Sand Migration Simulation during Gas Production from Gas Hydrate Reservoir at Kuparuk 7–11–12 site in the Prodhoe Bay Unit, Alaska

Abstract

Uncontrolled sand production impedes continuous gas production from a hydrate reservoir as observed in the past field-scale gas production tests. Sand mobilization is strongly linked with sediment deformation and high pressure gradient. Sand production occurs when the mobilized sands reach the well. Throughout gas production from a hydrate reservoir, because of hydrate dissociation, deformation and pressure gradient change both in time and space. Therefore, it is necessary to consider the entire process to identify where sand is likely mobilized and how much mobilized sand could reach the well. This study utilizes a coupled thermal, hydrological, chemical, and mechanical (thermo-hydro-chemo-mechanical) sand migration model to simulate a year long gas production from the hydrate reservoir at the Kuparuk 7–11–12 site in the Prodhoe Bay Unit, Alaska. It is found that sand would mainly come from the lower portion of the production zone where faster hydrate dissociation occurs. The relatively faster hydrate dissociation coupled with the fact that hydrate-bearing sediments and hydrate-free sediments have similar stiffness but different strengths causes complex stress transfer, which results in excessive shear deformation when the upper portion of the production zone starts to dissociate. This is evident not only near the well but also away from the well, leading to a large amount of sand mobilization. Another focus of the modeling study is evaluation of the effect of sand migration on gas production. The comparison of two extreme caseswith sandscreen and without sandscreensuggests that migrated and settled solids around a sand control device can prevent pressure drop across the near-wellbore zone and lead to reduction of the gas production rate.

Scientific Results of the Hydrate-01 Stratigraphic Test Well Program, Western Prudhoe Bay Unit, Alaska North Slope

“…Notably, significant water production is obtained through water sourced from the bounding non-hydrate-bearing sections. , These are phenomena that may not be evident in the production histories from prior, short-duration field tests but are anticipated from a range of potential water sources . Initial geomechanical studies explore phenomena related to initiation and localization of sand mobilization within the reservoir during depressurization, which can be expected to hinder effective wellbore pressure drawdown . Further numerical simulations designed to address likely depressurization schedules, including either planned or unintended operational upsets (shut-ins), reveal that such interruptions may drive complex reservoir responses, including the potential for overall increases in well productivity …”

Numerical Simulations in Support of a Long-Term Test of Gas Production from Hydrate Accumulations on the Alaska North Slope: Reservoir Response to Interruptions of Production (Shut-Ins)

“…To address this issue, a long-term field test of hydrate production from a permafrost-associated reservoir on the Alaskan North Slope has been pursued, with the recent drilling of the Hydrate-01 Stratigraphic Test Well confirming the occurrence of a suitable test site within the Prudhoe Bay Unit . In preparation for this test, extensive geologic, − engineering, and numerical simulation studies , are being undertaken in an effort to assess the system response under a wide range of circumstances, explore the technical challenges of long-term production from hydrate reservoirs, and prepare an appropriate engineering design. This study is part a larger numerical simulation investigation seeking to provide answers and inputs to the design of the proposed production test in northern Alaska.…”

Virtual Special Issue of Recent Advances on Gas Hydrates Scientific Drilling in Alaska

“…Nakajima et al 28 provide extensive sensitivity analyses to identify the most leveraging input parameters and explore the implications of various elements of data uncertainty on the results of gas hydrate reservoir production predictions. Lastly, Uchida et al 29…”

“…Nakajima et al provide extensive sensitivity analyses to identify the most leveraging input parameters and explore the implications of various elements of data uncertainty on the results of gas hydrate reservoir production predictions. Lastly, Uchida et al conduct initial scoping studies of the nature and potential end-member implications of sand mobilization during reservoir depressurization at the Hydrate-01 site.…”