Session: 11-02-03-Well Drilling Fluids and Hydraulics-3

Paper Number: 104712

104712 - Application of Drilling Fluid Circulation Technology to Lifting System of Deep-Sea Mineral Resources 

Various types of mineral resources such as mud containing rare earth elements, manganese nodules, cobalt rich crust and massive methane hydrate are found on deepwater sea floor around the world. Lifting systems for mining these resources using gas lift or submersible pumps have been studied by many researchers. Because the water depth where these subsea resources are discovered is quite deep, these currently proposed lifting systems that require electric power may have some problems such as malfunctions of the subsea equipment in an extremely high-pressure condition. The objective of this study is to propose a novel lifting system applying the drilling fluid circulation technology, and to evaluate the system through numerical simulation.

 

The newly proposed lifting system of deep-sea mineral resources consists of a marine riser pipe and a work string inside the riser that is similar to the deepwater drilling riser system. Inside the bottom part of the riser pipe, a hydraulic jet pump that utilizes the Venturi depressurization effect and was applied to some type of junk fishing tool is equipped. The working fluid flowing from the floating vessel through the work string is depressurized at the downstream of the Venturi nozzles in the hydraulic jet pump that can generate suction flow in the fluid containing mineral resources even if the lower end of the system is open-ended. The novelty of the system is that no subsea electric power nor complex analysis of multiphase flow containing gas are needed. Thus, the system has high robustness, high maintainability and long-term integrity.

 

In this study, two types of numerical simulations are conducted. One is to evaluate the lifting capability of deep-sea mineral resources through the entire lifting system using a transient solid transport model which was originally developed for hole cleaning study in oil well drilling and can evaluate how cuttings are removed in a wellbore. In this simulation, the drilling fluid simulate as the fluid containing mineral resources, and the cuttings simulate as the agglomerated small particles of mineral resources. Another one is to evaluate the ability of hydraulic jet pump system to generate suction flow under the deepwater condition using a commercial finite-element computational fluid dynamics (CFD) simulator.

 

Numerical simulations were conducted to evaluate the proposed system for lifting seafloor mud containing rare earth elements from an assumed 6000 m ocean depth. It was found that the pressure increase due to solid particle loading is larger when the input volume concentration of rare earth mud at seafloor is larger, and that the loading effect is larger in the case of 21” to 13-3/8” tapered riser than the case of 16” uniform diameter riser. It was confirmed that production rate of 3500 ton/day rare earth mud that is considered to be required for commercial operation with sufficient flow assurance could be achieved in the following two cases; (1) the input concentration of solid was 10 vol% and the working fluid flow rate was 1500 gal/min, (2) the input concentration was 20 vol% and the working fluid flow rate was more than 900 gal/min.

 

Based on the result of the entire system simulation, we set the boundary conditions in the CFD simulation of hydraulic jet pump. At the inlet boundary, the constant fluid velocities of 3.704 m/s (900 gal/min), 4.94 m/s (1200 gal/min), and 6.174 m/s (1500 gal/min) were assumed. At the outlet boundary, the constant pressure of 60 MPa is exerted. Using seawater as the working fluid, we evaluated the ability to generate suction flow in a high concentration of rare earth mud fluid at the lower end of the riser.

Presenting Author: Ryuta Kitago Akita university

Presenting Author Biography: Mr. Ryuta Kitago is currently a first-year Master's course student in the Graduate School of International Resource Sciences at Akita University, Japan under the supervision of Professor Shigemi Naganawa. His research interests include numerical simulation related to deep-sea mineral resources. He received his B.S. degree in Resource Science and Engineering from Akita University.

Authors:

Ryuta Kitago Akita university
Shigemi Naganawa Akita University
Elvar Karl Bjarkason Akita University