Evaluating time-lapse borehole gravity for CO2 plume detection at SECARB Cranfield

Abstract

a b s t r a c tMonitoring of CO 2 storage processes provides a renewed challenge of adapting oil and gas monitoring technology to provide measurements required of operator, regulatory authorities and the public. These requirements include providing measurements that will support an understanding of safe containment of the CO 2 plume, and inform evidence that injected CO 2 remains in the storage complex for the purposes of green house gas accounting, cost effectively. These roles for monitoring demand a re-evaluation of deep reading measurements besides seismic, such as gravitational and electromagnetic technologies, sensitive to density and electrical properties of the fluids. In particular this paper explores the operational and interpretational challenges of borehole microgravity in a CO 2 timelapse survey in two wells at the SECARB Cranfield injection site.The Southeast Partnership (SECARB) test at Cranfield, Mississippi, was the first of the commercial scale projects comprising a staged array of field deployments testing key issues of capacity and best methods for assuring storage permanence. More than 3 million metric tons of injected CO 2 will have been injected since the start of injection in July of 2008. The site is an historic oilfield at a depth of 2500 m in the Cretaceous fluvial Tuscaloosa Formation, developed by Denbury Onshore LLC. The project was unique in deploying a range of geophysical measurements including cross-well seismic and electrical resistivity tomography, from two monitoring wells positioned in line from the injector and several 100 ft down-dip in the Tuscaloosa. The CO 2 Capture Project (CCP) took advantage of the multiple field acquisitions of borehole data during the injection phase of this project to acquire timelapse borehole gravity in the two monitoring wells. The objective was twofold; the first to understand the operational aspects and design of the acquisition, while the second was to assess the ability of the surveys to detect the injected CO 2 . The baseline acquisition occurred in October 2009 and the repeat survey in September 2010.

Using surface and borehole time‐lapse gravity to monitor CO2 in saline aquifers: a numerical feasibility study

“…Gaussian noise with a 10 μgal standard deviation is added to gravity changes simulated in the borehole. Borehole time‐lapse measurements are expected to be noisier that surface measurements because of a combination of instrumental and set‐up errors due to depth positioning of the borehole gravimeter …”

“…Its amplitude is comparable to that of the errors associated to time‐lapse gravity surveys, typically 5 μgals . To overcome the issue of distance between the measurements and the plume, borehole time‐lapse measurements have been suggested and numerically studied, and the first results from actual measurements are promising and hint at the detection of density changes associated to CO 2 storage at SECARB Cranfield site …”

The state of the art in monitoring and verification—Ten years on

“…Natural tracers (isotopically distinctive CO 2 ) and dissolved methane in reservoir brine and emplaced pulses of SF 6 , PFT, and noble gas tracers provided data on fluid flow not available from imaging (Lu et al, 2012a). A well-bore gravity tool was deployed and was able to detect changes due to substitution of CO 2 in relatively thin intervals (Dodds et al, 2013). In addition, a baseline 3-D seismic survey was conducted over the field with a repeat survey after injection of the first 1 million metric tons.…”

“…Well-based gravity was tested at Cranfield and was successful in obtaining signal from injected CO 2 (Dodds et al, 2013) and is in testing at several EOR fields.…”

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).…”