Exploration Application of Temperatures Recorded on Log Headings--An Up-the-Odds Method of Hydrocarbon-Charged Porosity Prediction

Abstract

Using the least accurate type of temperature data, temperature anomalies called hotspots, which are believed to be hydrocarbon temperature anomalies, have been defined by application of a new analytical technique. To date the technique has been successful to a significant degree when applied to known fields using only dry hole data and, in some cases, using only dry hole data for wells drilled prior to field discovery as initial steps toward before-the-fact analysis. Technique testing by the drill has not been done. The hypothesis accepted herein is that heat flows from the earth's hot interior toward its colder surface is nature's attempt to establish temperature equilibrium. The following three facts are accepted. 1. Hydrocarbon fluids have very low thermal conductivities (oil about one-fifth that of water and gas about one-fourteenth that of water). 2. Equal heat input elevates the temperature of a largely hydrocarbon fluid volume relative to a laterally equivalent volume of largely water-filled porosity. 3. There are fewer grams of hydrocarbon fluids to warm than there are grams of water filling an essentially equal porosity volume. Hydrocarbon fluids insulate more (fact 1) and their temperatures are elevated more easily (facts 2 and 3) than contiguous waters. Hydrocarbon reservoirs whose heat flow effects are not obscured by the anisotropic effects of adjacent water reservoirs, may cause definable temperature anomalies. The technique formulated involves the following steps: (1) calculation of geothermal gradient values, (2) creation of a geothermal gradient field areally, (3) vector analysis or contouring of created data, and (4) anomaly definition. Technique application to 10 fields representative of a range of complexities shows promise for this up-the-odds exploration tool. Results for three examples (Black Lake field, Louisiana; Haverhill field, Kansas; and Salt Creek field, Texas) may demonstrate the principal use to be as a grading method for prospects based initially on classical study.