Basin Evaluation Using Burial History Calculations: an Overview

Abstract

Burial history calculations available to the petroleum geologist include plots of burial history and geohistory, porosity, and conductivity as a function of depth and lithology, as well as the results obtained from algorithms to handle unconformities and backstripped crustal subsidence, calculations that predict the breakdown of kerogen to hydrocarbons in terms of time and temperature, and methods for determining heat flow from geologic models and vitrinite reflectance. Data inputs required for these calculations include depths of formation tops, ages of formation tops, lithologies of formations, depths of water at deposition of the different formations, porosities of the formations as a function of depth, bottom-hole temperatures and/or formation temperatures, and any ke ogen content and vitrinite reflectance values as functions of depth. Sources of many of these data may be well logs, well reports, geologic papers, and/or seismic sections. The paper considers how parameters can be extracted from burial-history calculations to construct maps that can be compared to the current locations of oil and gas fields, and so used to locate and rank prospective acreage. These parameters include the potential source rock maturity of a formation plotted as a function of time and depth, the thermal history of any hydrocarbons associated with the potential source rock, the rate of sediment accumulation of a formation as a function of time, and subsidence rate of a formation as a function of time. Subsidence rate includes total subsidence, compaction-induced subsidence, isostatic response to sediment load, and backstripped crustal subsidence (total subsidence minus the effects of compaction and isostatic response).