PREDICTION FROM LOGS OF RECOVERABLE HYDROCARBON VOLUME, ORDOVICIAN CARBONATES: WILLISTON BASIN

Abstract

The objective of this study was to develop techniques for predicting from well logs the quantity of recoverable oil by primary depletion from the upper Red River formation (Cedar Creek Anticline) in the Williston Basin. Means of providing appropriate rock type zonation from routinely, run logs for geological purposes were also desired. A technique for calculating from logs the ratio k/ϕ where k is permeability to air measured in cores and ϕ is porosity, was determined. The confidence limit for the predicted k/ϕ value from logs is the same as that measured on the cores themselves. In the Red River, the parameter k/ϕ is useful for classifying rocks by pore‐size ranges. A quantitative correlation between primary oil recovery from production decline curves and [Formula: see text] calculated from logs is developed for the Red River formation. In this quantity, [Formula: see text] is oil saturation, h is interval thickness, and the summation is carried out in each well over all zones where [Formula: see text] percent. The method employs the calculated values of k/ϕ to divide zones into appropriate classes of rock quality in terms of pore‐size range for the summation.