Assessing the geomechanical stability of interbedded hydrate-bearing sediments under gas production by depressurization at NGHP-02 Site 16

Abstract

Establishing the geomechanical stability of marine sediments in the vicinity of a production well is one of the key design considerations in planning offshore gas production from marine hydrate reservoirs. This paper presents an assessment of the sediment stability at India's National Gas Hydrate Program, Expedition 2 (NGHP-02) Site 16 Area B offshore eastern India, for which gas production is to be carried out by depressurization. One important feature of the study is that extensive calibration of constitutive model parameters has been conducted based on laboratory test data from pressured core samples. From analysis perspective, the site is challenging because the hydrate reservoir consists of thin layers of hydrate-bearing sands interbedded with mud. Moreover, depressurization at the depth of a reservoir more than 2750 m below sea surface will lead to a pore pressure drop, and accordingly an effective confining stress increase as high as 25 MPa. In dealing with thin interbedded hydrate-bearing strata, meshing requirements for flow and geomechanical analysis are quite different from those for reservoirs with thicker massive layers, An axisymmetric model and one-way coupling simulations were thus adopted for this study, in which the geomechanical study utilizes pore pressure and hydrate saturation output from the flow study, but the flow study does not takes the porosity changes from the geomechanical analysis. Instead, the reduction of porosity due to sediment deformation in the flow study is based on a pressure-dependent pore compressibility relationship derived from geomechanical modeling. The rationality is validated through back computing the pore compressibility from the geomechanical deformation results. The study shows that large compression in the reservoir will result in movement of the sediments from above and below, as well as laterally in smaller magnitudes; and the sediment is deemed stable during the gas production period.

Review of Gas Hydrate Research in India: Status and Future Directions

“…Optimal pressure drawdown to control the geomechanical instability would be required. Further, numerical simulations were performed to study the depressurization method for gas recovery from hydrate reservoir at prospective the NGHP-02-16 site. , In addition, assessments of sand migration analysis and geomechanical stability were performed at the same site. A 2-D micromodel study on the hydrate reservoir was performed to investigate the clogging behavior of fine sediments .…”

State‐of‐the‐art brief review on sanding problem of offshore natural gas hydrates sediments

“…The comparison results show that the calculation process of the Lade-Duncan yield criterion is very complicated and the results sometimes are not feasible. 94 Besides the Tresca criterion, the Mohr-Coulomb criterion is the most used yield criterion in the NGH formation failure simulation and sand production mechanism study. 17,94,95,96 .…”

“…94 Besides the Tresca criterion, the Mohr-Coulomb criterion is the most used yield criterion in the NGH formation failure simulation and sand production mechanism study. 17,94,95,96 . Mohr-Coulomb criterion has been used to establish the peak strength of the NGH sediment with reasonable and acceptable results.…”

“…As the direction effect, different geological conditions lead to various reservoir physical properties, such as reservoir stability and compaction, which further affects the sand production. 94 Deng et al (2019) identified pore compressibility as the main geological factor in the physical properties of hydrate reservoirs. 168 It is because that the offshore NGH reservoir should be treated as an unconsolidated reservoir because of shallow depth.…”

Numerical Investigation on Gas Production Performance in Methane Hydrate of Multilateral Well under Depressurization in Krishna-Godavari Basin

“…The study area is located on the Krishna-Godavari Basin in the southeast of India which is an important petroliferous basin with abundant organic matter contained. This basin was divided into four geographic areas (Area A, B, C, and D) during the NGHP-02 expedition (Figure 2) according to seismic data sets in which Area B and C were deep-water channel-levee-fan systems with gas hydrate at high saturation [33,34]. 4).…”