The World's First Successful Implementation of Solid Fluidization Well Testing and Production for Non-Diagenetic Natural Gas Hydrate Buried in Shallow Layer in Deep Water

Abstract

Based on the characteristics of shallow buried, non-trap structure and close cover, non-diagenesis, weak cementation and easy fragmentation of natural gas hydrate deposits in China, a solid fluidization well testing and production scheme to develop these kind of natural gas hydrate is proposed. The main idea is to transfer the non-diagenetic natural gas hydrate sediments buried in shallow layer of deep-water into a closed multi-phase transporting and lifting system through mechanical crushing fluidization, during the lifting riser system from seabed to surface, hydrate will be dissociated gradually based natural rule of sea water temperature rising and the hydrostatic pressure decrease with the change of water depth during the lifting process, to turn the uncontrollable decomposition process of non-diagenetic hydrate into controllable, and to achieve safe field exploitation of natural gas hydrate in the surface and shallow layer of deep-water. After the validity was verified by the laboratory experimental study, CNOOC successfully implemented the world's first solid fluidization well testing and production of marine non-diagenetic hydrate with the water depth of 1310m and the hydrate sediments layers 117~196m depth in May 2017. It means China has found an innovation way about natural gas hydrate exploration and development with self-developed key technology and tools. The implementation relied on the Deepwater Engineering & Survey Vessel "HYSY708" at the station of Li Wan 3 in the South China Sea and it was supported by fully self-developed technology, process and facilities.

A cohesionless micromechanical model for gas hydrate-bearing sediments

“…To date, methane gas has never been extracted from methane hydrate-bearing sediments on a commercial scale. A few short-term field trials of gas production have been performed: at the permafrost Mallik gas hydrate site, Canada, in 2007 and 2008 [6]; at the permafrost Ignik Sikumi well, Alaska, in 2012 [28]; at the offshore Eastern Nankai Trough, Japan in 2013 and 2017 [34]; at the coast of India, in 2006 and 2015 [4,19]; and at the South China Sea, in 2017 [31]. In most of the field trials, geomechanical issues intervened with the production, leading to a recognition that better understanding of the geomechanical behavior of gas-hydrate bearing sediments is needed.…”

Investigation into the Water Jet Erosion Efficiency of Hydrate-Bearing Sediments Based on the Arbitrary Lagrangian-Eulerian Method

“…At present, common methods of NGH exploitation include depressurization, thermal stimulation, inhibitor injection, and carbon dioxide (CO 2 ) replacement [9][10][11][12]. However, these NGH exploitation methods have some limitations for NGH reservoirs in the South China Sea, which are characterized by shallow burial depth, non-trap structure, low consolidation strength, non-diagenesis, and low permeability [13,14]. Hydrate secondary formation and ice formation are easily caused by depressurization [15,16], which may block the permeability path of the non-diagenetic NGH reservoirs and be unfavorable for long-term exploitation.…”

“…Therefore, the above common methods cannot meet the requirements for safe, long-term, and efficient exploitation of NGH reservoirs in the South China Sea. On the basis of this, an innovative exploitation method, namely, the solid fluidization mining method, which is suitable for exploiting non-diagenesis and weakly cemented marine NGH reservoirs, was proposed by Zhou [13,20]. Figure 2 illustrates the schematic diagram of this method [20].…”

“…Finally, methane gas is obtained by decomposition, separation, and other postprocessing operations. Furthermore, the solid fluidization method was successfully applied to the trial production of NGH in the Shenhu sea area of the South China Sea [13,14]. The successful application of the solid-fluidization method shows that it is feasible to exploit NGH with a high-pressure water jet.…”

The Distinct Elemental Analysis of the Microstructural Evolution of a Methane Hydrate Specimen under Cyclic Loading Conditions

“…From May to July 2017, China tested the production of methane hydrate gas from MHS in the South China Sea [5]. In May 2017, China investigated the extraction of methane hydrates using the solid fluidization method [6]. Based on these extraction tests, a series of in situ mechanical property tests were conducted on MHS.…”