December Newsletter. Crisman Week A Success. In this issue:

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1 December Newsletter Issue 11, December 2010 Crisman Week A Success Crisman Week was very successful! During the three-day meeting event from December 7-9, we received some great feedback and held some very useful discussions on the research currently being performed by our graduate students, both for the Crisman Institute and non- Crisman parties such as RPSEA and the Department of Energy. Thirteen member companies were represented as well as one visiting company. A total of 44 industry members participated on campus as well as 10 or more individuals (or groups) online. There were a total of 30 presentations made 23 Crisman and 7 non-crisman throughout the week which covered the areas of Heavy Oil Recovery, Well Construction, Well Stimulation, Shale Gas, Environmental, and Tight Gas. New projects and some non-crisman research projects were highlighted in 17 posters displayed near the meeting room for attendees to view. Students were available as their time permitted during lunch breaks to discuss their research with industry members and visitors. Additional posters submitted by students also working on ongoing research but not able to be printed were made available to members on a flash drive, which also contained software and some of the presentations from the meetings. These posters are now available to members online. In this issue: If you would like to view the meeting agendas, attendees, presentations, or video of any of the meetings, please visit our meetings page here. Crisman Week 1 Characterization of Rock Transport Properties in Tight Gas and Shale Effect of Chemical Environments on Shale for Fracture Growth Optimization Occurrence of Multiple Fluid Phases across a Basin, in the Same Shale Gas Formation Eagle Ford Shale Example Brine for Reuse in Unconventional Gas Wells

2 Characterization of Rock Transport Properties in Tight Gas and Shale Transport Properties Characterization of Tight Gas Shales Professor Ahmad Ghassemi Student Vahid Serajian Objectives The main objective of this work is to study the permeability of very low permeability rocks such as tight sandstone and gas shale and their variations with stress. This will be done using the Pressure Pulse Permeameter instrument. Approach A Pressure Pulse Permeameter machine can be used to separately determine the porosity of the rock matrix, the permeability of the rock matrix, the effective width of the fractures, and the permeability of the fracture in a fractured core sample. It can measure the matrix properties as low as the nano-darcy range, which makes it unique in comparison to other permeability measurement techniques such as the steady state method. This capability enables the instrument to measure petrophysical parameters of tight (fractured) shale/sandstone samples precisely and, more importantly, in a much shorter time under reservoir confining pressure, pore pressure, and temperature. The Pulse Permeameter device also includes a data acquisition system and an automatic history matching software. To carry out the tests, the core sample is loaded into the instrument and saturated with a system (pore) pressure. A desired confining pressure is applied to the core sample (Fig. 1). Then a pulse of upstream differential pressure is injected to the core. Depending on the permeability/porosity of the sample, the upstream pressure decreases and the downstream pressure increases with time, which is acquired and recorded by the data acquisition system (Fig. 2). The recorded pressure drawdown values are then reduced and prepared to be used in the history matching program. The last program, using analytical calculations and history matching, indicates permeability, porosity, and other petrophysical parameters in the core sample. Achievements Fig. 1 Schematic of the Pressure Pulse Permeameter Figure 3 shows (Δp-Δt) behavior after injecting the gas in a Kentucky sandstone core under 880 Psi pore pressure, ~2850 psi confining pressure, and room temperature conditions. The falloff in the upstream pressure followed by an increase in downstream pressures is related to the gas flow through and partial retention in the core sample. A code was developed in MATHEMATICA for recorded pressure-time data management and its reduction and calibration. Recorded data at different time steps (i.e. 0.1, 1.0, 10.0, and 30.0 seconds) in every test are automatically reduced and calibrated and using the log normal sampling method the best representative data are selected. These representative points will be used in the history matching software. 2 Fig.2 Pressure Pulse Permeameter Instrument Knowing that σ eff = σ conf - σ pore, the intact Kentucky sandstone sample was evaluated with ~300 psi pore pressure and ~1400 psi confining pressure or 1100 psi effective pressure (shown with UP and DN in Figure 4). The sample was cracked from the middle and was evaluated under similar stress conditions. Comparison of the sample under intact and fractured conditions is presented in Figure 4. In the differential pressure vs. time curves of a core sample: Time for initial convergence of pressure: used in fracture conductivity estimation Final equilibrium pressure value: used in matrix permeability determination (Continued on page 3)

3 Time of final equilibrium pressure: used in matrix permeability determination The time of the initial convergence is shorter in the fractured core. Also, in the fractured core the upstream pressure declines faster than the decline observed with the intact rock because the injected gas preferably flows through the fracture rather than the matrix. The pressure-time values are used in a history matching program to obtain the porosity/ permeability values. Six tests were carried out on intact Kentucky sandstone under different pore and confining pressures (Fig. 5). It is observed that the permeability changes with effective stress variations. Permeability changes are more significant at higher values of effective stress. Significance It was found that the Pulse Permeameter Method: Measures nano-darcy scale permeabilities (Perfect for shale gas rock samples) Is fast and precise (in respect to steady state methods) Gives distinct fracture and matrix permeability values in fractured samples Can help in validating new correlations and methods ( i.e. application of image processing in special core analysis) Is used in stress dependent permeability analysis and effects of reservoir depletion on porosity/permeability Is useful for core samples from fractured/low permeability reservoirs, because other methods can only measure effective permeability Can be used to measure the permeability/porosity in exact reservoir pore and confining pressures and reservoir temperatures, so the obtained results are much more realistic. Future Work We recommend saturating the core sample and running drainage-imbibition tests by forcing the injected gas to replace the wetting phase and evaluate the petrophysical properties. Some mechanical changes will need to be made in the instrument in order to study the Biot coefficient effect on the pore pressure distribution. Related Publications and References Ning, X.: The Measurement of Matrix and Fracture Properties in Naturally Fractured Low Permeability Cores Using a Pressure Pulse Method. PhD Dissertation. Texas A&M U., College Station, Texas. Ning, X., Fan, J., Holditch, S.A., and Lee, W.J. The Measurement of Matrix and Fracture Properties in Naturally Fractured Cores. Paper SPE presented at the 1993 SPE Joint Rocky Mountain Regional and Low Permeability Reservoirs Symposium, Denver, Colorado, April. 3 Rushing, J.A., Newsham, K.E., Lasswell, P.M., Cox, J.C. and Blasingame, T.A. Klinkenerg- Corrected Permeability Measurements in Tight Gas Sands: Steady-State Versus Unsteady-State Techniques. Paper SPE presented at the 2004 SPE Annual Technical Conference and Exhibition, Houston, September.

4 Effect of Chemical Environments on Shale for Fracture Growth Optimization Fracture Fluid Re-Use and Optimization Advisors Robert Lane David Burnett Student Aderonke Aderibigbe Objectives Evaluate and develop improvements in shale gas hydraulic fracture performance through improved frac fluid-shale chemistry interactions. Investigate fluid contributions to the improvement of microfractures in shale. Approach We will carry out experiments to determine the fracture toughness and crack propagation stress of shale samples in different chemical fluid environments. We will also investigate the effect of chemical fluid environments on crack and hydraulic fracture propagation. An analysis of the properties of the shale sample will be performed before and after contact. Accomplishments Rock-fluid Interaction This project will utilize fracture mechanics to evaluate the role of chemical environments in optimizing hydraulic fracturing of shales. Previous mechanisms have been proposed by Rehbinder et al. (1944) that the material strength is altered by a change in the surface free energy of a developing crack or fracture due to adsorption of chemicals. Westwood (1974) also proposed that surfactant alters dislocation density and mobility around a crack tip as a function of zeta potential of a surfactant-test material system. Fracture toughness is a measure of a material's resistance to brittle failure when a crack is present. In an aqueous environment, the initiation and propagation of the crack is influenced by the hydrodynamic and adsorption characteristics of solution and mineralogical make-up of the rock surface. In the work by Dunning et al using synthetic quartz, crack propagation stress decreased to a greater extent the more positive the zeta potential of the environment (as seen in Fig. 1). In the work by Karfakis and Akram 1993 using samples of limestone, quartzite and granite, a significant decrease was observed in fracture toughness when in an aqueous environment (compared to air) for all the samples except quartzite as shown in Fig. 2. Selecting of Test Environment Chemical environments with a wide range of zeta potential were selected for investigation. Five environments have been identified: ambient air, distilled water, brine, brine + anionic surfactant, brine + cationic surfactant. The choice of environments will also extend the understanding of the evolving development of viscoelastic surfactants as polymer free fracturing fluids for shale formations. Significance Fig. 1. The variation in crack propagation stress as a function of chemical environment for the environments used in this study. The error bars represent one standard deviation on either side of the mean value. This research will provide more information on shale fracturing fluid interaction and evaluation of the mechanisms involved in chemically activated fracturing. The integration of the mechanical and chemical effects will improve prediction and optimization of the rock fracturing processes in aqueous environments. Future Work Design of Experiment We will work with TAMU Materials Testing Lab to determine the fracture toughness and crack propagation stress impacts of surface-active materials that alter the zeta potential of shale (Continued on page 5) 4

5 surface. This will include equipment modification as needed to handle chemical fluid environments. Preparation of shale samples Shale samples will be obtained commercially (from core carcasses, for example). Shale sample preparation and contact with chemical fluid environments will be arranged. Adsorption mechanics between the shale sample and fluid environments will be studied. Related Publications and References Atkinson, B.K Subcritical Crack Propagation in Rocks: Theory, Experimental Results and Applications. Journal of Structural Geology 4 (1): Fig. 2. K ic test results for all rocks tested. Dunning, J.D. and Huf, W.L The Effects of Aqueous Chemical Environments on Crack and Hydraulic Fracture Propagation and Morphologies. Journal of Geophysical Research 88 (198341): Dunning, J.D., Lewis, W.L., and Dunn, D.E Chemomechanical Weakening in the Presence of Surfactants. Journal of Geophysical Research 85 (198103): Karfakis, M.G. and Akram, M Effects of Chemical Solutions on Rock Fracturing. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 30 (7): Lewis, W.L.: Effect of Aqueous Surfactants on Crack Propagation Rate in Crab Orchard Sandstone. PhD Dissertation. North Carolina U., Chapel Hill, North Carolina (197751). Roegiers, X.L.Z.J.-C Creep Crack Growth in Shale. Paper presented at the the 35th U.S. Symposium on Rock Mechanics (USRMS), Reno, NV. A. A. Balkema, Rotterdam. Permission to Distribute - American Rock Mechanics Association

6 Occurrence of Multiple Fluid Phases across a Basin, in the Same Shale Gas Formation Eagle Ford Shale Example Occurrence of Multiple Fluid Phases across a Basin, in the Same Shale Gas Formation Eagle Ford Shale Example Professors Walter Ayers walt.ayers@pe.tamu.edu William McCain bill.mccain@pe.tamu.edu Student Yao Tian Objectives Eagle Ford Shale produces oil in the updip region, gas in the downdip region, and condensate between the two regions. Knowledge of the extents of these fluid zones is necessary for reservoir development and for analysis of geologic controls on well production. The main objectives of this study are to: establish extents of the different hydrocarbon fluid types; determine regional variations of Eagle Ford reservoir and geologic properties and to evaluate the controls that these properties exercise on Eagle Ford Shale well performance; clarify controls of reservoir mechanical properties on production; and use a reservoir simulator to investigate methods to optimize well production rates. Approach We will conduct stratigraphic and petrophysical evaluations of the Eagle Ford Shale to provide a framework for assessing vertical and lateral variability of reservoir and rock mechanical properties, as well as fluid composition. We will identify mappable stratigraphic units in regional cross sections, correlate those units throughout the study area, make the isopach maps, and evaluate key petrophysical parameters. Petrophysical analysis may include both well log evaluation and integration of routine and special core analyses, including relative permeability. Typical triple-combo log analysis will provide basic shale properties including mineralogy, lithology, total organic carbon, and fluid analysis. Within the framework provided by the stratigraphic and petrophysical analyses, we will map Eagle Ford fluids. Then we will build a reservoir-scale geological model and perform history matching based on available production data. Well deliverability will be modelled to optimize the oil and gas production rates by designing appropriate stimulation strategies and bottom hole pressures. Secondarily, we will investigate the possibility of controlling formation pressure in the condensate region using CO 2 injection wells. Sensitivity analysis will be conducted to investigate the methods to reduce condensate bank and increase production rates. Also, we will forecast Eagle Ford regional variations in fluid compositions over time. Significance Regional oil and gas occurrences in the Eagle Ford Shale, South Texas. Successful exploration and development of the Eagle Ford Shale play requires reservoir characterization, recognition of regions where condensate will be an issue, and the application of optimal operational practices in all regions. The model developed in this study should assist operators in making critical decisions in Eagle Ford exploration and development, and the concepts and results may be transferable to similar shale gas plays. 6

7 Brine for Reuse in Unconventional Gas Wells Low Impact Oil and Gas Activity; Environmentally Friendly Drilling Systems Advisors David Burnett Gene Beck Student Uche Eboagwu Objectives This project is designed to meet the following objectives: Reduce the disposal requirement and environmental footprint in well sites by using membrane technology as a treatment option in the treatment of oilfield produced brine and frac flow back. Select the best membrane media for effective hydrocarbon removal, suspended solids removal, and brine softening while minimizing fouling of the membrane surface with solids from contaminants in a field membrane technology unit. Evaluate membrane technology for optimal water quality recovery and reuse in unconventional gas wells, analyze testing techniques amenable to field operations and cleaning requirements for membrane systems. Approach The approach is to select a membrane which will combine the properties of high flux separation efficiency, high tolerance for solids and fluid treatment, efficient solids rejection as measured by NTU, and hydrocarbon removal. The choice membrane performance will be validated thorough a small scale pilot plant testing in the laboratory and tests in a field environment. Dependable rapid cleaning procedures with appropriate formulas of cleaning solutions for high salinity systems with gas condensate content will be tested in the laboratory and also field engineering tested. Extended duration and combination tests will also be performed for analysis of water chemistry to determine the best options for membrane media. Achievements A comprehensive screening program by A&M (Olatubi et al. 2008) identified Corning ceramic filters (0.2micron) as the optimal selection to use for produced water TSS rejection, but the manufacturer of these membranes is discontinuing commercial development of these filters, therefore there is a need to replace them with other membranes. In field trials in October, 2009, UF membranes were successfully cleaned after filtration of produced brine. Through preliminary tests, small scale flat sheet membrane tests have been employed in the pilot plant to select the best microfiltration and nanofiltration spiral wound membranes to incorporate into the mobile laboratory. Work has expanded to include testing with hollow fiber membranes. These new configurations will allow back pulsing and back washing to minimize fouling. A 2 gpm membrane technology mobile treatment unit was designed to accommodate removal of most organics and some particulates, along with a backwash capability to remove fines during operations. An analytical testing system is also built in the new mobile treatment unit. Significance The purpose of this test is to successfully identify membranes whose supplier will provide commercial quantities of materials that can meet performance standards on the field for oilfield produced water treatment. The success of membrane treatment of produced water lies in maintaining the flux and filtration efficiency of systems over long periods of time. An effective cleaning system will aid in the attainment of filtration efficiency through reduced membrane fouling with lower cost of chemicals. (Continued on page 8) 7

8 Future Work Configuration of a test using hollow fiber membranes for an extended duration test continues, after which data obtained will be analyzed. Combination tests using a hollow fiber membrane and a flat sheet membrane are in progress. Formulating and preparing cleaning solutions for membrane systems continues in order to minimize fouling. Related Publications and References Oluwaseun, O., Burnett, D.B., Hann, R., Haut, R. Application of Membrane Filtration Technologies to Drilling Wastes. Paper SPE presented at the 2008 SPE Annual Technical Conference and Exhibition, Denver, Colorado, September For more information on other research projects, please visit the Crisman website: crisman/ Newsletter Information Stephen A. Holditch, Director Robert Lane, Deputy Director Nancy H. Luedke, Editor Kathy Beladi, Editor info@pe.tamu.edu Harold Vance Department of Petroleum Engineering 3116 TAMU College Station TX Harold Vance Department of Petroleum Engineering at Texas A&M University. All rights reserved. 8