Study On Extreme Extension Ability Of Horizontal Wells In Gas Drilling

The combination of gas drilling technology with horizontal drilling technology can reduce the pollution of the reservoir stratum, increase its area of exposure, and exploit the low permeability reservoir better. For the horizontal drilling or larger displacement drilling, the frictional resistance can become larger and larger along with the continuous extension of the wellbore during the drilling process, resulting in frequent drilling troubles, for example, sticking of the tool. When the frictional resistance is larger than the drilling tool’s driving force, the bit pressure cannot be put onto the drill successfully to break the rock, and the drilling cannot be continuous successfully. This is extremely important in the gas horizontal drilling. Because the mud cakes, formed by drilling fluid in the conventional drilling, will not be formed on the wall to reduce the coefficient of friction resistance, the frictional resistance is much larger than that of the conventional drilling, causing major obstacles to drilling successfully.Aiming at the limited extended capability in gas horizontal drilling, the author, on the basis of consulting the related document literature, understands the necessity and importance of this research. Laboratory tests are designed to analyze the frictional coefficient and the theoretical analysis and digital analog computation are combined to comparatively analyze on several factors which have a significant influence on this competence and have not been dealt with much. In addition, several advices on the improvement of the limited extended capability in gas horizontal drilling are given.The arrangement and the conclusion obtained from this research are as follows:(1) By theoretical analysis, the author probes into the factors which affect on the limited extended capability in gas horizontal drilling.(2) The laboratory test platform used by the frictional coefficient of gas horizontal drilling is set up to measure and carry out contrast experiments on the frictional coefficient of drill pipes with varisized casing pipes and drill pipes with open hole sections under the gaseous environment on the basis of different cuttings’ particle sizes, different cuttings wrap angles, different cuttings’thickness and different drilling rates. According to the experiment, when the cuttings’particle size is between Omm-lmm, the coefficient of frictional resistance is the minimum.(3) On the basis of this experiment and taking tool joints into consideration, three-dimensional simulation models about gas horizontal drillings are built:single arc pattern, double augment pattern and double augment-azimuth pattern. Besides, the dynamic simulation is conducted for major factors. Through analysis, choosing a reasonable rotate speed to match the drift angle, and increase the radius of curvature make for limited extension.Through the laboratory test on frictional coefficient, theoretical analysis and three-dimensional digital simulation, this paper analyzes the major factors affecting the limited extended capability in gas horizontal drilling and reveals the change rules affected by these major factors. It contributes to further recognize the limited extended capability in gas horizontal drilling and has a theoretical reference value of the related construction.