WO2017161556A1

WO2017161556A1 - Process for oil recovery

Info

Publication number: WO2017161556A1
Application number: PCT/CN2016/077328
Authority: WO
Inventors: Lingli Wei; Diederik Michiel BOERSMA
Original assignee: Shell Internationale Research Maatschappij B.V.
Priority date: 2016-03-25
Filing date: 2016-03-25
Publication date: 2017-09-28

Abstract

A process for recovering oil by injecting an enhanced oil recovery formulation comprising of from 80 to 95% by weight of carbon dioxide and of from 5 to 20% by weight of dimethyl sulfide comprising (i) reacting carbon with oxygen in the presence of steam to obtain a reaction product containing hydrogen, carbon monoxide, carbon dioxide and steam, (ii) optionally combining carbon monoxide obtained in step (i) with further steam to obtain a reaction product containing carbon dioxide and hydrogen, (iii) separating carbon monoxide and hydrogen from the product of step (i) and optionally hydrogen from the product of step (ii) and converting hydrogen and carbon monoxide to methanol, (iv) reacting at least part of the methanol with hydrogen sulfide to obtain dimethyl sulfide, and (iv) injecting enhanced oil recovery formulation comprising dimethyl sulfide obtained in step (iv) and carbon dioxide obtained in step (i) and optionally step (ii).

Description

PROCESS FOR OIL RECOVERY

Field of the invention

The present disclosure relates to a process for recovering oil and gas from an oil-bearing formation by injecting an enhanced oil recovery formulation into the formation.

Background of the invention

In natural mineral oil deposits, mineral oil is present in the cavities of porous formation rocks which tend to be sealed toward the surface of the earth by impermeable top layers. The cavities may be very fine cavities, capillaries, pores or the like.

In mineral oil production, a distinction is drawn between primary and subsequent production such as secondary and/or tertiary production.

In primary production, after commencement of drilling of the deposit, the mineral oil flows of its own accord through the borehole to the surface owing to the autogeneous pressure of the deposit. The autogeneous pressure can be caused, for example, by gases present in the deposit, such as methane, ethane or propane. The autogeneous pressure of the deposit, however, generally declines relatively rapidly on extraction of mineral oil, such that usually only a limited amount of the mineral oil present in the deposit can be produced in this way. Primary production is no longer feasible if natural reservoir drive diminishes. In these instances, secondary recovery methods can be applied. Secondary methods typically rely on the supply of external energy into the reservoir in the form of injecting fluids to increase reservoir pressure, hence replacing or increasing the natural reservoir drive with an artificial drive. Reservoir pressure may be increased through the injection of carbon dioxide, steam and/or water. The injected fluid is typically immiscible, or predominantly immiscible with the in-situ hydrocarbon fluids.

After primary and/or secondary production, enhanced oil recovery can be applied. Enhanced oil recovery methods generally comprise injecting into a production well an enhanced oil recovery formulation which can contain various compounds.

WO2014210110 describes a method for recovering oil and/or gas from an underground formation by injecting an enhanced oil recovery formulation comprising at least 75 mol ％of dimethyl sulfide. The dimethyl sulfide can be prepared from methanol obtained by reacting carbon monoxide and hydrogen and from hydrogen sulfide separated from sour gas.

It has now surprisingly been found that the recovery of oil from an underground formation with the help of an enhanced oil recovery formulation can be improved.

Summary of the invention

The present invention relates to a process for recovering oil and optionally gas from an oil-bearing formation by injecting into the formation an enhanced oil recovery formulation comprising of from 80 to 95 ％by weight of carbon dioxide and of from 5 to 20 ％by weight of dimethyl sulfide, which process comprises

(i) reacting carbon with oxygen in the presence of steam to obtain a product containing hydrogen, carbon monoxide, carbon dioxide and steam,

(ii) optionally combining at least part of the carbon monoxide obtained in step (i) with further steam to obtain a product containing carbon dioxide and hydrogen,

(iii) separating carbon monoxide and hydrogen from the product of step (i) and optionally hydrogen from the product of step (ii) and converting at least part of the hydrogen and the carbon monoxide to methanol,

(iv) reacting at least part of the methanol obtained in step

(iii) with hydrogen sulfide to obtain dimethyl sulfide,

(v) injecting into the underground formation enhanced oil recovery formulation comprising at least part of the dimethyl sulfide obtained in step (iv) and carbon dioxide obtained in step (i) and optionally step (ii) , and

(vi) recovering oil and optionally gas from the underground formation.

Detailed description of the invention

The enhanced oil recovery formulation to be injected into the formation comprises of from 80 to 95 ％by weight of carbon dioxide and of from 5 to 20 ％by weight of dimethyl sulfide. Preferably, the enhanced oil recovery formulation comprises of from 85 to 90 ％by weight of carbon dioxide and of from 10 to 15 ％by weight of dimethyl sulfide. Additionally, the enhanced oil recovery formulation can comprise further compounds specifically compounds chosen from the group consisting of hydrogen, nitrogen, carbon monoxide, hydrogen sulfide, methane and ethane. Generally, the enhanced oil recovery formulation will comprise at most 5 ％by weight of such further compounds, more specifically at most 3 ％by weight. Thiols, more specifically methanethiol, can be formed as a by-product of dimethyl sulfide and can be beneficial in enhanced oil recovery. An embodiment is injecting an enhanced oil recovery formulation comprising of from 80 to 94 ％by weight of carbon dioxide, of from 5 to 20 ％by weight of dimethyl sulfide and of from 1 to 10 ％by weight of methanethiol. Preferably, the amount of methanethiol is at most 8％, more specifically at most 5 ％by weight.

Surprisingly, it was found that the enhanced oil recovery formulation of the present invention has beneficial properties in the recovery of oil. Oil which is present in the formation is miscible in the mixture of carbon dioxide and dimethyl sulfide according to the present invention while oil is substantially immiscible with carbon dioxide per se. Additionally, oil was found to swell if contacted with a mixture of carbon dioxide and dimethyl sulfide which allows for high recovery. A mixture of dimethyl sulfide and carbon dioxide further is thought to have a high injectivity and limited risk of asphaltene flocculation and deposition.

In step (i) of the process of the present invention carbon reacts with oxygen in the presence of steam. Such process is also referred to as gasification. Generally, coal is blown through with oxygen and steam while also being heated at ambient or increased pressure. The amount of oxygen generally is controlled to ensure that the oxidation is incomplete and carbon monoxide is formed. Any gasification process can be used which is known to be suitable to the person skilled in the art.

Carbon can be obtained from any sources known to be suitable to a person skilled in the art. Preferably, the source of the carbon is petroleum coke or coal. Most preferably, the source of the carbon is coal. Low-grade coals can contain significant amounts of water in which case it may not be required to separately add water or steam. Coal gasification can be carried out underground by injecting gaseous oxidizing agent such as air and bringing the resulting product gas to surface through production wells drilled from the surface.

Typically, coal contains from 0.1 to 5 ％by weight of sulfur, dry weight, which tends to be converted to hydrogen sulfide and/or carbonyl sulfide during gasification. These sulfur containing compounds preferably are removed before reacting hydrogen and carbon monoxide to obtain methanol. Preferably, hydrogen sulfide which is removed from the reaction mixture obtained in step (i) is subsequently used in step (iv) .

Step (ii) is known as catalytic shift conversion. Carbon monoxide present in the mixture obtained in step (i) is reacted with water to convert carbon monoxide to carbon dioxide and more hydrogen. Preferably, the carbon monoxide has been separated from the reaction mixture of step (i) before being subjected to step (ii) . The catalytic shift reaction can be carried out at relatively low temperature in the presence of a catalyst containing copper oxide, zinc oxide and aluminum oxide. Alternatively, this step is carried out at relatively high temperature in the presence of a catalyst containing iron oxide, chromium oxide and a minor amount of magnesium oxide.

It depends on the amount of carbon dioxide available from other sources and on the amount of carbon dioxide to be present in the enhanced oil recovery formulation whether step (ii) is carried out.

In step (iii) , hydrogen and carbon monoxide obtained in step (i) and optionally step (ii) are reacted to obtain methanol. Subsequently, at least part of the methanol obtained in step (iii) is reacted in step (iv) with hydrogen sulfide to obtain dimethyl sulfide. In step (iii) and step (iv) any process can be used which is known to be suitable to the person skilled in the art. Hydrogen sulphide can be obtained from a single or from various sources. Besides the gasification of step (i) , a viable source can be hydrogen sulphide present in sour gas in either the formation from which the oil is to be recovered or an adj acent or nearby formation.

Carbon dioxide generally will be separated from the reaction mixture obtained in step (i) and optionally step (ii) before being used in the enhanced oil recovery formulation. The separation prevents that substantial amounts of contaminants are incorporated in the enhanced oil recovery formulation.

The dimethyl sulfide present in the enhanced oil recovery formulation is obtained from step (iv) . At least part of the carbon dioxide present in the enhanced oil recovery formulation is obtained from step (i) and optionally (ii) . Preferably, all of the carbon dioxide present in the enhanced oil recovery formulation is obtained from steps (i) and optionally (ii) .

In some embodiments, a first well or group of wells may be used for injecting a miscible enhanced oil recovery agent, and a second well or group of wells may be used for producing oil and/or gas from the formation for a first time period； then the second well or group of wells may be used for injecting a miscible enhanced oil recovery agent, and the first well or group of wells may be used for producing oil and/or gas from the formation for a second time period, where the first and second time periods comprise a cycle. In some embodiments, multiple cycles may be conducted which include alternating wells or well groups between injecting a miscible enhanced oil recovery agent, and producing oil and optionally gas from the formation, where one well group is injecting and the other is producing for a first time period, and then they are switched for a second time period.

The recovery of oil and optionally gas from a formation may be accomplished by any known method. Suitable methods include subsea production, underground production, surface production, primary, secondary, or tertiary production.

Releasing at least a portion of the enhanced oil recovery formulation and/or other liquids and/or gases may be accomplished by any known method. One suitable method is injecting the enhanced oil recovery formulation into a single conduit in a single well, allowing the formulation to soak, and then pumping out at least a portion of the formulation with liquids and optionally gas. Another suitable method is injecting the enhanced oil recovery formulation into a first well, and pumping out at least a portion of the enhanced oil recovery formulation with liquids and optionally gas through a second well.

In some embodiments, enhanced oil recovery formulation may be injected into a well, followed by another component to force the formulation across the formation. For example air, water in liquid or vapor form, carbon dioxide, nitrogen, alcohols, other gases, other liquids, and/or mixtures thereof may be used to force the enhanced oil recovery formulation across the formation. Preferably, injection of enhanced oil recovery formulation is followed by injection of water.

A specific preferred embodiment comprises multiple cycles of injecting the enhanced oil recovery formulation followed by injecting water. In a more preferred embodiment, a process comprises of from 1 to 5 cycles, 2 to 3 cycles of injecting the enhanced oil recovery formulation wherein the last water injection of these cycles is followed by injecting alternatingly carbon dioxide and water. It has been found that the subsequent cycles can use a formulation to which dimethyl sulfide has not been added. The carbon dioxide flood preferably contains at most 5 ％by weight of other compounds, more specifically at most 2 ％wt by weight of other compounds. Most preferably, the carbon dioxide flood used in the subsequent cycles consists of carbon dioxide. The use of alternatingly injecting water and enhanced oil recovery formulation in this fashion allows improving the recovery of oil compared with the use of carbon dioxide only while requiring a reduced amount of dimethyl sulfide. It has been found possible to reduce the weight ratio of total amount of dimethyl sulfide to total amount of enhanced oil recovery formulation to at most 20 ％by weight, more specifically of from 5 to 15 ％by weight, based on total amounts of these compounds/formulations injected during the time when enhanced oil recovery is being carried out.

In some embodiments, the enhanced oil recovery formulation is liquid at the wellhead.

Oil and optionally gas which is produced from the formation, can be sent to a production facility where gas and liquid may be separated, and gas may be sent to gas storage and liquid may be sent to liquid storage. Dimethyl sulfide may be sent to enhanced oil recovery formulation production /storage. Enhanced oil recovery formulation may be recycled in that it is recovered and subsequently injected again into the formation.

Oil and optionally gas produced may be transported to a refinery and/or a treatment facility. The oil and/or gas may be processed to produce commercial products such as transportation fuels such as gasoline and diesel, heating fuel, lubricants, chemicals, and/or polymers. Processing may include distilling and/or fractionally distilling the oil and/or gas to produce one or more distillate fractions. In some embodiments, the oil and/or gas, and/or the one or more distillate fractions may be subjected to a process of one or more of the following: catalytic cracking, hydrocracking, hydrotreating, coking, thermal cracking, distilling, reforming, polymerization, isomerization, alkylation, blending, and dewaxing.

In some embodiments, oil as present in the formation prior to the injection of any enhanced oil recovery agents has a viscosity of at least about 0.01 centipoise, or at least about 0.1 centipoise, or at least about 0.5 centipoise, or at least about 1 centipoise, or at least about 2 centipoise, or at least about 5 centipoise. In some embodiments, oil as present in the formation prior to the injection of any enhanced oil recovery agents has a viscosity of up to about 500 centipoise, or up to about 100 centipoise, or up to about 50 centipoise.

Those skilled in the art will appreciate that many modifications and variations are possible in terms of the disclosed embodiments of the invention without departing from their spirit and scope. Accordingly, the scope of the claims appended hereafter and their functional equivalents should not be limited by particular embodiments described herein, as these are merely exemplary in nature.

Claims

A process for recovering oil and optionally gas from an oil-bearing formation by injecting into the formation an enhanced oil recovery formulation comprising of from 80 to 95 ％ by weight of carbon dioxide and of from 5 to 20 ％ by weight of dimethyl sulfide, which process comprises

(i) reacting carbon with oxygen in the presence of steam to obtain a product containing hydrogen, carbon monoxide, carbon dioxide and steam,

(ii) optionally combining at least part of the carbon monoxide obtained in step (i) with further steam to obtain a product containing carbon dioxide and hydrogen,

(iii) separating carbon monoxide and hydrogen from the product of step (i) and optionally hydrogen from the product of step (ii) and converting at least part of the hydrogen and the carbon monoxide to methanol,

(iv) reacting at least part of the methanol obtained in step

(iii) with hydrogen sulfide to obtain dimethyl sulfide,

(v) inj ecting into the underground formation enhanced oil recovery formulation comprising at least part of the dimethyl sulfide obtained in step (iv) and carbon dioxide obtained in step (i) and optionally step (ii) , and

(vi) recovering oil and optionally gas from the underground formation.
A process according to claim 1 in which the carbon is coal.
A process according to claim 2 in which the coal further comprises sulfur and the product of step (i) further comprises hydrogen sulfide at least part of which is used in step (iv) .
A process according to claim 1 in which injection of the enhanced oil recovery formulation is followed by injection of water.
A process according to claim 4 which process comprises multiple cycles of injecting the enhanced oil recovery formulation followed by injecting water.
A process according to claim 5 which process comprises 1 to 5 cycles of injecting the enhanced oil recovery formulation followed by injecting water and subsequently injecting alternatingly carbon dioxide and water.
A process according to claim 1 in which the enhanced oil recovery formulation comprises of from 85 to 90 ％ by weight of carbon dioxide and of from 10 to 15 ％ by weight of dimethyl sulfide.
A process according to claim 1 in which the enhanced oil recovery formulation comprises of from 80 to 94 ％ by weight of carbon dioxide, of from 5 to 20 ％ by weight of dimethyl sulfide and of from 1 to 10 ％ by weight of methanethiol.