An excursion through water saturation methods from cased hole logging

Transcription

1 An excursion through saturation methods from cased hole logging Chiara Cavalleri Principal Petrophysicist, Schlumberger London, 13-Dec-2018

2 Outline Introduction Formation evaluation behind casing Saturation methods and examples An integrated approach Summary 2

3 Introduction Cased-hole formation evaluation has a primary role for the proper description of the existing reservoir systems; but also new players in particular conditions. Help finding that additional drop of oil Assisting completion design or intervention programs Characterization of new reserves managing costs and operational risks. Alternative saturation methods are available behind casing; with or without open hole logs Current technology is the enabler, even in tough logging conditions.

4 Petrophysics Logging Behind Casing Logging behind casing mostly with open hole logs.with its own value and limitations. Casing / Completions Single Multiple Casing or hole size range Sigma and Full Spectroscopy Large Pulse neutron and Spectroscopy Slim Pulse neutron, Inelastic GR, Full Spectroscopy Slim CH res. slim CH resistivity large CH Density Acoustic Wide Band Frequency Acoustic Slim Neutron Poro Thermal Neutron Porosity Epithermal Spectral Gamma Ray Gamma Ray

5 Petrophysics Logging Behind Casing 1. Sigma 2. Sigma + Resistivity 3. Carbon/Oxygen 4. TOC 5. FNXS Needs to consider many diverse conditions Open hole log availability: yes/no Formation salinity: fresh/saline, known/unknown Lithology: known/unknown, simple/complex Hydrocarbon type: oil,, mixed, kerogen?, bitumen? Other: CO2; dynamic conditions, Saturation

6 Water Saturation from Sigma Log Water saturation when formation salinity has sufficient contrast with hydrocarbon and rock Lithology and porosity effects S log = V matrix * S matrix clay * S clay + fs w S w + f(1-s w ) S h Material Sigma (c.u.) TPHI Quartz Calcite Dolomite Wet Illite Kerogen (CH 1.3g/cm 3 ) Water ppk NaCl Diesel (CH g/cm 3 ) CH 4 (0.15 g/cm 3 ) CO 2 (0.6 g/cm 3 )

7 Saturation from Sigma in Depleted Reservoirs; Complex Wellbore configuration Formation type: Clastic, 20% porosity; 50ppk salinity (found to be variable) Borehole fluid CaBr2 and formation oil; chrome tubing Depleted zone Tubing, Casing (in) 7 (casing) + 9-7/8 (Casing) Borehole (in) Formation salinity change; fresher Saturation at original condition Tubing, Casing (in) 4.5 (Tubing), 7 (casing) + 9-7/8 (Casing) Borehole (in) Raw Measurement Interpretation Saturations

8 Oil Saturation from Carbon/Oxygen Logging Classical measurement for cased hole reservoir monitoring of oil content and fresh conditions Rw independent Dynamic range function of porosity and oil carbon density Carbon/Oxygen FCOR vs NCOR (Yields)

9 Oil Saturation from Cased Hole Carbon/Oxygen Spectral Analysis Shaly sand formation; low unknown salinity Bypasses oil from Carbon/Oxygen logging in absence of complete open hole logs standalone cased hole evaluation Cased hole FE Far and Near C/O Yields Ratio Oil Volume and Saturation from C/O

10 Oil Saturation from Spectroscopy (TOC) Organic Carbon (TOC) = TC - TIC S (oil) is computed from TOC and Porosity S hc = TOC r ma (1-f T ) r hc X hc f T Total Carbon (TC) is measured; Carbon Minerals Minerals are computed Inorganic carbon is calculated from minerals TIC = 0.120*Calcite *Dolomite *Siderite *Ankerite TC - TIC = TOC S (oil) Full Closure Spectroscopy Elements, Matrix, Minerology, Inorganic Carbon from Minerals SPE # , 2013

11 Oil Saturation from Cased Hole In-Situ Total Organic Carbon Measurement Shaly sand formation; low unknown salinity Bypasses oil from Carbon/Oxygen logging in absence of complete open hole logs standalone cased hole evaluation Cased hole FE Far and Near C/O Yields Ratio Oil Volume and Saturation from C/O S hc = TOC r ma (1-f T ) r hc X hc f T SPE # MS 2017

12 TOC Independent Oil Volume in variable Salinity and Porosity Volumetric interpretation N-D Porosity Porosity Oil wt% Spectroscopy OH S hc Spectroscopy Dielectric CH S hc Spectroscopy, C/O 8.75 BS; 7 Casing; 50 ft/hr 50 p.u p.u. 0 0 wt% Open Hole Cased Hole Heavy oil under steam-injection (EOR) N-D crossover Resistivity fails Oil Saturation from TOC in good agreement with C/O analysis Solving for complex mineralogy Density Neutron 100 ft

13 Cased Hole Spectroscopy in large hole 9 Years After Drilling Petrophysics and well integrity logging behind in casing; in front of 14.5in bit size XX000 XX100 XX200 XX300 XX400 High Def spectrosco py Well integrity XX500 XX600 Formation testing XX700 Critical present day oil saturation from TOC FSAL estimate from Sigma, also shedding light on the complex reservoir environment

14 FNXS (1/m) Gas Saturation from Fast Neutron Cross-section New Measurement Probability of fast neutrons to interact with atoms; directly sensitive to filled porosity Quantify volume in low porosity rock together with Sigma and neutron porosity logs. Detected inelastic GR fresh CH4 (0.1g/cc) HI Sg 0% Sg 100%

15 Saturation from Gas (FNXS) Inelastic hydrogen in Tight Gas Sand Producing oil and field; shaly sand formation with low porosity -filled and very low porosity alternating in bit size, 4.5 in casing; 11.6 lbm/ft casing weight with cement thickness more than 2 in. FNXS Mineral Solver SIGM TPHI SIGMA = V TPHI = V FNXS = V 1 = V SIGMA TPHI FNXS TPHI clay SIGMA FNXS SIGMA TPHI FNXS clay clay clay TPHI SIGMA clay FNXS clay clay

16 Fast Neutron Cross Section Measurement Applied to Petrophysics o Shaly sand, variable rock quality; o Casing and tubing, open perforations; crossflow conditions o FNXS Fast Neutron Cross Section; environmental corrections applied to account for different conditions than EECF.FNXS vs TPHI analysis value Sg 0% Sg 100%

17 Three Phase Saturations Computation in Carbonate Differentiate Gas Filled Porosity from oil filled rock; variable porosity Standalone cased hole evaluation FNXS SIGM Mineral Solver TPHI Elements Dry Weights SIGMA = V TPHI = V FNXS = V DWCA = V DWSI = V 1 = V calcite SIGMA TPHI FNXS DWSI DWCA calcite TPHI FNXS calcite SIGMA SIGMA TPHI FNXS calcite calcite calcite TPHI SIGMA calcite FNXS calcite calcite

18 Three Phase Saturations behind Casing and Another Complex scenario Standalone evaluation of rock and fluids, through quantitative use of FNXS with Sigma, TOC, and full spectroscopy recorded behind casing Multi-mineral solver plot with reconstructed curves and computed rock and fluid volumes: ELAN Multi-mineral analysis integrating Pulsar measurements FNXS SIGM Mineral Solver TPHI Elements Dry Weights SPWLA 58 th, 2017 Solving for reservoir saturations using multiple formation property measurements from a single PNL tool

19 Saturation Calculation and Monitoring Behind Casing - Summary Condition SIGM R T C/O TOC FNXS Remarks f<15% (low f) 15%<f, C salt <20 ppk (fresh) 15%>f, C salt >20 ppk (saline) Mixed salinity Flowing well Fluid contact in hole Washed-out holes Near wellbore effect Acid effect Run in small tubing Multiple casing/tubing string Deviated/HZ well Lithology Limit on R T,max Limit on R T,max Favorable contrast conditions Need C salt profile Need Y o measurement Inaccurate near contact Shallow DOI on C/O Shallow DOI on C/O Effect of high S acid element Slim measurement available with good calibration Conveyance dependent Need matrix data State of art technology and Integrated approach help reducing Sw uncertainty in complex setting Ref.: after Aulia et al., 2001 (Schlumberger) - extended

20 Conclusions Alternative methods for saturation measurement from logs behind casing and within completion exist. The results can be obtained as a standalone measurement approach or data integration to open hole. The choice of the logging program and computational workflow depends on the logging environment and its complexity; and the particular evaluation objective.

21 Slide 26 Paper # Paper Title Presenter Name