Study On Adjustment Method Of Water Flooding Development In The High-Water-Cut Stage Of Low Permeability Reservoir

Water cut increases rapidly and production decreases sharply in the high-water-cut stage of low permeability reservoir.If reasons for this phenomenon were not clear,it is difficult to formulate the subsequent adjustment plan.Take a water flooding block of Yan’an formation in Ordos Basin as an example.Clarify the reservoir geological characteristics and production performance characteristics through fine reservoir description,production performance analysis and water injection development effect evaluation.The adjustment plan of the whole study area is formulated,and the feasibility of the horizontal well sectional injection-production technology in the study area is demonstrated.Firstly,clarify the structure characteristics and microstructure characteristics in the study area by layer correlation,single sand body division,sedimentary microfacies identification and oil layer interpretation.Divide Formation Y9 into 5 layers.25 maps and 16 profiles are drawn.Channel detention is identified as the dominant facies.NW-SE is the source direction.Distribution of sandstone is controlled by the distribution of sedimentary microfacies.The recalculated geological reserve is 784.88×10⁴t.Layer Y9₂¹ is the main layer.Secondly,according to differences of oil production capacity of production wells,the whole area is divided into high-yield area and low-yield area.Analyses of typical effective characteristics of production wells and production performance of 53 well groups suggests that the most important factor affecting the effect of water injection development is the effective type of wells affected by water injection.And the relationship between the connection direction of oil-water wells and the direction of material source is the most important factor affecting the speed of waterline.After evaluating the effect of water injection development by 7 indexes,the analysis shows that the main problems are low degree of water flooding control,high proportion of one-effect production wells and large number of shut-down production wells in this stage.Production well closed by the reason of lacking of liquid supply.Then,demonstrate the rationality of production and injection well measures from geological conditions and production performance.Put forward 7 wells to reperforate,10 production wells to put back on production,and 4 production wells to convert into injection well.After the measures,the controlled reserves of water drive is expected to increase by 25.23×10⁴t.The reasonable technical policy is demonstrated.The minimum bottom hole flowing pressure of production well is 1.01 MPa.The maximum wellhead injection pressure of injection well is 10.63 MPa.The injection production ratio in low production area is too high and should be reduced to about 1.12-1.25.The liquid production rate of production well in the northwest of study area and the injection rate of injection well in the central region of study area are considered too low.Suggest 12wells to increase liquid production rate or injection rate.Predict production index of typical well group by geological modeling and numerical simulation.It is predicted that the recovery of implementing adjustment plan after 15 years is 2.81 percentage points higher than implementing the original development plan.Finally,two kinds of mixed well patterns of vertical and horizontal wells are designed and deployed in the high-yield area.The horizontal wells adopt the wellbore structure of sectional injection and production and the water injection system is periodic water injection.Demonstrate the feasibility of the horizontal well sectional injection-production technology in the study area.The reasonable interval between production section and injection section of horizontal well is 100m.Through numerical simulation,the length of horizontal section,the length ratio of production section to injection section and the optimal time of injection stage are optimized.The recovery of using sectional injection-production horizontal well pattern scheme after 15 years is 10.4 and11.31 percentage points higher than the original well pattern scheme.