Integrated Rock Physics Model to Predict Sweet Spots in an Unconventional Jurassic Carbonate Source Rock

Abstract

The exploration of unconventional hydrocarbon resources mainly targets the tight source rock reservoirs where hydraulic fracturing is needed for an effective hydrocarbon production. This project aims to predict new areas with high hydrocarbon production potential that can be effectively stimulated/fractured, known as sweet spots, in a tight Jurassic carbonate source rock. A rock physics model was developed to link the seismic properties to rock properties of the target formation. Three main rock properties are used in this study to define the sweet spots: total organic content (TOC), Young's modulus (YM) and Poisson's ratio (PR). TOC is a geochemical property that is related to the production potential and is obtained in the laboratory from core, while YM and PR are rock elastic properties that are related to the frackability and are obtained from density and sonic (compressional and shear) logs. Sweet spots are generally characterized by high values of TOC, high values of YM and low values of PR. Using well data, these three properties were cross-plotted against two derivative elastic properties (lambda-rho and mu-rho) that are calculated using sonic (compressional and shear) and density logs to obtain a linear relationship. Lambda and mu are measures of incompressibility and shear rigidity, respectively, while rho is density. Cutoffs of lambda-rho and mu-rho were chosen to represent the sweet spots. The distribution of sweet spots in the study area was then mapped using a rock physics model that is built by integrating two inverted 3D seismic volumes; lambda-rho and mu-rho. Results show that sweet spots are characterized by low values of lambda-rho and mu-rho, and are well distributed in the study area. In addition, results show that TOC has an inverse relationship with frackability which means that there should be a balance between reservoir quality and completion quality when targeting sweet spots for more economical hydrocarbon production.