Mud Analysis Logging And Its Use In Formation Evaluation

Abstract

Introduction Mud logging is the term applied to the process of analyzing the drilling mud and cuttings for oil and gas and correlating these shows with the depth of the formations from which they came. The amounts of oil and gas found in the mud and cuttings from productive formations vary widely due to variations in drilling practice and in formation characteristics. Hence, mud logging does not furnish quantitative information useful to engineers in calculating reserves for productivity of formations. Its principal usefulness is as an aid to formation evaluation in exploratory wells by detecting and locating oil and gas occurrences as the well is drilled. In contrast to other logging methods in which the presence of oil and gas is inferred from the measurements of physical properties of the formation, mud logging affords a direct determination of oil and gas in the formation. It is an around-the-clock program to assure that all oil and gas-bearing formation will be detected during the drilling of the well. The wide application of mud logging on exploratory wells attests to its usefulness. Approximately 300 units of mud logging equipment are now being used in this country. Scope and Applications Mud logging is done in a mobile laboratory at the wellsite while the well is drilled. The operator with the equipment at his command does the following:Detects gas in the drilling mud continuously and in the cuttings intermittentlyDetects oil in drilling mud and cuttings samples intermittentlyDescribes the well cuttings by mineral content, color, texture, etc.Logs the progress of the drill, the depth and drilling rate, and the circulation of drilling mud through the hole, and relates showings to their depth of originDetermines mud properties intermittently and observes the rig operation as it may affect the mud logging results From the results obtained a log such as that of Fig. 1 is drawn.