Dynamic Well Testing in Petroleum Exploration and Development (eBook)

HuiNong Zhuang (Autor)

eBook Download: PDF | EPUB

2012 | 1. Auflage
728 Seiten
Elsevier Science (Verlag)
978-0-12-397785-4 (ISBN)

Infos

Data accumulation, analysis, and interpretation technology are critical in hydrocarbon exploration and extraction to maximize petroleum recovery and development. Dynamic Well Testing in Petroleum Exploration and Development presents modern petroleum exploration and well testing interpretation methods, emphasizing their application and development under special geological and development conditions in oil and gas fields. More than 100 case studies and 250 illustrations-many in full color-aid in the retention of key concepts. Extensive analysis of pressure data acquired from well testing through advanced interpretation software can be tailored to specific reservoir environments. This timely, state-of-the-art reference will be of particular interest to petroleum geoscientists and engineers working for oil and gas companies worldwide. - Includes graphs that can be used as templates to accurately plot hydrocarbon reservoir data accumulation, analysis, and interpretation - Field-practical case studies break information down into real-world examples which can be put into practice-not found in other books on well testing - Illustrations-many in full color-help you retain key concepts

Zhuang HuiNong, a professor and senior engineer, graduated from Peking University in 1962. He took part the research of development program in its early stage of Daqing Oilfield after graduation and then since 1965 he served in Shengli Oilfield and was interested in oil/gas well test. In 1980's took charge and operated interference tests and pulse tests in an oilfield in carbonate reservoir successfully; during this period he invented the interpretation type curves for interference well test in dual porosity reservoirs and applied these type curves in field practice; took charge of research of downhole differential pressure gauge and applied these gauges in data acquisition in fields and consequently won the invention award from China Nation Science and Technology Committee and was present the First International Meeting on Petroleum Engineering in Beijing in 1982,and his paper was published in the JPT. Since 1990 he served Research Institute of Petroleum Exploration and Development of CNPC, was concerned with the exploration and development of several large- or medium-scale gas-fields in China and has been doing dynamic performance research in about recent 20 years. Now is serving SPT Energy Group Inc. as its chief geologist. He has been devoting himself to dynamic performance analysis and well test for more than 40 years.

Textauszug

Chapter 2

Basic Concepts and Gas Flow Equations

Contents

1 Basic Concepts

1.1 Steady Well Test and Transient well Test

1.1.1 Steady Well Test

1.1.2 Transient Well Test

1.2 Well Test Interpretation Models and Well Test Interpretation Type Curves

1.3 Dimensionless Quantities and Pressure Derivative Curve in Well Test Interpretation Type Curves

1.4 Wellbore Storage Effect and its Characteristics on Type Curves

1.4.1 Implications of Wellbore Storage Effect

1.4.2 Order of Magnitude of Wellbore Storage Coefficient

1.4.3 Characteristics of Wellbore Storage Effect on Well Test Interpretation Type Curves

1.5 Several Typical Flow Patterns of Natural Gas and their Characteristics on Interpretation Type Curves

1.5.1 Radial Flow

1.5.2 Steady Flow

1.5.3 Pseudo-Steady Flow

1.5.4 Spherical Flow and Hemispherical Flow

1.5.5 Linear Flow

1.5.6 Pseudo-Radial Flow

1.5.7 Flow Condition in Formation Having been Improved or Damaged

1.6 Skin Effect, Skin Factor and Equivalent Borehole Radius

1.7 Radius of Influence

1.8 Laminar Flow and Turbulent Flow

2 Gas Flow Equations

2.1 Definition of Reservoir as a Continuous Medium

2.2 Flow Equations

2.2.1 Deriving Flow Equations Based on Three Basic Equations

2.2.2 Average Flowing Velocity and Flow Velocity of Unit Cell

2.2.3 Darcy’s Law Applied for Flow of Viscous Fluid

2.2.4 Continuity Equation

2.2.5 State Equation of Gas

2.2.6 Subsurface Flow Equations of Natural Gas

2.2.7 Dimensionless Expressions of Gas Flow Equations

2.2.8 Boundary Conditions and Initial Conditions for Solving Gas Flow Equations

3 Summary

Just as what was introduced in Chapter 1, this book tries to help reservoir engineers involved in gas field development to utilize knowledge of the well test and relevant computer software to resolve problems in gas reservoir descriptions and to establish a bridge linking well test interpretation results and the solution to gas reservoir development problems, thereby allowing well test results to play their due roles and make up its shortcomings and deficiencies that have long been existing in this field.

The interpretation and application of well test data fall into the category of “solving inverse problems” in the well test discipline. Solving an inverse problem does not require starting from deriving and solving the partial differential equations describing subsurface flow. However, readers are expected to have an overall understanding of well test theory, to know that it is strictly established on the basis of mechanics of fluids flow in porous media, that the methods and formulae applied in the well test were established through careful research and development done by several generations of scientists, and that these methods and formulae are therefore reliable and trustworthy.

In addition, the experiences gained by engaging in well testing for so many years also remind us that many basic concepts frequently encountered in our daily work seem sometimes specious. These concepts must be further elaborated clearly, their original definitions and basis must be found out, and they must be explained accordingly under gas field conditions and discussed when necessary.

1 Basic Concepts

1.1 Steady Well Test and Transient well Test

There are two kinds of well test, that is, steady well test and transient well test, if classified by the stability conditions of the flowing or working system during testing.

1.1.1 Steady Well Test

During steady well testing, the flow rates (including gas rate, oil rate, and/or water rate) and pressures (including bottom-hole flowing pressure and wellhead pressure) of the tested well (oil, gas, or water well) must keep steady under each working system (usually the choke size) or, from the requirement of engineering, their fluctuation must be less than a certain limit, which is regarded as basic steady state. The steady well test process is shown in Figure 2.1.

Figure 2.1 Variation of gas rate and pressure during steady well test.

Figure 2.1 often serves as the diagram of basic results of the steady well test. It shows the following:

1. The flow duration of individual selected flow rate.

2. Whether the flow rate has reached steady state within the selected time interval, and how much the steady flow rates are.

3. Under the selected flow rate conditions how much the producing pressure differential (the difference between formation pressure and flowing pressure) roughly is, and how much the ratio of the producing pressure to the formation pressure is.

The steady well test of gas wells is also called the back-pressure test, which is an important method for determining the deliverability of gas wells. Data obtained from a steady well test can be used to draw the relationship plot of flowing pressure (or producing pressure differential) and the flow rate, as shown in Figure 2.2a and 2.2b.

Figure 2.2 (a) The index curve (pwf vs qg) or IPR obtained from the back-pressure test of a gas well. (b) The index curve (Δp vs qg) obtained from the back-pressure test of a gas well.

The result obtained from the steady well test in oil wells is the productivity index Jo or the specific productivity index JoR, while it is generally the absolute open flow potential qAOF and the inflow performance relationship curve (IPR) that are determined from the back-pressure test of gas wells.

1.1.2 Transient Well Test

The transient well test is a well test method widely used during the exploration and development of oil and gas fields. Its procedure involves changing the working system of oil, gas, or water wells, such as opening the well under the shut-in condition or instantaneously shutting in the well that is originally producing so as to cause redistribution of pressure in the reservoir and then measuring the variation of bottom-hole pressure during the whole process. Based on pressure variation data, combined with the flow rate and the properties of the oil and gas and the reservoir, the characteristic parameters of the tested well and the area influenced by the testing, that is, in the tested zone, are studied. These parameters include formation permeability k, flow coefficient kh/μ, formation pressure pR, skin factor S, and characteristics of inner and outer boundaries.

Commonly used transient well test methods include pressure drawdown test, pressure buildup test, pressure fall-off test, injection well test, and multirate test.

1.2 Well Test Interpretation Models and Well Test Interpretation Type Curves

Just as described in Chapter 1, a well test analysis model simply means using physical or mathematical methods to reproduce the hydrocarbon flow process in the actual reservoir.

A physical model of a well test is the physical reproduction of flow in oil or gas layers. Such reproduction first offers a kind of physical description about the physical conditions of the oil and/or gas layers and fluid (oil, gas, and water) conditions in the layers, and it can also be achieved by material objects in a laboratory. For example, man-made or natural cores can be used to construct a formation model, which are saturated with oil and/or gas and/or water and pumped to simulate injection and withdrawal, and the pressure variation at individual points of which are simultaneously measured. There are some other physical models, such as the electric model and vertical pipe model.

A mathematical model of the well test, however, reproduces the flow process in a gas field using differential equations with proper internal and external boundary conditions (i.e., bottom-hole and formation conditions) and the initial condition of the well test. Also, it is the resolution of these differential equations that reflects the variation of pressure with time that reproduces the flow process. For well test analysis, the variation of pressure with time is usually expressed in graphical forms, that is, by a Cartesian plot of pressure vs time, semilog plot of pressure vs time, and log–log plot of pressure and its derivative vs time. Also, because the log–log plot can best reflect the flow characteristics, log–log plots are often used to represent well test analysis models in modern well test analysis.

A well test analysis model is used to interpret actual well test data, that is, to resolve the inverse problems; the log–log plot for this typical analysis model is called a well test interpretation type curve. There are...

Produkt-Details

• Erscheint lt. Verlag: 31.12.2012
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Geologie
• Themenwelt: Technik ► Bergbau
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• Themenwelt: Wirtschaft
• ISBN-10: 0-12-397785-1 / 0123977851
• ISBN-13: 978-0-12-397785-4 / 9780123977854