A Study On Hydraulic Fracture Vertical Propagation In Tight Sandstone Reservoirs

Hydraulic fracturing is one of most important stimulation methods for unconventional reservoirs.During the treatment of hydraulic fracturing,the initiation and propagation of hydraulic fractures plays an important role in stimulation performance.In layered reservoirs,the propagation of hydraulic fractures can be affected by many factors such as geological factors,rock mechanics characteristics,interface features,hydraulic fracturing operational parameters and so on.Fracture propagation is really complex because of these influential factors.During fracturing practice,coal layers also affect the performance of the treatment.This paper conducts both numerical simulation and indoor experiments to investigate fracture vertical propagation in tight sandstone reservoirs.Tight sandstone reservoir,as an unconventional reservoir,has a very low permeability and porosity.During hydraulic fracturing,its rock mechanical characteristics can exert a strong influence on fracture propagation behavior.Firstly,this paper conducts indoor experiments to acquire the static elastic parameters,strength parameters and fracture strength of tight sandstone reservoirs.These results can be used as basic parameters for numerical simulation.Then,according to the conditions of interface cementing,we divide the reservoirs into two types.The one is well cemented in the interface and the other is not well cemented.For these two types of reservoirs,we investigate the influence of geological factors,rock mechanics characteristics,operational parameters on the vertical propagation of hydraulic fractures.For the well cemented case,we conduct indoor experiments and numerical simulation to compare the results.For the uncomplete cementing case,we just perform numerical simulation to investigate the influence of all the above parameters on fracture vertical propagation.Besides,the interface characteristics are also considered for the uncomplete cementing case.During the practice of hydraulic fracturing,it is very typical for the tight sandstone reservoirs being interbedded with coal beds.Compared with conventional formations,coal beds have lower strength,lower modulus,higher passion ratio and lower fracturing pressure.Therefore,it is easier for fractures to initiate and propagate in coal beds than tight sandstone formations.This paper conducts both numerical simulation and indoor experiments to study the influence of coal beds on fracture vertical propagation in layered reservoirs.Finally,we compare the results from the experiments and numerical simulation and get some results.These results can help us better understand the fracture propagation behavior and then make some suggestions to real practice.