Economic Optimization For Multi-stage Fracturing In Tight Gas Reservoir

Horizontal drilling and multi-stage fracturing are two reliable technologies which have made recovery of tight gas economically viable.Economic optimization design was necessary before fracture operation by taking reservoir properties and investment constraints into consideration.Two key issues need to be solved in economic optimization: The first question is how to predict the cumulative gas production more quickly and accurately;and the second issue is under the premise of NPV maximization how to find a proper method to evaluate economic benefits.In this paper,a new integrated but constrained economic optimization model to optimize fracture parameters has been developed to maximize NPV with minimum treatment cost,the model was applied in the Sulige tight gas reservoir to get optimal fracture parameters.Parametric studies were conducted to investigate the effects of several factors on well performance,the result shows there exists only one fracture geometry would maximize production for any fractured well.Combining gray relational theory to analyze the sensitivity of each parameter to get the weight of each factor,these factors are in the descending order of porosity,matrix permeability,drainage area,horizontal wellbore length,number of fractures,fracture length and fracture conductivity.Developing the GA-BP production forecast software based on the theory that genetic algorithm is used to optimize the weights of the BP neural network.Not only the prediction result meets the precision,but also the software’s flexibility is higher than other commercial simulators.Considering the impact of non-Darcy flow,the effective permeability is introduced to correct the proppant number which makes the result more accurate.Considering the shape difference of reservoir,shape factor is used to amend the conventional UFD theory under different aspect ratio.Based on the NPV theory,using the GA-BP software to predict cumulative gas production,and the economic optimization model is developed to help the design engineer to optimize fracture parameters in horizontal well.