May 2002 Report

Draft Hydrogeology Program Planning Group Final Report Contributors: Barbara Bekins John Bredehoeft Kevin Brown Earl E. Davis Shemin Ge (PPG Chair) Steven M. Gorelick Pierre Henry Henk Kooi Allen F. Moench Carolyn Ruppel Martin Sauter Elizabeth Screaton Peter K. Swart Tomochika Tokunaga Clifford I. Voss Fiona Whitaker Submitted to Gilbert Camoin and Tim Byrne Science Steering and Evaluation Panels May 20, 2002 CONTENTS Executive Summary ……………………………………………………...………………..…. I Key Scientific Questions Research Methodologies in Hydrogeologic Studies Recommendations 1. Introduction …………………………….......………………………...……………………. 1 2. Key Scientific Questions ………………………………………………………………...… 1 3. Governing Principles of Sub-ocean Fluid Flow and Fluid-related Processes …….…… 2 3.1. Governing Principles for Fluid Flow 3.2. Driving Forces for Fluid Flow 4. Methodologies in Hydrogeologic Study ………………………………..………………… 6 4.1. Establishing Conceptual Models 4.2. Hydrogeologic Testing 4.3. Hydrogeologic Modeling 4.4. Existing Tools and Techniques for Hydrogeologic Measurements 5. Recommendations ……………………………………………………………………….... 12 5.1. Global Sub-ocean Hydrogeologic Observation Stations …………………………..12 5.2. Dedicated Hydrogeology Legs …………………………………………………….13 5.2.1. Mid-ocean Ridges and Flanks 5.2.2. Subduction Zones 5.2.3. Seismogenic Zones 5.2.4. Coastal Zones 5.2.5. Carbonate Platforms 5.2.6. Flow Systems Supporting the Deep Biosphere 5.2.7. Gas Hydrates 5.3. Collection of Routine Hydrogeologic Data on All Legs…...…………………….. 33 5.4. Developing, Improving, and Maintaining Tools.…………………………………. 36 5.5. Pre- and Post-cruise Modeling Studies ……………………………………………. 38 5.6. Encourage Large Hydrogeological Community Involvements…………..……...… 39 6. Appendix ……..……………………………………………………………………………... 40 6.1. Coastal Zones (supplement to 5.2.4.) 6.2. Carbonate Platforms (supplement to 5.2.5.) 6.3. Fluid Flow in Continental Margins (supplement to 5.2.4. and 5.2.5.) 6.4. PPG Members, Liaison, Goals, Mandate, Meetings 6.5. Acknowledgment 7. References ……………………………………………………………………………………56 Executive Summary The hydrosphere, along with the atmosphere, lithosphere, and biosphere is an integral part of the complex earth system. Fluids play a vital role in linking various physical and chemical processes by transporting energy and solutes in the earth at a wide range of spatial and temporal scales. Over the last decade, the Ocean Drilling Program (ODP) has made significant technological advances in measuring and monitoring hydrological parameters. However, many important questions remain concerning the role of fluids and associated hydrogeologic processes in sub- seafloor environments. Fluid flow is a critically important factor in seismogenic zone dynamics, global chemical cycles, gas hydrate formation, mid-oceanic hydrothermal systems, sub-seafloor biological community development, and diagenetic processes in carbonate platforms (Figure 1). Topography Density driven flow driven flow Car bonat e plat for m Fr esh Te ct o ni c Biological water compaction communities Gas hydrates Mineral Thermally driven flow dehydration Diffuse flow ? Seismically induced flow ? Figure 1. Schematics showing the involvement of sub-seafloor fluid flow systems in a variety of geologic processes [modified from a figure courtesy of Earl Davis]. The need for long-term monitoring of in-situ pore pressure and fluid flow is well articulated in Integrated Ocean Drilling Program’s (IODP) Initial Science Plan, ODP’s Long-Range Plan and the Complex Report. The transition from ODP to IODP presents our scientific community with an unprecedented opportunity to develop new tools and to integrate hydrologic studies into future scientific ocean drilling endeavors. These studies will provide important new insights into the poorly understood realm of sub-seafloor hydrogeology, and broaden the perspective and deepen the understanding of numerous scientific issues that have long been central to ocean drilling research. JOIDES established the Hydrogeology Program Planning Group (PPG) at the end of 1999. The overall goal of this PPG was to define and prioritize the main problems in submarine hydrogeology. The group met three times during 2000 and 2001, leading to the production of this report. In the main body of the report, we first outline the important hydrogeologic questions. We I then provide an overview of the fundamental principles of fluid flow in coupled geologic processes. Next we review the methodologies in hydrogeologic studies focusing on modeling and hydrogeologic testing. Finally, we make six recommendations for addressing the scientific issues and suggest strategies for implementing the recommendations. Key Scientific Questions It is our strong consensus that one can comprehend the dynamics of geologic processes within the earth only if one can understand how fluids move and how they transport mass and energy. Once rocks are formed in the earth's crust, the moving fluids become the principal transport mechanism by which mass and energy are redistributed. It is, therefore, vital for geoscience researchers to understand the following fluid-related questions: • What is the current state of the fluids in terms of pressure, temperature, and composition? • What are the sources of fluid and driving forces for fluid flow? • What is the direction and rate of flow? • How are the moving fluids transporting mass and heat? • What was the past state of fluid systems (paleohydrogeology)? • How did the paleohydrogeologic system transport mass and heat? • What are the magnitude and distribution of porosity and permeability? Research Methodologies in Hydrogeologic Studies Studying hydrogeologic systems begins with establishing conceptual models. A conceptual model is a description of the postulated flow system and includes the expected direction and rate of flow, the driving forces and boundary conditions, whether flow is steady or transient, the postulated sources and sinks of fluid and solutes, and the spatial variation in flow due to varying permeabilities or changes in driving forces. An important part of a conceptual model is the development of a water budget. This requires specification of water sinks, sources, and flow directions. Water inputs may involve thermally driven seawater, topographically induced flow of meteoric water, and compaction and diagenetic scource of pore waters. Some fluid outputs may be readily identified based on direct observation of seafloor vents. Diffuse discharge may be more difficult to identify. Compared to focused flow, manifestations of diffuse flow in processes such as gas hydrate accumulations, perturbations to geothermal or geochemical profiles, seafloor mineralization, and seafloor biological communities are more subtle. By implementing the important features of the conceptual model in computer simulations, the scientific hypotheses related to fluid flow can be tested. Feasibility can be explored, which is an essential step in formulating a sample plan. Hydrogeologic mathematical models, derived from the governing principles of hydrogeology, quantify conceptual models of sub-seafloor hydrogeologic flow systems. The mathematical models frequently turn into numerical or computer models in practice. Conceptual models of fluid flow are usually based on scanty observations and the intuition of hydrogeologists. Formalization of the conceptual model with a computer model is an essential part of any comprehensive hydrogeologic study. Computer models of flow systems are developed from formation geometry, boundary and initial conditions, and formation properties. Such models are II useful and cost effective tools for testing hypotheses and assessing conceptual model feasibilities. The complexity of hydrogeologic modeling endeavor varies. When limited data is available, it is often best to start with one- or two-dimensional analytical solutions derived from well-defined boundary value problems. Such solutions provide insights for the systems of interest. In sub-seafloor settings, numerical models are often necessary in order to account for complex formation geometry, rock-property heterogeneity, variable-density fluids, simultaneous heat and solute transport, chemical reactions, and rock deformation. To incorporate as many relevant geologic features as possible, new computer models may need to be developed and tested. The broader the capability of the computer model, the greater is the range of conceptual models that can be quantified. Hydrogeologic tests in sub-seafloor environments are carried out to estimate the hydraulic parameters that control the transmissive and fluid storage capacity of a formation, e.g., geometry, permeability, porosity, and compressibility. Knowledge of these characteristics is essential for successful modeling of hydrogeologic flow systems. In the past three or four decades, there have been many attempts to constrain hydrogeologic parameters through indirect means, e.g., the analysis of borehole temperature logs, seismic profiles, and fluid chemistry. Efforts to determine hydraulic parameters through direct methods by borehole hydraulic tests and naturally occurring seafloor loading processes have been quite limited. Existing methods include shipboard experiments using drill-string packers for pressurized slug and constant-rate injection or withdrawal tests, experiments using submersibles to conduct constant-drawdown and constant- discharge tests at CORKed boreholes, and interpretation of pressure fluctuations in multiple sealed boreholes due to natural variations in

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