Gas Injection

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Gas Injection.

Course Work

Of

Reservoir Engineering.

Eng. Guido Piccone.

Faculty of engineering, Science and the built Environment 2010-2011 M-Level.

23th of November 2010

Table Contents

Introduction 3

Chapter I 5

1.1. Mechanisms of the production in the oil field. 5

1.2 Types of gas injection 7

2. Chapter II. 10

2.1. Case study 1. 10

Mexico'sCantarell field 10

2.2. Case study 2. 12

ENHANCED OIL RECOVERY BY MISCIBLE CO2 INJECTION A CASE STUDY OF THE RANGLEY WEBER UNIT. 12

Conclusion. 18

References. 19

Figure 1. Solution Gas Drive. 6

Figure 2. Gas cap Drive. 6

Figure 3.Gas Injection internal or dispersed. 7

Figure 4. Internal gas Injection. 8

Figure 5.Location of the RWSU. 13

Figure 6. History RWSUproduction. 13

Figure 7. Process of CO2 Injection. 15

Figure 8. Incremental oil, Fractional Comparison 16

Figure 9. Curbing the increasing trend in gas rate. 17

Table 1. Showing comparison and criteria of Gas Injection. (Tzimas. E, 2005) 4

Table 2. RWSU Reservoir and Fluid Property. 14

Introduction

Oil production is usually carried out in two or three phases, given that it iseconomically viable, during the lifetime of a reservoir.

Initially the recovery process starts off with natural drive mechanisms of the reservoir, which is determined by a number of factors as will be discussed in this report, followed by a secondary recovery process as Enhanced Oil Recovery (EOR) using water or gas injection. With gas injection, the gas is injected into the reservoir; the gascreates favourable conditions which increase oil recovery. The injection of the gas into the reservoir has the following desirable consequences and they are:

1. It reduces the capillary forces that usually inhibit the flow of oil through the pores of the reservoir, by reducing the interfacial tension between the oil and the reservoir rock.

2. The gas results in the expansion of the oil volumewhich in return reduces the oil viscosity.

3. It develops complex phase changes in the oil which increases its fluidity.

4. It improves the volume sweep efficiency.

There are two main types of gas injection, and these are:

– Miscible Gas Injection: The gas is usually injected in the reservoir at or above the minimum miscibility pressure (MMP) which causes the gas to be miscible in theoil. However, this method is used more in the tertiary recovery method.

– Immiscible Gas Injection: The gas is injected below the minimum miscibility pressure, either into the gas cap or directly in the oil, this is done to maintain the pressure which in turn maintains the oil production.

The gases that can be used for injection include nitrogen, natural gas (hydrocarbons), and CO2.

1.1CO2 gas injection

CO2 gas injection has been in use for over 40 years, and recently it has been more appreciated as a carbon sequestration method. There are two types of CO2 injection that are being used worldwide:

– The Water Alternating Gas (WAG): In this method, the CO2 is injected into the well first followed by a water injection. The function of the gas here is to swell the oil andfluidise it, and then the water displaces the oil and pushes it towards the producing well.

– The Gravity Stable Gas Injection (GSGI): Here, the gas in injected in the crest where it forces the oil to move downwards towards the producing well

1.2 Nitrogen gas Injection

The process is similar to that of CO2 injection, however it behaves differently under varying conditions; at 4000 psiaNitrogen’s viscosity increases with temperature increment, and on the contrary, at 6000 psia and with increasing temperature increments, the viscosity decreases.

Other inert gases may be used for the conditional displacement by miscibility similar to the nitrogen injection done under high pressure. This strips hydrocarbons with low molecular weights from the oil causing a new two-phase equilibrium...