Special Session- Gas Hydrates: Pressure Coring And Pressure Core Analysis Developments For The Upcoming Gulf Of Mexico Joint Industry Project Coring Expedition
Authors: Schultheiss Peter , Aumann James T. , Humphrey Gary D. 
Published: July 2010

This paper describes the pressure coring and pressure core analysis tools to be used on the upcoming Gulf of Mexico Joint Industry Project (GOM-JIP) Expedition III. Pressure cores and pressure core analysis have become more important as scientists, exploration geologists, and geohazard engineers strive to understand gas-rich formations, including but not limited to gas-hydrate-bearing marine sediments, coalbed methane reserves, and shale gas reservoirs. After the highly successful GOM-JIP logging-while-drilling Expedition II, gas-hydrate-rich sections have been identified and will be cored on GOM-JIP Expedition III. Extensive use of pressure coring tools is anticipated, providing both samples for laboratory studies as well as data collected under pressure for the scientific community. The new HPTC (High Pressure Temperature Corer) will collect 3.5-meter-long samples of core at in situ pressures, while the one-meter-long FPC and FRPC (Fugro Pressure and Rotary Pressure Corers) will be used as alternate coring systems. All coring tools will be adapted to work in a flexible bottom hole assembly negating any need to trip pipe between changes of tools. PCATS (Pressure Core Analysis & Transfer System) will provide the infrastructure to both handle and conduct non-destructive testing of all these cores under pressure, providing gamma density, ultrasonic P-wave velocity, and X-ray computed tomography (CT) of the cores at full pressure. PCATS moves cores under pressure with linear and rotational precision for use with other purpose-built, compatible measurement systems and also cuts subsections of core under pressure, pushing these pieces into customized pressure cells for further analysis and testing. It is anticipated that together these four tools will collect and provide to the scientific community more pressurized core samples from GOM-JIP Expedition III than from all previous gas hydrate expeditions.

Introduction

The Gulf of Mexico Joint Industry Project (GOM-JIP) has completed two gas hydrate drilling expeditions and is preparing for a third. This upcoming expedition is focused on gas-hydrate-bearing sands, which have been identified in the logging-while-drilling (LWD) data from GOM-JIP Expedition II. The collection of pressure core data to verify and ground truth the LWD data is a major goal of GOM-JIP Expedition III. An intensive pressure coring program is being planned to achieve these goals.

Pressure cores are vital to gas hydrate studies as they preserve gas hydrate and the sedimentary structures in which it forms, allowing geophysical studies of the sediment-hydrate matrix as well as quantitative estimates of hydrate concentration. In non-pressurized core, gas hydrate dissociates during or soon after core recovery as a result of decreasing pressure and increasing temperature. The dissociation of gas hydrate creates large volumes of gas that expand and often destroy the complete fabric of the core prior to it reaching the surface. Cores recovered at or near in situ hydrostatic pressures and temperature preserve the contents for detailed analysis in the laboratory.