Stefani D. Whittaker; The Discovery Group; Denver, CO Daniel Hallau; The Discovery Group; Denver, CO James P. Lewis; Intrepid Potash; Denver, CO

Transcription

1 Characterization of slim-hole Gamma- Ray Sonde for Potash Exploration Applications in a Simple Test Pit Environment Stefani D Whittaker; The Discovery Group; Denver CO Stefani D. Whittaker; The Discovery Group; Denver, CO Ryan Sharma; The Discovery Group; Denver, CO Daniel Hallau; The Discovery Group; Denver, CO James P. Lewis; Intrepid Potash; Denver, CO Robert M. Cluff; The Discovery Group; Denver, CO

2 OUTLINE Purpose The Basics Initial Tests Horizontal Depth of Investigation Vertical Resolution Conclusions

3 PURPOSE Intrepid Potash, Inc. wanted to estimate and map grade of potash ore using the Gamma Ray response by tools logged in mining core holes and nearby oil and gas wells. Horizontal Depth of Investigation Ore beds are laterally variable Vertical Resolution There are very thin ore beds There was no existing empirical evidence to support the theoretical depths of investigations for gamma ray tools

4 Sylvite and Halite Sylvite %K2O Langbeinite Kainite Carnallite 20 Polyhalite 10 Halite 0 Anhydrite R 2 = Gamma Ray [API]

5 Gamma Ray Basics Potassium, Uranium, Thorium This study dealt with TOTAL gamma ray response From Spectral Gamma Ray only trace amounts of U and Th Oilfield Logging Tools Length: Diameter: Weight: lbs. 2PGA-1000 Gamma Ray (Mt. Sopris Instruments) Styrofoam standoffs NaI Crystal long diameter -7 lbs - Metal housing with neoprene heat shrink wrap

6 40 Calibration of Mt. Sopris GR tools Definition of Calibration in Houston TX test pits: API = High Average cps - Low Average cps Therefore for the Mt. Sopris Tools: 32 1 API = 0.84 cps 1 cps = 1.19API 30 A.P.I. RP #33 Third Edition, April Depth [ft] High Average = 183.7cps Low Average = 15.4cps GR [cps]

7 Background Radiation Central Denver 3 miles NE of downtown Sitting on radioactive Denver Formation Shales ~93 cps (111 API) when tool was adjacent to floor. ~82 cps (98 API) from tool hanging 4 ft in air

8 Count rate increases linearly with increasing volume of radioactive product R 2 = Gamma Ra ay count [A API] Gamma Ray count [cp ps] # of 50 lb bags of KCl

9 Count rate increases with increasing volume of radioactive material even in mixtures R 2 = Gamma a Ray Cou unts [API] Gamma Ra ay Counts [cps] % KCl in Total Volume of NaCl + KCl

10 Repeatability of Tools ±3 cps Gamma Ray [API] Gamma Ra ay [cps] #4435 # # of bags of potash

11 30 second Stationary Tests Stationary Mode unning ave erage, cps Software summed gamma 8 ray counts every 6 second to get counts per 4 second, counter 2 flushed after 0 every second and cycle -2 repeats. -4 std dev viation of r standard deviation running average 75.5 cps Time, t, sec cps running average,

12 Tank and Equipment TANK: 7 diameter by 3 tall polyethylene tank BOREHOLE: OD PVC pipe Plastic pipe flange to secure on bottom of tank AUXILLARY EQUIPMENT: Mt. Sopris Matrix Box (MGXII) Mt. Sopris software (Matrix) Short (100 ) logging cable

13 PRODUCT Halite (2 palettes / 80 bags / 2 tons) Sylvite (2 palettes / 80 bags / 2 tons) 50 lb. bags Single plant run Quality and weight of each bag of Potash QC d at plant

14 Horizontal Depth of Investigation Held GR Total Flux Constant Varied the distance of tool from radioactive product as a series of concentric rings Measured GR s at borehole Solved for adsorption coefficient and density

15 Experimental Setup Inner diameter Mid-ring diameter [X] Outer diameter Thickness of Sylvite ring had to be varied to accommodate the constant volume of Sylvite

16 Test Tank Configurations 9 Total Tests 5 tests with air 3 tests with NaCl 1 test with KCl directly around borehole

17 Basic Response Equation for GR tool = J e 0 J 0 μρχ Gamma Ray Flux [Measured by tool] Total Gamma Ray Flux [Constant with constant volume of Sylvite] Mass adsorption Coefficient and Bulk Density [unknown] Distance over which Gamma Rays are being attenuated [known]

18 Theoretical Radial Geometric Factor for Oilfield Tools For 1.46 MeV Gamma Ray: -90% of response is within ~27 cm(10.6 ) -50% of signal is within ~15 cm(5.9 ) Gamma Ray Logging J.S. Wahl Geophysics, Vol. 48 No. (Nov.1983) pgs

19 Radial response (background corrected) Potash with air ring minus background Potash with 39% porosity NaCl ring minus background Potash with air ring projected Potash with NaCl ring projected GR [cps] y = e x R 2 = y = e x R 2 = Diameter from edge of borehole in feet

20 Horizontal Response μ[ cm 2 Wahl φ [%] = / g] = N / A ρ[ g / cm 3 ] = 2.2 fluid = liquid B. H. S. = 8" Eccentered SolidHalit e μ[ cm 2 / g] = φ[%] = 0 3 ρ[ g / cm ] = fluid = air B. H. S. = 4.5" Centralize d J(r) ~4.3 ~12.2 J = J 0 e μρχ In air with no NaCl 61% NaCl Solid NaCl sandstone Wahl 1983, fig 17, 8 in borehole Radius from borehole center (cm) Depth of Investigation Schlumberger Halliburton Baker Weatherford 9 ~ 15 in. 90%:11" 50%: 4" 12" for 8" hole with 20% φ 24"

21 Vertical Resolution Experiment Varied thickness of radioactive layer from 0-32 in 2 increments Logged stationary measurements across a single interface (Halite below, Sylvite above) Ignored air half-space above and assumed a symmetrical response. Vertical resolution is defined as the minimum thickness required to achieve maximum reading of material.

22 Vertical Resolution Challenges DEFINITIONS: Vertical Resolution: The minimum bed thickness for one point to measure full response Full Response: The maximum signal a bed can produce CHALLENGES: Logging Speed: Oilfield Max Speed 3600 ft/hr (1ft/sec) -Asymmetrically skews the signal -Dampens the signal Bassiouni 1994 We made stationary measurements to simulate very slow logging speed Bassiouni, 1994, SPE Textbook Series, Vol.4

23 7 ft tall x 2.5ft radius tank Experimental Setup Added 1 of sylvite up to 5 thick and then 2 of sylvite up to 32 of sylvite. After each layer of sylvite added the entire 6 ft of borehole was logged. Measurement taken every 3 25 station measurements (6 of total tool movement)

24 Vertical Resolution Results (background corrected) 80 bove tank bottom [in] sensor position a Sylvite NaCl Tool response to air half-space 1 in KCl 6 in KCl 12 in KCl 18 in KCl 24 in KCl GR [CPS] 28 in KCl 30 in KCl background in salt

25 Min. Thickness for Max. Response 90 Sensor position above grou und [in] Air KCl 27 inches KCl NaCl MAX: 36 inches (3 ft) (833 API) GR [CPS] For Sylvite with 33% Porosity: 27 thick bed for one point at full response For solid halite with 0% porosity: 19 thick bed for one point at full response Vertical Resolution Schlumberger Halliburton Baker Weatherford Wahl Tool Model 24 in 18 in N/A 12 in ~12-14 in

26 In Conclusion A GAMMA RAY TOOL CAN QUANTIFY A PROTECTABLE POTASH BED COMPARISON: Horizontal Resolution: Wahl Model:10.6 (27cm) Calculated from experiment Solid Halite: 12.2 (31cm) Vertical Resolution: Wahl Model: (30-35cm) 35cm) Calculated Solid Halite: 19 (49cm) Difference due to experimental condition differences (i.e. borehole size, fluid in hole, centralization)

27 Acknowledgements THANK YOU Intrepid Potash Wilton Manufacturing Mt. Sopris

28 QUESTIONS?