Major Factors Impacting Situmulated Reservoir Volume During Network Fracturing In Tight Oil Reservoir

Geological factors and engineering factors have significant impact on network fracturing in the tight oil reservoir,which directly decide the possibility of forming complex fracture network and the size of stimulated reservoir volume(SRV).And the SRV has an evidently positive correlation with cumulative production.Therefore,based on discrete fracture network model,a network fracturing modeling has been built for block A in Chang 7 tight oil formation of the Ordos basin,by which the influence on the SRV from the major geological factors(brittleness index,natural micro-fracture development degree and horizontal stress difference)and the major engineering factors(fracturing scale,pumping rate,cluster space,pad fluid proportion,average sand liquid ratio and fluid viscosity)has been methodically simulated and analyzed.This study has important theoretical value and practical significance to the understanding of controlling factors of hydraulic fractures extending into network and can improve the science of tight oil reservoir fracturing design.This study proposed the criteria for formation selection of network fracturing for block A in triple ways: the brittle index,the natural micro-fracture development degree and the horizontal stress difference.Aslo the suitable ranges of the fracture operation scheme are given.This study shows that there is a critical brittleness index to create complex fracture network for a given operation condition and tight reservoir properties.Above the critical brittleness index and the greater the brittleness index is,the greater the stimulated reservoir volume.The SRV would increase at first and decrease later with the increase of natural micro-fracture development degree,while the secondary fractures increase all the time.When the horizontal differential stress is less,the width of the fracture network would reach up to hectometre and its SRV is more than one hundred times of the bi-wing fractures’.The great pumping rate and large amount of fracturing fluid are the condition of creating complex fracture network.The greater the pumping rate and the bigger the fracturing scale are,the greater the stimulated reservoir volume and the higher the production rate.For multi-cluster fractures,fractures with non-synchronous cracking will yield non-synchronous extensions of the fractures.The late cracked and extended fracture has strong trend to extend in traverse direction under the stressshadow effect of the early extended fracture,which may connect nearby natural micro-fractures and easily create complex fracture network with bigger SRV.Larger pad fluid proportion will be constructive to more complex fracture network and greater SRV.Due to the sand primarily used to improve the conductivity of main fractures,the sand liquid ratio has little effect on the size of complex fracture network and the SRV.It is proven that using the slickwater as prepad fluid is much important than lower viscosity for enlarging the SRV.