Review of Heavy Oil: Formation, Properties and Recovery

Introduction

Oils with highly high densenesss and viscousnesss are termed as heavy oils. They are composed of long and high molecular weight compounds. Heavy oils are categorized with scope that is less than 220API to 100API ( American Petroleum Institute ) gravitation. Heavy oils that are less than 100API are to be referred as the excess heavy oil or Bitumen. The fluctuation between the excess heavy oils and bitumen is non merely the affair of API gravitation or their chemical composings but their Viscosity. The excess heavy oil is a type of oil that may resemble pitch sand bitumens and do non flux easy. They are recognized as holding mobility in the reservoir when compared with pitch sand bitumen which is incapable of mobility under the reservoir conditions. The word pitch sand is used to depict the sandstone reservoirs that are impregnated with a heavy and syrupy black petroleum oil that can non be retrieved through good conventional production techniques. Bitumen, referred as native asphalt includes a broad assortment of ruddy brown to black stuffs of semisolid, syrupy to brittle character that can be in nature with no mineral dross or with mineral affair contents that may transcend 50 % by weight. Bitumen is more syrupy than excess heavy oil at reservoir force per unit area and temperature conditions. Bitumen is immobile and excess heavy oils have some grade of mobility at reservoir conditions. The ultra-heavy or excess heavy oils are denser than that of H2O which has an API gravitation of 100API. While the gravitation units API, do non depict the whole fluid belongingss of the petroleum which is represented by the oil viscousness. Like some petroleums might be of low gravitation but they have comparatively low viscousness at reservoir temperatures when compared with lighter petroleums. Heavy oils occupies scope along the continuum between ultra-heavy oils and visible radiation oils.

The above estimations are mentioned by the Energy Information Administration ( EIA ) . EIA revealed that there were 1646 billion barrels of proven militias in 2013.

Globally, the recoverable militias of heavy oil and natural bitumen are equal to the staying militias of the conventional oil. Harmonizing to the informations analyzed informations Middle East states dominates in footings of the conventional oil militias while the South America, well the Venezuela leads the universe in footings of the heavy oil militias.

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Harmonizing to the above representations of conventional oil, heavy oils and bitumen sedimentations, the conventional oil production in Canada has diminution over the past few old ages from 1.2 million bd to 1 million bd including the visible radiation and medium classs oil every bit good as the heavy oil from Alberta and Saskatchewan Fieldss as of 2006. Harmonizing to the Canadian Association of Petroleum Producers ( CAPP ) , during the same period of five twelvemonth span from 2001 to 2006 the entire production from the mined oil littorals and oil littorals produced in situ by the assistance of Steam Assisted Gravity Drainage ( SAGD ) or may be through other methods increased from the 659000 bd in 2001 to 1.1 million bd in 2006 and this estimations might travel every bit high as 4 million bd in 2020. Russia has approximately 246.1 billion barrels of natural bitumen of which 33.7 billion barrels which is about merely the 14 % of entire is recoverable. The staying 86 % can non be realistically recovered as they exists in distant countries or scattered in many little sedimentations.

The nature of heavy oil is a job for recovery operations and for polishing due to high viscousness due to which makes the rendering recovery disbursal and the presence of sulfur content may be high and increases the disbursal of polishing the oil. When compared to conventional crude oil, heavy oil typically has the low proportions of volatile components with low molecular weights and well higher sums of high molecular weight compounds of lower volatility. The high molecular weight fraction of heavy oils are comprised of complex mixture of different molecular and chemical types incorporating a assorted bag of compounds which might non needfully be merely paraffin components or asphaltene components with higher thaw points and pour points that may greatly lend to hapless fluids belongingss and low mobility of the heavy oil. The presence of asphaltene components are non merely the primary cause for the high specific gravitation of the heavy oils nor are the premier cause for production jobs. It is besides indispensable to see the content of rosin components and aromatic components presence in the heavy oil during its recovery and production.

Heavy oil, as a resource is ever overlooked due to its trouble and the higher production costs involved in conveying the heavy oil onto the surface from reservoirs. As described by the geochemists that when crude oil beginning stone is generated, the petroleum oil produced by it is non heavy but it becomes heavy after the significant debasement during migration and after the entrapment. Degradation occurs through a assortment of biological, chemical and physical procedures in the earth’s subsurface beds. Bacteria borne by surface H2O metabolise the paraffinic, napthenic and aromatic hydrocarbons into heavier molecules. Formation Waterss besides remove hydrocarbons by solution, rinsing off lower molecular-weight hydrocarbons, that are soluble in H2O. The petroleum oil besides finally degrades by the devolatilization if hapless quality seals allow lighter molecules to divide and get away. The heavy oil typically forms from the younger geological stone formations like Pleistocene, Pliocene and Miocene stones. Those reservoirs possess the tendancy to be shallow deepnesss and less effectual seals in the stone formations.

By early periods of 1900s, new progressed oil recovery procedures were deevloped such as Cold Production which is a primary recovery procedure. By executing the Cold Production at reservoir temperatures, the recovery effeciencies range from merely 1 % to 10 % boulder clay it reaches the maximal economical recovery factors. Oilfield companies requires long term investing for heavy oil recovery and due to the ground that heavy oil creates conveyance troubles, is a more dearly-won and polishing techniques for bring forthing marketable merchandises. Therefore their engineering value is assessed by their ability for cut downing its entire cost. Most of the heavy oil Fieldss are shallow makes the boring costs non a dominant factor but the increasing factor of figure of many-sided Wellss and horizontal Wellss makes it to present some costs durng the development phases. Within these costs, the primary costs if for the doing the heavy oil to mobilise by shooting the steam required. Every part in the universe has oil possessing different physical belongingss and is at different phase of procedure adulthood, therefore every part uses different development and production techniques forheavy oil recovery.

Mechanism of formation of Heavy oil:

As the specific gravitation of reservoir oil lessenings with deepness, API graity additions with deepness. The ripening phenomenon of oil takes topographic point in beginning and reservoir stones which makes the kerogen bring forthing lighter oil with deepness in the latter. Hence, the mean tendency observed worldwide is that the higher API gravitation oil is found at th increasing depths though less oil is produced with deepness. This must be pointed out that these are general tendencies but there are exclusions.

There are assorted procedures that change the original oil that is produced during the migration procedure of oil and due to its subsequent accretions. Different procedures inculdes the biodegradation, H2O lavation, oxidization, deasphalting/evaporation and discriminatory migration of the igniter constituents.

Biodegradation of the petroleum oils can alter the composings and physical belongingss over a certain geological timescales. Different micro-organisms that are present in the deposits of the oil bearing stones and bearing the crude oil reservoirs. They utilize the hydrocarbons as the beginning of C for their metabolic procedures. That procedure may be aerophilic or anaerobiotic. Largely the hydrocarbons are oxidized into intoxicants and acids. Simple consecutive ironss are prefered, but as the biodegradation continues, more of the complex molecules are increasingly being consumed. The long chained paraffins are oxidized for giving di-acids. Similarly, napthene and aromatic rings are oxidized to di-alcohols. This biodegradation phenomenon consequences in the loss of saturated and aromatic hydrocarbon content, roll uping rosins and asphaltenes and besides lessening of API gravitation which autmatically defines as addition in denseness of the oil. The biodegradation procedure an go through if the reserrvoir temperatures do non transcend 800to 820.

Heavy oils influence on Physical Properties of Rocks During Production:

  1. Heavy oils have a shear modulus, act like a solid at low temperatures.
  2. They are strongly temperature dependant.
  3. Gas coming out of the solution might be it smallest sums can bring forth a big geophysical signature.
  4. Heavy oils normally acts as the cementing agent in unconsolidated littorals.
  5. During the production, reservoir stone matrix is frequently changed structurally.
  6. Physical belongingss of the stones possesing heavy oils are largely teperature dependant and frequence dependant every bit good.
  7. Simple Gassmann permutation will neglect in heavy oil reservoirs.

Crude oils which chiefly has hydrocarbons or the coompounds consisting H and C merely. Other elements such as S, N and O are besides present in small sums and are combined with C and H in complex molecules. As these oils get heavier and becoome more viscours, their composing becomes complex and they forms concatenation and sheet constructions with the addition in thir molecular weights.

Heavy oil, unlike conventional crude oil can non be recovered as an accretion unless there is any reservoir trap and that requires the boundary between the cap stone or any other waterproofing agent, and the reservoir stone by and large be in a bulging upward projection form, but the exact signifier of the boundary varies widely. Many of the oil and gas accumuylations are trapped in the anticlines or domes, these constructions are more conviniently detected than any other types of traps.

Heavy Oil Recovery Techniques:

Surface excavation:

Surface excavation procedure is a wide class of excavation in which dirt and stone overlying the mineral sedimentations are removed. It is the antonym of belowground excavation, in which the overlying stone is left in topographic point, and the mineral removed through shafts or tunnels. Surface excavation began in the mid-sixteenth century [ 1 ] and is practiced throughout the universe, although the bulk of surface excavation occurs in North America.

Surface excavation consists of three chief stages. After depriving off and carrying the site’s peculiarly fertile overburden, the pitch sand which is in the signifier of an ore is removed utilizing prodigious power shovels and shit trucks. In the 2nd stage the ore is washed in hot H2O, bitumen, and mulcts. A dissolver is added to the mixture to advance seperation of the bitumen. eventually the residuary mixture of H2O and sand is normally transferred to big deposit basins. The clarate is recycled and the settled solids are used to make full the cavity at the terminal of extraction operations. At the surface, the sites are rehabilitated which includes replacing an replanting the fertile overburden that was stockpiled at the beginning of the the undertaking.

Mentions:

  • Schlumberger Oilfield Review Magazine, Autumn 2002

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