Systems for collecting and preparation of oil and gas and criteria for their selection

Diplomarbeit von Muhammed Abed Mazeel

Introduction:

The production of oil is a complex technological procedure consisting of several equally important segments. One of the most important phases is the collection and preparation of oil, which affects the process of production from technical as well as from economical aspects. The choice and method of designing systems for oil collection and preparation is a very complex task that depends on the number of concrete parameters; this carries with it, above all, the difficulty in finding technology that will enable optimal work of wells as well as finding the continually and quality functioning of the entire production process. It is important to mention that each well is a case in itself; there are no broad or typical solutions for oil collection and preparation. Each production project on a field is involves individual solutions dependent upon situation-specific conditions.

The most important factors in finding the best solutions are experience and knowledge of problem-solving methods in similar fields worldwide. As this is the case, this thesis is based on analysis of a selection of different fields from around the worlds that, combined, represent one system of oil collection and preparation and should satisfy even the strictest criteria.

At oil-gas field (X), 27 wells are drilled and prepared in the development phase for oil and gas production. The average production of peripheral wells involves around 20 m3/24h of oil, 10 m3/24h water, 800 m3 s/24h gas; while central wells involve the production of 35 m3/24h oil 1000 m3 s/24h of gas. Pressure at the well head of the well is 30 [bar], and the temperature is 30° C. The shape of the field and layout of wells are shown in diagram (1).

The following are needed to define the design:

- optimal scheme for collection of production fluids; - optimal technological scheme for collective station with basic elements; - basic parameters of all elements for collective station.

When defining the collection scheme, it is necessary to take in account the number of wells, geographic layout of the wells, technical and economical functionality of the chosen scheme of collection etc. In defining the scheme of the collective station, it is necessary to design technology that enables the collection of produced fluids and their separation as well as the preparation of further transport, disposing of and sending the water without endangering the human environment etc. Additionally, the technology of the collective station must ensure the continuous monitoring of elements of station as well as each well in order to observe well behaviour and adjust regimes of production according to conditions in wells.

When assembling a collective station, it is necessary to design equipment that enables functionality of the station. That means designing measuring separators, dehydrators, reservoirs for hydration and storage, systems for collecting and measuring the gas, and onward transport, etc.

Table of Contents:

1.	INTRODUCTION	1
1.0	ASSIGNMENT	2
1.1	Entry data for defining-projecting system for collecting and collective station	3
1.2	Physico-chemical characteristics of layer fluids	5
2.0	SYSTEM FOR COLLECTING PRODUCED FLUIDS	6
2.1	Introduction	6
A.	Individual / single system	8
B.	Group system	8
C.	Central system	9
2.2	Basic characteristics of oil field	10
2.3	The choise of system for collection	12
2.4	Oil pipeline for the well	14
2.4.1	Introduction	14
2.4.2	Calculation of temperature fall	17
A.1	Input data for calculation	17
A.2	Procedure of calculation	18
2.4.3.1	Equation for pressure fall at isotermal oil flow	23
a	For laminar flow	23
b	For turbulent flow	23
2.4.3.2	Equation for pressure falls at non isothermal flow	24
a	laminar flow	24
b	turbulent flow	24
2.4.4	Mechanical calculation of oil pipeline for well	31
2.4.5	Underground corrosion	33
2.4.6	Isolation of pipeline	36
2.4.7	Cathodic protection	37
3.0	COLLECTIVE STATION	40
3.1	Introduction	40
3.2	Technical description of collective station	41
3.2.1	Separators	42
3.2.1.1	Horizontal cylindrical two-phase separators	44
3.2.1.2	Vertical cylindrical two-phase separators	47
3.2.1.3	Spherical separators	49
3.2.2	Multilevel separation of oil and gas	51
3.2.3	Selection of separation system at collective station	62
3.2.3.1	Two-phase vertical measuring separator of working pressure 16bar	63
3.2.3.2	Cumulative two-phase vertical separator of working pressure 16bar	65
3.2.3.3	Cumulative two-phase vertical separator of working pressure of 3 bar	67
3.3	Measuring of regulation	69
3.4	Dehydration of raw oil	71
3.4.1	Emulsions	71
3.4.2	Mechanical dehydration of oil	72
3.4.3	Electrical dehydration of oil	73
3.4.4	Physical-chemical dehydration of oil	73
3.4.5	Oil preparation / dehydration / at oil field	74
3.5	Disposal of layered water	78
3.5.1	Solving problems of disposal of layered water at considered field	80
3.6	Reservoirs for collecting the oil	83
3.7	Despatching the oil	86
3.8	Supporting system	87
4.1	Measures of protection of workforce, facilities and equipment	89
4.2	Measures of protection from explosion, fire and fire extinguishing plan	90
	SUMMARY	91
	LITERATURE	93

Textsample:

Chapter 2.4.6, Pipeline Insulation :

Basic passive protection of pipeline from the aggressive influence of field activities is called pipeline insulation. Before laying the pipeline into canal, it is purposely insulated to stop direct contact between pipelines with aggressive surroundings.

In order to ensure quality insulation, it is necessary to prepare the pipes to lay down (attaching) the insulation. Immediately before attaching insulation, the surface of the pipes must be completely clean of metal shine, what means that dirty substances like paint, old insulation, oil corrosive products, mud, dust humidty, etc. must be removed. Before mechanical cleaning, oil and grease are easily removed by vaporizable solvents.

Mechanically cleaning pipes involves using wired brushes. It is important to remember that pressure of the brushes on the pipes needs to be adjusted correctly to enable the cleaning of the metal shine from the pipes. This is due to the fact that the brushes are warn out at the time of replacement.

A basic layer of primer is put on the quality cleaned and dusted pipe. The reason for this is multi-fold: primer contains materials that neutralize the remaining products of corrosion, fills small uneven areas on pipe surface, and enables adhesion of pipe insulation.

Primer needs to be evenly spread on the entire surface of pipe in the quantity that will enable the neutralization of all remaining corrosion products, filling all uneven areas on pipe surface and enabling enough solvents for valid attachment of insulation onto the pipe. This amount depends mainly on the quality of the surface of the pipe (if it is smooth or corroded) and is defined by the manufacturer. The type and sort of primer that is being used must be compact with insulation that is laid over the primer onto the pipe.

As per the rule, primer should always be used as well as the insulation from the manufacturer. Tape for insulation is two-sided. The tape ‘body’ itself, which creates insulation and is the same shape as thermoplastic masses, is an attached layer of butyl rubber. Tape for insulation is wrapped on the primer treated pipeline so that the side of insulation with butyl rubber comes into contact with the primer. Under the influence of the primer, the insulation attaches to the pipelines, that is, chemical bondage happens between the primer and butyl rubber, what gives very strong connection between pipeline wall and isolation.

Normal insulation tape is created by wrapping it and folding it over 10 to 25 mm, depending on the pipeline diameter. In wetlands and very aggressive fields, enhanced insulation is used. While attaching the insulating tape, the same machine is laying a protective paper tape, which is intended to keep the insulation from mechanical damages when lowering the pipeline into dugout and filling it.

Just before lowering the pipelines into the dugout, it is necessary to test the electro-permeability voltage from 15 to 20 KV, depending on the quality of used insulation. With pipelines that deliver oil and gas to the complex ‘Mokrin – Jug’ after 30 to 60 days, the insulation’ condition should be tested by a detector. It may be necessary to dig up and repair the insulation in places where damages has occurred during the lowering of pipelines into canal or during filling or settling of fields.

After five years of pipeline exploitation, detailed testing of the pipeline insulation is necessary as well as eventual reparations. More tests should follow in the seventh year of exploitation. These tests will optimize the cathodic protection and extension of the pipeline’s lifetime.

At intersections with roads, pipeline insulation is enhanced additionally, and from its protection pillar it is separated by placing insulation distance spacers that keep the pipeline centered in the protection column.

Cathodic Protection:

Insulation of pipeline, even that of high quality and precision, has a limited life span because it is subjected to relatively rapid destruction due to aging and mechanical damages.

Only eliminating corrosion processes or minimizing them will in turne extend the life span of underground pipelines. Changing the energy condition of pipeline, which is done by cathodic polarization, results in counter currents to the corrosion currents which stop the corrosion processes. At cathodic polarization, pipeline potential becomes more negative than the most negative electrode of a multi- electrode system. This is that same as pipeline in the ground where oxidation of metal is thermodynamically impossible.

Pipeline is considered protected from corrosion if it ultimately achieves a potential of minimum – 0,87 V, measured by protective copper – copper sulphate control electrode.

The system of cathodic protection consists of:

- correcting unit – cathodic protection station; - anodic bed; - anodic, drainage and control measuring columns and cables.

Cathodic protection stations are used for the polarization of the pipeline onto the protective potential. The cathodic protection station is constructed for outer assembly onto its own base with extraction cables for feeding the station itself, as well as for anodic connection, projected structures and control probes.

In order to simplify achieve control, cathodic protection stations are equipped with an amper measuring gage, voltmeter and counter.

An anodic bank is used as a positive pole of cathodic polarization with the purpose of protecting from corrosion. Position and distance of the anodic bank from the pipeline depends on the length of the protection zone that the station with that bank covers, position of pipelines, specific electric current field resistance and other factors.

Anodes are being worn out by the transfer into ionic condition during the system operation of cathodic protection and therefore need to be replaced. Banks are designed for a normal operating time of 10 years; therefore it is necessary to calculate the time and replace them during regular maintenance of the cathodic protection system.

Anodes are by rule built in buffer layers made of coke flour, and their individual cables are brought into an anodic column where they are attached to an anodic cable.

For control and set up of the system of cathodic protection, it is necessary to put control-measuring extractions on all characteristic places.