Combined natural gamma ray spectral/litho-density measurements applied to complex lithologies
Well log data has long been used to provide lithological descriptions of complex formations. Historically, most of the approaches used have been restrictive because they assumed fixed, known, and distinct lithologies for specified zones. The approach described in this paper attempts to alleviate this restriction by estimating the ''probability of a model'' for the models suggested as most likely by the reservoir geology. Lithological variables are simultaneously estimated from response equations for each model and combined in accordance with the probability of each respective model. The initial application of this approach has been the estimation of calcite, quartz, and dolomite in the presence of clays, feldspars, anhydrite, or salt. Estimations were made by using natural gamma ray spectra, photoelectric effect, bulk density, and neutron porosity information. For each model, response equations and parameter selections are obtained from the thorium vs potassium crossplot and the apparent matrix density vs apparent volumetric photoelectric cross section crossplot. The thorium and potassium response equations are used to estimate the volumes of clay and feldspar. The apparent matrix density and volumetric cross section response equations can then be corrected for the presence of clay and feldspar. A test ensures that the clay correction lies within the limits for the assumed lithology model. Results are presented for varying lithologies. For one test well, 6,000 feet were processed in a single pass, without zoning and without adjusting more than one parameter pick. The program recognized sand, limestone, dolomite, clay, feldspar, anhydrite, and salt without analyst intervention.
- Research Organization:
- Schlumberger Well Services
- OSTI ID:
- 5466736
- Report Number(s):
- CONF-820927-
- Journal Information:
- Soc. Pet. Eng. AIME, Pap.; (United States), Vol. SPE11143; Conference: 57. AIME Society of Petroleum Engineers annual technical conference and exhibition, New Orleans, LA, USA, 26 Sep 1982
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
03 NATURAL GAS
NATURAL GAS WELLS
WELL LOGGING
OIL WELLS
RESERVOIR ROCK
CHEMICAL COMPOSITION
LITHOLOGY
SIMULATION
CROSS SECTIONS
DATA ANALYSIS
EXPLORATORY WELLS
GAMMA SPECTRA
PHOTOELECTRIC EFFECT
POTASSIUM
RESPONSE MATRIX METHOD
THORIUM MINERALS
ALKALI METALS
ELEMENTS
EQUATIONS
MATERIALS
METALS
MINERALS
PHOTOELECTROMAGNETIC EFFECTS
RADIOACTIVE MATERIALS
RADIOACTIVE MINERALS
REACTOR KINETICS EQUATIONS
SPECTRA
WELLS
020300* - Petroleum- Drilling & Production
030300 - Natural Gas- Drilling
Production
& Processing