The successful exploitation of tight-gas reservoirs requires fracture networks, sometimes naturally occurring, often hydraulically stimulated. Borehole microseismic data acquired in such environments hold great promise for characterising such fractures or sweet spots. The loci of seismic events delineate active faults and reveal fracture development in response to stimulation. However, a great deal more can be extracted from these microseismic data. For example, inversions of shear-wave splitting data provide a robust means of mapping fracture densities and preferred orientations, useful information for drilling programs. They can also be used to track temporal variations in fracture compliances, which are indicative of fluid flow and enhanced permeability in response to stimulation. Furthermore, the frequency-dependent nature of shear-wave splitting is very sensitive to size of fractures and their fluidfill composition. Here we demonstrate the feasibility of using such analysis of shear-wave splitting measurements on data acquired during hydraulic stimulation of a tight-gas sandstone in the Cotton Valley field in Carthage, West Texas.
Surdam, Ronald C. (U. of Wyoming) | Dahl, S. (Los Alamos Natl. Lab) | Hurless, R. (Los Alamos Natl. Lab) | Jiao, Zunsheng (U. of Wyoming) | Ganshin, Yuri (U. of Wyoming) | Bentley, R. (Los Alamos Natl. Lab) | Garcia-Gonzalez, M. (Los Alamos Natl. Lab)
Wellbore integrity is essential to ensuring long-term isolation of buoyant supercritical CO2 during geologic sequestration of CO2. In this report, we summarize recent progress in numerical simulations of cement-brine-CO2 interactions with respect to migration of CO2 outside of casing. Using typical values for the hydrologic properties of cement, caprock (shale) and reservoir materials, we show that the capillary properties of good quality cement will prevent flow of CO2 into and through cement. Rather, CO2, if present, is likely to be confined to the casing-cement or cement-formation interfaces. CO2 does react with the cement by diffusion from the interface into the cement, in which case it produces distinct carbonation fronts within the cement. This is consistent with observations of cement performance at the CO2-enhanced oil recovery SACROC Unit in West Texas (Carey et al. 2007). For poor quality cement, flow through cement may occur and would produce a pattern of uniform carbonation without reaction fronts. We also consider an alternative explanation for cement carbonation reactions as due to CO2 derived from caprock. We show that carbonation reactions in cement are limited to surficial reactions when CO2 pressure is low (< 10 bars) as might be expected in many caprock environments. For the case of caprock overlying natural CO2 reservoirs for millions of years, we consider Scherer and Huet's (2009) hypothesis of diffusive steady-state between CO2 in the reservoir and in the caprock. We find that in this case, the aqueous CO2 concentration would differ little from the reservoir and would be expected to produce carbonation reaction fronts in cements that are relatively uniform as a function of depth.
Bloys, James Benjamin (Chevron Corp.) | Gonzalez, Manuel Eduardo (Chevron ETC) | Lofton, John (Chevron ETC) | Carpenter, Robert Bennett (Chevron Corp.) | Azar, Scott (Chevron) | Wiliams, Deryck (Chevron) | McKenzie, James Denley (Chevron N America Upstream) | Cap, Jesus (Chevron) | Hermes, Robert E. (Los Alamos Natl. Lab) | Bland, Ronald G. (Baker Hughes Inc) | Foley, Ron Lee (Baker Hughes Drilling Fluids) | Harvey, Floyd Ernest (Baker Hughes Drilling Fluids) | Daniel, John Phillip (D.A. Daniel Inc.) | Billings, Floyd (Lucite International, Inc.) | Robinson, Ian M. (Lucite International UK Limited) | Allison, Marlon (Flow Process Technologies, Inc.)
In deepwater or other sub-sea completed wells, fluids, usually spacers or drilling fluid, are commonly trapped in casing annuli above the top-of-cement and below the wellhead. When these trapped fluids are heated by the passage of warm produced fluids, thermal expansion can create very high pressures (10,000 -12,000 psi or more) and cause the collapse of casing and tubing strings.1,2,4,12,15
Mitigation methods such as vacuum insulated tubing to limit heat transfer,6,7,14 nitrogen-based foam spacers to give highly compressible trapped fluids,8,9,10,11 crushable urethane foam,3 etc. are somewhat successful but are either very expensive, logistically troublesome or have unacceptable failure rates. This paper continues the discussion of a new approach which has created a water-based spacer fluid that will be used just ahead of the cement. The spacer contains perhaps 10-30% of emulsified liquid methyl methacrylate monomer (MMA). Upon polymerization, the MMA phase shrinks by 20%, creating room for the remaining fluid to thermally expand without creating catastrophic pressure. The polymerization is triggered by heat and a chemical initiator. The target temperature can be controlled by choosing an appropriate type and concentration of chemical initiator. Premature polymerization during spacer placement can be prevented by an appropriate type, and amount, of inhibitor. The initial lab work and a mid-scale field trial of this technology were reported in detail in SPE/IADC 104698.1
This paper covers the development and field testing (land) of all the equipment and processes necessary to apply the technology in deep water.