Permeability Measurement and Prediction with Nuclear Magnetic Resonance Analysis of Gas Hydrate-Bearing Sediments Recovered from Alaska North Slope 2018 Hydrate-01 Stratigraphic Test Well

Abstract

Permeability of porous media, such as oil and gas reservoirs, is the crucial material parameter for predicting their hydraulic behavior. A nuclear magnetic resonance (NMR) analyzer is widely used as a powerful tool to predict permeability of various media. NMR T 2 (transverse or spin−spin) relaxation time distribution, which is related to pore size distribution, gives the information to allow calculation of effective (initial) permeability. In this study, we investigate effective, intrinsic (absolute), and relative water and gas permeabilities of hydrate-bearing pressure core samples. These samples were recovered from the Alaska North Slope 2018 Hydrate-01 Stratigraphic Test Well by sidewall pressure coring and then analyzed in a laboratory using both fluid flow test and NMR analyzer. The peak of the NMR T 2 distribution was measured at 10−20 ms using a laboratory NMR analyzer, which compares well with in situ measurements obtained via logging while drilling NMR data for two samples with high gas hydrate saturations (S h = 76% and 74%). Further, comparison of laboratory NMR T 2 distribution after hydrate dissociation revealed that the hydrate existed in large pore spaces. Effective permeabilities predicted by the Timur-Coates (TC) model and the Schlumberger-Doll-Research (SDR) model, with T 2 cutoff 33 ms, were about an order of magnitude less than the laboratory measured values. Alternative TC model-based calculations with the T 2 cutoff reduced to 10 ms and a newly developed hydraulic radius model better matched the laboratory data. For the analysis of the intrinsic permeabilities, the TC model with a T 2 cutoff of 33 ms and SDR model were greater than the laboratory derived values, while the hydraulic radius model more closely matched the laboratory-derived values. In addition, permeability measurements were also made relative to gas and water under constant three-phase flow (water−gas−hydrate) conditions. After hydrate dissociation, a relative permeability curve was developed for each of the analyzed core samples based on the Corey petrophysical model. The results indicate that the gas permeability changed rapidly at high water saturation around 90%. Thus, we infer that the selection of relative reservoir parameters should focus on the higher water saturation conditions.

Planning and Operations of the Hydrate 01 Stratigraphic Test Well, Prudhoe Bay Unit, Alaska North Slope

“…Standard methods of NMR analyses suggest low values (on the order of 0.1 mD) are associated with high bound-water fractions . However, reevaluation of the NMR log data indicates that higher permeability values consistent with those obtained from pressure cores are possible for the gas hydrate-bearing reservoir sections logged and cored in the Hydrate-01 STW. ,, …”

“…Sidewall pressure cores were collected in the Hydrate-01 STW using Halliburton’s CoreVault tool to gather grain size and other data needed for the design of the project production test wells. ,, The CoreVault tool is a wireline deployed mechanical (rotary) coring instrument that can obtain up to 10 cores (each measuring 2.25 in. in length with diameter of 1.5 in.)…”

“…There were a total of 39 attempted coring events over the 5 wireline CoreVault core runs with 34 cores successfully recovered (Table ). A total of 13 pressure core samples were extracted, preserved in liquid nitrogen, and shipped to the laboratories of the National Institute of Advanced Industrial Science and Technology in Sapporo, Japan, for advanced laboratory analysis. , The remaining 21 core samples were shipped to the Stratum Reservoir laboratories in Golden, Colorado, for routine and advanced core analysis …”

“…Mineralogy and grain-size studies of the recovered CoreVault sidewall cores indicated that the targeted reservoirs in the Hydrate-01 STW are well sorted and quartz rich, with the grain size of the sampled reservoir section ranging from coarse silt to very fine sand. Additional analysis of the recovered pressure cores yielded in situ effective permeabilities measured in the B1 and D1 sands on the order of 10 mD. , …”

“…A total of 13 pressure core samples were extracted, preserved in liquid nitrogen, and shipped to the laboratories of the National Institute of Advanced Industrial Science and Technology in Sapporo, Japan, for advanced laboratory analysis. 35,36 The remaining 21 core samples were shipped to the Stratum Reservoir laboratories in Golden, Colorado, for routine and advanced core analysis. 35 As described in refs 14, 35, and 36, planning for the subsequent project test wells necessitated the collection of grain-size data from the Hydrate-01 STW.…”