Research and Application of Rigless Radial Drilling Technologies in China and Middle East
Authors: Chen Chen , Guobin Yang , Qifeng Pan , Longlian Cui , Bingshan Liu , Shanshan Liu , Shufen Zhao , Jin Fu 
Published: October 2024

Rigless radial drilling, or radial jet drilling involves drilling lateral holes from a vertical wellbore to enhance reservoir contact. Radial jet drilling system components (diverter, hose, and bit) are conveyed via coiled tubing. A high-pressure hose and jetting bit drill lateral holes. Without a drill string, axial force cannot transfer to the bit. As a result, the bit is hydraulically propelled. Radial jet drilling bits utilize back-jetting nozzles in addition to front-jetting nozzles. Maximizing penetration rate and hole length requires hydraulic optimization. Existing hydraulic models rely on field-measured parameters (discharge coefficient and flow rate ratio) that vary by bit design to predict propulsion force, bit hydraulic power, and maximum lateral hole length. This study aims to develop a generalized hydraulic model without requiring field-measured parameters for predictions. This model can optimize radial jet drilling by selecting suitable bit designs and lateral hole geometries.

Based on fluid dynamics theory, the calculation model of circulation pressure loss in a horizontal well with a radial lateral is established; according to the on-site situations and characteristics of horizontal well with radial lateral, with the purpose of optimizing the maximum pressure drop of the drill bit, considering the constraint conditions such as breaking capability, rated pump pressure, strength of the equipment and rated pump power, the optimization model of hydraulic parameters of water jet radial horizontal drilling is built, which provides a new idea for the design of hydraulic parameters. The optimum displacement and maximum pressure drop of the drill bit increase with the increase of continuous tubing, diameter of high-pressure flexible hose and allowable value of maximum pump pressure, and decrease with the increase of drilling fluid viscosity. The technology of "high pump pressure and low displacement" is recommended in the operation of horizontal drilling with radial laterals.

This paper discusses the deployment of the rigless radial drilling technology on two wells, one is in China, and the other is in Kuwait. Based on movement characteristics of the universal joint, its 3-dimension model and static simulation were respectively analyzed via CATIA Mechanical Design Model and ANSYS Software. The conventional diverter was compared with the novel one for CT radial drilling technologies, so that the effective curvature of the later was determined according to accurate calculation, mathematical modeling, and simulation experiment. BHA was optimized based on the circle equation, while the cutter's blade, material and PDM were all studied in accordance with mechanical theories.

After many years of production, this technology has demonstrated its reliability and durability. Radial drilling processes have been optimized to maximize the value of radial drilling and mitigate any potential formation damage during lateral drilling. This has been confirmed by extensive testing, which has demonstrated and validated a significant improvement in well productivity and other ESP operating parameters. The results are encouraging and support technical decisions for production optimization leading to significant oil recovery for CNPC and Kuwait Oil Company in mature oil fields. Additional advancements are currently being considered to optimize and maximize the impact of this technology, including extending laterals beyond 300 ft in length, developing an advanced directional nozzle to target lateral holes in specific reservoir areas, and evaluating the use of larger nozzles to drill lateral holes.