No abstract

Air drilling with hammer is generally recognized as an effective drilling method, but the hole obtained in thick conglomerate formation is very irregular, and the control of hole deviation is very difficult. Although many studies have been carried out, the mechanism of this phenomenon has not been found out yet. In this paper, based on the numerical simulation of rock breaking process of air hammer, the influence of the heterogeneity of conglomerate on the wellbore regularity and hole deviation is analyzed. The results show that the direction of the bit will be changed due to the heterogeneous distribution of gravel particles, which make the wellbore with a severely irregular shape. On this basis, the finite element models of BHA in regular and irregular wellbores are established respectively, and the influence of wellbore irregularity on the stress of BHA is analyzed. It can be found the irregular wellbore is easy to form additional fulcrum, shorten the effective swing distance of pendulum bottom hole assembly. The additional fulcrum greatly changes the mechanical characteristics of the BHA, reducing the angle dropping force on bit, or even produce the angle building force.

In the drilling process of horizontal and highly deviated well sections, cuttings are deposited on the lower side of annulus under the action of gravity during its transport, which affects the normal drilling operation. A variety of cuttings removal tools have emerged and achieved good results, but they are only effective when the drill string is rotating, while it is difficult to ensure the removal effect of cuttings in sliding drilling. In the drilling process of directional well and horizontal well, rotary drilling is sometimes difficult to meet the requirements of wellbore control, and sliding drilling is often used at this time. Therefore, there is an urgent need for a tool that can effectively remove cuttings in sliding drilling. In the present work, an efficient vortexing cuttings removal tool (VCRT) has been developed and the Computational Fluid Dynamics (CFD) simulation technology was used to study the cuttings removal mechanism of VCRT. The cuttings removal effect under the action of VCRT was compared with that of the conventional cuttings removal tool (CCRT) and the conventional drill pipe. The results show that VCRT has good cuttings removal effect in both sliding and rotary drilling conditions. The average cuttings volume fraction under the action of VCRT during sliding drilling is 59% lower than that of the conventional drill pipe, and 26% lower than that of CCRT. The average cuttings volume fraction under the action of VCRT during rotary drilling is 78% lower than that of the conventional drill pipe, the removal efficiency is similar to CCRT, but VCRT can send more cuttings into the annulus. The research reveals the mechanical mechanism of VCRT which provides a scientific basis for the cuttings removal mechanism of VCRT.

The more and more severe drilling conditions make the load conditions of tool joint extremely complex. Under the complex load conditions, the stress concentration of tool joint is serious, so failure of tool joint often occur in the oilfield. However, few researchers have studied the stress concentration of tool joint under complex loads. In this paper, the stress distribution of an API tool joint, NC38, was analyzed with 3D elastic-plastic finite element method under complex loads. The stress concentration factors of the tool joint were calculated, and the influence of tensile and bending load on it was analyzed in detail. The results show that the existing model cannot effectively reflect the fact that the stress concentration of tool joint will increase with large tensile load in the crooked hole section. Based on the 3D finite element analysis, a stress amplification model is proposed and used to reflect the failure risk of tool joints under the combined action of axial tension and bending moment. The results show that this model is consistent with the fact that the failure risk of tool joint will increase with large tensile load in the crooked hole section.