Thermal Extraction Chromatography-A New Technique For Rapid Wellbore Evaluation

Abstract

Abstract The need for early identification of hydrocarbon productive zones penetrated by wellbores has been greatly increased by escalating exploration and development costs. Unfortunately, the formation evaluation techniques now commonly employed possess significant limitations in hydrocarbon specificity and can be used only after the well has been drilled. This paper describes an evaluation technique based upon the analysis of residual petroleum hydrocarbons present in wellbore samples. The technique, Thermal Extraction Chromatography, is hydrocarbon specific and can be used while drilling is in progress. It is applicable to drill cuttings, drilling mud, and core fragments. The analysis produces both richness and compositional data for the hydrocarbons in these samples. This data, used alone or in combination with porosity or permeability measurements, has been employed to define hydrocarbon productive zones and transition zones in several hundred wells in the United States. It has also proved effective in predicting the type of fluid to be expected from these wells. The method has been adapted recently to distinguish between indigenous hydrocarbon and mud filtrate contamination fff downhole formations. Other new applications include the determination of hydrocarbons in sidewall core samples, hydrocarbon fingerprinting for reservoir identification, and source rock evaluation. The method appears applicable to any type of sample from which hydrocarbons can be vapourized. Introduction There is a continuing need in petroleum exploration and production efforts for better wellbore evaluation data. This need has become even more important in recent years because of rapidly increasing drilling costs and the decreasing probability of major petroleum discoveries. These circumstances make it very desirable that hydrocarbon productive zones penetrated by wellbores be identified as soon as possible and that even small commercial deposits of hydrocarbon not be overlooked. It is equally important that any deposit discovered be completed in a manner that will yield optimum hydrocarbon recovery. Unfortunately, the formation evaluation techniques now commonly employed possess significant limitations in hydrocarbon specificity. In addition, most of these procedures can be used only after the well has been drilled. This paper describes a relatively new wellbore evaluation method which has proved effective in both discovery and completion applications. For several years now, a number of investigators have been working to develop a sensitive method to measure and fingerprint residual hydrocarbons in bits of petroleum reservoir rock. Pixler(1) indicated as early as 1968 that information of this type could be useful in evaluating potentially productive formations penetrated by wellbores. Giraud(2) added to this developing technology in 1970 when he demonstrated [hat pyrolysis techniques could be coupled with gas chromatography to provide an effective analysis of residual hydrocarbon in formation samples. Our early efforts with an analysis of this type were described by Maness(3, 4) in 1973. Development of a practical analytical system to obtain the desired hydrocarbon data was announced by Maness and Price(5) in 1977. The method described in the latter paper, Thermal Extraction Chromatography or TEC has been considerably improved and extensively evaluated since that time.