Optimization Design Of Gas Injection Scheme After Water Flooding In Block 28

Block 28 was put into production in 1990,after a long period of water injection development resulting in the development of dominant seepage channels and strong inhomogeneity between levels and layers,although a series of production enhancement measures have achieved a rebound in production,the overall development effect is still poor.By 2021,the comprehensive water cut of the reservoir reaches 96.84%,and the effect of continued water injection development is poor.Moreover,Block 28 has a large dip angle and high temperature,and it is difficult to preferentially select the replacement medium to increase the recovery rate.Through the investigation of efficient development methods in reservoirs at home and abroad,combined with the physical properties of the block and the development experience of similar blocks,it is considered that it is better to adopt gas injection development in Block 28.For this reason,this thesis proposes to carry out the optimization design of gas injection scheme after water flooding in Block 28,aiming to provide technical support for further recovery improvement in this block.This thesis uses Petrel software to establish a three-dimensional geological model of Block 28,which can accurately describe the fault changes and geological characteristics of Block 28.Based on the development process of the block and actual production data on site,a numerical simulation model for water flooding in Block 28 was established using CMG software on the basis of geological models,and the water flooding history was fitted.It was determined that the remaining oil reserve after water flooding was 56.5×10⁴t,the remaining oil distribution types are structural high position type and thick oil layer top type.Using numerical simulation technology,a gas flooding simulation model was established for Block28.By comparing the enhanced oil recovery values,gas flooding gravity,and economic benefits of natural gas flooding and CO₂ flooding,it was finally determined that the natural gas flooding extraction method would be adopted in Block 28,and the injection and production parameters of natural gas flooding were optimized.After optimization,the optimal parameters for Block 28 are:the injection rate of 0.08HCPV/a,the shut-in limit of 2500m³/m³,the injection method of alternating gas and water injection,the injection cycle of 1:2,and the liquid production rate of 8%.Three gas injection development schemes were designed based on parameter optimization results.By analyzing the economic benefits and enhanced oil recovery effects of the three schemes,the optimal scheme was determined to be:high gas injection+central oil production+low liquid discharge,with an increase in oil recovery value of 17.89%.Development indicators were predicted for this scheme,and it was predicted that the cumulative oil production in 10 years would be 10.108×10⁴t,indicating the significant natural gas flooding effect.It can be used as a further efficient development technology for Block 28.