Understanding Log Analysis in Reservoir Management

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Questions and Answers

What is the temperature gradient (m) given in the content?

0.0012°/ft

0.012°/ft (correct)

1.2°/ft

0.12°/ft

How can formation water resistivity (Rw) be determined?

By measuring directly in the well

By analyzing water samples and spontaneous potential logs (correct)

Only from a drill stem test

Only from water resistivity values

What is the formula used to calculate the formation temperature?

y = mx + d

y = mx^2 + c

y = c + m/x

y = mx + c (correct)

What value is used for the surface temperature (c) in the given calculation?

70°F Signup and view all the answers

At what depth (x) is the formation temperature being calculated?

8,000 ft Signup and view all the answers

What is porosity defined as?

The ratio of voids to the total volume of rock Signup and view all the answers

What does effective porosity exclude from its definition?

Pore volume occupied by adsorbed water Signup and view all the answers

What is the primary purpose of detailed petrophysical analyses?

To maximize the return on investment Signup and view all the answers

What type of logs are most frequently used in hydrocarbon exploration?

Open hole logs Signup and view all the answers

What is the significance of interconnected voids in a rock?

They enhance fluid transmission capabilities Signup and view all the answers

What is referred to as total porosity?

The sum of all void spaces in the rock Signup and view all the answers

What can be a significant challenge for geologists when interpreting logs?

The lengthy and unfamiliar terminology Signup and view all the answers

Why are open hole logs named so?

They are recorded in the uncased portion of the wellbore Signup and view all the answers

What is the primary purpose of maintaining a high density in the drilling mud?

To ensure the mud pressure exceeds formation pressure Signup and view all the answers

What is formed when solid particles from the drilling mud are trapped on the side of the borehole?

Mud cake Signup and view all the answers

What does the term 'mud filtrate' refer to in the context of borehole drilling?

Fluid that filters into the formation during invasion Signup and view all the answers

What causes the diameter of the borehole to potentially be larger than the size of the drill bit?

Washout and collapse of poorly cemented formations Signup and view all the answers

What is the resistivity characteristic of the mud cake formed in the borehole?

Greater than the drilling mud resistivity Signup and view all the answers

What is the invaded zone in the context of borehole drilling?

A zone where original fluid is replaced by mud filtrate Signup and view all the answers

Which of the following factors is NOT commonly associated with borehole size variations?

Temperature of the drilling environment Signup and view all the answers

Common borehole sizes usually range from which of the following dimensions?

7-7/8 to 12 inches Signup and view all the answers

What is the primary function of the flush zone in resistivity measurements?

To determine the resistivity of the invaded zone Signup and view all the answers

How is the residual oil saturation (Sro) calculated?

Sro = 1.0 - Sxo Signup and view all the answers

What are the depths of invasion that can be assessed with resistivity measurements?

Depth of both invaded and uninvaded zones Signup and view all the answers

What is the role of deep reading resistivity tools?

To measure the uninvaded zone's true resistivity Signup and view all the answers

What can shallow-reading resistivity logging tools determine?

Resistivity of the flushed zone Signup and view all the answers

In a transitional profile, which resistivity measurement indicates the properties of the transition zone?

Ri Signup and view all the answers

What is indicated by the uninvaded zone's resistivity?

Pores saturated with formation water Signup and view all the answers

Which statement about mud invasion is true?

Mud invasion can occur even in hydrocarbon-bearing reservoirs Signup and view all the answers

In a water-bearing zone, how does the resistivity of the flushed zone (Rxo) compare to the resistivity of the invaded zone (Ri)?

Rxo is greater than Ri Signup and view all the answers

What condition must be met for true resistivity (Rt) to equal wet resistivity (Ro)?

The formation must be completely saturated with formation water Signup and view all the answers

Which of the following statements is true about the resistivity values in a water-bearing zone?

Rt is the lowest resistivity Signup and view all the answers

What causes the decrease in resistivity of the invaded zone (Ri) as one moves away from the borehole?

Decreased amount of mud filtrate Signup and view all the answers

Which relationship between resistivity values is accurate based on water saturation in formations?

Rxo > Ri > Rt Signup and view all the answers

Study Notes

Formation Water Resistivity (Rw)

Resistivity of formation water (Rw) measured as m = 0.012°/ft or 1.2°/100 ft.
Values obtained from drill stem tests, water-producing wells, or water resistivity catalogs.
Can also be determined from the spontaneous potential log or apparent water resistivity (Rwa) method in water zones.

Formation Temperature Calculation

Temperature gradient (m) assumed to be 0.012°/ft.
Formation depth (x) is 8,000 ft, and surface temperature (c) is 70°F.
Key equation: y = mx + c, leading to y = (0.012 * 8,000) + 70.

Importance of Petrophysical Analyses

Enhanced management of hydrocarbon reservoirs through detailed analyses.
Monitoring, simulating, and enhancing reservoir performance critical for maximizing return on investment.

Porosity

Defined as the ratio of voids to total volume of rock, expressed as a decimal fraction or percentage (φ).
Total porosity accounts for all voids; effective porosity considers only interconnected voids that transmit fluids.

Well Logging Types

Open-hole logs used for hydrocarbon exploration, recorded in uncased wellbore portions.
Understanding various log types and their curves essential for interpreting potential hydrocarbon reservoirs.

Borehole Diameter and Characteristics

Borehole size determined by the bit's outside diameter; typically between 7-7/8 in. to 12 in.
Conditions such as washout or mud cake can alter borehole diameter.
Drilling mud maintains pressure to ensure it exceeds formation pressure, preventing collapse.

Invaded Zone

Area where original fluid is largely replaced by mud filtrate.
Efficient differentiation between the flushed zone, invaded zone, and uninvaded zone essential for interpretation.

Resistivity Measurements

Shallow-reading tools measure resistivity of the invaded zone (Ri); deeper tools measure true resistivity of the uninvaded zone (Rt).
Relationship between resistivities in water-bearing formations is Rxo > Ri > Rt.

Transition and Uninvaded Zones

Transition zone characterized by two invasion diameters and is more realistic than the step profile model.
Uninvaded zone contains uncontaminated pores filled with formation water, oil, or gas.
In this zone, true resistivity (Rt) equals wet resistivity (Ro), as it is completely saturated with formation water.

Summary of Resistivity in Water-Bearing Zones

Flushed zone resistivity (Rxo) is greater than invaded zone resistivity (Ri), which is greater than uninvaded zone resistivity (Rt).
This relationship is crucial for understanding water-bearing formations and their analysis through well logging techniques.

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Description

This quiz focuses on the essential properties of log analysis and its significance in reservoir management. It highlights the importance of detailed petrophysical analyses and their role in monitoring and simulating reservoir behavior. Gain insights into effective log interpretation techniques and concepts critical for advanced studies in the field.