Flow Analysis Of Complex Flow Path Of Gas Drilling Based On

Compared with conventional drilling method, gas drilling has the characteristic of drilling rate; low reservoir damage and can effectively reduce drilling cost, therefore attracted widely attention and application in the field of drilling. In the process of gas drilling, due to the formation reasons, the phenomenon of hole enlargement is often happened, coupled with the existence of the annulus joints, making complex flow channel area appeared in the annulus, namely mixing region of the annulus hole enlargement segments and the joints. In the region with cuttings-carried problem become the important factors which restrict the development of the gas drilling. This paper will focus on the study of the gas flow pattern, elastic dried cuttings particles migration rule and water-wet cuttings migration mechanism of annulus complex flow channel in gas drilling.Based on the annular gas dynamics in this paper, annular gas dynamics model and annular two phase flow of gas-solid dynamics model were deduced. Combined with the actual working condition of the X block, modeling and analog simulation by CFD software, annular complex flow channel velocity field is obtained. Import the velocity field into Mathcad program, annular complex flow channel elastic dried cuttings particles migration rule is obtained. And in the condition of annular complex flow channel water production, the agglomeration and dispersion mechanism of non-hydration water-wet cuttings and hydration water-wet cuttings were studied.(1) Combined with the actual working condition of the X block gas drilling, simulate the gas drilling annular complex flow channel. The following conclusions are obtained by CFD software analog simulation:annulus gas velocity distribution present the law of gradually diminishing from the annulus center area to the annulus wall; gas backflow phenomenon occurs at the annular complex flow channel, the gas velocity is reduced; in the case of drilling tool rotation, the rotation of drill pipe has little effect on annulus gas distribution.(2) Study on the migration mechanism of elastic dried cuttings. Through the force analysis of annulus cuttings particles, the migration model of cuttings in the annulus is obtained. Study on the collision mechanism of elastic dried cuttings, the collision model elastic dried cuttings is obtained. Through analog simulation and numerical calculation confirms the dynamic suspension phenomenon of elastic dried cuttings in the annulus complex flow channel. The main factors of affecting the dynamic suspension phenomenon are the gas inlet velocity, cuttings particle size and the size of the annular cross-sectional area. Finally though the results of the calculating program got the range of cuttings size can be successful migration of the annular, got the range of cuttings size can be dynamic suspension in the annular, and got the cuttings size can’t be carried by gas.(3) Visual experimental aircraft of the gas drilling cuttings migration in complex flow channel is developed independently. Visual laboratory experiments on cuttings migration is conducted, indicating the existence of dynamic floating debris particles in complex flow channel. The accuracy of the model is verified through experiments with different injection volume and different particle size cuttings migration.(4) Study on the mechanism of water-wet cuttings aggregation and dispersion in the annulus flow channel. The non-hydration water-wet cuttings and hydration water-wet cuttings were studied while a small amount of water production in the annulus. This paper focuses on the mechanism of aggregation and dispersion of non-hydration water-wet cuttings, it is concluded that increasing gas injection can reduce the non-hydration water-wet cuttings aggregation. Research on hydration water-wet cuttings main stays in the theoretical research, hydration water-wet cuttings occur hydration expansion after meeting water, east to gather, at the step of hole enlargement segment and joints in the annular complex flow channel prone to balling. Only convert drilling way after balling, change the gas drilling to aerated mud drilling or conventional mud drilling.To study the flow pattern in annular complex flow channel of gas drilling in this paper, can provide certain theoretical basis for gas drilling site construction.