Study on Gas Hydrate Reservoir Reconstruction for Enhanced Gas Production in the Shenhu Area of the South China Sea Based on a 3D Heterogeneous Geological Model

Abstract

Natural gas hydrate (NGH) has the huge exploitation potential for clean energy in the current world energy pattern. Its total organic carbon storage is about twice the sum of carbon content of oil, gas, and coal and hence attracts the attention of the world. China has carried out some gas hydrate exploitation works and delineation of three gas hydrate deposits whose reserve scale is over 100 billion cubic meters, and the NGH resource is abundant. The NGH reservoir in the South China Sea is of low porosity and permeability, is unconsolidated, has poor cementation, and is easy to fragment in hydrate production. On the one hand, the condition of low porosity and permeability around the well would severely reduce the production effect; on the other hand, the hydrate decomposition would more easily bring wellbore instability caused by stratum stress change. Therefore, to achieve safe and efficient exploitation of NGH, proper reservoir reconstruct technology needs to be chosen for enhancing the reservoir’s permeability and stability. This paper chose the Shenhu area of South China Sea as the research area, constructed the three-dimensional heterogeneous geological model of hydrate-bearing sediments which can be approximated realistically to depict, then used high-pressure jet grouting (HPJG) technology to reconstruct the hydrate reservoir, optimized the grouting hole direction, location, and spacing, and assessed the productivity increasing effect. The research results show the following: (a) Because of the higher hydrate saturation (SH) and lower permeability (k) around the well, the HPJG in the vertical direction was profitable for reservoir productivity. (b) Considering the heterogeneous SH and k in the horizontal direction, the HPJG in the front of the horizontal well was profitable for the reservoir productivity. (c) The HPJG spacing needs to be properly designed in combination with the absolute standard (V P), the relative standard (R GM), and the specific production index (J). (d) Under the conditions of this paper setting, the optimal HPJG reconstruction scheme is as follows: the HPJG in the vertical direction was arranged at the front of the horizontal well, and the spacing between the holes was 10 m. The productivity after reconstruction ranged up to 55.69% compared with before.

Comparative Study on Improving the Production of Class 1 and Class 3 Reservoirs by Using Enlarged Permeable Well Wall Technology

“…Natural gas hydrate (NGH) is a kind of ice-like compound formed by water and methane molecules under high pressures and low temperatures. It has the advantages of large storage capacity and high energy density, and its total organic carbon reserves are about twice as large as those in oil, natural gas, and coal combined, and is considered as one of the important energy sources needed for human economic development in the 21st century. − …”

Improving the Production Performance of Low-Permeability Natural Gas Hydrate Reservoirs by Radial Water Jet Slotting and Grouting in a Horizontal Well

“…One of the key factors causing unsatisfactory trial production capacity is poor reservoir permeability. , Reasonable artificial reconstruction is a promising route to improve reservoir seepage conditions. , Many active explorations have been carried out, including hydraulic fracturing, near-well reconstruction, chemical stimulation, etc., by laboratory experiments and large-scale numerical simulations. In terms of experiments, hydraulic fracturing tests were carried out with NGH-free sediments, , sandy NGH-bearing sediments, − and clay silt NGH-bearing sediments. − The fracturing mode of unconsolidated NGH-free sediments is related to fluid intrusion and shear action at the crack front as well as the internal interface, which is different from the tensile fracture mode in intact rocks .…”

“…22,23 Reasonable artificial reconstruction is a promising route to improve reservoir seepage conditions. 24,25 Many active explorations have been carried out, including hydraulic fracturing, near-well reconstruction, chemical stimulation, etc., by laboratory experiments and large-scale numerical simulations. In terms of experiments, hydraulic fracturing tests were carried out with NGH-free sediments, 26,27 sandy NGH-bearing sediments, 28−30 and clay silt NGH-bearing sediments.…”

Sensitivity Analysis of Multi‐phase Seepage Parameters Affecting the Clayey Silt Hydrate Reservoir Productivity in the Shenhu Area, South China Sea

“…Jin et al (2020Jin et al ( , 2021 went on to establish a twodimensional axisymmetric reservoir model to study the influence of vertical heterogeneous permeability distribution controlled by the lithological rhythm of sediments on gas production, and found that a high permeability region was conducive to the transport of gas and water. Li et al (2022b) established models for sandy hydrate and clayey silt hydrate reservoirs, and compared the difference in effects of the multi-phase seepage parameters on hydrate productivity in HBS with different lithologies. However, they did not consider the influence of multi-phase seepage parameters over time scales.…”