No abstract

Erosive and abrasive wear effect of water-based drilling fluid (WBM) on down-hole tools may reduce the service life of down-hole tools, and its magnetic contamination on Measurement-While-Drilling (MWD) directional tools may cause azimuth errors and reduce the wellbore trajectory accuracy. The erosive and magnetic effects would be worse when a high density WBM densified with a high content weighting agent was employed. One of the main reasons of the erosive and magnetic effect is related to the weighting agent used. To reduce the erosive effect and magnetic interference of weighting agent, a micronized barite as a new weighting material was prepared in this paper, and then characterized by scanning electron microscope (SEM) and laser particle size analyzer.In our experiments, two conventionally weighting agents, barite and hematite were chosen as the comparing samples. The erosive effects, magnetic contaminate tests, lubricity and rheological properties of high density WBM weighting with micronized barite, barite and hematite were evaluated on erosion instrument, a fluxgate magnetometer, an EP lubricity tester and a rotational viscosimeter, respectively. It was found that the high density WBM weighted with micronized barite showed less erosion, lower magnetic susceptibility, better rheological properties, and smaller lubricating coefficient than that weighted with hematite or barite.Comparing with hematite or barite, the micronized barite could effectively reduce erosive wear on down-hole tools, reduce magnetic contamination on MWD directional tools, and control the rheological property of high density WBM, which would significantly contribute to the service life of down-hole tools, the wellbore position accuracy and the safety of drilling operations.The prepared micronized barite, as a new weighting agent of high density WBM, has a great promise of application in reducing the drag, erosion and magnetic interference along the horizontal section of large extended-reach wells and horizontal wells. It can also be used in high pressure high temperature (HPHT) wells and coiled tubing drilling technology.

During the drilling of deep/ultradeep wells, water-based drilling fluids (WBDFs) often experience harsh conditions of ultrahigh temperature and high salt. Ultrahigh temperatures and high salts cause rheological instability in drilling fluid, reducing its suspension and cutting-carrying capacity. In this study, a comb polymer, P-TPEG with isopentenol polyoxyethylene ether (TPEG) as the side chain, was prepared via free radical polymerization in an aqueous solution and then compounded with nanolaponite (LAP) to obtain a composite rheological modifier (LAP/P-TPEG). In situ Fourier transform infrared spectroscopy and thermogravimetric analysis showed that LAP/P-TPEG had an excellent thermal stability. The LAP/P-TPEG solution test showed a shear thinning behavior. The results demonstrate that LAP/P-TPEG can improve the rheology of WBDFs before and after aging at 240 °C and can resist 15 wt % NaCl. LAP/P-TPEG formed a strong adsorption with bentonite through hydrogen bonds and electrostatic interactions. LAP, P-TPEG, and bentonite formed a “reversible” “dual” spatial network structure in WBDFs, improving the rheology and the suspension, cutting-carrying, and wellbore-cleaning abilities of the drilling fluid under ultrahigh temperature and high salt.