Fluid identification (water and oils have different NMR properties)
Bound Fluid / Free Fluid via a T 2 cutoff
Prediction of permeability
Trend analysis and response typing to identify major bed/unit boundaries and flow units
Identification of clays and asphaltines
… and potentially wettability
What information can NMR achieve?
NMR Interpretation Data (T2 Distribution) 0.1 1.0 10.0 100.0 1000.0 10000.0 Rock Bulk Volume Rock Matrix Clay Clay bound water Total Porosity Effective Porosity Capillary bound water Free water Hydrocarbons Minerals T2 cutoff NMR is unique it measures total porosity and can be partitioned into pore-size and fluid component
Hydrocarbon effect on T2 distribution 100% Brine Saturated Water wet with oil Producible water (free fluid) Bound fluid (irreducible water) Producible hydrocarbon (free fluid) Bound fluid (irreducible water) T2 increases since hydrocarbon Is not limited by pore-size T2 is limited by pore size in 100% Sw rocks
CPMG pulse sequence f s s s s s s f f f f f 90 180 180 180 echo echo 90 180 180 180 180 180 180
The echo-train of a complex system, e.g. fluid in pore system, comprises many exponential decays. Time Domain T 2 Domain INVERSION Magnetization amplitude T 2 amplitude Time (ms)
The catalogue is designed to aid understanding of NMR response in carbonate rocks. The primary use is to guide acquisition, processing and interpretation of NMR logs in carbonate hydrocarbon reservoirs.
What does it contain?
The catalogue contains laboratory data from core plugs and whole cores in brine-saturated and de-saturated state. The samples were selected to capture variation in pore geometry. The samples include:
· Chalk (including diagenetic chalk)
· Microcrystalline dolomite
· Oolitic limestone
· Sucrosic dolomite
· Vuggy dolomite
A Library of NMR Response Characteristics in Carbonate Rocks.
Use core calibration (i.e. porous plate de-saturation)
Remove free fluid from T2 distribution
Substitute in ‘hydrocarbon’ with bulk properties
Model raw data
Spectral Bound Fluid Model Bound fluid = Capillary bound + Surface film b W = f(T2) Carbonate Model: m = 0.0113; b = 1.
Fluid Substitution Method Spectral bound fluid = Swirr 2. Remove free-fuid (water) 3. Add in free fluid water so that T2LM of free fluid = T2 predicted for hydrocarbon 1.
Modelling Example 1: Optimising Inversion of Log Data Inversion: SVD T1 min = 0.3 T2 max = 3000 No Bins = 30 T2 maximum is not long enough to capture Long T2 associated with carbonate Analogue Model Inversion
Modelling Example 1: Optimising Inversion of Log Data Inversion: SVD T1 min = 5 T2 max = 5000 No Bins = 30 Analogue Model Inversion New bin range better captures the full T2 spectrum
Modelling example 2: Fluid Substitution 3 CP Oil T2 = 1130 msec (150 deg F) Analogue Model Inversion Fluid Sub
Modelling Example 3: Decreased Wait Time (1 sec) Analogue Model Inversion Fluid Sub Tw = 1 sec Lost porosity With Tw = 1 sec