Original Gas in Place

Test Your Knowledge

Quiz: Understanding Original Gas in Place (OGIP)

Instructions: Choose the best answer for each question.

1. What does OGIP stand for? a) Original Gas In Place b) Oil Gas In Production c) Oil and Gas Industry Partners d) Original Gas Industry Production

2. Which of these is NOT a factor influencing recoverable reserves? a) Reservoir permeability b) Production technology c) The color of the reservoir rock d) Economic factors

3. OGIP represents: a) The total volume of gas that can be extracted from a reservoir. b) The amount of gas that is currently being produced. c) The total volume of gas originally present in a reservoir at standard conditions. d) The maximum amount of gas that can be extracted from a reservoir using current technology.

4. Why is OGIP an important concept in oil and gas exploration? a) It helps determine the best location to build a gas station. b) It helps estimate the potential profits from a project. c) It helps determine the best type of gas to extract. d) It helps determine the best time to start drilling.

5. Which of these is a step involved in estimating OGIP? a) Determining the reservoir's porosity. b) Analyzing the gas's flavor. c) Determining the reservoir's aesthetic appeal. d) Analyzing the gas's ability to conduct electricity.

Exercise: OGIP Calculation

Scenario:

You are an exploration geologist working on a new gas field. You have gathered the following information:

• Reservoir volume: 10 million cubic meters
• Porosity: 20%
• Gas Saturation: 75%
• Gas Specific Gravity: 0.6
• Reservoir Temperature: 100°C
• Reservoir Pressure: 300 bar

Task:

Using the information provided, estimate the OGIP of this gas field.

Assumptions:

• Standard conditions are 15°C and 1 atm.
• Use the following formula: OGIP = (Reservoir Volume x Porosity x Gas Saturation x Gas Specific Gravity x Reservoir Pressure) / (Standard Pressure x (1 + (Reservoir Temperature - Standard Temperature) x Gas Expansion Coefficient))

Note: You will need to find the gas expansion coefficient for the specific gas. You can research this online or use a reference book.

* Convert reservoir pressure to atm: 300 bar * 1 atm / 1.01325 bar = 296.07 atm
* Convert reservoir temperature to Kelvin: 100°C + 273.15 = 373.15 K
* Convert standard temperature to Kelvin: 15°C + 273.15 = 288.15 K
* Assume the gas expansion coefficient is 0.0035/K (This is a typical value for natural gas, but you should always consult specific data for the gas in question).

* OGIP = (10,000,000 m³ x 0.2 x 0.75 x 0.6 x 296.07 atm) / (1 atm x (1 + (373.15 K - 288.15 K) x 0.0035/K)) 
* OGIP ≈ 3,280,000,000 m³ of gas at standard conditions.

**Therefore, the estimated OGIP of this gas field is approximately 3,280,000,000 cubic meters of gas at standard conditions.**

Techniques

Chapter 1: Techniques for Estimating Original Gas in Place (OGIP)

This chapter delves into the various techniques employed to estimate the original volume of natural gas present within a reservoir. These techniques are crucial for understanding the potential resource and assessing its economic viability.

1.1 Volumetric Method

• This traditional method relies on the fundamental relationship between reservoir volume, porosity, and gas saturation.
• It involves:
  • Reservoir Characterization: Determining the reservoir's geometry, size, and boundaries using seismic data, well logs, and core samples.
  • Porosity Assessment: Analyzing core samples and well logs to estimate the percentage of pore space within the reservoir rock.
  • Gas Saturation Determination: Analyzing well logs and core samples to measure the proportion of pore space occupied by gas.
  • Gas Density and Compressibility: Determining the density and compressibility of the gas at reservoir conditions using compositional analysis and pressure-volume-temperature (PVT) data.
  • OGIP Calculation: Multiplying the reservoir volume, porosity, gas saturation, and gas density to obtain the total gas volume at standard conditions.

1.2 Material Balance Method

• This method utilizes a mathematical model that accounts for the depletion of reservoir pressure and the volume of gas produced.
• It requires:
  • Reservoir Pressure and Production History: Gathering data on pressure decline and cumulative gas production over time.
  • Reservoir Properties: Determining reservoir properties like porosity, permeability, and water saturation.
  • Material Balance Equation: Applying a complex equation to relate the initial gas volume, produced gas volume, pressure depletion, and reservoir properties.
  • OGIP Estimation: Solving the material balance equation for the original gas volume (OGIP).

1.3 Decline Curve Analysis

• This technique involves analyzing the production rate decline over time to estimate the initial gas volume in place.
• It requires:
  • Production Rate Data: Gathering data on the rate of gas production over time.
  • Decline Curve Modeling: Fitting the production data to various decline curve models to project future production and estimate initial gas volume.
  • OGIP Calculation: Extracting the initial gas volume from the decline curve model parameters.

1.4 Reservoir Simulation

• This sophisticated approach uses computer models to simulate the flow of fluids within the reservoir.
• It involves:
  • Reservoir Characterization: Defining the reservoir geometry, rock properties, and fluid properties.
  • Simulation Model Development: Building a detailed computer model of the reservoir.
  • Scenario Analysis: Running simulations with different production scenarios to estimate the original gas volume and assess production strategies.
  • OGIP Estimation: Extracting the initial gas volume from the simulation results.

1.5 Other Techniques

• Analogue Method: Using historical data from similar reservoirs to estimate OGIP.
• Geostatistical Methods: Utilizing statistical techniques to interpolate reservoir properties and estimate OGIP based on limited data points.

Conclusion

Choosing the appropriate technique for estimating OGIP depends on the availability of data, the complexity of the reservoir, and the desired level of accuracy. Combining multiple techniques can provide a more robust and reliable estimate of the original gas in place.