A Comprehensive Water Saturation Model for Low-Porosity Sandstones*

Size: px

Start display at page:

Download "A Comprehensive Water Saturation Model for Low-Porosity Sandstones*"

Rodger Daniels
6 years ago
Views:

1 A Comprehensive Water Saturation Model for Low-Porosity Sandstones* Darrell Hoyer 1 Search and Discovery Article #40445 (2009) Posted September 30, 2009 *Adapted from oral presentation at AAPG Annual Convention, Denver, Colorado, June 7-10, Hoyer Petrophysics Inc., Fort Collins, CO (dlhoyer@comcast.net) Abstract Technical advances on many aspects of producing hydrocarbons from low-porosity sandstone have led to increased exploration in basins around the world. It is critical for commercial success to understand the porosity and hydrocarbon saturation relationships associated with these systems. In many basins where tight sandstones are being evaluated for the potential of commercial hydrocarbon accumulations, prospective intervals range in thickness from a few feet to several thousand feet and may cross stratigraphic horizons with various depositional environments. Determining formation water resistivity (RW) is a critical component in determining if sandstones may be at or close to irreducible water saturation (SWirr). Often during exploration efforts there is very little information available for RW estimates. Calculating RW from SP curves can be misleading due to low porosity/permeability, sand body thickness and the potential for the presence of variable anions associated with formation water. Pickett plots have been used for RW determination for many years, but the technique requires prior knowledge or assumption for the value of the Archie saturation exponent m and representative sandstones that are watersaturated. A cornerstone to improved petrophysical understanding of low-porosity sandstone was recently published by the DOE/KGS project, Regional petrophysical properties of the Mesaverde lowpermeability sandstones (Byrnes et al., 2007) and Evidence for a variable Archie porosity exponent m an impact on saturation calculations for Mesaverde tight gas sandstone: Piceance, Uinta, Green River, Wind River and Powder River basins (Cluff et al., 2008). Results of the Byrnes et al. project document several physical aspects of low-porosity sandstones in the Rocky Mountain region including a core-derived relationship indicating that a decrease in porosity and/or water salinity results in a decrease in the Archie saturation exponent m. Pickett plots from productive wells from several basins in Colorado, Utah, and Wyoming are presented to demonstrate the application of the variable m as described by Byrnes et al. Results indicate the variability of the formation water salinity not only areally between wells within a particular field but between sand bodies within a single well bore over the potential interval of interest. Pickett plots are also demonstrated to be a good tool for determining the bulk volume of irreducible water and consequently a porosity cutoff for hydrocarbon storage. Copyright AAPG. Serial rights given by author. For all other rights contact author directly.

2 A Comprehensive Water Saturation Model for Low-Porosity Sandstones AAPG June 10, 2009 by Darrell Hoyer Hoyer Petrophysics Inc.

3 Low Porosity Sands - Issues Drilled but not often tested The sands may have gas shows Are the sands porous/permeable reservoirs? Is the gas/oil saturation high enough to flow?

4 Low Porosity Sands - Issues Drilled but not often tested The sands may have gas shows Are the sands porous/permeable reservoirs? Is the gas/oil saturation high enough to flow? Log/Core data base Wells may span many years Several logging company tools Core data is limited Little room for errors

5 Low Porosity Sands - Issues Drilled but not often tested The sands may have gas shows Are the sands porous/permeable reservoirs? Is the gas/oil saturation high enough to flow? Log/Core data base Wells may span many years Several logging company tools Core data is limited Little room for errors Several 1000 s of feet of potential reservoir Span several geologic horizons Lack of evident water-bearing intervals Variable formation water resistivity (RW) Questionable SP development Low/unstable water recovery from tests

6 Low Porosity Sands - Issues Drilled but not often tested The sands may have gas shows Are the sands porous/permeable reservoirs? Is the gas/oil saturation high enough to flow? Log/Core data base Wells may span many years Several logging company tools Core data is limited Little room for errors Several 1000 s of feet of potential reservoir Span several geologic horizons Lack of evident water bearing intervals Variable formation water resistivity (RW) Questionable SP development Low/unstable water recovery from tests Hydraulic fracture stimulation completions Cost - $$$

7 Petrophysical Water Saturation Model Archie water saturation equation is empirical Laboratory experiments and observation Several shaly sand equations have been developed All regress to the basic Archie equation at 0% clay volume Is the water saturation model consistent at in situ conditions?? SW = ( RW / RT * a / PHIE m ) 1 / n Bulk Volume Water BVW = Porosity * SW

8 Piceance Basin I 70 Corridor Rulison Denver Parachute I 70 Grand Valley Mamm Creek

9 Pickett Plot - Piceance Rulison Upper Williams Fork Water Saturated Sands POROSITY WMF 135degF _VCLAY <.1 Rul A RESISTIVITY Archie Water Saturation Equation SW = (RW/RT * a/phie m ) 1/n

10 Pickett Plot U WMF Water Sands Often Assumed Archie Exponents a=1, m=2 and n=2 POROSITY Porosity = 1.0 RW *a = 0.3 Salinity ~ 12 kppm WMF 135degF Slope of 100% SW Trend Represents m=2.0 Rw = 0.3 a = 1 m = 2 n = 2 _VCLAY <.1 Rul A RESISTIVITY.1 Increased Hydrocarbon Saturation; n= Archie Water Saturation Equation SW = (RW/RT * a/phie m ) 1/n

11 POROSITY Porosity = 1.0 RW *a = 0.3 Salinity ~ 12 kppm Pickett Plot WMF Gas Cell Assumed Archie Constants a=1, m=2 and n=2 WMF Sands; 160 degf Slope of 100% SW Trend Represents m=2.0 Rw = 0.3 a = 1 m = 2 n = 2 _VCLAY <.1 Rul A RESISTIVITY.1 Increased Hydrocarbon Saturation; n=2.0 SW > EUR ~ 1.6 BCF

Recent published data (July, 2008) from the DOE/KGS project; Regional Petrophysical Properties of Mesaverde Low-Permeability Sandstones Byrnes, Cluff & Webb Systematic Characterization of Kmv

12 Recent published data (July, 2008) from the DOE/KGS project; Regional Petrophysical Properties of Mesaverde Low-Permeability Sandstones Byrnes, Cluff & Webb Systematic Characterization of Kmv lithofacies over Rocky Mtn. region 44 wells / 6 Basins Described ~7000 ft. of core (digital) 2200 core samples advanced properties samples Wind River Powder River Wyoming Green River N Washakie Utah Uinta Piceance Colorado

13 DOE / KGS Project Results; 335 Kmv 4 Water Salinities Archie Cementation Exponent m decreases with Porosity and Water Salinity Archie Cementaiton Exponent (m, a=1) In situ Porosity (%) 200K 80K 40K 20K 4 Water Salinities Behavior is consistent with increasing electrical efficiency with decreasing porosity, whatever the pore scale architecture.

14 DOE / KGS Results; 335 Kmv 20,000 ppm NaCl - Archie Cementation Exponent m decreases with Porosity m, (a=1) Porosity m ~ 5% Porosity m ~ 10% Porosity m ~ 16% Porosity

15 POROSITY Porosity = 1.0 RW *a = 0.4 Salinity ~ 8 kppm Rw = 0.4 a = 1 m = 1.85 n = 1.85 Piceance Rulison U WMF Water-Saturated Sands 11 % Porosity WMF 135degF ~8 kppm Porosity = 0.11 _VCLAY <.1 Rul A RESISTIVITY

16 POROSITY Porosity = 1.0 RW *a = 0.4 Salinity ~ 8 kppm Piceance Rulison U WMF Water-Saturated Sands 11 % Porosity 5 % Porosity Rw = 0.4 a = 1 m = 1.65 n = 1.65 WMF 135degF ~8 kppm Porosity = 0.11 Porosity = 0.05 _VCLAY <.1 Rul A RESISTIVITY

17 POROSITY Porosity = 1.0 RW *a = 0.18 Salinity ~ 17 kppm Rw = 0.18 a = 1 m = 1.65 n = 1.65 Piceance Rulison WMF Gas Cell 11 % Porosity 5 % Porosity WMF Sands; ft.@ 160degF ~17 kppm Porosity = 0.05 _VCLAY <.1 Rul A RESISTIVITY EUR ~ 1.6 BCF

18 POROSITY Porosity = 1.0 RW *a = 0.3 Salinity ~ 12 kppm Pickett Plot WMF Gas Cell Assumed Archie Constants a=1, m=2 and n=2 WMF Sands; 160 degf Slope of 100% SW Trend Represents m=2.0 Rw = 0.3 a = 1 m = 2 n = 2 _VCLAY <.1 Rul A SW > RESISTIVITY EUR ~ 1.6 BCF

19 POROSITY Porosity = 1.0 RW *a = 0.24 Salinity ~ 12 kppm Piceance Rulison U WMF Water-Saturated Sands 11 % Porosity 5 % Porosity WMF Sands; ft.@152 degf ~12 kppm Porosity = 0.11 Rw = 0.24 a = 1 m = 1.85 n = 1.85 Porosity = 0.05 _VCLAY <.1 Rul B RESISTIVITY

20 POROSITY Porosity = 1.0 RW *a = 0.35 Salinity ~ 8 kppm Rw = 0.35 a = 1 m = 1.65 n = 1.65 Piceance Rulison WMF Gas Cell 11 % Porosity 5 % Porosity WMF Sands; ft.@ 165 degf ~8 kppm Porosity = 0.05 _VCLAY <.1 Rul B RESISTIVITY EUR ~ 0.5 BCF

21 Piceance Rulison Formation Water Salinity Gas-Water Contact Rul A; EUR ~ 1.6 Bcf _PHIE _SW 1 DEC 0 _TENS W _RT mi. RW ~ 12 kppm E Rul B; EUR ~ 0.5 Bcf _PHIE _SW 1 DEC 0 _TENS _RT TOG 5200 RW ~ 8 kppm TOG RW ~ 17 kppm

22 SW Cutoff - Varies with Porosity BVW Cutoff = SWirr Irreducible Water Sat. vs. Porosity POROSITY BVW = Porosity * SW

23 Piceance Mamm Creek U WMF Water-Saturated Sands POROSITY RW *a = 0.4 Salinity ~ 10 kppm Rw = 0.4 a = 1 m = 1.65 n = F, Salinity~10 kppm NaCl- Porosity = 0.11 Porosity = 0.05 Mamm 13A Mamm 22B RT

24 Piceance Mamm Creek U WMF Gas Cell POROSITY RW *a = 0.35 Salinity ~ 10 kppm Rw = 0.35 a = 1 m = 1.65 n = F, Salinity~10 kppm NaCl- Porosity = 0.05 Mamm 13A Mamm 22B RT Gas Storage - Porosity > 6%

25 Piceance Mamm Creek L WMF Gas Cell POROSITY RW *a = 0.3 Salinity ~ 10 kppm Rw = 0.3 a = 1 m = 1.65 n = 1.65 L 157 F, Salinity ~10 kppm NaCl- Porosity = 0.05 Mamm 13A Mamm 22B RT Gas Storage - Porosity > 6%

26 Piceance Mamm Creek Gas-Water Contact Mamm13A; EUR ~ 1.3 Bcf _PHIE 0.25 v/v 0 _SW ( _TENS ) _RT 1 v/v ohmm Mamm13A; EUR ~ 1.8 Bcf _PHIE 0.25 v/v 0 _SW ( _TENS ) _RT 1 DEC ohmm TOG 4500 RW ~ 10 kppm TOG

27 Piceance Rulison Seismic PHIE *H vs. EUR EUR vs. Lithseis PHIE*H (PHIE > 0.08) EUR - Bscf Rulison Well A Well B Well C Well D Well E Well F Increasing Productivity LithSeis (PHIE*H) After; Hoyer & Young RMS AAPG

28 Piceance Basin Rulison vs. Mamm Creek EUR vs. Lithseis PHIE*H (PHIE > 0.08) EUR - Bscf Rulison Well A Well B Well C Well D Well E Well F Increasing Productivity Mamm Creek 13A 22B LithSeis (PHIE*H) After; Hoyer & Young RMS AAPG

29 POROSITY Rw = 0.3 a = 1 m = 1.85 n = 1.85 North East - Piceance Basin Example; Critical Gas Saturation WLMF GCell; ~ F~20 kppm BSM 6-22 BSM Delta RT ~ 20 ohmm s.1 Delta SW ~ 10% RESISTIVITY BSM 6-22 ~ Tested mostly water & Slight Gas BSM ~ Tested mmscfd

30 PHIE_SM Rw = 0.23 a = 1 m = 1.7 n = 1.7 North West - Piceance Basin Corcoran & Sego Sands Gas & Water Production degf~11 kppm NBC 2-12 VCLAY_SM < R_DEEP Production Log Results; 0.5 mmscf/d & 320 bbls Water

31 Wyoming; - L. Fort Union & Lance Gas Saturated Sands Rw = 0.2 a = 1 m = 1.65 n = 1.65 SAND: degf~10 kppm Porosity = 0.05 _VCLAY <.1 OCF 1-18 AMF WR OCF mmcf/d, 70 bbls/d Oil & 132 bbls/d Water

32 Conclusions Rigorous petrophysical evaluation of lowporosity sands require error minimization Log QC & Normalization Core data DOE/KGS study Formation water chemistry/distribution Pickett Plots are valuable visual tools for development & QC of the SW model Log inputs RT and PHIE Archie exponents a, m & n RW determination Saturation profile Gas/Oil Storage

33 Conclusions Rigorous petrophysical evaluation of lowporosity sands require error minimization Log QC & Normalization Core data DOE/KGS study Formation water chemistry/distribution Pickett Plots are valuable visual tools for development & QC of the SW model Log inputs RT and PHIE Archie exponents a, m & n RW determination Saturation profile Gas/Oil Storage A Coherent petrophysical model optimizes exploration & development efforts Saves - $$$

34 References Byrnes, Alan P., Robert M. Cluff, and John C. Webb, 2007, Regional petrophysical properties of Mesaverde low-permeability sandstones (abstract): Rocky Mountain Section AAPG Meeting, Snowbird, Utah, October 7-9, 2007; Search and Discovery Article #90071 (2007) ( Cluff, Robert M., Alan P. Byrnes, Stefani Whittaker, and Dan Krygowski, 2008, Evidence for a variable Archie porosity exponent m an impact on saturation calculations for Mesaverde tight gas sandstone: Piceance, Uinta, Green River, Wind River and Powder River basins: Kansas Geological Survey ( Hoyer, Darrell, and Roger Young, 2008, Seismic petrophysics in tight gas sands - a Piceance Basin, Mesa Verde example (abs.): Rocky Mountain Section, AAPG Meeting, Denver, Colorado, July 9-11, Web accessed 20 August

Regional petrophysical properties of Mesaverde low-permeability sandstones

Regional petrophysical properties of Mesaverde low-permeability sandstones Alan P. Byrnes, KGS John C. Webb, Discovery Robert M. Cluff, Discovery http://www.kgs.ku.edu/mesaverde US DOE # DE-FC26-05NT42660