Seismic velocities are derived from multichannel seismic reflection data. These velocities provide a two- and three-dimensional image of the subsurface but are of lower resolution than the log-based approaches discussed in Chapters 5 and 6. Seismic velocities are often the first information available to predict pressure in frontier basins. I discuss how to invert velocity from seismic data and some of the challenges therein. Once the seismic velocities are derived from the seismic data set, the approaches to predict pressure are identical to the techniques presented in Chapters 5 and 6. I then present two examples of how to predict pressure with the vertical effective stress method. I close with a discussion of how to predict pressure where complex stress states are present with an approach called the full effective stress method. Several recent review papers summarize the approach of pressure prediction from seismic velocity (Chopra & Huffman, 2006; Dutta, 2002b; Sayers et al., 2002).

Mudrock is the most abundant material in the uppermost 5 km of the Earth’s crust (Petley, 1999). It has low permeability and undergoes enormous compaction during burial. When mudrock is loaded sufficiently rapidly (e.g., by burial or tectonic loading), the load is borne by both the solid grains (as effective stress) and the pore fluid (as overpressure) because the fluid cannot escape at the rate the loading occurs. The compressibility of the rock defines how much fluid will be expelled, and its permeability defines how rapidly that fluid can be expelled. Because of mudrock’s high compressibility and low permeability, these overpressures can be maintained for geological timescales. Thus, the compaction behavior of mudrocks is one of the most important controls on whether overpressures will form. The degree of compaction is a sensitive indicator of the effective stress. I show in Chapters 5 and 6 how the compaction state is used to interpret the effective stress and ultimately the pore pressure.

In this chapter, I review how overpressure is generated and preserved in sedimentary basins. I begin by describing how pore pressure is generated and how it dissipates under conditions of uniaxial strain. I then explore the overpressure that results during sedimentation under conditions of vertical uniaxial strain. I present several numerical solutions in one and two dimensions to extend these concepts. I illustrate how these types of basin models provide insight into the evolution of pressure and stress in basins. I also use these results to explore the role of thermal expansion and smectite-illite diagenesis in generating pore pressure. I then discuss hydromechanical models that couple the full stress state with pore fluid flow under three-dimensional strain. I use these models to illustrate the role of non-uniaxial loading in salt systems and thrust belts. Finally, I explore the potential role of viscous compaction in pore pressure generation.

In Chapter 5, I described how to predict pressure from a single normal compaction trend (NCT). Given the porosity, a compaction trend, and the total vertical stress, the pore pressure is determined (e.g., Eq. 5.2). This is a simple way to predict pressure that is useful, fast, and intuitive. Unfortunately, it does not successfully predict pressure in many settings. This is illustrated in Figure 5.4 where the normal compaction trend approach underpredicts the observed pressures.

I describe three mechanisms by which traps fail (Fig. 9.1), and I describe how to predict the maximum column of immiscible fluids (e.g., oil, gas, CO2) that can be trapped. I first describe capillary sealing (Fig. 9.1a) and then explore two types of mechanical seal: hydraulic fracturing (Fig. 9.1b) and shear failure (Fig. 9.1c).

As described in Chapter 10, the water phase pressure within a laterally extensive aquifer bounded by overpressured mudrocks follows the hydrostatic gradient. As a result, at structural crests, the effective stress is low because the pore pressure in the reservoir follows the hydrostatic gradient but the overburden stress follows the lithostatic gradient. There is a limiting case where the structural relief of the permeable body is so large that the aquifer pressure converges on the least principal stress and mechanical failure of the overlying seal occurs.

The Deepwater Horizon blowout of the Macondo well in Mississippi Canyon block 252 in the deepwater Gulf of Mexico began on April 20, 2010 (Figs. 1.1 and 1.2). Eleven people died and approximately four million barrels of oil leaked into the Gulf of Mexico (Boebert & Blossom, 2016). Through this event, the general public became aware of the enormous pressures encountered in sedimentary basins and of the extraordinary complexity and risk associated with finding and producing hydrocarbons in the deep ocean.

In this chapter, I describe how to characterize reservoir pore pressures that are under capillary and gravity equilibrium (e.g., Fig. 2.1). This is approximately the state of a geological reservoir prior to production. Pore pressure is commonly described with a pressure versus depth plot (Fig. 2.1b). The reservoir pressure (and average equivalent density (mud weight) plots (Fig. 2.1c, d).

Total stresses are an important control on pore pressure and fluid flow in sedimentary basins. The magnitude of the total stresses must be known in order to estimate the pore pressure. When pore pressure exceeds the least principal stress, hydraulic fracturing can occur and, if so, fluids are rapidly drained. This can occur naturally or during drilling. I first describe how to estimate the overburden stress, which is commonly assumed to equal the vertical stress and the fracture initiation pressure in a borehole. Zoback (2007) provides an extensive overview of these issues.

In this chapter I describe how to predict pressure from the compaction state of mudrocks. The compaction state is either measured directly (e.g., from cuttings and core) or indirectly (e.g., from resistivity, velocity, or density). I present a detailed example from the Eugene Island 330 (EI-330) oil field, Gulf of Mexico. I then review two common challenges: (1) how to pick mudrocks and (2) how we establish normal compaction trends in overpressured basins. I close with a review and comparison of five different compaction models.

I have focused on interpreting pressure in one dimension (e.g., in a well profile). However, one of the most fundamental advances in the field of pore pressure prediction in recent years is the recognition that pressure distribution varies systematically and predictably in three and even four (time) dimensions as a result of the presence of permeable and laterally continuous beds (commonly sandstones) that are encased in low permeability mudrocks. In overpressured basins, these permeable bodies provide pathways that focus flow and perturb the pore pressure distribution. This process has been termed “flow focusing,” “lateral transfer,” and the “centroid effect.”