Why Are Unconventional Oil and Gas So Unconventional?

Transcription

1 Why Are Unconventional Oil and Gas So Unconventional? Tight Oil Optimization Workshop Calgary, Alberta, Canada March 12, 2015 James Sorensen Senior Research Manager 2015 University of North Dakota Energy & Environmental Research Center.

2 Bakken CO 2 Storage and Enhanced Recovery Program Sponsoring Partners

3 What Is Tight Oil? Extremely low permeability (<0.1 md) reservoir rock, which impedes the ability of the oil in the formation to flow freely. Tight oil formations are associated with organic-rich shale. Some produce directly from shales, but much tight oil production is from lowpermeability siltstones, sandstones, and carbonates that are closely associated with oil-rich shale. Fluid flow is dominated by natural and artificially induced fractures. 3 Core from Bakken Middle Member

4 Bakken and Three Forks Production Production (December 2014) Over 8000 wells in North Dakota Over 1,200,000 bbl/day of oil Over 1 Bcf/day of gas Horizontal wells and hydraulic fracturing (fracking) 4

5 Bakken Petroleum System Lithology Upper Bakken Shale: Brown to black, noncalcareous, organic rich. L5: Siltstone, massive, dense, mottled, fossiliferous, slightly bioturbated. L4: Packstone to fine-grained sandstone with interbeds of shale. L3: Sandstone, fine-grained, to gray limestone. Sandstone contains cross-bedding and few fossils. L2: Siltstone to silty sandstone. Siltstone is bioturbated, fossils, and dolomitic. L1: Siltstone. Massive dense, very calcareous, highly fossiliferous. Lower Bakken Shale: Brown to black, fissile, noncalcareous, organic-rich, where present fractures are smooth and conchoidal. Pronghorn Member: Mixed sandstone, siltstone, dolomite, and shale. Three Forks Formation: Interbedded dolostone and limestone; argillaceous, silty, cross-laminated, mottled, with mud cracks; anhydritic, pyritic, fossiliferous, and with shale interbeds.

6 Conventional vs. Nonconventional Reservoir Bell Creek Sand (250x) Bakken Middle Member (250x) 6

7 Conventional vs. Nonconventional Reservoir Bell Creek Sand (250x) Lower Bakken Shale (250x) 7

8 Comparison of Pore Throat Sizes Conventional Bakken Conventional Clastic Reservoir Dominant pore sizes fall within expectations of traditional petroleum reservoirs. Poor-Quality Reservoir/Lower Seal Pore sizes considered to be a geologic barrier to injected fluids, including CO 2, because of increasing capillary forces. Upper Bakken Shale Middle Bakken 8

9 Size of the Bakken Oil Resource Currently, only a 3% 10% recovery factor. Small improvements in recovery could yield over a billion barrels of oil. Can CO 2 be a game changer in the Bakken? 9

10 Challenges of Enhanced Oil Recovery (EOR) in Tight Oil Formations Mobility and effectiveness of fluids through fractures relative to very low matrix permeability. How will clays react to CO 2? The role of wettability (oil-wet and mixed-wet) with respect to CO 2 in tight oil reservoirs is not well understood. High vertical heterogeneity of the lithofacies complicates our understanding of flow regimes (fractures and matrix). Multiphase fluid flow behavior varies substantially depending on the size of the pore throats. Fluid viscosity and density are much different in nanoscale pores than in macroscale pores. How does the sorptive capacity of the organic carbon materials affect CO 2 mobility, EOR, and storage? 10

11 Pore Size Affects Fluid Phase Behavior Conceptual pore network model showing different phase behavior in different pore sizes for a bubble point system with phase behavior shift. Source: Alharthy, Nguyen, Teklu, Kazemi, and Graves, 2013, SPE Colorado School of Mines and CMG 11

12 How Does CO 2 Interact with a Tight Oil Reservoir? We need to understand: Rock matrix Nature of fractures (macro and micro) Effects of CO 2 on oil Early research efforts have: Examined the viability of using CO 2 for EOR in the Bakken. Developed reconnaissance-level estimates of Bakken CO 2 EOR potential and storage capacity. 12

13 Analysis of Fractures Analysis of macrofractures Fracture properties Measure aperture, length, and orientation Core SEM Image Microfractures studied by scanning electron microscopy (SEM): Morphologies of each lithofacies Identified microfractures Open vs. closed Fracture properties Measure aperture and length Utilize macrofracture and microfracture data to help populate fracture properties in the static geologic model. Fracture Intensity, #/ft All and O+PO FI vs. Depth, Dunn Co. Well # All Fracs 0 10,660 10,670 10,680 10,690 10,700 10,710 10,720 10,730 Measured Depth, ft

14 Natural vs. Induced Fractures Illite K-Feldspar Illite 14

15 Reservoir Characterization is Key to Understanding Fluid Movements Movement of fluids (CO 2 in and oil out) relies on fractures. Microfractures accounted for the majority of the porosity in the most productive zones of the Bakken. Some lithofacies are more prone to fracturing than others. Four to seven distinct lithofacies typically occur in the Middle Bakken, resulting in significant vertical heterogeneity. Generating macrofracture, microfracture and matrix data and integrating those data into modeling are essential to develop effective EOR strategies. 15

16 CO 2 Interactions with Bakken Rocks and Oil Laboratory Experiments to Examine the Ability of CO 2 to Extract Oil from Lower Bakken Shale and Middle Bakken Silty Packstone CO 2 Oil Matrix 16

17 Lab-Scale Experiments CO 2 Extraction of Oil from Tight Rocks 17

18 Pump (Isco 260D) Rock Core Sample Cell (heated) Flow Control Extract Collection 18

19 CO 2 Extraction of Source and Reservoir Rock to Mimic Fracture- Dominated Flow Expected in Tight Systems ca. 11-mm-dia. rod Laboratory Exposures Include: >VERY small core samples (11-mm rod, to <3-mm crushed rock). Rock is bathed in CO 2 to mimic fracture flow, not swept with CO 2 as would be the case in confined flowthrough tests. Recovered oil hydrocarbons are collected periodically and analyzed by gas chromatography/flame ionization detection (GC/FID) (kerogen not determined); 100% recovery based on rock crushed and solvent extracted after CO 2 exposure. All exposures at 5000 psi, 110 o C to represent typical Bakken conditions.

20 CO 2 Oil Recovery from Upper, Middle, and Lower Bakken from One North Dakota Well Oil can be recovered from Middle Bakken rock and Bakken Shales in the lab, but: Rates are highly dependent on exposed rock surface areas. Recoveries are highly dependent on long exposure times. A much deeper understanding of the mechanisms controlling oil recovery processes in tight hydraulically fractured systems MUST be obtained to exploit these lab observations in the field. Oil Recovery from Middle Bakken and Bakken Shales using CO2 Conv. 1-cm rod Low Bak, <3.5 mm Up Bak, <3.5 mm Mid Bak, 1-cm rod Up Bak, 1-cm rod Low Bak, 1-cm rod 20

21 CO 2 and Bakken Oil Miscibility Study Minimum Miscibility Pressure (MMP) by Capillary Rise 7 Bakken Crude Oil X, Capillary MMP 6 RSQ = Capiillary Height, mm y = x R² = y = x R² = MMP = MEAN SD RSD % 1 y = x R² = Pressure (psi) Patent pending Partners provided live and dead oil samples, as well as slim-tube MMP results and pressure, volume, temperature (PVT) results. These results agree very well with slim-tube and equation of state (EOS) values.

22 CO 2 and Bakken Oil Miscibility Study Rising capillary approach appears to be a costeffective, quick-turnaround means of studying effects of CO 2 on Bakken oil. Allows for direct observation of phase changes. Can examine effects of gas stream impurities and/or reservoir gases on MMP. Data can be generated in minutes to hours versus days to weeks for standard techniques (i.e., slim tube, interfacial tension [IFT]). 22

23 Building a Static Model to Support Simulations of EOR Scenarios Core Description, X-Ray Diffraction (XRD) and X- Ray Fluorescence (XRF) Analysis Routine Core Analysis, XRD Results Core Description to Log Breaks Core Permeability and Porosity Petrophysical Modeling Structural Modeling Matrix Modeling Petrophysical Model Quality Control (QC) Clip Drill Spacing Unit Model from Larger Study Area Model Fracture Modeling Prepare for Dynamic Simulation 23 Core and SEM Fracture Analysis

24 Dual Porosity Dual Permeability Model Fracture Model Four sets of fractures - Two sets at 45 degrees azimuth - Two sets at 135 degrees azimuth Matrix Model Σ Fracture 24

25 Triple Porosity Triple Permeability Model Testing Hydraulic Fractures Perpendicular to wellbore 30 stages with 300-ft distance between 0.54-inch width 600-ft half-length

26 Dynamic Simulation Workflow 26

27 Simulation Results Highlights Simulated a variety of huff-n-puff and injector producer EOR schemes. Best cases showed reasonable improvement in oil production (some over 50%). Production response is delayed compared to CO 2 EOR in a conventional reservoir, which is in line with what we saw in the lab. From NW McGregor (Mission Canyon) DFN From NW McGregor (Mission Canyon) 27

28 Pore- and Core-Scale Models and Simulations Use CT scans to build matrix and fracture rock properties. Lithofacies and variogram ranges from thin sections. Pore quantification from SEM

29 Other Relevant Observations Regarding CO 2 movement and behavior in tight rocks: If the oil in the pores of the matrix can be recovered by CO 2, then CO 2 must be capable of permeating into the rock matrix. Regarding the role of rock wettability: Interfacial tension between CO 2 and oil hydrocarbons in rock will be less than between CO 2 and water in rock Therefore, it is possible the rate of CO 2 permeation through oil-wet rock will occur at lower pressures and be faster than for a water-wet rock. Storage capacity (rate of storage) may be higher in an oil-wet rock than in a water-wet rock. Mixed-wet rocks will obviously complicate the matter. 29

30 Take Home Thoughts Unconventional resource will take unconventional approach to EOR. Diffusion is more important than displacement. Patience required, but reward may be substantial. Innovative injection and production schemes. Use unfractured wells as injectors; rely on natural fracture system for slower movement of CO 2 through the reservoir and improved matrix contact time. Injectors in the shale paired with producers in the Middle Bakken and/or Three Forks. 30

31 Thanks! 31 Andrew Burton / Getty Images

32 Bibliography/References Alharthy, N.S., Nguyen, T.N., Teklul, T.W., Kazemil, H., and Graves, R.M., 2013, Multiphase compositional modeling in smallscale pores of unconventional shale reservoirs: Paper presented at SPE Annual Technical Conference and Exhibition, New Orleans, Louisiana, September 30 October 2, SPE Hawthorne, S.B., Gorecki, C.D., Sorensen, J.A., Steadman, E.N., Harju, J.A., Melzer, S., 2013, Hydrocarbon mobilization mechanisms from Upper, Middle, and Lower Bakken reservoir rocks exposed to CO 2. Paper presented at the SPE Unconventional Resources Conference Canada, Society of Petroleum Engineers, SPE MS. Klenner, R.C.L., Braunberger, J.R., Sorensen, J.A., Eylands, K.E., Azenkeng, A., and Smith, S.A., 2014, A formation evaluation of the Middle Bakken Member using a multimineral petrophysical analysis approach: Paper presented at Unconventional Resources Technology Conference Denver, Colorado, USA, August 25-27, 2014, 9 p., URTeC: Kurtoglu, B., Sorensen, J., Braunberger, J., Smith, S., and Kazemi, H., 2013, Geologic characterization of a Bakken reservoir for potential CO 2 EOR: Paper presented at 2013 Unconventional Resources Technology Conference, Denver, Colorado, August 12 14, URTeC Liu, G., Sorensen, J.A., Braunberger, J.R., Klenner, R., Ge, J., Gorecki, C.D., Steadman, E.N., and Harju, J.A., CO 2 - based enhanced oil recovery from unconventional resources: a case study of the Bakken Formation: Presented at SPE Unconventional Resources Conference, The Woodlands, Texas, April 1 3, 2014, SPE MS, 7 p. Nuttall, B.C., Eble, C.F., Drahovzal, J.A., and Bustin, M.R., 2005, Analysis of Devonian black shales in Kentucky for potential carbon dioxide sequestration and enhanced natural gas production: Kentucky Geological Survey Final Report to U.S. Department of Energy, 120 p. Sorensen, J.A., Hawthorne, S.A., Smith, S.A., Braunberger, J.R., Liu, G., Klenner, R., Botnen, L.S., Steadman, E.N., Harju, J.A., and Doll, T.E., 2014, CO 2 Storage and Enhanced Bakken Recovery Research Program: Subtask 1.10 final report for U.S. Department of Energy Cooperative Agreement No. DE-FC26-08NT43291, May, 79 p. 32

33 Contact Information Energy & Environmental Research Center University of North Dakota 15 North 23rd Street, Stop 9018 Grand Forks, ND World Wide Web: Telephone No. (701) Fax No. (701) James Sorensen, Senior Research Manager 33

34 Acknowledgment This material is based upon work supported by the U.S. Department of Energy National Energy Technology Laboratory under Award No. DE-FC26-08NT Disclaimer This presentation was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government, nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. 34