Development of annular pump to enhance drilling distance and cuttings return in horizontal directional drilling

Abstract

In many shallow horizontal directional drilling (HDD) projects, the annulus fluid pressure soon reaches the blowout or frac-out pressure of the soil formation. The pressure at single-source pump therefore must be limited. This limits the maximum drilling distance (borehole length), maximum attainable rate of penetration (ROP), and maximum distance over which cuttings can be returned. A novel concept involving a series of annular pumps distributed along the borehole length to aid in generation of distributed annulus pressure boost and cuttings transport in HDD was conceived. The success of the above concept, designated as distributed pumping system (DPS), relies on the ability to design and power an annular pump that can fit in the constricted annulus geometry of HDD boreholes while satisfying the performance requirements. We present the laboratory-scale development of three annular pumps based on the turbomachinery design principle of axial blade propellers. The pump prototypes were 3D printed and tested in the laboratory test rig flow loop built to simulate the annular flow configuration of HDD boreholes. The annular pump was powered using the axial propeller turbine housed inside the hub of each annular pump. The turbine converts hydraulic energy from the inner flow (analogous to drilling fluid flow within drill rod) to power the integrated setup of the axial inner turbine and annular pump, in short, designated as integrated turbine-pump (ITP). Results from the tests on three preliminary prototypes of the annular pump using water as the medium in the test rig yielded a maximum pressure boost of 44 kPa–enough to space the annular pumps 80 m apart when designed for a typical annular pressure drop rate of 0.54 kPa/m. The performance index (i) of the ITP, defined as the ratio of pressure boost provided by the annular pump in the outer (annular) flow to the pressure drop created by an inner turbine in the inner flow, reached a maximum value of 0.6. The results from the study promise a technology that can enable long-distance HDD cuttings return without the risk of blowout or the need for an external power source.