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The technical problems during the development of unconventional oil and gas reservoirs are becoming more and more difficult to handle with conventional drilling and production methods. Supercritical carbon dioxide has so many good properties such as high rock-breaking drilling efficiency, strong dissolved displacement performance and unharmful effect on the reservoir that it can be used as a drilling, completion and production medium to effectively exploit the unconventional oil and gas reservoirs. The global distribution of unconventional oil and gas resources is introduced, application status of carbon dioxide in oil and gas development is discussed, and development prospects of supercritical carbon dioxide in the unconventional oil and gas reservoirs are systematically analyzed. Using supercritical carbon dioxide as a medium in the whole development process is an important trend of unconventional oil and gas development technologies.

The technical problems existing in deep well drilling are becoming more and more predominant during the exploration and development of oil-gas field. The poor formation drillability, low drilling rate and complicated pressure system cause the underground accidents frequent, extend well construction cycle, and make the cost of the project much higher. Therefore, it is urgent to develop new technologies to improve the efficiency of the exploration and development in deep unconventional oil-gas reservoir. The particle jet technology is a new energy-saving way which has a broad application prospect. It can take the way of sucking in particles in annulus space to cycle use the particles, and promote the drilling rate. The feasibility of particle jet as a drilling medium is verified by the theoretical and experimental study, which provides the basis for the design of particle jet tool.

Drill-string vibration excitation longitudinally is a potential drilling method for reducing friction between drill-string and borehole rock. This article assumes that borehole rock surface is composed of elliptical asperities, based on elastic-plastic contact theory, a modified model for friction reduction by vibrating drill-string longitudinally is developed. The results show that the tangential stiffness of borehole rock surface decreased with increasing ovality of asperity. Further, at the same ovality, thin and tall asperity has bigger tangential stiffness than short and fat asperity. Only when the tangential stiffness of borehole rock is greater than a certain threshold, the friction force calculated by proposed model in this paper can appear reverse phenomenon. When the tangential stiffness tends to infinity, the result tends to Coulomb model. The conclusions provide basis for research and application of drill-string vibration longitudinally friction reduction technology.

Practically, the distribution and variation of the bottom-hole hydraulic energy has significant influence on drilling rate, and it’s helpful to induce bottom-hole hydraulic pulse to improve the rock breaking and drilling efficiency. The analysis of bottom-hole rock stress condition and cuttings start-up mechanism indicates that, bottom-hole hydraulic pulsation can decrease the bottom hole pressure, reduce the fracture strength of rock, and strengthen bottom-hole purification, thus improve the efficiency of rock breaking and drilling. The higher the pulsation value is, the more effective of the acceleration of the drilling rate, while well depth increases, the acceleration effect diminishes gradually. Simulation of jet flow field drilled by 3-nozzle 3-cone bit, combined with field application, verify the mechanism that bottom-hole hydraulic pulsation could improve ROP. The result of the study provides a basis for the development of practical technology.