SS: Exploration Prospect Interpretation and Risking Using Modern Geophysical Technology - Using Modern Geophysical Technology to Explore for By-Passed Opportunities in the Gulf of Mexico
Authors: Young Roger A. , Holt William Garret , Klefstad Gil 
Published: July 2009

The Gulf of Mexico Shelf is a mature oil and gas province that has been producing hydrocarbons since the early 1950's. Technology advances during the last five decades have led to the identification of new exploration prospects on deep structures, subtle traps, and direct detection of hydrocarbons via seismic amplitude anomalies and AVO (amplitude vs. offset) studies. There are good opportunities remaining in old fields that require another " step change?? in technology application.

Seismic inversion is the process of determining the physical characteristics of rocks and fluids which have produced the seismic record. Inversion attempts to remove the effects of the seismic wavelet and therefore is the opposite of forward modeling. Inversion is a dataset that ties all the wells in an area and also honors all the seismic data.

Multi-disciplined asset teams benefit from advanced seismic technologies by using an integrated rock-property based solution to maximize results in exploration, well planning, drilling, production, and reservoir management. The key to success in to understand the rocks with tools to interpret and define lithology, porosity, fluids, pore pressure and reservoir quality; providing seismic data in a geologically meaningful and multi-disciplinary useable format.

Conventionally seismic inversion produces P velocity, S velocity and density. Log analysis, also an inversion process, starts with velocity and density, as well as other measurements, and finishes with lithology, porosity and fluids. The relatively new science of Seismic Petrophysics bridges the gap between these two workflows by starting with seismic data and resulting with 3D seismic volumes of lithology, porosity and fluids. An old field was purchased with intent of applying new technology in the search of bypassed opportunities. This case study will document the results of the work.

Introduction

For decades, the rudimentary process by which geologists determine optimal oil and gas drilling locations for exploration companies has remained intact.

Exploration companies have come to expect that many of the wells they drill will come up empty, despite preliminary research indications to the contrary. But the evolution of seismic petrophysics, combined with new proprietary technologies, provides geologists and engineers with dynamic, 3-dimensional models of the subsurface environment that more accurately reveal the reservoir properties and the likely locations of gas or oil.

The integration of well logs with seismic data is challenging because they are presented in different domains. Well logs are displayed in units of microseconds/ft, gm/cc, gapi, ohm-m, etc., while seismic is displayed in terms of reflectivity. When inversions are carried out to put seismic into a more log-similar domain, acoustic impedance is often chosen. This seems somewhat odd since well logs ultimately are inverted to lithology, porosity and fluids.