Abstract
We characterize the in-situ porosity and compressibility of a coarse-grained hydrate reservoir in Green Canyon Block 955 in the deepwater Gulf of Mexico by performing experiments both on a hydrate-bearing sandy silt pressure core and on the same reservoir material after reconstituting. Uniaxial consolidation experiments demonstrate a small difference in porosity between a reconstituted sandy silt sample (Sh= 0,n= ~ 0.38) and a hydrate-bearing sandy silt (Sh= 83%,n= 0.39-0.40) at in-situ effective stress (3.8 MPa). Both measured porosities generally agree with the in-situ porosity (~0.38 to 0.39) of the reservoir formation that was best-estimated from both LWD and calibrated PCATS densities. The compression index of pressure core at 3.8 MPa is ~ 0.05 to 0.1, slightly stiffer than reconstituted sandy silts (Cc= 0.11). This difference in porosity and compression behaviors between hydrate pressure cores and reconstituted material implies that (1) analysis of reconstituted sediments from hydrate-bearing pressure cores provides a simple and intuitive approach to understand some petrophysical components of the hydrate reservoir; and (2) the high-saturation hydrate in the pores of sediments makes the hydrate reservoir slightly less compressible, suggesting a non-contact-cementing hydrate morphology in the pressure core.
Highlights
Methane hydrate is a crystalline solid composed of methane molecules trapped in cages of water molecules [1]
We describe 4 approaches to estimate the porosity of hydrate-bearing pressure cores: (1) Pressure Core Analysis and Transfer System (PCATS) porosity; (2) the logging while drilling (LWD) porosity; (3) the moisture and density (MAD) porosity; (4) the mercury injection capillary pressure (MICP) porosity
The porosity measured at in-situ stress matches the LWD porosity (n = ~0.38), and the PCATS porosity (n = ~0.38) interpreted for hydrate-bearing sandy silt core sample (Table 1), confirming that the in-situ porosity of sediments is about 0.38
Summary
Methane hydrate is a crystalline solid composed of methane molecules trapped in cages of water molecules [1]. It is stable at low temperatures and high pressures, which in natural environments is commonly found in permafrost regions, outer continental margins, and shallow basin sediments [2, 3]. Methane hydrate has been considered as a potentially vast resource of fossil fuel energy, which has a high energy density, large storage, and widespread distribution across the globe [4]. Methane hydrates comprise a large global pool of organic carbon and may play a role in Earth’s climate system [5, 6]. To make intelligent judgments about how hydrate deposits formed and how they might be produced in an environmental and economic manner, all of these models require the best possible knowledge of the reservoir’s petrophysical nature
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