Ge Hongkui

Key issues and investigation of horizontalwell drilling and multistage fracturing in shale gas reservoir

Unconventional shale gas is rapidly increasing as an available source of natural gas in the worldwild. Horizontal well drilling and multistage fracturing are two principle techniques of shale gas resources production. Benefiting most from these two techniques, the United States, Canada, and China have become only three countries to produce shale gas in commercial quantities. The key technical issues emerged in the horizontal drilling and fracturing involve the rock fragmentation issues, wellbore trajectory optimization and control, wellbore stability, cementing and its quality control for long horizontal lateral, and hydraulic fracturing design. Although some progress associated with those technical issues have been achieved in China, there are still many geologic and engineering challenges: (1) the low rate of penetration and fast bit wearing for both PDC and Cone bits are still the primary issues, which makes hard achieve the “one-trip” drilling; (2) wellbore collapse and lost circulation are serious with a certain collapsing period due to natural fractures system; (3) complex multi-fractures propagation behaviors still need to be understood and the fundamentals of fracturing design should be established after undstanding multi-fractures propagation behaviors.

Grain Crush and Its Evolution in Granular Material: a Two-Dimensional Distinct Element Model Approach

A crush criterion and a simplified post-crush process for spherical grains are introduced into the traditional distinct element model (DEM). The crush criterion is based on Hertzian contact, and it indicates a negative relation between critical force Fcr and radius R via Fcr∝R−3/2. Effects of grain crush on deformation pattern and statistical features of crush evolution for samples under uniaxial strain load are intensively investigated. Influences of maximum crush times and particle size distribution (PSD) are also discussed. It is found that: (1) Grain crush will blur the localization of deformation. (2) Crush is prone to occur in larger grains, due to force concentration and lower critical force Fcr for larger grains. (3) Grain crush only temporarily reduces contact force, which results in the most rapid increase of the number of grains with maximum crush time.