Distribution of the Sizes of Rock Cuttings in Gas Drilling At Various Depths

摘要

In the process of gas drilling, the mechanism of transport of the cuttings up the annulus is significant, because it controls the minimum amount of volume of the required gas, the cost of cleaning the borehole, the stability of the borewell and the drill pipe erosion, etc. However, current studies in this area are only limited to theoretical discussions. The reason why drill cuttings are of very fine sizes, in air drilling, is believed to be due to the repeated crushing action of drill bit at the bottom of the hole, and the collision between cuttings themselves and the collision of the cuttings with the wellbore wall, and with the drill pipe, during the transport of the cuttings in the annulus. In this study, a mathematical model describing the crushing of the cuttings in gas drilling is developed by coupling the gas/solid two phase flow with rock failure mechanics. Using the presented model a numerical simulation was carried out on five particle sizes to study the particle distribution during the transport of the cuttings in the annulus. The simulation results clearly demonstrate the effect of the size of the cuttings on the distribution of the concentration of the cuttings along the annulus, and explains the fact why only small cuttings are observed at the wellhead. Samples of the cuttings were collected from the field in gas drilling, and sieve tests were conducted. The results prove that the presented mathematical model is valid. Consequently, this study helps understand the process of the transport of drill-cuttings in gas drilling, and contributes to an optimal design of separating/filtering equipment in recyclable gas drilling.