Tight sandstone reservoirs have the character-istics of small pore throat radius,strong heterogene-ity,large shale influence,and development of micro-fractures,making them particularly vulnerable todamage caused by external intrusive fluids,resultingin decreased reservoir permeability.During the drill-ing process,the drilling fluid will invade the for-mation,which is harmful for the development of oiland gas wells after production.Considering thesecharacteristics and drawbacks of the current drillingfluid system,this paper compares six major drillingfluid systems commonly used in China's three majoroilfields (Huabei Oilfield,Zhongyuan Oilfield,andChuanqing Drilling).Plugging agent were added tothe original formula,and the experiment shows thatthe drilling fluid formula of Huabei Oilfield has thebest blocking effect.Compared with the other drill-ing fluid,there is one more ammonium salt in theformula,indicating that the ammonium salt sand dischas a better fluid loss reduction effect.Observationby optical microscope shows that the pollution on thesand disc surface is the least after the drilling fluid iscontaminated.The lowest degree of damage indi-cates the strongest reservoir protection ability.Anti-pollution experiments show that the anti-NaCl pol-lution can reach more than 15% and the anti-gypsumpollution can reach more than 2%.The EP-B ex-treme pressure lubrication instrument is used to ana-lyze the drilling fluid lubrication selected in this ar-ticle.The coefficients are large and the performanceis average.The experiment using the JHTP new hightemperature and high pressure non-contact smart dil-atometer shows that due to the low content of the res-ervoir swelling clay minerals,the hydration swellinginhibition effects of each system are better,and at thesame time in the drilling fluid system KCl is addedto improve the inhibition of the system.
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