ThermalKPoster

THERMAL CONDUCTIVITY, THERMAL GRADIENT, AND HEAT FLOW ESTIMATIONS FOR THE SMACKOVER FORMATION, SOUTHWEST ARKANSASLea Nondorf, Arkansas Geological Survey, Little Rock, ARBekki White, State Director and GeologistAbstractSubsurface thermal conductivity, thermal gradient, and heat flow are significant parameters when determining the feasibility of utilizing a geologic unit to generate industrial geothermal power. Core samples from 18 wells of the subsurface Jurassic Smackover Formation in southwest Arkansas were analyzed at the Arkansas Geological Survey where estimated thermal conductivity, thermal gradient, and heat flow values were determined. Thermal conductance of several samples was obtained using a KD2 Pro Thermal Analyzer at room temperature. Thermal gradients were estimated from Smackover borehole temperatures, and estimated heat flow was calculated from thermal conductance and thermal gradient values. Average estimated thermal conductance values for the Smackover Formation are greatest in northeastern Lafayette County at 2.57 Watts per meter Kelvin, or W/mK, followed by south- ern Columbia and western Calhoun Counties at 2.47 W/mK each. Northwestern Columbia and northeastern Lafayette Counties exhibit the highest estimated thermal gradient and heat flow with values averaging 3.29C/100m and 63.8 milliWatts per meter per meter, or mW/m2, respectively. Interpretation of these parameters suggests that this area exhibits the highest geothermal potential for the Smackover Formation in southwest Arkansas. Investigations further characterizing the Smackover Formation, including in situ thermal properties and borehole temperature measurements, are recommended for future geothermal feasibility studies.IntroductionWorldwide interest in renewable energy resources has created a need for more data to help determine the feasibility of develop- ing these energy alternatives. Geothermal energy is one potential resource which is currently being evaluated by each state in par- ticipation with the State Geothermal Data Project, a collaborative project organized by the Association of American State Geolo- gists (AASG) and funded by the Department of Energy (DOE). The Arizona Geological Survey, under the direction of Lee Allison, was designated by the AASG to collect and contribute digitized legacy geothermal data from all 50 states to the National Geother- mal Data System (NGDS), a publicly available database network. The Arkansas Geological Survey (AGS) contributed geothermal data primarily from the Smackover Formation in southern Arkansas in the form of borehole temperatures (BHTs), driller logs, and thermal conductance measurements (available at http://services.usgin.org/track/report/AR). Observed high temperature data of the Smackover Formation prompted further investigation into its potential as a geothermal reservoir for the state.The purpose of this research is to characterize the subsurface thermal conductivity, thermal gradient, and heat flow of the Smackover Formation as a potential geothermal energy resource in southwest Arkansas. Thermal data was collected over a two- year period starting in 2010.Smackover Formation in South ArkansasAThermal Conductivity of the Smackover FormationThermal conductivity is a measure of the ability of heat to flow through a particular material, and is a function of temperature in Watts per meterKelvin, (W/mK). A total of 83 Smackover core samples from 18 wells in southwest Arkansas were measured for thermal conductance at the AGS owned Norman F. Williams Core Sample Library in Little Rock, Arkansas. Some samples in- clude lower sections of the overlying Buckner Formation, typically a red to gray shale (Figure 1). Core samples selected for analy- ses were chosen based on (1) even distribution of well locations across southwest Arkansas, and (2) competency for drilling and thermal testing. Thermal measurements took place over a three month period beginning in mid-February 2012.Equipment Used for Thermal MeasurementsKD2 Pro Thermal Analyzer (version 1.08) using beta probe for conducting thermal measurementsProbe dimensions are 6.4 cm (2.5 in.) long by 0.40 cm (5/32 in.) in diameterAfter cooling to room temperature, thermal measurements were set to run for 10 minutes on high power modeResults were downloaded into a Microsoft Excel spreadsheetHilti Rotary Hammer for drilling holes, drilled to depth equal to length of beta probeArctic Alumina thermal grease applied to drilled hole to improve thermal contact between thermal probe and coreCorrected Thermal Conductivity Values for the 18 Smackover Wells (W/mK)Thermal Gradient of the Smackover FormationThermal gradient is a vector dependent on temperature distributed in three dimensions with the maximum thermal gradient in the vertical direction within the upper crust of the Earth; therefore, thermal gradient is simplified to T=T/z, or change in tem- perature per change in depth (Kelvin/meters). Thermal gradients were determined for each well by first correcting BHT data for in situ borehole conditions using the Harrison Correction Equation (Harrison et al., 1983). Then, T was calculated by the difference between the corrected BHTs and the average surface temperature in south Arkansas at 17.2C (63.1F). z is the depth, in meters, in which maximum BHTs were recorded. For logs in which several runs were recorded, consecutive corrected BHTs and depth values were used to find T and z values, respectively, where T/z was averaged to find T for each well. The (harmonic) aver- age thermal gradient estimated for southwest Arkansas is 0.033 K/m (Table 2).Heat Flow of the Smackover FormationHeat flow (milliWatts per meter per meter, or mW/m2), is the transfer of thermal energy from one body to another. Heat within the crust is generated by either radioactive decay, primarily from uranium, thorium, and potassium, or through conduction and con- vection from the Earths interior. The conveyance of heat through the crust is primarily related to rock type and structure (Smith and Fishkin, 1988). Heat flow (Q) is the product of the average thermal conductivity (avg) (Table 1) and the average thermal gradient (T) (Table 2). For southwest Arkansas, the (harmonic) average heat flow is around 64 mW/m2 (Table 2).Discussion and ConclusionFor comparison of thermal conductance results measured at the AGS, samples from 2 Smackover wells, permit numbers 21661, an oolitic to pisolitic crystalline limestone at a depth of 10,839 ft (southwest Lafayette County), and 25774, a fine-grained grain- stone at a depth of 9,441 ft (southeast Columbia County), were sent to the University of North Dakota (UND), Harold Hamm School of Geology and Geological Engineering Laboratory, for thermal conductance testing. The UND samples were measured using a Portable Electronic Divided Bar (PEDB) in an isolated system with vertical heat flow at a constant temperature of 20C (68F). Each sample was measured twice and averaged.UND results for permit numbers 21661 and 25774 are 2.91 and 2.47 W/mK, respectively (3.5% accuracy). For these wells, Table 1 shows that UND results are comparable to the results measured at the AGS at similar depths, helping to verify the AGS re- sults (corrected) as reasonable estimations of in situ thermal conductivity of the Smackover Formation.For the Smackover Formation, northwestern Columbia and northeastern Lafayette Counties demonstrate high geothermal po- tential exhibiting the greatest heat flow for southwest Arkansas, as evidenced by the estimated thermal properties of existing wells for this area. Permit number 24227 has the highest thermal gradient (6.3C/100m) along with a moderate thermal conductivity (2.2 W/mK), producing the highest heat flow value near 137 mW/m2.Based on these thermal estimations for southwest Arkansas, utilizing thermal resources from the Smackover Formation in north- western Columbia and northeastern Lafayette Counties is the most feasible location for future industrial geothermal power plants. Only a small set of wells were sampled in this area; therefore, further in-depth investigations characterizing in situ BHTs and ther- mal properties of the Smackover Formation are recommended for future geothermal feasibility studies.AcknowledgmentsThis publication was written to provide geothermal results generated by the Arkansas Geological Survey for the State Geothermal Data Project, sponsored by the U.S. Department of Energy under prime award number DE-EE0002850, awarded to the State of Arkansas under sub award number AR-EE002850. I would like to thank Corbin Cannon for helping to collect, drill, and measure core samples, Jason Tipton for providing well log and core information and for assisting me in generating the raster maps, and the AGS staff for the editing of this content.ReferencesHarrison, W.E., K.V. Luza, M.L Prater, and P.K Cheung, 1983. Geothermal Resource Assessment in Oklahoma. Special Publications 83-1. Oklahoma Geological Survey. Nondorf, L. Thermal Conductivity, Thermal Gradient, and Heat Flow Estimations for the Smackover Formation, Southwest Arkansas. Misc. Pub 23. Arkansas Geological Survey. Sekiguchi, K., 1984. A Method for Determining Terrestrial Heat Flow in Oil Basinal Areas. Tectonophysics, Vol. 103, Issue 1-4, p. 67-79.Smith, D.L. and L. Fishkin. 1988. New Heat Flow Investigations in Arkansas. Contributions to the Geology of Arkansas. Arkansas Geological Commission. Misc. Pub 18-C, V. III, p. 79-84. Vestal, J.H., 1950. Petroleum Geology of the Smackover Formation of Southern Arkansas. Information Circular 14, Arkansas Geological Commission. 37 p.Weeks, W.B., 1938. South Arkansas Stratigraphy with Emphasis in the Older Coastal Plain Beds. Am Assoc Pet Geol Bull, Vol. 22, No. 8, p. 953-983.Figure 1. General stratigraphic chart of the subsurface Jurassic section indicating relative stratigraphic position of the Smackover Formation in south Arkansas.In southern Arkansas, the Upper Jurassic (Oxfordian, 161-156 Ma) Smackover Formation, named after the Smackover Field, Union County, Arkansas (Figure 1), was one of the first major oil producing units in the state contributing hundreds of millions of barrels of oil and condensate during the 1930s and 1940s (Vestal, 1950). The Smackover Formation is informally divided into the upper and lower Smackover.The upper Smackover Formation was the major hydrocarbon producer in southern Arkansas, primarily from the Reynolds oolite (where present). The upper section consists mostly of a white to brown, porous oolitic to pisolitic grainstone with local inclusions of calcite, pyrite, anhydrite, gypsum, and lignite (Figure 2). Sucrosic texture is also common as a secondary feature generated from the weathering of oolites and/or pisolites (Vestal, 1950). Bromine brines are associated with the upper Smackover in south Arkan- sas.The informal lower Smackover is the source rock for petroleum present in the informal upper Smackover as well as some Creta- ceous reservoirs (Figure 3). Due to the development of new drilling technologies, several oil and gas companies are currently ex- ploring the economic potential of the lower Smackover, or Brown dense, as a commercial and unconventional reservoir. The lower section is described as an organic-rich, very dense, dark brown, very fine-grained, calcareous mudstone (Weeks, 1938).Figure 2A. (A) Oolitic grainstone sample and (B) crysBtalline pisolitic sample of the upper Smackover Formation, or Reynolds oolite, southwest Arkansas.Figure 3. Informal lower Smackover Formation samples, or Brown dense, southwest Arkansas.Figure 6. Drilling of core sample with Hilti Rotary Hammer.Thermal conductance values were corrected for in situ conditions using the Sekiguchi Empirical Correction Equation (1984)Figure 7. Drilled sample, hole filled with Arctic Alumina compound for improved thermal contact between probe and sample.Figure 8. KD2 Pro Thermal Analyzer with beta probe in sample. Arctic Alumina grease shown in lower right.where = Corrected Thermal Conductivity = Thermal Conductivity at Laboratory Temperature, T = 1.05 W/mK, Calibration Coefficient00mT = Temperature (K) at which was measured (equal to initial temperature of core sample recorded by analyzer)00T = 1473 K (Calibration Coefficient)mT = Borehole Temperature= ( T0Tm )( ) (1 1 )+ T Tm00mTTmmFigure 9. Well locations of measured core samples, labeled according to permit number. A permit number is a numeric identifier assigned to each drilled well in the state by the Arkansas Oil and Gas Commission.Figure 10. Corrected thermal conductivity values per well. Refer to Figure 9 for permit numbers and well locations.1.902.47 2.57LAFAYETTE 1.861.582.472.181.551.862.282.472.171.371.811.691.732.311.79UNIONMILLERNEVADACOLUMBIAOUACHITACALHOUNHEMPSTEAD02040Miles101.370 - 1.5801.581 - 1.9001.901 - 2.3102.311 - 2.570Average Thermal Conductivity (W/m K)2642426489242272966729766COLUMBIA28603285912615030929218072830126677240872825818345275752577421661UNIONMILLERNEVADAOUACHITACALHOUNHEMPSTEADLAFAYETTE02040Miles10Smackover Sampled CoreFigure 4. Structural contours of top of Smackover Formation (modified from Vestal, 1950). Contour digitization by Jason Tipton, AGS.Figure 5. Isopach contours of top of Smackover Formation (modified from Vestal, 1950). Contour digitization by Jason Tipton, AGS.90009000400030008000900060007000100005000110002000400080005000200060007000600040006000600010006000700050005000110005000UNIONDREWPIKECLARKASHLEYDESHACHICOTMILLERDALLASSEVIERNEVADACOLUMBIAOUACHITABRADLEYHOWARDLINCOLNCALHOUNHEMPSTEADCLEVELANDLAFAYETTELITTLE RIVERStructural Contours Contour Interval = 1,000 ft4008000500100600700400300900100011001200300080003002006001004002000300300UNIONDREWPIKECLARKASHLEYDESHACHICOTMILLERDALLASSEVIERNEVADACOLUMBIAOUACHITABRADLEYHOWARDLINCOLNCALHOUNHEMPSTEADCLEVELANDLAFAYETTELITTLE RIVER Isopach Contours Contour Interval = 100 ft0204010MilesFigure 11. Geothermal gradient values for each well of the Smackover Formation. Refer to Figure 9 for permit numbers and well locations.Figure 12. Estimated geothermal gradient raster image of the Smackover Formation. Generated using the Natural Neighbor method in Spatial Analyst, ArcGIS 10.1Figure 13. Estimated heat flow for each Smackover Formation well in mW/m2. Labeled according to actual heat flow values. Refer to Figure 9 for permit numbers and well locations.Figure 14. Estimated heat flow raster image of the Smackover Formation. Generated using the Natural Neighbor method in Spatial Analyst, ArcGIS 10.1Table 1. Smackover thermal conductance results showing measurement ID number, permit number of core, depth measured (ft), thermal conductance, or (initial, corrected, and average per well), error value recorded by analyzer, measurement direction with respect to bedding (perp = perpendicular, para = parallel), and lithologic description of each sample. In order of increasing depth per well.Table 2. Harrison correction (T ), corrected temperature, estimatedaverage thermal gradient, and estimated heat flow values (describedbelow) for the 18 Smackover wells in southwest Arkansas.

Sheet1ID #Permit #Depth (ft)W/mKErrMeasDirLithologic Descriptionlo lcorr lavg

521661108104.042.971.790.02paraFine-grained grainstone221661108111.411.280.07perpFine-grained grainstone321661108122.381.440.21perpFine-grained grainstone1021661108203.062.360.02paraAnhydrite1221661108353.062.380.01perpOolitic, pisolitic crystalline limestone1121661108363.682.770.01paraOolitic, pisolitic crystalline limestone132615085453.763.012.470.01paraFine-grained, shaley dolopackstone142615085472.612.190.01perpFine-grained, shaley dolopackstone152615085492.402.030.01paraCrystalline limestone16261508550.53.853.100.02perpOolitic, pisolitic crystalline limestone17261508551.52.552.150.01paraOolitic, pisolitic crystalline limestone182615085592.592.180.03paraOolitic, pisolitic crystalline limestone192615085663.943.180.05paraOolitic, pisolitic crystalline limestone242577494002.331.932.310.01perpRed shale232577494023.422.690.01paraCrystalline dolostone252577494035.484.050.26perpFine-grained grainstone262577494063.602.780.01paraFine-grained grainstone272577494101.271.200.09perpOolitic, pisolitic crystalline limestone282577494112.532.060.00perpOolitic, pisolitic crystalline limestone292577494165.103.800.12paraOolitic, pisolitic grainstone302577494253.182.510.03perpOolitic, pisolitic grainstone312577494302.912.330.01perpOolitic, pisolitic grainstone322757552992.242.011.730.01paraOolitic, pisolitic grainstone332757553022.612.320.01paraFine-grained, grainstone382757553051.461.390.01paraFine-grained, grainstone; oomoldic f352757553101.941.770.01paraFine-grained oolitic, grainstone;oomoldic f362757553211.181.160.01paraFine-grained oolitic, grainstone;oomoldic f372757553222.101.900.02perpFine-grained, dolograinstone; oomoldic f392757553392.542.260.01paraFine-grained grainstone402757553491.851.700.01paraCrystalline limestone

Sheet1ID #Permit #Depth (ft)W/mKErrMeas. Dir.Lithologic Descriptionlolcorrlavg11221807106862.5622.072.470.02perpFine-grained dolograinstone11321807106973.0792.430.01paraCrystalline limestone11421807107003.0842.420.00paraCrystalline limestone, small amt of anhydrite11521807107914.2823.230.02perpWackestone to mudstone1162859182173.9283.182.570.01paraCrystalline limestone, small amt of anhydrite1172859182223.0352.520.00paraFine-grained dolograinstone; oomoldic f1182859182433.5032.880.02paraOolitic, pisolitic fine-grained grainstone1192859183292.9352.450.01paraFine-grained grainstone; oomoldic f1202859184412.4352.080.01paraFine-grained grainstone; oomoldic f1212966780281.8721.661.580.02paraFine-grained, oolitic grainstone1222966782181.4851.370.01paraFine-grained grainstone; oomoldic f1232966785281.6541.500.01paraDense, very fine-grained mudstone1242966785312.1791.890.01perpDense, very fine-grained mudstone1252976686032.3292.001.860.00paraOolitic grainstone1262976686212.1131.840.01paraFine-grained, oolitic grainstone1272976686542.4712.100.01paraFine-grained grainstone128297668727.51.7841.590.01paraFine-grained grainstone

Sheet1ID #Permit #Depth (ft)W/mKErrMeas DirLithologic Descriptionlo lcorr lavg

422860391411.901.651.900.01perpDense, very fine-grained mudstone432860391452.572.140.01perpDense, very fine-grained mudstone412860391482.662.200.01perpDense, very fine-grained mudstone452860391712.382.000.00perpDense, very fine-grained mudstone442860391741.681.500.01perpDense, very fine-grained mudstone462860391952.612.160.02perpDense, very fine-grained mudstone591834563281.821.671.690.01paraPossible lithic arenite601834563341.401.330.01paraOolitic dolostone611834564011.361.300.01paraFine-grained grainstone621834564232.252.000.01paraFine-grained grainstone with organics631834564252.221.980.01paraVugular crystalline limestone641834564892.732.400.01paraVugular crystalline limestone with bitumen742825861084.003.371.810.01paraCrystalline dolostone752825861191.851.680.02paraOolitic grainstone762825861251.391.320.01paraOolitic grainstone; oomoldic f772408757701.461.391.370.01perpOolitic grainstone; oomoldic f782408757821.431.370.00perpOolitic grainstone; oomoldic f792408758681.251.220.01perpFine-grained grainstone802408759521.631.530.00perpVery fine-grained grainstone812422779332.582.302.170.02perpOolitic, crystalline limestone822422779502.051.860.01paraOolitic, fine-grained grainstone832422779582.782.450.00paraFine-grained grainstone with organics882642442774.123.632.470.01perpShaley dolowackestone to dolomudstone892642442793.162.840.01paraFine-grained grainstone902642442921.821.700.00paraOolitic, fine-grained grainstone10930929110953.7262.862.280.00paraFine-grained dolograinstone11030929111192.4071.970.01paraOolitic, pisolitic crystalline limestone11130929111302.7082.180.01paraOolitic, dense, crystalline limestone912648977702.882.451.860.01paraOolitic grainstone922648977891.931.720.01paraOolitic, pisolitic grainstone932648978461.861.680.03perpOolitic, pisolitic crystalline limestone1042667754703.362.911.550.02paraFine-grained dolograinstone1052667754721.061.050.01perpFine-grained grainstone1062830157635.074.232.180.01perpRed shale1072830157943.372.880.01perpGray shale1082830158081.321.260.01paraOolitic grainstone

Sheet1Permit #Total Depth (m)MaxTemp (C) from well logHarrison Correction (Tc)CorrectedTemp CGeothermal Gradient C/100mGeothermal Gradient K/m (for determining heat flow)Heat Flow mW/m2 (refer to heat flow section below)21661334310718.35125.353.240.032458.12615026328015.3395.332.970.029873.425774297210017.07117.073.360.033777.627575169964.47.7572.203.240.032556.12860328899016.69106.693.100.031059.018345198168.8910.4779.363.140.031553.328258198373.8910.4984.383.390.034061.7240871755608.3368.332.910.029240.02422797779.44-0.9078.546.280.063013726677175866.678.3575.023.290.033051.128301193471.1110.0481.163.310.033272.430929341410518.52123.523.110.031271.221807330311018.25128.253.360.033783.32859125918515.08100.083.200.032182.429667260987.7815.19102.963.290.033052.229766273187.7815.89103.673.170.031759.026489243877.7814.0991.873.060.030758.126424137260.564.1364.693.460.034885.8Harmonic mean 3.290.033063.8