Monitoring System Design For Return Cuttings Of Gas Drilling

In the process of gas drilling,the drill cuttings need to be carried to the ground under the action of circulating medium through the cuttings discharge pipeline into cuttings pool.Whether the cuttings can be returned timely and effectively,which is related to the safety and efficiency of drilling.At present,there are three methods which were used to monitor the cuttings discharge,that is,artificial observation method on the outlet of cuttings discharge pipe,pressure variation analysis of gas injection,monitoring and analysis method of pipeline force,and so on.The mentioned-above methods work well in part for monitoring and analysis the cuttings discharge,but they have certain limitation in the aspect of real-time monitoring.For example,they can’t point out the cutting discharge variation promptly and effectively.To solve these problems,a cuttings discharge monitor system was designed in this paper for gas drilling.The cuttings amount was got by a microwave solid flow sensor,compared with the cuttings amount which generated by the drill unit footage.The comparison results determine the normal of cuttings discharge,provide the real-time information for the drilling warning which avoiding the down-hole accident and achieving the safely drilling production.The emphasis of this paper is to analyze the signal of microwave solid flowmeter.Draw the mass flow rate of the cuttings through the analysis and processing of the signal.Firstly,the characteristics of several kinds of methods which were used to determine the situation of cutting discharge were compared in this paper,including the advantages and limitations.Basing on the comparison result,a cutting discharge monitoring system was designed.Secondly,the fragmentation mechanism,migration mechanism,force and movement characteristic parameters of cutting grains in the gas medium were analyzed in the process of the cuttings discharge from the down-hole to the cuttings pool.Thirdly,it is proved theoretically that the velocity of the cuttings is linear with the Doppler frequency,and the Doppler echo power of the cuttings is linearly related to the square of the mass of the cuttings;The expression of cuttings flow is derived based on the velocity and concentration of cuttings;The expression of Doppler echo signal is derived under the reasonable assumption and approximation;It is proved that the Doppler echo signal is a generalized stationary signal,which satisfies the condition of the power spectrum;In addition,the Doppler echo signal is simulated on the computer.Finally,the average frequency and power of the signal are extracted from the power spectrum density,which is obtained by the power spectrum estimation of Doppler echo signal,then according to the relationship between the velocity of cuttings and the Doppler frequency and the relationship between the quality of the cuttings and the Doppler echo power,the mass flow rate of the cuttings is obtained.