Numerical Simulation And Experimental Research On The Oil Shale Hydraulic Fracturing

Oil is lifeblood of the economic development, especially for our country with thesharply increasing demand since the21stcentury. However, the traditional gasresources has been difficult to meet the demand of the economic development ofChina with a few large fields of aging. In this case, oil shale, as a very importantenergy, has been catching more and more attention, whose reserves are rich in7199.37billion ton with shale oil in476.44billion ton in China.Traditional methods of the oil shale mining have some high-cost and environmentpollution problems, even including the so-called oil shale in-situ mining technology,which has few environment pollution but long-term production problems. Therefore,it’s imminent to seek a efficient and economic mining method.The key problem for the oil shale in-situ mining is to improve the permeability ofthe shale rock, and the most effective way shall be creating some. Hydraulicfracturing technology shall be one of the important technical method to create thepermeability of oil and gas on the initial stage which will greatly improve the miningefficiency. And the Electro-frac TM technology experimental results showed that theoil shale in-situ hydraulic fracturing should be feasible.This paper mainly analyzed the crack stress in the hydraulic fracturing process,crustal stress condition and the influence regularity of the perforation parameters onthe crack stress with the theoretical analysis, numerical simulation and the labsimulation experiments.Through the theoretical analysis, the paper got the fracture pressures while the oilshale formation being hydrofractured in an open hole and perforation completionmethods, and calculated the theoretical values with the actual parameters of the shalefields in Huadian City and Nong’an County in two different completions above. Andthis paper analyzed the crustal stress distribution conditions of the formation near the wall in the open hole completion and near the hole wall in the perforation completion,getting two different fracture locations.Through the numerical simulation, the paper simulated the hydraulic fracturingprocess in the oil shale field of Nong’an City respectively in an open hole completionand perforation completion using a real failure process analysis software of thetwo-dimensional version, getting the crack stresses in the completions above andcomparing with the theoretical calculation results. At the same time, the papersimulated the crack initiation process of the hydraulic fracturing under the conditionsof different crustal stresses and perforation parameters in the perforation completionto analyze the influence regularity of the crustal stress and perforation parameters onthe crack stress.As for the lab simulation experiments, a true triaxial test bench was established inthe first place. The bench could be used to conduct some hydraulic fracturingsimulation experiments with some samples of a certain size, simulating and acquiringthe pressure changes in the casing. what’s more, the bench could be used to simulatethe hydraulic fracturing process of the oil shale. The samples used in the experimentwere prepared in the method of the oil shale coating with the concrete. Through theexperiments, the paper got the data of the hydraulic fracturing crack stress under threedifferent crustal conditions with a simulation of different burial depth, and the resultswere compared with that of the theoretical calculation.Considering the restriction that the indoor oil shale samples for hydraulicfracturing experiments could not bear perforation, the concrete samples were selectedinstead for studying the influence regularity of the crustal condition and perforationparameters on the crack stress in the perforation completion. To study the influenceregularity on the crack stress, the experiment changed the simulation loads in differentdirections as vertical crustal stress, maximum horizontal crustal stress and theminimum horizontal crustal stress. Furthermore, the experiment studied the influenceregularity of the perforation diameter, perforation and the maximum horizontal crustalangle and the perforation row number on the crack stress with the casing pipesembedded in different samples in advance.