Automatic determination of lithology from well logs
A procedure combining modern wireline measurements with a lithofacies database has been developed to produce an automatic lithological description of the formations crossed by a well. The database lithofacies are defined from petrographic knowledge and translated in terms of log responses. The assignment of depth levels to a lithofacies is done by reference to the database and a discriminant function (Bayesian decision rule). External knowledge can be taken into account using Artificial Intelligence methods. A confidence factor is produced for each result. Logs currently in the database are the density, neutron, sonic transit time, gamma ray, photoelectric cross-section, and thorium, potassium and uranium concentrations. Major lithofacies groups are represented in the database: sandstones, limestones, dolomites, shales, coal, evaporites, and miscellanea. They are subdivided by introducing cement and special minerals, and considering several porosity ranges. The construction of the database is a critical step. It is largely empirical and requires careful calibration against intervals whose lithology is well known (e.g. from cores). The database can be tuned to local conditions. The procedure has been tested in several environments and compared with cores and mudlogs descriptions. A detailed lithologic column can be produced at the wellsite and used as an aid to decision making. The results can also serve as input for further geological studies of facies and sequences or for quantitative evaluation of formations.
- Research Organization:
- Etudes et Productions Schlumberger
- OSTI ID:
- 6326778
- Report Number(s):
- CONF-8409104-
- Journal Information:
- Soc. Pet. Eng. AIME, Pap.; (United States), Vol. SPE13290; Conference: 59. annual Society of Petroleum Engineers of AIME technical conference, Houston, TX, USA, 16 Sep 1984
- Country of Publication:
- United States
- Language:
- English
Similar Records
Calculating lithology from wireline logs
Fallon FORGE: Lithology Logs and Well 21-31 Drilling Data