Abstract
Surprisingly, traditional programmed pyrolysis methods developed in the 1970s and interpretive guidelines developed for the Barnett in the 90s are still routinely used to assess the present day organic matter quality and quantity of potential source rocks/unconventional reservoirs. Recent advancements in pyrolysis technology and manufacturing have paved the way for organic screening via pyrolysis on larger numbers of samples with faster turnaround times. The results are now available for critical time sensitive drilling and completions decisions, but also provide a main input to the development of petrophysical models and geochemical trend maps. Investigation of huge numbers of pyrograms with ranges in organic matter type and maturity has exposed multiple caveats in the traditional pyrolysis method and those interpretive guidelines being applied particularly in regards to liquids rich source rocks. The most problematic of which is heavy hydrocarbon carryover from S1 to S2 also known as low temperature S2 shoulders complicating kerogen quality assessment, maturity determination and production quantity/quality estimates.
Bulk XRD mineralogy, traditional pyrolysis, elemental composition and Mass Spec mudgas data from a Midland Basin vertical well are integrated and presented as type log for our work focusing on the Wolfcamp and Sprayberry formations. We utilize the HAWK pyrolysis instrument to generate pyrograms and compare traditional pyrolysis results of samples from multiple wells across the basin to results obtained from modified pyrolysis methods and results obtained after organic solvent extraction on parallel samples. Modified initial isotherm temperatures designed to volatize a larger range of hydrocarbons without cracking kerogen directly address the S1 carryover providing a more reliable assessment of the cumulative oil (S1 peak) and "clean" S2 peak for more accurate kerogen and thermal maturity assessment. Additionally, pyrograms generated from both traditional temperature ramping and a more rapid pyrolysis temperature ramping are presented to fully investigate any effects on the S2 peak geometry/quantification and Tmax determination. In conclusion we discuss some innovative interpretive techniques utilizing this experimental data to better characterize and map organic quality and maturity. We then combine our new insight with our understanding of potential migratory contributions to better correlate production quantitatively and qualitatively.
