Studies On Blockage Of Water Influx To Wellbore In Air Drilling

Air drilling can improve drilling speed and cut down drilling costs greatly. However water breakthrough in formation is so seriously that traditional methods of water shutoff couldn't meet the demand of plugging while drilling, which restricts the spreading and application of the technology. Based on the investigation and analysis at home and abroad, this thesis develop a new method on blockage of water influx to wellbore in air drilling, which refers to a gel system and blocking agent bearing oppositely with higher molecular weight. The water shutoff method is as follows: firstly, the gelling fluid is injected into drill stems and carried to desired location, then the fluid changes into gel packer; secondly, the polymer block agent is injected from drill stems which can block water zones; finally, the gel packer in the annulus space breaks at a given time, which changes into fluid. Air is then injected from annulus space and drives the fluid out through drill stems.The gelatinizing and gel breaking formulas of this gel system as well as the effecting factors of the gel system and its loading capacity are studied in laboratory under a varied temperatures of 30℃~70℃. The Wurster fluid bed is applied to encapsulate gel breaking system. The study shows the compression strength of gel system can reach 3.5MPa/m, and materials such as sodium soil, scrap iron and kaoline that may exist in formations can barely affect the gelation time and strength, which proves that the gel system has an excellent pressure bearing capacity and suitability; oxides are adapted gel breaker for the gel plug, which has a optimum volume under different temperatures;Encapsulated breaker coating with eudragit RSPO, and the capsules are proved to have a good quality of slow releasing.An block agent bearing oppositely suitable for air drilling is also examined in labortory test. Two formulas of blocking agent including chrome gel and acrylamide gel are investigated, formulas of different gelation time and gel strength are also acquired by adjusting contents of each ingredient. According to the results of physical simulation, when the formation permeability is less than 2.0μm2, the breakthrough pressure gradient of chrome gel is more than 10MPa/m, besides, temperature has a small effect on formation blocking effectiveness, which indicates chrome gel is suitable to block water yield formations during air drilling.