Application of Seismic Frequency Based Pore Pressure Prediction in Well Design: Review of an Integrated Well Design Approach in Deep Water Gulf of Mexico

Saeed Salehi Tim Mannon

doi:10.4172/2329-6755.1000125

Abstract

Improving well design has and always will be the primary goal in drilling operations in the oil and gas industry. To address this issue, an analysis of wellbore stability and well design improvement has been conducted. This study will show a systematic approach to well design by focusing on best practices for mud weight window projection for a field in Mississippi Canyon, Gulf of Mexico. The field includes depleted reservoirs and is in close proximity of salt intrusions. Analysis of offset wells has been conducted in the interest of developing an accurate picture of the subsurface environment by making connections between depth, Non-Productive Time (NPT) events, and mud weights used. Commonly practiced petro physical methods of pore pressure, fracture pressure, and shear failure gradient prediction have been applied to key offset wells in order to enhance the well design for a proposed well. For the first time in the literature, the accuracy of the commonly accepted, seismic interval velocity based and the relatively new, seismic frequency based methodologies for pore pressure prediction are compared. Each of these methods is compared to the petro physically derived mud weight windows for the key offset wells and the proposed well in this field, showing higher reliability in the frequency based approach. Additionally, the interval velocity method yielded erroneous results in a fast-rock-velocity channel zone and the near salt proximity environments, whereas the frequency Based method appeared unaffected by either of these factors.

Highlights

With oil and gas plays in the offshore domain moving into ever increasingly hostile drilling environments, the time is more than ever to focus on best practices for well design
One objective of this study is to present a systematic approach to mud weight window design that can be applied to any proposed development well project
The application of seismic interval velocity and frequency based pore pressure prediction will be completed for each key offset wells and the proposed well

Summary

Introduction

With oil and gas plays in the offshore domain moving into ever increasingly hostile drilling environments, the time is more than ever to focus on best practices for well design. By observing “Normal Compaction Trends” in interval transit time and resistivity log measurements with depth, they were able to develop empirical relationships based on data point deviations from the Normal Compaction Trend Line (NCTL) that could predict the location and magnitude of abnormal formation pressures along a wellbore trajectory. The interval travel times were plotted verse depth, and much like the Hottman and Johnson method, overlays were made which would predict pore pressure magnitudes based on empirical relationships between the travel time data and their departure from a normal compaction trend line [9]. The use of a fluid gradient and elevation change can be used to predict the pressure at each elevation within that sand; depending on the orientation of the dipping sand bed, the sand pore pressure Equivalent Mud weight (EMW) could be higher or lower than that of the surrounding shale formations [19]. If a well is being drilled in an orientation that is stable for a normal faulting regime and comes in close proximity to a salt diapir, that wellbore could become unstable and more susceptible to collapsed hole, breakout, or lost circulation [32]

Methods

Discussion of Results

Conclusions