Analysis On The Influencing Factors Of Brittleness Of Shale Reservoir

The demand of energy is greater and greater. Shale gas exploration has been brought into the twelfth five year plan under the background of North American’s successful shale gas revolution. Both North American’s production practice and domestic shale gas exploration show that, the shale gas is a kind of natural gas mainly in adsorption state and free state, dotting in reservoir. The porosity and permeability of shale reservoir are very low, it needs fracturing stimulation to be commercially exploited. Brittleness evaluation of rock reservoir is an important part of the evaluation of reservoir before fracturing.For a long time, scholars have put forward many different methods, which are mostly based on the impact test, strength test, stress-strain curve test, to evaluate brittleness of rock, and gained fruitful achievements. While the exploration and development of shale gas in China are still in its infancy, related research is much less. Although the technology of shale gas exploitation in North America is relatively mature, there is no systematic reports on the mechanical properties, brittle mineral composition, and brittleness evaluation.Based on the research results of previous studies, the following works are carried out:(1) An analysis was taken on the characteristics of shale reservoirs. Volumetric fracturing stimulation is the best way to increase production for shale reservoirs of low porosity and low permeability. The ability of forming fracture network and increasing fractured volume is the criterion for brittleness evaluation of shale reservoir.(2) Analyzing on the influencing factors of brittleness, the mineral composition, mechanical properties, and the degree of development of the fractures turn out to be the main factors.(3) By discussing the weight of mineral composition to mechanical properties of shale, quartz content turns out to be positively correlated with elastic modulus, but negatively correlated with Poisson’s ratio. Clay content shows oppositely to quartz content.(4) By the end, an analysis on the influence of ground stresses to rock failure mode and fracture formation was taken. With the increase of confining pressure, the compressive strength, destruction peak strain and modulus of elasticity show an tendency of increase. The mechanical brittleness index of shale also increases with the confining pressure’s increasing.