Oil and Gas Reserve Estimation

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Questions and Answers

What does the unit-recovery factor for a saturated depletion type reservoir represent?

  • The total recoverable oil without any losses.
  • The oil initially in place minus residual oil at abandonment pressure. (correct)
  • The volume of water influx into the reservoir.
  • The cumulative production over time.

In a bottom-water drive reservoir, under what condition does this scenario occur?

  • The reservoir thickness exceeds the thickness of the oil column. (correct)
  • There is no water present in the reservoir.
  • The reservoir has a thin gas cap.
  • The thickness of the reservoir equals the oil column thickness.

Which method is commonly used to estimate remaining oil reserves based on performance trends?

  • Production Decline Curves (correct)
  • Pyramidal Formula
  • Volumetric Method
  • Material Balance Method

What is a primary characteristic of the dependent variable in production decline curves?

<p>Rate of production. (B)</p> Signup and view all the answers

What is typically plotted on the x-axis when estimating remaining reserves using production trends?

<p>Cumulative production or time. (B)</p> Signup and view all the answers

What can cause gradual changes in the production rate of a well?

<p>Decreasing efficiency of the lifting equipment. (D)</p> Signup and view all the answers

Which of the following best describes the volumetric method for oil recovery?

<p>Estimating oil recovery using stock-tank oil originally in place minus residual stock-tank oil. (A)</p> Signup and view all the answers

What is typically not used in the estimate of ultimate recovery based on performance trends?

<p>Stock change estimates. (C)</p> Signup and view all the answers

What does the variable 'N' represent in the equations provided?

<p>Reservoir oil in place, STB (A)</p> Signup and view all the answers

Which method is primarily used for estimating the initial reservoir oil volume 'N'?

<p>Material balance method (D)</p> Signup and view all the answers

How can the assumption that 'We' equals zero be validated?

<p>Comparing 'N' with the volumetric value of 'N' (A)</p> Signup and view all the answers

Which of the following methods is primarily used for estimating hydrocarbon resources?

<p>Material Balance Method (D)</p> Signup and view all the answers

What is the main purpose of the unit-recovery formula?

<p>To calculate potential ultimate recovery from a unit volume (B)</p> Signup and view all the answers

What is the purpose of net-pay estimation in petroleum reserves evaluation?

<p>To calculate the thickness of productive intervals (C)</p> Signup and view all the answers

Which value is used to assess if no water drive exists during early depletion stages?

<p>Volumetric method value of 'N' (A)</p> Signup and view all the answers

Which formula is often associated with determining reserves based on known recovery factors?

<p>Pyramidal Formula (B)</p> Signup and view all the answers

What is 'm' in the context of reservoir evaluations?

<p>The ratio between initial reservoir free gas volume and initial reservoir oil volume (B)</p> Signup and view all the answers

What is a key characteristic of reservoirs classified under volatile oil?

<p>They are produced at higher gravities than 45oAPI. (B)</p> Signup and view all the answers

What technique improves performance during later stages of oil depletion?

<p>Material balance method (D)</p> Signup and view all the answers

Which statement accurately describes the SPE-RMS approach to resource classification?

<p>It combines commercial certainty with recoverable quantities. (B)</p> Signup and view all the answers

Which factor is essential when estimating the cumulative water influx (We)?

<p>Reservoir pressure data (C)</p> Signup and view all the answers

What defines the recoverable quantity estimates of hydrocarbon-bearing reservoirs in the context of the SPE-RMS?

<p>Combination of recovery factors and project classifications (C)</p> Signup and view all the answers

Which type of reservoir fluid is primarily associated with condensation from a gaseous state?

<p>Gas-condensate (B)</p> Signup and view all the answers

What is a significant challenge in developing undeveloped reserves?

<p>Need for enhanced recovery techniques (D)</p> Signup and view all the answers

Flashcards

Unit Recovery Factor (Saturated Depletion)

Ratio of stock-tank oil initially in place (at pressure Pi) minus residual stock-tank oil (at pressure Pa), expressed per acre-foot.

Reservoir Oil in Place (N)

The total amount of oil initially present in the reservoir, measured in stock tank barrels (STB).

Cumulative Oil Produced (Np)

The total amount of oil extracted from the reservoir up to a particular time, measured in stock tank barrels (STB).

Water Drive Reservoir

Oil reservoirs where water influx increases oil production, typically from the reservoir edge or bottom.

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Gas-Oil Ratio (Rp)

The ratio of the volume of gas produced to the volume of oil produced, measured in SCF/STB.

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Bottom Water Drive

Water drive occurring when reservoir thickness exceeds oil column thickness, pushing oil upward from below.

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Ultimate Recovery Estimation

Predicting the total amount of recoverable oil from a reservoir by extrapolating performance trends.

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Gas Solubility Factor (Rs)

The volume of gas dissolved in a unit volume of oil at reservoir conditions.

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Production Decline Curves

Graphical representations of oil production over time, used to estimate remaining reserves.

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Water Influx (We)

The volume of water entering the reservoir during production, measured in barrels.

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Rate-Time Curve

A type of production decline curve where oil production rate is plotted against time.

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Material Balance Equation

An equation used to estimate the original oil-in-place (N) by relating production data to reservoir properties.

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Water Production (Wp)

The cumulative volume of water produced, measured in barrels.

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Rate-Cumulative Curve

A type of production decline curve where oil production rate is plotted against cumulative production.

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Volumetric Method

A method for estimating initial oil-in-place (N) by calculating the reservoir volume and multiplying by the oil saturation.

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Production Rate (Dependent Variable)

The variable measured and plotted in production decline curves.

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Unit Recovery Factor

The theoretical maximum amount of recoverable oil from a unit volume of reservoir rock.

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Reservoir Thickness

The vertical extent of a reservoir, impacting water drive mechanisms.

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Oil Column Thickness

The thickness of the oil layer in a reservoir.

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Undeveloped Reserves

Reservoir resources expected to be recovered from new wells or deepening existing ones, or requiring substantial investment in well recompletion or improved recovery facilities.

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SPE/WPC/AAPG Petroleum Resources Management System 2007

A system for guiding consistency in estimating hydrocarbon resource quantities, incorporating industry best practices and a rigorous approach to hydrocarbon-bearing reservoirs.

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Resource Management System

A two-dimensional framework classifying projects by commercial certainty and categorized by recovery certainty in petroleum resources evaluations.

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Oil Reservoir

A reservoir containing liquid hydrocarbons (oil).

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Gas/Gas-Condensate Reservoir

A reservoir containing mostly gas, which may contain condensate that forms as the gas pressure decreases.

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Volatile Oil Reservoir

A reservoir producing oil from deep depths, characterized by high API gravity, high formation volumes, and high solution gas-oil ratios.

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Condensate

A light hydrocarbon fluid, often produced by retrograde condensation from reservoirs with high-pressure gas.

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Black Oil

Any liquid hydrocarbon other than oil, gas condensate, or volatile oil.

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Study Notes

Oil and Gas Reserve Estimation

  • Calculation of hydrocarbon reserves and prediction of future recoveries are crucial for evaluating oil/gas properties.
  • Reserves represent the recoverable oil and/or gas, and production rate determines the economic viability.
  • Primary recovery involves natural reservoir forces, while secondary recovery (secondary reserves) uses subsequent methods.
  • Reserve evaluation should be performed periodically to ensure their accuracy, which depends on available data quality and quantity.
  • Reserve estimations become more precise as more data accumulates throughout exploration and production stages.
  • Stages of reserve evaluation include: prior to drilling and development, just after drilling and completion, after one year of production, when production declines, and at depletion stage.

Methods for Analyzing Oil Reserves

  • Volumetric calculation, material balance, production decline curves, and comparison with similar properties are common methods of estimating reserves.
  • Comparative methods, including reservoir comparisons and field comparisons, are used.
  • Different methods are applicable at various stages of the property's life, with varying accuracy percentages.
  • Different methods are used for evaluating oil and gas properties (oil-in-reservoir, free gas, solution gas) with specifics calculations and formulas

Reserve Classification

  • Reserves are classified as proved, probable, and possible (SPE/WPC classification).
  • Proved reserves are estimated with reasonable certainty.
  • Probable and possible reserves have lower certainty about recoverability.
  • Reserve status categories define the development and producing status of wells or reservoirs (developed/producing/undeveloped).
  • Unproved reserves are further divided into probable and possible subgroups.

Production Decline Curves

  • Production decline curves show the relationship between production rate, time, and cumulative production.
  • Production decline curves are used to estimate ultimate recovery and remaining reserves using different types of declines (constant percentage, hyperbolic, harmonic curves), using data such as production rate over time, or water percentages.
  • Several different types of curves exist, including those representing production rate against time or cumulative production.

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