Discussion Surface fracture systems:

Transcription

1 NETL/University Research Collaboration Annual/Final Report A Portfolio Portrait Date: 09/14/07 Project # and Title: 26 - Integrated Geoscience Approach to CO2 Leakage Prediction and Detection at Geologic Sequestration Sites Lead University PI Name: Wilson, Tom Report Type: X Year 1 Annual Report (check if project will receive year 2 funding) Final (check if project will NOT receive year 2 funding) Proposed Purpose of Research Project: Develop integrated remote sensing, soil gas analysis, groundwater chemistry, geophysical, and geological methodologies to detect existing and potential macro- and microseeps in the vicinity of potential combined EOR/sequestration sites. The research objective has broader application to the general assessment of CO 2 leakage potential and monitoring at combined geologic carbon sequestration/eor sites. NETL has entered an accelerated phase of activity centered on carbon sequestration field tests in progress through the regional CS partnerships. At the initiation of this project NETL was considering involvements with the Southwest Regional Partnership (SWP), the Midwest Region Carbon Sequestration Partnership (MRCSP), and/or the Plains CO2 Reduction Partnership (PCOR). At the time of the project award, the SWP began laying the groundwork for injection of CO2 into the Fruitland coal seam in the northern San Juan basin of New Mexico. The current plan is to inject 75,000 tons of CO2 over the span of one year in to the lower Fruitland coal. The scale of the operation serves as a major bridge between the pilot studies with which we currently have experience (in which injection volumes are limited to a few thousand tons of CO 2 ) and the larger injection volumes of several tons per day anticipated during full-scale deployment in future carbon sequestration efforts. The other two partnerships plan much smaller injections, but NETL is interested, because they are lacking in MMV plans. The MRCSP will inject up to 10,000 tons of CO 2 into a saline aquifer somewhere in the midwest, and the PCOR have both EOR and ECBM experiments planned in North Dakota. The results of research conducted under this project will be used to help identify potential leakage mechanisms associated with site geology and to make recommendations to our NETL collaborators for placement of monitoring technologies for CO2 leakage detection. The characterizations are an integral part of the NETL s SEQURE MMV technologies. Results Section 1 Describe the technical results and conclusions. Summary The initial phase of this study has concentrated on site characterization activities over the Southwest Regional Partnership s San Juan Basin pilot site. Characterization activities incorporated analysis of remote sensing imagery, field mapping and geophysical surveys. Lineament and fracture trace mapping activities conducted using Landsat, QuickBird and satellite radar imagery were combined with extensive field mapping of surface fracture traces. This integrated analysis reveals the presence of systematic fracturing of the near-surface. Two dominant fracture sets are observed with approximate trends of N30W and N50E. Coal cleat trends measured in a nearby well have a dominant face cleat trend of N35E. Variability in the trends of near-surface fracture systems is observed and suggests that some local variability in face cleat orientation may also occur in the area.

2 Terrain conductivity surveys were conducted in the area surrounding the site in an effort to locate near-surface fluid migration pathways and open conduits through which leaked CO2 might migrate back to the surface. The results reveal the presence of well drained areas adjacent to the flanks of the mesa with irregular extensions into the interior of the mesa. Local topography and vegetation also influence the distribution of conductivity anomalies observed at the site. The results suggest the presence of a complex subsurface drainage network. Ground water monitoring well locations have been proposed based on geological and geophysical field surveys and topographic features over the site. Arrangements to drill and sample these wells are moving forward. Our research efforts also included development of a database of logs of an extensive subsurface mapping and evaluation of the structural and stratigraphic development of the area. Interferrometric synthetic aperture radar data were collected over the site to determine if short term surface motion has occurred in response to production from oil and gas reservoirs in the area. Information related to the potential influence of fracture systems on CO2 escape, the control exerted by near surface fracture systems on surface landform development along with the distribution of conductivity anomalies in the near surface intervals has been provided to the NETL MMV team as results unfolded. Suggestions regarding optimal locations of NETL tracer and soil gas sampling were made as direct outgrowth of the observations and analysis conducted in this research effort. Discussion Surface fracture systems: Extensive fracture studies were conducted at two pilot site locations within the San Juan basin area. The pilot site location was a moving target throughout the first year and a half of the study. Results obtained from the latest and final site are reviewed briefly here. The locations of fracture traces measured on the QuickBird image over the new site (Figure 1) Figure 1: QuickBird image centered over the location of the new injection well in section 32. Mapped fracture traces are highlighted.

3 are generally clustered along the edges of the mesa As in our study of the site to the southwest, we see significant influence of fracture systems on the development and control of canyon orientation. The canyon heads southwest and southeast of the injection well (as shown in Figure 1) appear to develop primarily through groundwater sapping. This process is common throughout the area and was initially observed along the perimeter of the mesa to the southwest. The massive sands that form the resistant mesa floor and prominent benches along the canyon wall are underlain by seeps in places. The seeps undercut and weaken the overlying section eventually leading to collapse. Rock falls often point up slope to seep locations. Headword erosion continues through this process, widening and extending the canyon head. The rose diagram of QuickBird fracture traces measured in the West Canyon (see Figure 1) reveals prominent N50E and N35W trending sets (Figure 2). Fracture trends in the Southeast Canyon are dominated by the N50E set. The trends in this area are rotated about 10 degrees east from those observed to the southwest shown at the top of this panel. A) B) Figure 2: Rose diagrams of QuickBird fracture traces measured in the (A)West and (B) Southeast canyons near the new injection well. NW and NE trending fracture sets observed to the southwest at the previous site persist through the new site with some eastward rotation. The N50E trend likely represents the high permeability production trend within the Fruitland. Perhaps early break through of injected CO2 into production wells will occur along this trend.

4 Subsurface mapping: The Southwest Regional Partnership s San Juan Basin pilot site is located near the hinge of the San Juan basin (Figure 3). Local flexures are observed in the Huerfanito Bentonite and Pictured Cliffs Formation (Base of the Fruitland). Figure 3: Cross section through the San Juan Basin taken from Fassett (2000). The location of the pilot site is shown by the red line at right near the structural hinge point. Our detailed subsurface mapping effort covers an approximately 42 square mile area surrounding the injection well location (Figure 4). As with other phases of the work, development of the Basin Axis Injection well Figure 4: Structure on the Pictured Cliffs Formation in the vicinity of the San Juan Basin pilot well (red dot in section 32). database was complicated by the shifts in pilot site location during the initial 1.5 years of the project. A variety of subsurface maps have been compiled including: structure on the Pictured Cliffs Formation, structure on the Huerfanito Bentonite, Fruitland Formation Top, Fruitland Formation Isopach, Fruitland Formation Net Coal, Fruitland Formation Basal Net Coal, Fruitland Formation Upper Net Coal, Structure on an internal Fruitland coal shale marker bed and others.

5 The Fruitland Formation contains three coal intervals in the area as shown in the log below (Figure 5). CO2 injection will take place in the basal coal gm/cm 3 coal cutoff Fruitland Fm. Top Upper coal Middle coal Shale Marker 2 Shale Marker 1 Basal coal Figure 5: Type log for the Fruitland Formation shows three distinct coal zones. Persistent shale markers have been interpreted through the area. Shale Marker 1 divides the lower coal into two intervals. The thickness of the basal net coal varies significantly through the area (Figure 6). It thickens toward the basin axis and thins to the southwest across the structural hinge observed in the Pictured Cliffs and other formations in the area. In the vicinity of the injection well the coal basal coal is approximately 24 to 26 feet thick.

6 Figure 6: Net thickness of the basal Fruitland coal. Structure on the base of the Fruitland (Figure 4) inferred from wells within section 32 is absent. The coal dips very gently at less than a quarter of a degree (30 feet over 1.4 miles) to the northeast toward the axis of the basin. Structural analysis reveals no significant faulting. The isopach of the basal coal (Figure 6) reveals no influence of local structural movement during coal formation. Based on log scale observations there do not appear to structures in the area that might compromise the integrity of the carbon storage effort. Additional information on the results of the surface fracture analysis and subsurface mapping efforts are reported in and also Some results are also presented on the American Association of Petroleum Geologists site Near Surface Geophysical Studies Near-surface geophysical studies at the site were focused on the use of multifrequency terrain conductivity surveys. The GeoPhex GEM2 terrain conductivity meter was used. This instrument is capable of collecting data simultaneously at multiple frequencies. During site surveys data were collected at 1050 Hz, 4110 Hz, Hz and Hz. The high frequency response (Figure 7) reveals a complex pattern of conductivity variation through the area.only the initial survey conducted during April is reported here as an outgrowth of the first year funding effort. Approximately sixteen kilometers of multifrequency terrain conductivity data were collected over the new site in late April & early May. The surveys went well and considerable aerial coverage over the site was obtained (see Figure 1).

7 Generally ground conductivity is lower toward the canyon edges (bluer colors in Figure 7). This could be partly due to an edge effect, however, the effect is not uniform and a nice high conductivity feature extends out to the mesa edge on the west side of the survey. It also seems possible that these are well drained areas and therefore may represent more permeable areas in the near surface. Other surface erosional features controlled by near surface fracturing have low conductivity signature and extension. Figure 7: Terrain conductivity variations observed over the San Juan basin pilot site. Conductivity lineaments have been interpreted in blue. The proposed injection well (red dot) and NETL tracer and soil gas sample points are located on the map for reference to conductivity features. The outgrowths of the terrain conductivity surveys over the site reveal a complex network of potential near surface migration pathways. These observations were passed along to our NETL MMV collaborators. It will remain to be seen what role these features may play in the migration of CO2 if it should escape to the surface. Tracer and soil gas sample points are located in proximity to or within several of these features and should reveal any relationship to nearsurface CO2 migration should it occur. The locations of surface conductivity anomalies were also used, in part, to help locate near-surface groundwater monitoring wells. If the low conductivity zones mapped across the mesa are high permeability and well drained near surface areas, they may also groundwater filtration pathways into underlying aquifers. Hydrogeologic Characterization (Dr. Henry Rauch, Co PI) Hydrogeology work involves the selection and characterization of existing springs and water wells for monitoring near the final CO 2 injection well site; design and construction of 2 or 4 shallow water monitoring wells near the final CO 2 injection well site; monitoring and sampling of the selected springs and water wells for discharge and water chemistry over time (during preinjection, during injection and post injection phases); and analysis of all hydrogeologic data for trends and any signs of CO 2 gas microseepage to shallow ground water aquifers.

8 To date initial field work was done to locate existing domestic water well supplies and springs for potential sampling in the vicinity of the planned old CO 2 injection well site of August, 2006 (since moved to new locations), and a few such wells or springs were located. Topographic maps for the general study area were also obtained. No other significant hydrogeologic information has been collected. The hydrological studies are more sensitive to these changes in pilot site location. Student retention on the project also presented additional obstacles to progress. Rauch s funded geology graduate student, Gary Daft, quit the project in August, 2006, and to date no replacement graduate student in geology or civil engineering has been found to continue work as a research assistant on this research project. Both Rauch at West Virginia University, and Brian McPherson at the University of Utah, have been searching for a new replacement graduate student, with no success. As a result, Rauch and McPherson decided in late February, 2007, to seek a new graduate student at New Mexico Tech University (NMT), to do Rauch s field research work. This is the most practical solution to the problem, as field work travel between NMT and the San Juan Basin field site is about 4 hours time one way by road vehicle. Rauch has initiated action to hire a NMT student as his field assistant, by communicating with Ms. Geri Peterson of the Petroleum Recovery Research Center of New Mexico Tech, and with West Virginia University (WVU) research budget officials (of the Executive Business Office (EBO) of the Eberly College of Arts and Sciences, and of the Office of Sponsored Programs (OSP)). With permission of RDS and NETL, a portion of Rauch s budget will be transferred to NMT to make possible the hiring of a student there. As work shifted to the latest pilot site, Rauch located possible shallow ground water monitoring wells in the vicinity of the CO2 injection well (Figure 8). A) B) Figure 8: Proposed ground water monitoring wells are located on the topographic map of the area (A) and google earth image (B) Locations of groundwater monitoring wells were based on topographic lineaments and drainage and EM conductivity anomalies. Interferometric Synthetic Aperture Radar Evaluation Satellite radar images were collected and processed to determine whether differential subsidence related to historical oil and gas production could be detected over the region. One RADARSAT archive image and 3 new-collects were processed for this evaluation. View times spanned the January 2004 and October 2006 period and included images collected on January 22, 2004, August 15, 2006, October 2, 2006 and October 26, 2006.

9 Line of site differentials were converted to vertical displacements. All data were phase corrected for topographic variation. Temporal coherence between the August 15 and October 2, 2006, images was very high, while coherence between the January 22, 2004 and August 15, 2006 was very poor. Poor long term coherence is believed to result primarily from seasonal changes (winter versus summer). MDA analysis of vertical differentials concluded that significant differential subsidence was not observable over the month and a half to two and a half month time periods for which coherent differentials could be calculated. However, on the local scale change is observed that does not appear to be entirely restricted to topographic variability. In the longer term differentials (Figure 9) we see some unusual features cross cutting the canyon flanks of the mesa on which the pilot well will be located. A) B) Figure 9: Differential surface displacements observed during the August 15 to October 26. The differentials are superimposed in the QuickBird image of the area (A) and draped over the DEM for a more local view in the vicinity of the future injection well (B). The steep gradient circled in Figure 9B is located on the canyon wall. A sharp change in vertical displacement occurs southwest and northeast along the canyon wall and does not have any association with local canyon wall topography. The response is quite interesting, and is most likely associated with a local rock fall. Rock falls are common in the area and the PI was nearby at the time one rock fall occurred. Well logging, 2D Seismic andvsp The research effort was adapted to incorporate a detailed logging program. Logging efforts at the pilot site were missing from the Partnerships original characterization plans. However, detailed logging of the injection well is critical to understanding how CO2 will interact with the coal and overlying formations. The logs will provide a detailed description of the local geology at the injection point. We developed a logging plan that will provide detailed views of fracture systems in the geologic section overlying the injection zone and extending 500 feet through the cap rock 500 feet into overlying strata using Schlumberger s FMI logging tool. These logs will help modelers assess the potential for upward migration of injected CO2 through

10 the capping strata and will also help them accurately model flow through the Fruitland coals. Detailed compressional wave and shear wave velocity log measurements along with density observations in the well will provide a complete description of the mechanical properties of the overlying section from the near-surface casing at about 300 feet below the surface down to the top of the Fruitland Formation for use in geomechanical simulations. These simulations will help attempt to predict the extent of surface uplift in response to injection and provide comparative reference to extensive tiltmeter observations being collected at the surface. The impact of the logging operation on Partnership and NETL efforts is extensive. This effort will take place with the year 2 follow-on funding. We also took the lead in developing the SWP s seismic monitoring efforts. Our proposed 2D seismic monitoring effort had to be abandoned because of the company contracted to do the work did not honor their bid. In the follow-on period we are developing plans to undertake a vertical seismic profiling (VSP) monitoring effort that has been accepted by the SWP and promises to provide high resolution seismic observations in the vicinity of the injection well. The VSP will be repeated and we hope these monitor surveys will reveal the migration of CO2 into the Fruitland coal during the injection process. Section 2: Relevance of the technical results to the objectives of the NETL/University Collaboration Geological and geophysical characterization efforts are an integral part of NETL s SEQURE MMV technologies. The studies we conducted in this project on the San Juan basin pilot site have been designed to help ensure effective deployment of the Southwest Regional Partnership s carbon storage efforts. Thorough characterization of site geology involved studies of both surface and subsurface geologic settings. In this study, we used high resolution remote sensing imagery to help identify possible near-surface fracture zones and faults. The physical significance of these features was examined further using multifrequency terrain conductivity surveys. Extensive subsurface characterization efforts were also conducted within the confines of existing resources which included public domain log data from the pilot site and surrounding area. Our research effort remained flexible and innovative throughout the period of performance discussed above. We adapted our research effort to incorporate the use of novel multifrequency terrain conductivity survey methods, the use of interferometric synthetic aperture radar methods (INSAR) and detailed surface fracture mapping of the area for ground confirmation of remote sensing observations. We also helped expand and fill critical gaps in the SWP monitoring and characterization efforts through the incorporation of an injection logging program and VSP seismic monitoring efforts a part of our follow-on and year 3 efforts. The geological and geophysical characterization activities helped establish confidence that large scale migration pathways in the form of faults are unlikely at the site. Near-surface fracture characterization efforts revealed the presence of significant systematic fracturing of massive sands supporting the mesa s in this area. The fracture systems exert significant control on headward erosion and development of canyons that dissect Pump Mesa. Terrain conductivity surveys suggest the presence of near-surface drainage pathways that might serve as CO2 migration conduits if CO2 escape were to occur. Recommendations have been made to our NETL colleagues regarding monitoring of likely avenues for CO2 escape. As we complete our follow-on activities and move into the third year of our effort, we look forward to the results of NETL monitoring efforts along with our companion ground water monitoring effort. Year 3 efforts will evaluate the context of monitoring observations to local geologic conditions revealed in our studies and to forthcoming log and VSP observations.

11 Deliverables: PDF attached. See also