The Optimization Research Of Multi-stage Fracturing In Vertical Wells For Low Permeability Reservoirs

The low permeability reservoirs have become the focus of exploration and development as the recoverable reserves of conventional petroleum resources gradually reduce.There are some features: deep buried,low abundance,low permeability,large span,single thin layer in low permeability reservoirs of Shengli Oilfield.With the influence of inter-layer heterogeneity,the reservoirs can not be stimulated evenly using general fracturing technology and it is difficult to realize equilibrium development.In order to solve the problem above based on the technology of multi-stage fracturing in vertical wells the productivity analysis and economic evaluation are done on the basis of some multi-stage fracturing vertical wells of Shengli Oilfield,and the seepage characteristics of multi-stage fracturing vertical well are analyzed;the method of calculating limit well spacing between the injection and production wells and determining water flooding extent is built;the algorithm of layer combination and fracturing parameters optimization of multi-stage fracturing is established.The productivity of several multi-stage fracturing vertical wells in Yi 171-1 Block and Zhuang 23 Block is analyzed.Based on the principle of break-even balance,the economic evaluation of multi-stage fracturing is done.And the economic policy boundaries and the corresponding charts of different condition are obtained.Using the conceptual model of low permeability reservoirs multi-stage fracturing vertical well,the pressure,the streamline and the pressure gradient field are analyzed horizontally and vertically and development rules of multistage fracturing vertical well are studied.Based on the model of "one injection and one production",the pressure gradient distribution between injection and production wells is calculated and the limit well spacing between the injection and production wells of non-fracturing layer and fracturing layer is obtained.The concept of water flooding extent is defined,and the algorithm of determining water flooding extent of multi-stage fracturing vertical wells in low permeability multi-layer reservoirs.The evaluation result of some block in Bonan shows that the water flooding extent can increase by 14%.Based on the equivalent well diameter model and productivity model considering TPG for low permeability reservoirs,the on-site requirement of multi-stage fracturing in vertical wells,economic benefits of each fracturing stage,and the balanced development target the multi-stage optimization method of multi-stage fracturing of vertical wells for long-span multi-layer low permeability reservoir is established to optimize the layer combination and fracture parameters.