Page 293 - Applied Petroleum Geomechanics

282 Applied Petroleum Geomechanics

8.8.4 Real-time pore pressure detectiondfrom connection gas or total gas 322
8.8.5 Abnormal pore pressure indicators and detections in real-time drilling 323
8.8.5.1 Indicators from logging-while-drilling logs 324
8.8.5.2 Direct indicators of pore pressuredwell influxes and mud losses 325
8.8.5.3 Indicators from mud gas 325
8.8.6 Abnormal pore pressure interpretation from wellbore instability 327
8.8.6.1 Indicators from wellbore failures 327
8.8.6.2 Indicators from abnormal cuttings 328
8.8.7 Summary of real-time indicators for abnormal pore pressures 330
Appendix 8.1. Derivation of pore pressure prediction from porosity 330
Appendix 8.2. Derivation of sonic normal compaction equation 333
References 333
Abstract

This chapter systematically introduces pore pressure prediction methods. Pore pres-
sure prediction in hydraulically connected formations is studied with consideration of
the centroid effect. Pore pressure elevation by hydrocarbon columns or faults is
investigated to examine shallow gas flow. The commonly used methods for pore
pressure prediction from well logs are reviewed. Resistivity, sonic, porosity, and
d-exponent methods are modified using depth-dependent normal compaction trends
for easy applications. Methods and procedures of real-time pore pressure detection
and monitoring are presented. Abnormal pore pressure indicators in the real-time
drilling are summarized, which can be used for identifying underbalanced drilling
conditions to reduce drilling risks. Case studies in deepwater wells and shale oil and
gas reservoirs illustrate how to conduct pore pressure prediction in sedimentary
formations.

Keywords: Normal compaction trend; Pore pressure indicators; Pore pressure
prediction; Real-time detection; Resistivity; Porosity; Velocity and transit time; Well logs.

8.1 Introduction

Numerous hydrocarbon reservoirs are situated in abnormally high pore
pressure or overpressure formations. Drilling through these formations poses
serious challenges and potential risks to operations, if the overpressures are
not accurately predicted before drilling or while drilling. Abnormal pore
pressures can greatly increase drilling nonproductive time and cause serious
drilling incidents (e.g., fluid influx, pressure kick, well blowout). The ability
to safely drill through abnormal pressure zones requires a multidisciplinary
approach in understanding overpressure mechanisms, accurately predicting