The 4D microgravity method for waterflood surveillance: Part 3 — 4D absolute microgravity surveys at Prudhoe Bay, Alaska

Abstract

The 4D microgravity method is becoming a mature technology. A project to develop practical measurement and interpretation techniques was conducted at Prudhoe Bay, Alaska, from 1994 through 2002. Beginning in 2003 these techniques have been systematically applied to monitor a waterflood in the gas cap of the Prudhoe Bay reservoir. Approximately 300 stations in a [Formula: see text] area are reoccupied in each survey year with sub-[Formula: see text] precision absolute gravity and centimeter precision Global Positioning System (GPS) geodetic measurements. The 4D gravity measured over epochs 2005–2003, 2006–2003, and 2007–2003 has been successfully modeled to track the mass of water injected since late in 2002. A new and improved version of the A-10 field-portable absolute gravity meter was developed in conjunction with this project and has proven to be a key element in the success of the 4D methodology. The use of an absolute gravity meter in a field survey of this magnitude is unprecedented. There are substantial differences between a 4D absolute microgravity survey and a conventional gravity survey in terms of station occupation procedures, GPS techniques, and the 4D elevation correction. We estimate that the overall precision of the 4D gravity signal in each epoch is less than [Formula: see text].

Time-lapse gravity data at Prudhoe Bay: New understanding through integration with reservoir simulation models

“…The interpretation of these data have demonstrated a successful and insightful tool to reveal the water movement during previous studies in one of the most complete and well recognized studies in time-lapse gravity ( Hare et al (1999), Ferguson et al (2007), Ferguson et al (2008). Although the time-lapse gravity data has sufficient information for recovering the injected gas cap water mass, the recovery of the changing water distributions is still ambiguous, and an integration of different data types is always beneficial.…”

“…The result is one of the most successful and insightful applications of time-lapse gravity for reservoir monitoring to date (Hare et al (1999), Ferguson et al (2007), Ferguson et al (2008), Hare et al (2008) ).…”

“…Additional details on the time-lapse gravity surveys and data processing at Prudhoe Bay can be found in Ferguson et al (2007) and Ferguson et al (2008).…”

“…(a) Time-lapse gravity data for full epochs: 2003-2005, 2003-2006, 2003-2007, 2003-2008. (b) Time-Lapse gravity data for sub-epochs: 2005-2006, 2006-2007, 2007-2008 Ferguson et al (2008). Solid lines delineate the coast-line.…”

Feasibility of time-lapse gravity and gravity gradiometry monitoring for steam-assisted gravity drainage reservoirs

“…Time-lapse gravimetry has been used extensively in oil and gas production monitoring (e.g., Alnes et al, 2008;Brady et al, 2008;Eiken et al, 2008;Ferguson et al, 2008;Alnes et al, 2011;Dodds et al, 2013) and in groundwater and aquifer studies (e.g., Cogbill et al, 2006;Davis et al, 2008;Gehman et al, 2009). A more comprehensive review can be found in Krahenbuhl and Li (2012).…”