Abstract

The Niobrara Formation with low matrix porosity (6 to 16%) and permeabilities less than 0.01 md requires an open fracture system for economic oil recoveries. Several models have been proposed as mechanisms for creating these open oil productive fractures in the brittle chalk members of the Niobrara Formation at Silo Field. These models include: 1) differential compaction over paleotopographic highs; 2) folding or flexuring over basement features; 3) the presence of a regional fracture system; 4) increased pore fluid pressures derived from the oil generation/expulsion process; 5) reactivation of wrench faults; and 6) extension fractures created by Permian salt withdrawal.

Integrating high-resolution proprietary seismic data, information from five fracture-identification logs, and wellbore fluid communication data, it is proposed that salt dissolution is not the primary mechanism for Niobrara fracture genesis. This can be supported by isochron mapping which outlines the Permian salt edge and illustrates the inconsistencies between the orientation of the open fractures and the salt outline. Variable horizontal production results also fail to substantiate the salt theory.