Study On Sealing Drilling Fluid System Of Mud Shale In Luo Jia Area

Although researchers have made tireless efforts on wellbore stability of crack formation, also had made some progress, wellbore instability is still a common problem in oilfield exploitation and development. For fractured old oilfield, most of them can get target layer, but still has possibility of caving, Borehole Diameter Expanding, which cannot meet well logging and cementing request. People cannot know the stratigraphic configuration character and pressure traverse exactly while drilling the new area, also have no pointed anti-sloughing technique, which lead to caving often. Besides, when drill complex the lay that has multi-pressure strata and unusual lithological character in strong geostress, wellbore instability problem is outstanding.LuoJia area in ShengLi Oil field is the typical fractured reservoirs of shale. Recently some well blocks that the High Productivity Enrichment of reservoirs have been found such as Luo 42.In this area, the pore size is abort 5-15μm, which detected through X-ray diffraction analysis, electron microscope scanning, pore size determination of shale in LuoJia area. Except the micron order pore, there are nanometer throat, all of which is the important factor of wellbore instability. The important measures of preventing caving is how sealing this micro-crack.This paper focus on sealing the nano-sized pore throats. We study the possibility of using nanometer silicon dioxide as sealing agent by analyzing the particle-size of nanometer silicon dioxide and consulting internal and external documents. The laboratories show that nanometer silicon dioxide not only can seal nano-sized pore throats, but also can restrains clay hydration effectively,improve lubricity and stability of drilling fluid.We mainly focus on selecting the inhibitor and sealing agent in this study. We selected organic amine as the inhibitor using dispersive drillings recycling test and shale expansion test. The results show organic amine has the best inhibit effect. We also analyzed the particle size distribution of different systems which has different sealing agents by laser particle size analyzer. Finally we get the best proportion of the sealing agents using the D90 rule and PP and HTHP tests. We found that Nanometer silicon dioxide can optimize particle size distribution of system, which can get a maximum effect.After knowing the inhitior and sealing agent, We ultimately formed a sealing drilling fluid system which applies in shale of LuoJia area. Drilling fluid analysis such as rheological properties and fluid loss are studied together with other important properties. Expect having the beteer sealing ability, the system can restrain caly hydration effectively, having a high salt resistance and strong anti-contamination ability, reaches a high temperature resistance of 150℃. It can meet the challenge of shale exploration, keep wellbore stability and protect the reservoir efficiently. The system showed well sealing effect on Boyeping1-2 well during the secondary drilling.