Study On The Shale Gas Reservoir Production Decline Analysis And Forecasting Methods

In the current situation of international energy's contradiction of supply and demand is increasingly prominent,the effective exploitation of new energy is great significance to the national strategy,and shale gas as a new unconventional energy,especially after the successfully develop by North American countries,it gets the attention of the world.This thesis based on the shale gas reservoir characteristics and the seepage flow rule,obtained the change permeability formula of shale matrix and fracture,and then established unsteady seepage flow partial differential equation which considering the multi-scale seepage of gas in matrix and the stress-sensitive effect of fracture.Based on all survey,we get infinite large shale gas reservoir and the non-vertical fracturing horizontal production decline model,and then carried out the sensitivity analysis via the Stehfest numerical inversion and Visual Studio C++ programming.Get the following understanding and conclusions:(1)The relative contents of mineral is directly affect the gas storage and fractured growth.The more clay minerals and the more space for gas storage,and more brittle mineral are beneficial for micro fracture produce.(2)Shale matrix pores are mostly in the micron and nano scale,and make the gas flow appear multi-scale.So the effect of slippage effect and diffusion can not be neglected,established the change permeability formula of shale matrix and fracture.(3)Considering the multi-scale seepage,desorption and fracture stress-sensitive effect get shale gas reservoir double medium seepage formula and then obtained infinite large shale gas reservoir and the non-vertical fracturing horizontal production decline model.Through numerical inversion and programming calculations,the results show:the higher storage capacity ratio,the higher production in the beginning of stage and the slower decline;adsorption mainly affect the flow stage after crossflow period and the stronger adsorption have more production;the number of fractures affect the whole seepage stage,the more number of fracture,the bigger permeability and production;the larger half-leagth of the fracture,the greater fracturing area formed,and the higher production in the initial production stage;stress sensitive effect mainly appear the later flow period,and the bigger stress sensitive modulus,the fast production decline.(4)The more time used to calculation,the prediction results more accurate.When the fitting length is short,comparison to PLE model and SEPD,the prediction result of Duong model is relatively accurate.With the increase of fitting time,the prediction error of PLE model rapidly decreases.If PLE parameters are not defined,may lead to the prediction results deviation the real data;the parameter of q? in the Duong cumulative production model changing with production time;in order to reduce the risk of prediction,an optimal combination of shale gas production prediction method is proposed based on Combinatorial Theory.