The effects of the working angle on pneumatic down-the-hole (DTH) hammer drilling was investigated since these hammers were developed for vertical drilling and their performances in inclined positions need to be tested. The investigation begins by establishing a calculation model with which to simulate the percussive drilling of the hammer. The model consists of two parts. The first gives the kinetic energy of the piston at impact by simulating the thermodynamic cycle of the DTH hammer, and the second simulates the percussive drilling process according to the analyses of stress-wave propagation. In the meantime, a laboratory-scale test device was made for multi-angle hammer drilling tests. This device is based on a small pneumatic DTH hammer used in deep well drilling. By analyzing the force acting on the rock during impact at different angles, the percussive drilling process is carefully examined. Theoretical predictions and experimental results appear in fairly good agreement. The hammer's working performance in inclined positions can be obtained directly using the proposed model. Furthermore, when detailed evaluation is required, the hammer can be tested using the method proposed in this paper.

Due to the differences of stress and physical property in the pay zone, the fractured horizontal well may be different in length and azimuth angle. Furthermore, because of the mutual disturbance among fractures, the accurate prediction of production of fractured horizontal wells become more complicated. This paper presents a new model to predict the production of the fractured horizontal wells by considering the effects of fracture number, fracture length, fracture interval, fracture symmetry, azimuth angle and conductivity. Compared with the numerical simulation, this model needs less parameter and calculating time, and is easy to be applied to the designs of segmentation fracturing in horizontal wells. The model in this paper has been applied to the optimizing designs of hydraulic fracturing for two horizontal wells in North China oilfield and the predicted results agree with the actual production well.