| The reserves of unconventional oil and gas resources are very high.Multi-stage fracturing of horizontal Wells is one of the most critical techniques for economic and efficient development of such reservoirs.At present,when studying the law of fracture propagation in multi-stage fracturing of horizontal Wells,the injected fluid is mostly pure liquid,and proppant is seldom considered.In the optimization of fracture parameters in horizontal Wells,it is generally assumed that the fracture length,width and height of each cluster fracture are equal,without considering the fact that the fracture morphology is very complex in the actual multi-cluster fracturing process.And the conventional fracture parameter optimization method only finds the most suitable and ideal fracture parameters in the block,without considering what kind of fracture can be pressed by the actual fracturing construction.Therefore,it is urgent to master the multi-fracture propagation law of horizontal well staged fracturing,and optimize the construction parameters and predict the productivity of fractured horizontal well based on the actual fractures formed by multi-cluster fracturing,so as to scientifically guide the construction design and production,and provide technical support for the efficient development of unconventional oil and gas reservoirs in China.The main achievements and understandings of this paper are as follows:(1)On the basis of literature research,a mathematical model of multi-fracture propagation was established by comprehensively considering such factors as fracture induced stress field,fluid flow in fracture and wellbore,and fracture propagation criterion.The accuracy of the proposed model is verified by comparison with the analytical model of single fracture propagation and the existing numerical model of multiple fracture propagation.(2)Fracturing fluid with low formation elastic modulus and high viscosity is easy to form short and wide fractures after fracturing;Fracturing fluid with high formation elastic modulus and low viscosity is easy to form long narrow fractures after fracturing.However,long and wide fractures are easy to be formed for fracturing fluid with high displacement.With the increase of in-situ stress difference,the deflection Angle of edge cracks decreases rapidly.When the local stress difference exceeds 5MPa,the deflection of edge cracks almost does not occur.With the decrease of stratum elastic modulus,the increase of stress difference,the decrease of cluster spacing,the increase of hole diameter and number,the effective fracture length,average fracture width and liquid injection amount of edge fractures all increase,but the effective fracture height changes little.The effective seam length,average seam width,liquid injection amount and effective seam height of intermediate cracks all decrease.(3)Combined with the average physical property parameters of block M in Jilin Oilfield,a single stage and three cluster fracturing mechanism model of horizontal well is established.The optimal number of fracture clusters,cluster spacing,fracture length and fracture conductivity for single stage fracturing of horizontal Wells were analyzed by conventional optimization method.The actual fracture parameters were simulated by the mathematical model of multi-fracture propagation in this paper,and then imported into the homogeneous model after reasonable simplification.The optimal fracture distribution mode and fracturing fluid parameters were optimized with the goal of maximizing cumulative oil production within 10years.The optimal number of fracturing clusters in this block is 3,the optimal cluster spacing is 40m,the optimal fracturing fluid viscosity is 10m Pa?s,and the optimal fracturing fluid flow rate is 12 m~3/min.Finally,the fracturing fractures under this fracturing construction method are reasonably simplified and arranged into the actual geological model of the block,so as to predict the productivity of horizontal Wells after multi-cluster fracturing.The block adopts single horizontal well development,and the cumulative oil production in 5 years is 45190 m~3. |
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