The Subsurface Environment

Revision:

1. Seal2. Structural trap3. Stratigraphic trap

Introduction

We shall discuss about subsurface waters

The effects of pressure and temperature on the

condensation and evaporation of gas and oil.

Fluid dynamics in sedimentary basins

Genetic ClassificationNormally, four types of subsurface water can be defined according to their genesis:

1. Meteoric waters: Occur near the earth surface. Involved in hydrogeological cycle.

2. Formation waters (connate waters): water trapped in the pore spaces or rocks in sedimentary basins, and have not recently been involved in the hydrogeological circle. These waters evolve with time as a result of water-rock interactions and gain high salinity.

3. Juvenile waters: These are igneous or metamorphic origin

4. Mixed water

Meteoric

Mixed

Connate

Juvenile

Settings of Earth’s Water Observe all the places where

water is present

Rivers

Oceans: 96.5% of near-surface water

Lakes: fresh or salty

Swamps and wetlands

Atmosphere

Glaciers: 69% of freshwater

Biological water

Groundwater: 30% of freshwater

Water in minerals: may be large amount

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How Does Water Move? Observe how water moves between settings

Air currents

Evaporation(oceans, lakes, rivers,…)

Condensation Precipitation(rain, snow, hail)

RunoffInfiltration:

water seeps

into ground

Groundwater flows

Groundwater flows onto surface

Most precipitationinto ocean; some evaporates on way down

Transpiration from plants

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Reduction potential (also known as redox potential, oxidation / reduction potential, ORP, pE or Eh) is a measure of the tendency of a chemical species to acquire electrons and thereby be reduced. Reduction potential is measured in volts (V), or millivolts (mV).

Each species has its own intrinsic reduction potential; the more positive the potential, the greater the species' affinity for electrons and tendency to be reduced. ORP is a common measurement for water quality

Note: Conductivity increases and gradient decreases with depth & declining porosity

Regional variations in heat flow affect petroleum generation. In areas of high heat flow & high geothermal gradient, the optimal tempt. Will be reached at shallower depth.

Questions?