Improving Tight Oil Recovery

Considerable tight oil reservoirs in China usually encounter the problem of low formation pressure,so the oil production rate declined rapidly during the primary stage.It is necessary to maintain formation pressure by fluid injection.However,based on the field experience,fluid injection by the vertical well in tight oil reservoirs has a low injection rate and limited sweep efficiency,leading to inefficient pressure maintenance level.This paper proposes using Allied In-situ Injection and Production(AIIP),which divides one horizontal well into 2 segments for injection and production,to increase fluid injectivity and sweep efficiency for the tight oil reservoir with a long horizontal well group.This paper proposes 3 kinds of schemes for AIIP,constituency AIIP(C-AIIP),pulse AIIP(P-AIIP)and asynchronous AIIP(A-AIIP),to achieve a better improving oil recovery(IOR)performance than vertical well injection and prevent the risk of gas breakthrough during AIIP with gas injection.Based on the condition of a tight oil formation in Ordos Basin,this paper studies the feasibility of AIIP by the simulation approach.Different injection schemes and injection fluids are discussed in this study.After that,the sensitivity analysis of AIIP is conducted to study the influence of several parameters.The IOR performance of AIIP is also evaluated based on a geological model in the same tight oil formation of Ordos Basin.Simulation results indicate that AIIP can increase the injection rate by 6 times and up to 21.8%more oil recovery compared with the vertical well injection.So AIIP method has a better formation pressure maintenance level and a better sweep efficacy,it is a promising method for IOR in tight oil reservoirs.Under the same gas injection volume per period,A-AIIP has a higher oil recovery,later gas breakthrough time,and it is less affected by penetration fractures among horizontal wells.Therefore,A-AIIP is more adaptable than C-AIIP and P-AIIP for the tight oil reservoir development.Natural gas shows the best IOR performance among 4 kinds of injected fluids.Sensitivity analysis of AIIP indicated that the optimal parameter for well pattern,injection-production segments length proportion,well spacing,hydraulic fracture half-length,injection fracture half-length,fracture conductivity,injection volume for one well per period,injection rate,soaking time should be staggered co-current horizontal well pattern,1:2,400 m,125 m,75 m,60×10^-3?m²·m,90×10⁴ m³,3×10⁴m³/d,15 to 30 days,respectively.Simulation results for the geological model indicate that AIIP has a better IOR performance than natural gas huff-n-puff,and A-AIIP has the best IOR potential among A-AIIP,C-AIIP,P-AIIP.This study provides a new approach for the horizontal well development of tight oil reservoirs.