Quantitative Log Evaluation of the Prairie Evaporite Formation in Saskatchewan

Abstract

Abstract The problem of solving for the fraction of sylvite, carnallite, halite and insoluble material in the Prairie Evaporite formation can be performed by a suitable interpretation program based on Gamma Ray, Sonic, Neutron and Caliper logs. Empirical relations were established between the log values and the formation parameters, the result being a set of four simultaneous equations which may be reduced to obtain the desired fractions. Tedious hand calculation can be eliminated by using computer techniques and automatic log digitizing machines. Correlation between core and log analysis is good, and the speed and efficiency of the method is valuable in initial formation studies. Introduction The Prairie Evaporite formation has been the object of extensive study in the past several years (1) (2). It is the richest known potash-bearing bed in the world, and, as such, it is important that any information gathered concerning the zone be accurate and immediately useful. Electrical and radioactivity well logs have proved to be of value for formation evaluation in the oil industry. A recent paper (3) illustrates their use for both qualitative and quantitative interpretation in evaporite sequences in various parts of North America. This paper will outline the theory and technique used for a quantitative interpretation procedure in the potash beds of the Prairie Evaporite formation in the Province of Saskatchewan. The data are set up so that they can be handled by an electronic computer. The equations can also be computed by hand at the well site to supplement the data already available. The computer program is presented as an Appendix. An extensive bibliography covering potash geology, development and logging techniques, is included. Theory It is well known that potassium has a radioactive isotope which emits gamma ray energy. This isotope comprises a constant fraction of the total amount of potassium, so that a Gamma Ray Log, which measures the amount of natural radioactivity in a formation, frequently gives a measure of the potassium content.