True Vertical Depth (TVD) in Reservoir Engineering

True Vertical Depth (TVD) is the vertical distance from a reference point (typically sea level) to a specific point within a reservoir, measured along a straight line perpendicular to the earth's surface.

In reservoir engineering, TVD is crucial because it helps us:

• Understand the vertical position of reservoir features: By knowing the TVD of different zones within a reservoir, we can understand the depth at which different formations, fluids, and pressures exist. This information is crucial for designing wells and optimizing production.
• Calculate the volume of the reservoir: TVD is a critical component in calculating the volume of the reservoir, which is essential for estimating the amount of hydrocarbons present.
• Determine the vertical extent of hydrocarbon accumulations: TVD helps us to understand the vertical limits of hydrocarbon accumulations within the reservoir, allowing for more accurate estimates of recoverable reserves.
• Analyze pressure gradients and fluid flow: By knowing the TVD of different points in the reservoir, we can analyze pressure gradients and understand how fluids flow within the reservoir. This information is critical for designing production strategies and optimizing well performance.

Why not just use measured depth?

While measured depth (MD) is the total length of a wellbore, it doesn't accurately reflect the vertical position of a point within the reservoir. This is because wells are rarely drilled vertically. They often follow a deviated path to reach target formations, which means MD doesn't accurately reflect the actual vertical distance to the reservoir.

Key points about TVD:

• TVD is always shorter than the measured depth (MD) of a well.
• TVD is calculated using survey data obtained during drilling operations.
• TVD is an important parameter in many reservoir engineering calculations and analyses.

In essence, TVD provides a more accurate representation of the true vertical distance within a reservoir, offering essential insights for understanding and managing the reservoir's characteristics.