Petrophysical Tutorial, Lessons Learned, and Evaluation Workflow: A Case Study in the Power River Basin

Stephanie E Perry,Matthew White

doi:10.4236/ns.2021.135014

Abstract

The objective is to empower the reader and scientific community with the knowledge and specific applicable equations to then reproduce the critical rock and fluid attributes in the Powder River Basin. To then continue to unravel the basin and its potential (both conventionally and unconventionally). The overall goal is to ensure the transfer of knowledge and communication of a petrophysical workflow that can then also influence application to other basins worldwide. The Powder River Basin is in southeast Montana and northeast Wyoming and is a prolific oil and gas (hydrocarbon-prone) sedimentary basin related to the greater Rockies chain/series of hydrocarbon-bearing basins (ex. Big Horn, Greater Green River, Denver-Jules). In this study, we briefly set-up the geological background of the Powder River Basin and the importance/ relevance to then tackling subsurface petrophysical evaluation on a regional scale. Approximately, 200 wells were evaluated petrophysically by a combined deterministic and inversion-based workflow representing an effort to share best practices, approaches, and the relative trends to apply in the basin to unravel the stratigraphic hydrocarbon potential in place. An extensive workflow involving basic petrophysical approaches such as raw log applicable cutoffs and volume of clay determination are shared as well as extending knowledge and application into advanced petrophysics through geochemical property derivation and impact of those derived properties as well as bound versus free water and hydrocarbon understanding. Results of the petrophysical analysis highlight the varying properties in conventional and unconventional formations (example Niobrara). The results of how and why the petrophysical approach was calibrated and then applied are the primary efforts accomplished.

Highlights

For the purposes of this study, while we recognize the continued potential and need for further characterization of the pre-Cretaceous stratigraphy, we focus our evaluation on the Cretaceous to present primarily liquids-bearing hydrocarbon stratigraphy whose base/lower depth zone we will define as the Muddy formation and at its shallowest we will define as the Teckla formation (Figure 3, i.e., Stratigraphic type log section with wireline response defined)
We focused on the normalization of the gamma ray (GR) and RHOB raw wireline logs as a deliverable for the geologist or stratigrapher correlating well tops across the basin
Conventional opportunities primarily being defined as reservoirs with >12% total porosity and >1 - 5 mD of permeability where generated hydrocarbons have charged and migrated either locally or a long-distance from the source rock responsible for the hydrocarbon generation

Summary

Introduction

The Powder River Basin is in southeast Montana and northeast Wyoming and has historically been known for its coal bed methane potential and production [1,2,3]. In addition to the coal bed methane potential, the basin has been utilized for conventional vertical wellbore production since the early 1980’s. For the purposes of this study, while we recognize the continued potential and need for further characterization of the pre-Cretaceous stratigraphy, we focus our evaluation on the Cretaceous to present primarily liquids-bearing hydrocarbon stratigraphy whose base/lower depth zone we will define as the Muddy formation and at its shallowest we will define as the Teckla formation (Figure 3, i.e., Stratigraphic type log section with wireline response defined)

Methods

Results

Conclusion