As we move forward into the new year, it's a good idea to rehash older topics and refresh our memories about a subject that doesn't get enough attention on a day-to-day basis: high-density/high solids drilling fluid returns and its effect on the drilling process. We've all seen it before where a large solid plug of clay or a semi-solid mix of silt and sand that looks like pudding comes out of the borehole, and then in the blink of an eye, loss of circulation and or inadvertent returns (frack out for us older drilling guys) pops up along the bore path. Afterward, it's all hands on deck with squeegees and hydro-vacs trying to clean up the mess while dealing with the stuck drill pipe and all the other attributes that come with high-density drilling fluid pressures exceeding what the formation can withstand..
Be it vertical or horizontal directional drilling, the goal is to excavate a borehole by removing the existing soil so that a product can be installed. As the bit or reamer cuts into the formation, it also mixes drilling fluid and soil together into what needs to be a flowable mixture that can transport drill cuttings to the surface. Drilling fluid must be matched to soil conditions to maintain borehole integrity, control reactive clays, and suspend and transport drill cuttings to the surface. Like drilling fluids, pumping volume must also be matched to soil conditions to maintain flowable drilling fluid returns that will not raise annular pressures, which can cause many problems.