Production Decline Analysis On Volumetric Fractured Horizontal Wells In Tight Reservoir

With the development of national economy and increasing demand of oil and gas,unconventional oil and gas resources like dense oil reservoirs have been the development hot spots on the current energy situation.However,it's difficult to gain economic production in dense reservoirs using the development methods of the conventional oil and gas reservoirs,owing to their dense lithology and poor properties.Now large-scale application of horizontal well volume fracturing technology increases the reservoir fluid velocity and realizes economic development of dense oil reservoirs.Because of complex distribution of features in dense reservoirs by volume fracturing and different production decline characteristics of production wells in dense reservoirs from that in conventional reservoirs,it's necessary to research further.This paper established a half analytical model of matrix-fracture compound flow in a volume fracturing horizontal well in dense reservoir.Based on the features of dense oil reservoirs and complex distribution of fracture network by volume fracturing,the model used the method of point source function and superposition principle and considered the influence of different fracture conductivity and fracture angle.And then it was solved by Stehest numerical inversion method.Based on this model,the influences on production decline law were studied,and the influences on flowing phase were analyzed by using flowing phase partitioning method in volume fracturing horizontal wells considering production characteristics.And then the main control factors and their effect weight of volume fracturing horizontal well production decline were calculated by using orthogonal design method and considering factors influencing production.Finally,the method of mathematical statistics was used for production forecast and the applicability of following models was analyzed: power rate exponential decline model,extension exponential decline model and Duong model.And it shows that Duong model has a good application to dense reservoirs.So the model was used to predict the production in a dense oil reservoir.By improving the clustering analysis method,a new method of production prediction was proposed based on mathematical statistics analysis of old well field.And it was then applied to the instance.The results show that the flow phases in volume fracturing horizontal well of dense oil reservoir include linear flow,quasi radial flow,compound linear flow,elliptical flow and boundary control flow.And the higher initial production and the longer compound linear flow stage,the larger cumulative production can be obtained in horizontal well.However,the compound linear flow duration time was controlled by fracture half length,fracture spacing,fracture angle and other factors.The main control factors and their weights are: fracture number(24.47%)> fracture half length(20.21%)> well length(19.16%)> matrix permeability(12.76%)> porosity(9.57%)> fracture angle(7.45%)> fracture conductivity(6.40%).The prediction error of the improved clustering analysis method is within 5%,which conforms to the requirements of the field,and it can be used to predict the production of new horizontal wells.This research has theoretical guidance meaning for the effective development of dense oil reservoir.