1806 words - 8 pages

Contents

1-Abstract 2

2-Introduction 3

3-Theory 4

3.1-Total and effective porosity: 4

3.2Primary and Secondary porosity: 5

4- Experimental Set-up and Procedure 5

4.1-Materials and equipment 5

4.2- Experimental set-up and procedure 5

5-Results and calculations 7

6-Discussion and conclusion 8

6.1- Discussion of the results 8

6.2- Conclusion 8

7- References 9

1-Abstract

The aim of this report is to be familiar with the basic procedures of preparing rock samples and to measure the density of and porosity of rock samples.

Firstly the rock size and mass was measured to determine the density and bulk volume using an electronic ruler and mass balance. Then using the ...view middle of the document...

These experiments only measure the effective porosity, which is of the main interest to petroleum engineers.

This report documents a laboratory experiment for measuring porosity and density of 6 different core plugs using a helium porosimeter, a mass balance and an electronic ruler. The report outlines theoretical concepts of porosity underlying the experiment and the experimental setups and procedures. This report also documents the results and calculations furthermore it goes through a brief discussion and conclusion of those results.

3-Theory

Porosity is defined as the ratio of void volume of the rock to the bulk volume. Pore spaces in the rock are filled with fluids which could be oil, gas or water. Porosity is essentially needed to estimate the potential volume of hydrocarbons in the reservoir rocks. Well sorted (grains of approximately all one size) materials have higher porosity than similarly sized poorly sorted materials (where smaller particles fill the gaps between larger particles). Figure 1 illustrates how some smaller grains can effectively fill the pores, drastically reducing porosity, while only being a small fraction of the total volume of the material. Porosity data is obtained from direct measurements on the core samples and/or indirectly from well logging. Mostly, porosity data from core samples is used to calibrate the data from well logs.

Figure [ 1 ] comparison of well and poorly sorted grains

The porosity is usually denoted by the symbol Ø and is calculated by the following equation

Porosity=Pore VolumeBulk volume

Expressed in terms of symbols, this equation is represented as:

Ø = Vp/Vb

In the equation above Vp represents pore volume of the rock and Vb represents bulk volume. Pore volume is the total volume of void spaces where as bulk volume is the total volume of the rock.

3.1-Total and effective porosity:

Porosity is classified as total and effective porosity. Essentially total porosity is the ratio of total void spaces to bulk volume of the rock and includes isolated pores and the space occupied by clay-bound water. Whilst effective porosity is the only the ratio of interconnected pores to the bulk volume and is the main interest to petroleum engineers.

3.2Primary and Secondary porosity:

Porosity for both sandstones and limestone’s can be greatly modified by post-depositional events or digenesis. Cementation, chemical action and fracturing are events which can modify the original porosity of rocks. The original porosity of a formation is usually referred to as primary porosity. Porosity modified by post-depositional processes is referred to as secondary porosity. (UNSW, 2012)

Direct measurements of porosity from core samples in laboratory are determined from bulk and grain volume of the core samples. For irregular shaped core samples, volume is determined by gravimetric methods. In gravimetric methods, the apparent loss in weight of the sample when immersed completely in liquid of known...

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