Infill Adjustment Of Development Well Patterns And Research On EGR Feasibility Of CO₂ Flooding In Zhao 10 Block

Tight sand gas is the main type of unconventional natural gas,and it has great resource potentiality and considerable reserves in China.It is important to improve development efficiency of such gas field.Zhao 10 block is the typical example of low-permeability and tight sandstone gas reservoirs,and infill drilling is an effective method to improve the recovery of tight sandstone gas reservoirs.However,the present design of well spacing density in Zhao 10 block is relatively low.What's more,the well patterns are extremely uneven for progressive development and concentrated well construction,which cause severe stable situation.Therefore,This paper is funded by CNPC with the project of "Research on Infill Adjustment of Development Well Patterns and Enhanced Gas Recovery Technique in Zhao 10 Block" and conducts the study on infill adjustment of development well patterns and EGR feasibility of CO₂ flooding in Zhao 10 block,which can provide technical support to further increase of the ultimate recovery.This paper takes Zhao 10 block as research object,calculates the single well control reserves of 90 production wells with multiple methods,estimates drainage radius under single well control by combining geological static information,and analyzes the adaptability of current well pattern.Besides,gas reservoir engineering method is used to determine the optimum well spacing of different well types.Then the geology model is established on the basis of integrated analysis to static and dynamic data of Zhao 10 block,and the total grid nodes number of the geology model is 5967360?240 × 224 × 111?.Based on predictions of 15 kinds of well patterns in numerical model,a combination of natural gas engineering and economic evaluation is applied to assess and evaluate reasonable well spacing and well infilling.Even after infill adjustment,the recovery of tight sandstone gas reservoir is still lower than that of conventional gas reservoir.So the feasibility of carbon sequestration with enhancement gas recovery of a typical well group is studied.After CO₂ diffusion coefficient is obtained by experiment,designing 20 kinds of prediction scheme to optimize the placement of perforations,injection time,injection-production pattern,and injection rate.Research result shows that:?1?The cumulative control reserves of block existing production wells is 23.34×108m3,and reserves control degree is only 12.28%.?2?Although the current well pattern 600m×800m can be infilled directly to enhance gas recovery to some extent,this solution is not economical.For areas with established production wells,irregular partial infill is feasible and 18 infill well coordinates are provided.?3?Vertical well pattern can effectively improve the degree of producing reserves in the vertical,horizontal well pattern can effectively improve the degree of producing reserves on the plane.Therefore vertical well pattern?500m×600m?&horizontal well pattern?500m×1700m?is eventually adopted in Zhao 10 block,and this pattern can improve the gas recovery to 46.9%.?4?Based on numerical simulation model of typical well groups,the optimization scheme is verified,research area is developed by depletion for the first 20 years and then considered for CO₂ injection,gas injection in the base of producing layer,gas extraction at the top of producing layer and optimal daily injection volume is 3×104m3/d.Gas diffusion results in more uniformed CO₂ distribution in the whole formation,making ultimate storage pressure lower and the safety of the storage is higher,so gas diffusion is helpful to stable storage of CO₂.Eventually,typical well group improved recovery efficiency from 50.9%to 68.7%,and 1.10×106t CO₂ stably stored underground,indicating selected area a suitable place for carbon sequestration with enhancement gas recovery.