Research On The Identification Method Of Wellbore Cleaning While Drilling

In recent years,with the need of oil and gas exploratory,the emergence of extended reach wells and horizontal wells have achieved good economic benefits in engineering practice,but because of the long wellbore,the long open hole,horizontal segment and the hard and soft interaction sandwich lead to difficulties of borehole cleaning and produce cuttings bed easily in the drilling operation,the formation of cuttings bed can cause borehole problems such as sticking,blocking pump,drilling bucket and so on,which severely restrict the speed of drilling,so research the method of identifying borehole cleaning that can identify the borehole cleaning condition effectively along the horizontal section,and prevent the formation of cuttings bed which can create borehole problems causing borehole accidents,it is the key to the qualitative and efficient drilling of extended reach wells and horizontal Wells.therefore,based on the applications of borehole engineering parameters measuring instrument and PTWD in drilling operation,using by the theory of solid-liquid two-phase flow,mechanics of sediment transport,wellbore hydraulics and wellbore heat transfer theory,the research of the method of cleaning borehole while drilling identification has been carried out,and the main research achievements were as follows:(1)From the micro and macro two different perspectives,well cuttings migration characteristics for different segments and formation mechanism of the cuttings bed have been analyzed.Recognizing the main features of the borehole cleaning from the mechanism,starting with response characteristics of the pressure drop gradient,which has analyzed response characteristics of annulus pressure drop gradient in the state of cuttings transport state of different well sections.Studies have shown that annulus pressure drop gradient will increase with the increasing of concentration of debris and cuttings bed thickness.On the basis of the learning from the knowledge of sediment movement mechanics and original calculation of annulus pressure drop,considered voltage drop caused by the settlement aggregation effect of debris particles in the annulus,made up the annulus hydraulics calculation deficiencies,improved the accuracy of the annulus pressure.(2)Compared and analyzed annulus pressure variation under the conditions of normal drilling,overflow and leakage,the results shown:the conditions of overflow and leakage can lead to significantly reduce the annulus pressure,poor hole cleaning will lead to annulus pressure increase significantly,to some extent this has verified the feasibility of based on annular pressure while drilling identifying hole cleaning;and compared and analyzed wellbore temperature variation of the normal drilling,the overflow and leakage conditions,to a certain extent which provided a theoretical basis for eliminating the influence of other factors and improving recognition accuracy of borehole cleaning.(3)On the basis of the foregoing theoretical research and combining measured parameters of borehole engineering parameters measuring instrument and PTWD,established hole cleaning recognition criteria based on borehole pressure and borehole temperature.On the research of hole cleaning safety indicators,put forward the safe density window for borehole clean and the method of the feedback correction calculation of cuttings concentration or cuttings bed thickness,corrected the defects of previous hole cleaning recognition lagging and poor recognition accuracy,the hole cleaning recognition was applied to the real monitoring of cuttings concentration and cuttings bed thickness,which was of important guiding significance to the large displacement wells and horizontal wells of high quality and efficient drilling.(4)Combined with the mearsurement data of field descent down hole and explanation results of the recognition method in this paper shown:using wellbore cleaning while drilling recognition method could early identify the cuttings concentration in annulus,make clear the evolution of debris and changes of cuttings bed thickness,meanwhile prove that most of the literature with 5%cuttings concentration as the scientificity of hole cleaning standard.