Simple Pyrolysis Technique Using Well Cuttings to Map Source Rocks, Gas-Condensate Maturity, and Abnormal Fluid Pressures Associated with Fracture Reservoirs: Example from Anadarko Basin: ABSTRACT

Abstract

P. Trask showed that when small samples of kerogen-rich rock are pyrolyzed in a test tube, oil-like material may be generated and condensed as a brown residue around the walls of the tube. This technique is adaptable to the use of well cuttings and may be utilized to identify source rocks capable of generating oil. For any given source rock, the amount of pyrolysis yield decreases with increased thermal maturity as verified by vitrinite reflectance analysis. Samples from stages of maturity corresponding to the gas-condensate and dry-gas generation windows yield no pyrolysis residue because of their inability to generate dark oily liquids. We have used the test-tube-pyrolysis technique to map quickly and accurately (1) source rocks capable of generating oil, and (2) the maturity threshold of gas-condensate generation in part of the Pennsylvanian section of the Anadarko basin. The area of gas-condensate generation within the Atoka Formation, as mapped by the pyrolysis technique, is coincident with the presence of (1) abnormally End_Page 480------------------------------ high formation-fluid pressures, (2) fracture-type reservoirs, and (3) water-free gas-condensate production. Abnormal pressures are believed to be caused by high generation rates, volume expansion during conversion of kerogen to a gas phase, and rock-framework collapse. Indigenous fracturing is caused by a favorable stress condition accompanied by critically high formation-fluid pressure. Water-free hydrocarbon production is the result of the nearly complete saturation of available reservoir space by relatively large volumes of generated and only partially expelled gas-condensate. We believe that the simple pyrolysis technique and its interpretations are applicable to many basins. The method requires only a library of sample cuttings, a supply of test tubes, and a propane torch (or similar heat source) for implementation. End_of_Article - Last_Page 481------------