4-D Petroleum Systems Modelling of the Haynesville Shale Play— Understanding Gas in Place

Abstract

Six years ago, the Upper Jurassic Haynesville Shale play was largely unknown as an unconventional shale play. US government and oil company resource assessments for such unconventional plays vary significantly. Here we attempt to estimate resource potential using a full mass balance approach based on data from more than 1600 recently drilled wells, integrated into a 3D petroleum systems model.Numerous iterations were conducted to simulate heat flow in the study area. The simulated heat flow calibrated to vitrinite reflectance data from 26 wells suggests that a slight increase in heat flow may have occurred with every uplift event over the Sabine Uplift area.Laboratory analysis of a number of Haynesville Shale samples taken from six wells reported an original total organic carbon (TOC) content, which is on average 3% for all samples. Additional Rock-Eval analysis revealed that all of the samples taken from the wells are overmature. Adsorption isotherms were determined on one representative sample and implemented in the modelling approach to calculate adsorbed gas volumes.After simulation, the accumulation calculations in the Haynesville Shale revealed a total amount of 2056tcf of adsorbed gas (79.15% Methane) and 1511tcf of free gas (87.12% Methane). These numbers seem to be very high, but considering a recovery factor of 5 or 10% the combined producibility of gas based on our model will be equal to 178 or 357tcf respectively. Most of the primary production of gas occurred during the Aptian-Albian, and secondary cracking produced most of the free gas during the Early-Eocene.The model also shows wide variability in pore pressure and the generation of abnormal pressures. This variation in pore pressure occurs in the Haynesville Shale and results from a combined effect derived from the overlying Cotton Valley/Bossier Formation and the underlying Smackover Formation. As a final observation, the critical moment of the Haynesville Shale petroleum systems has been dated to be at the Turonian and Early-Eocene. At this point all petroleum system elements and process have been satisfied for the conventional and the nonconventional play respectively.