CA1255489A

CA1255489A - Process for the enhanced oil recovery of underground mineral oil deposits

Info

Publication number: CA1255489A
Application number: CA000473322A
Authority: CA
Inventors: Zoltan Heinemann; Heinz Konig.; Gerhard Stern
Original assignee: Chemie Holding AG
Current assignee: Chemie Holding AG
Priority date: 1984-02-14
Filing date: 1985-01-31
Publication date: 1989-06-13
Also published as: GR850285B; DE3405201A1; RO92218B1; EP0152762B1; EP0152762A2; EP0152762A3; ATE43403T1; US4640356A; HUT39831A; RO92218A2; BR8500650A; TR22335A; SU1367862A3; DE3570483D1

Abstract

Abstract A process for the enhanced oil recovery of under-ground mineral oil deposits, in which one or more sub-stances which are scarcely water- and oil-soluble at de-posit temperature but are well soluble or volatile in the hot flooding medium and whose melting point lies above the deposit temperature, are added to the flooding medium hot water and/or water vapor. They move with the hot flooding medium through the deposit and precipitate as a solid pre-ferably at that part of the temperature front which is advancing fastest, thereby constricting the pores of the deposit temporarily and reversibly, until the solid is dissolved or evaporated again by the hot flooding medium flowing on after, which has the overall effect of an areal and vertical equalization of the temperature front.
O.Z.757 9.2.1984

Description

Process for the enhanced oil recovery of underground mineral oil deposits The invention relates to a process for the enhanced oil recovery of underground mineral oil deposits by selective, reversible reduction of the permeability in hot-water and/or steam flooding.
Steam flooding and hot-water flooding are thermal EOR processes (EOR = Enhanced Oil Recovery) for the ~lin-ning of mineral oil from deposits and are used predomi-nantly for the production of relatively heavy oils ortars. In order to achieve a good ult;mate recovery, the ratio M of the mobility of the flooding medium (steam or water) to the oil mobility must be lowered. This is performed in steam flooding and in hot-~ater flooding by heating up the deposit utilizing the heat content of the flooding med;a. Since the oil viscosity usually drops more under a temperature increase than the visco-sity of the flooding media, the mobility rat;o M improves and an increase ;n the ultimate oil recovery of the deposit is thereby achieved.
In the ideal case of steam or hot-~ater flooding~
the heated zone spreads evenly in the deposit and the flooding medium displaces the oil evenly to the produc-tion ~ells. However, in practice this is never the case as deposits are not homogeneous and consist of beds having different properties and which may be separated from one another by impermeable embedments. Channels ` are produced, in ~hich part of the flooding medium :

, ' ~J l3~ 3 advances faster and reaches the product;on well prema-turely. This is to be preven~ed, for example according to U.S. Patent Specification 4,250,963 by the steam being accompanied by a monomer, eg~ styrene, which condenses at ~he temperature front and, at a temperature below about 120C, polymerizes to form a polystyrene. The disadvantage of this and many similar polymerization methods lies in the fact that the polymerization is irreversible, meaning that the deposit remains blocked 1U for ever more at this point.
According to U.S. Patent Specificat;on 4,232~741, a very complicated process utilizing a nitrogen-generating substance, a surface-active substance, a pH control sys-tem and an ac;d-liberating substance is used to produce a foam at a desired point of the underground forn,ationO
l;kewise blocking the formation. Apart from the fact that it is very difficult to instigate such a complicated process at a very precise point in a largely unknown underground formation, the foam formation causes irrever-sible blocking, which lasts as long as the foam exists.After decomposition of the foam, the formation is perme-able again at th;s po;nt and channel format;on can occur again.
Another reason for channel formation, and thus for inadequate oil recovery of the deposit lies in the fact that water vapor has a substantially lower density than oil and the tongue of steam therefore has a propensity to move into the upper part of the deposit bed and to reach the product;on ~ell ;n the form of a narrow finger.
~0 According to Canadian Patent Specification 1,080,614, this is to be prevented by separating the injected steam, which usually contains a greater or lesser proportion of water, into a gaseous and a liquid phase, and intro-ducing the liquid phase into the formation above the gaseous phase. Apart from the additional expenditure on equipment~ here too the gas phase has the propens;ty to drift upwards and compete with the liquid phase, and the bottom part of the deposit is again avoided by the ~ 3 flooding medium. If the deposit is inhomogeneous, and this inhomogeneity cannot be predicted, as is normally the case, the gas phase ~orms unforeseen fingers and again runs ahead of the liquid phase with the formation S of channels.
In contrast with this, it has now been possible to discover a process for the oil recovery of und~rground deposits in which the permeability of an underground formation is reduced selectively at the points of highest permeability and in a reversible form. The reduction in the permeability of the rock for the flooding medium can be equated ~ith a reduction in the ratio M of the mobil;ty of the flooding medium to the oil mobility, ~hich results in an increase in the ultimate oil recovery.
The subject of the present invention is con~
sequently a process for the enhanced oil recovery of underground mineral oil deposits by selective, reversible reduction of the permeability using hot-water and/or steam flooding, ~herein hot water and/or steam is injected, at least at times, into the deposit via one or more injection boreholes, as a flooding medium which contains an active amount of one or more substances scarcely ~ater- and oil-soluble at the temperature of the deposit but well soluble or volatile in hot water and/or water vapor, the melting point of which lies aboYe the temperature of the deposit and which ~ove with the hot ~ater or the steam through the deposit and ~hich, by precip;tation as a solid, temporarily and reversibly con-strict She pores of the deposit preferably at that part of the temperature front which is advancing fastest, until flooding medium flowing on after dissolves or evaporates ` the solid again, ~hich has the overall effect of an areal and vertical equali~ation of the temperature front.
In one of its aspects, the present invention provides a process for the enhanced oil recovery of underground mineral oil deposits by selective, reversible reduction of the permeability using hot water flooding at an injection temperature o~ 150 to 250C. and/or steam ~

' flooding at an injection temperature of 200 to 350C, wherein hot water and/or steam is injected, at least at times, into the deposit via one or more injection boreholes, as a flooding medium which contains an active amount of one or more substances scarcely oil soluble at the temperature of the deposit and a water solubil.ity of below 3 kg/m3 water at 20C. but well soluble or volatile in hot water and/or steam, the melting point of which lies above the temperature of the deposit and which moves with the hot water or the steam through the deposit and which, by precipitation as a solid ln an amount of up to 4.3% of the pore volume, temporarily and reversibly constricts the pores of the deposit until flooding medium flowing on after dissolves or evaporates the solid again, which has the overall effect of an areal and vertical equalization of the temperature front.

In the process according to the invention, a substance having a melting point above the temperature of the deposit, usually above 80C, which is well soluble in the flooding medium hot water or volatile with the flooding medium steam and is scarcely soluble at the ,. .
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initial temperature of the deposit, is forced together with the hot flooding medium into the deposit through an injection well and transported up to the temperature front, where it cools, solidif;es, ;e. usually crystal-lizes, and reduces the permeab;lity ;n th;s region forthe flood;ng med;um. In the hot flood;ng med;um flow-ing on after, the substance d;ssolves or sublimes accord-ing to its physical properties and the flooding medium together with the dissolved or evaporated substance drifts further until the substance again precipitates at the temperature front. The precipitation of the sub-stance as a solid and the accompanying reduction in the permeability for the flooding medium is temporary and reversibLe; a constant alternation between precipitation and re~dissolution or evaporation in the flooding medium takes place in the deposit, the flooding medium each time transporting a supply of substance to the tempera-ture front.
The ultimate oil recovery is made up of the volu-metric flooding efficiency Ev effective over a large area and the degree of displacement Ed effective locally. First of all, the physical processes will be described which result in the increase in flooding efficiency from the measures according to the invention.
If, for one of the reasons mentioned above, the flooding medium forms a channel or finger, not only does more flooding medium move forward in this finger than in the more slowly flooded part of the deposit, but the finger also contains more substance since the substance 3G is brought on with the flooding medium and the flooding medium advances substantially faster than the temperature front. The more substance precipitates at the tempera-~ure front, the greater the reduction in the permeability, the smaller the speed of the~ flooding medium and the less heat is available for heating up the part of the deposit concerned and thus for advancing the temperature front in this part~ In this part of the deposit, the rapid advance of the temperature front is slowed by the measure , ,~ , , ` ;~ : ' ` .

according to the invention. Those other parts of the deposit~ which lie beyond the main directions of flow either because they have from the outset a lower perme-ability or because they lie unfavorably in view of the S arrangement of the well, have however also advanced in the meantime, although at a correspondingly lower rate.
They have been given the opportunity o-f catching up, so that there is overall an equalization in the speed of the front in a self-regulating process.
Similar to this effect occurring over a large area, which increases the volumetric flooding efficiency Ev, by also including and recovering the oil from those parts of the deposit which are otherwise not reached by the flooding medium, an increase in the degree of oil dis placement Ed can also occur locally in the pore channels.
This local effect is predominantly demonstrable in hot-water flooding, where the relatively poor, low degree of displacement can be considerably improved. ~t is known that, when two phases~ water and oil, flow next to each other ;n the deposit rock, some of the possible flow paths, the so-called pore channels, are oil-carrying, some are water-carryinga ~n the process according to the invention, the hot flooding medium, together ~ith the dissolved or evaporated substance, first likewise moves in the water-carrying pore channels; however, as it is just these water-carrying pore channels which are constricted upon cooling at the temperature front due to precipitation of solid substance, the hot flooding medium is forced to divert to oil-containing pore channels and to recover the oil from these as well. Thus the degree of displacement Ed is also increased. Flooding medium flowing on after takes up the solid again and transports it further.
The flooding medium in the process according to the invention can be either hot water or water vapor or a mix-ture of the two. Hot water usually has an injection tem-perature of about 80 to 300C, preferably of about 150 to 250oc, ~ater vapor an injection temperature of about 110 to 380C, preferably of about 200 to 350C, mixtures of hot water and water vapor usualLy an injection ~empera-ture of about 150 to 350C, m;xtures of steam and condensate or wet steam of various quality being possible The expressions "water" and "hot water" used ;n the present description cover both water droplets carried with the steam and steam condensate, fresh water and water of all solinity degrees as occur in deposits (0 to 300 kg saltt m3).
I~ the aim is to reduce the permeability for the flooding medium hot water, a substance is used which has a low solubility in cold water, in particular a solu-bil;ty of less than 3 kg/m3 water at Z0C and good solubility in hot water, in particular a solubility of more than 5 kgtm3 water at 200C and a low oil solubility, in particular of less than 3 kg/m3 oil at 20C. Its melt-ing point is above the temperature of the deposit, usually above 80C, in particular above 150C, and under deposit conditions it is adequately stable both thermally and chemically.
Examples of such hot-water soluble substances are rigid, aromatic polyhydroxylated compounds, such as for example 2,6-dihydroxynaphthalene or 1,5-dihydroxy-naphthalene, substituted or non-substituted bis-, tris-or tetra-p-hydroxyphenylalkane or alkene or their deri-vatives, such as ~or example leucoaurin, or sparingly soluble aminoacids, such as for example tyrosine, par-ticularly preferred is 1,5-dihydroxynaphthalene.
If the aim is to reduce the permeability for the flooding medium steam, a substance is used whose melting point is likewise above the temperature of the deposit, usually above 120C~ in particular above 200C, and wh;ch is in a gaseous state to an extent, at ~his temperature appropriate to its vapor pressure. At 300C, it has, for instance, a vapor pressure of above 0.01 bar, in particular above 0.03 bar, likewise it has lo~ solubility in cold water and in oil and adequate thermal and chemi-cal stability under deposit conditions. Examples of such :
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g sublimable compounds are polynuclear compounds of rigid molecular structure, such as for example 9,10-anthra-quinone or acridoneu The process according to the invention can be used both in oil displacement by means of hot wa~er with a hot-uater soluble substance and in oil displacernent by means of steam with a steam-volatile substance~ S;nce, in steam flooding, usually wet steam is injected, it is also possible to introduce both a volatile substance and a substance soluble in the hot water fraction of the wet steam as well as both substances together or successively.
The volatile substance exerts its permeability-reducing effect during the transition from the gaseous to the solid state at the condensation front of the steam, ~hile the hot-water soluble substance precipitates at the transi-tion from hot water zone to cold water zone until it is again dissolved by the following hot water and trans-ported further, the hot water partly originating from the water of the wet steam, partly having been formed by condensation of the vapor phase and also being able to contain proportions of injection water and deposit water.
The process according to the invention has the efféct in hot-water flooding both of improvement in the flooding efficiency Ev and of improvement in the degree of disp~acement Ed, and in steam flooding, where there is above all the danger of tongue formation and of over-riding, the formation of a steam channel in the upper part of a thick bed, above all of an improvement in the volumetric flooding efficiency Ev. The process accord-ing to the invention can be used in the case of oil deposits which are suitable for thermal oil recovery processes, in particular in the case of oils having a density of between 11 and 25 API, a viscosity o-f between 20 and 100,000 mPas, a porosity of the deposit rock of over 15% and a permeability of above 0.05.10~1Zm2.
Since the temperature front moves toward the production well substantially slower than the front of ':, the ~looding medium, the process is possible both at the start of a flooding process and during the course o~
such flooding processes by sending on substance.
The substance is introduced with the flooding medium at a concentration of about O.OOOZ to 0.3 kg sub-stance/kg flooding medium. If the substance is intro-duced continuously, the concentration is about O.OOOZ
to 0.05 kg substance/kg flooding medium, if it is intro-duced discontinuously to achieve a build-up of substance supply, the concentration is about 0~002 to 0.3 kg sub-stancetkg flooding medium. It can also be introduced in ~he form of a saturated solution.
The reduction in permeability according to the invention is expressed by the reduction factor R, the ratio of the permeabiLity after substance saturation to the initial permeability.
The amount of substance necessary in implementa-tion of the process to achieve the permeability reduction is small. It can be seen from Example 1, Table 2, that, in the case of substance A at a substance saturation of just 0.64X of pore volume tPV), the reduction factor is ~ 0O45~ at a substance saturation of 0.84X PV, the reduction i factor is 0.22, and at a substance saturation of 1.37%
of PV, the reduction factor is 0.04. This means that the precipitation of substance A as a solid amounting to just 0~64X~of pore volume is adequate to reduce the permeability to about half tO.45). If 0.84% PV are filled with substance, the permeability is then only 22X
and if 1.37X PV are filled with substance, the perme-~0 ability is then only 4% of the initiaL value.
Example 2 shows that the permeability is like-wise reduced by using a substance sublimable with steam. While in the test without substance the pressure difference dropped due to the lower viscosity of the steam compared ~ith water, and after 1.8 PV was no longer measurable, in the test according to the invention, with precipitation of substance B in the pore space, the pressure difference between core entry and core exit .. ..
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became ever greater and the perrneability of the rock for the steam phase was lowered. For the deposit, a permeability reduction for the s-team phase means a re-duction in the mobility ratio M, which has the effet above all of an increase in the flooding efficiency over a large area.
Figure 1 illustratss the relationship between the reduction factor, Rl and the saturation of solid substance in one pore volume, Ss. The points in E'igure 1 represent the measured points from Examples 1, 3 and ~ as set out hereinafter in Tables 2, 5 and 6, respect-tively. Points in Figure 1 having an arrow point ng downward toward the direction of higher Ss are from Ex-ample 1 in which measurement was made by injecting sub-stance. Points in Figure 1 having an arrow point~ng upwardly toward the direction of lower Ss are frorn Ex-amples 3 and 4 in which measurement was made by d:is-solving substance.
While Examples 1 and 2 state that substance can be introduced into a deposit rock and reduce the permeability there for the water or steam phase, Ex-amples 3 and 4 show that the permeability reduction in the deposit is reversible; the precipitated substance can be dispelled again and transported further. The reduction factors R ound in Example 3 in the partial elution of substance A at 100 C are compiled in Table 5 , ~t~
- 9a -and, as Figure l illustrates, lie within measuring ac-curacy on the same curve as the reduction factors found in Example 1, Table 2, in saturation with substance A.
Example 4 shows that, after flooding with 1.4 PV water at 174 C, the reduction factor i5 0.92, and the sub-stance A dissolved completely and could be removed from the drill core. The deviation of the reduciton factor from the theoretical valu~ 1 is explain~d on the one hand by the measuring tolerance and on the other hand by possible structural changes in the drill core due to swelling or shrinking processes of the clay minerals.
Examples 5 and 6 show that, by hot-water looding using the process according to the invention, a reduction in permeability and an increased oil re-covery takes place even when oil occurs in the deposit rock. As revealed by Tables 8 and 10, the degree of oil displacement Ed in conventional hot-water flooding without substance addition is 0.34, 0.35 and 0.33, in flooding according to the invention with sub-stance A
is 0.46, 0.42 and 0.42, in flooding according to the invention with substance c is 0.46 and 0.49 and in flooding accoridng to the invention with substance D is 0~5 and 0.47. This signifies a considerable increase in oil recovery both when using substance A and when using substances C and D. While an improvement ~.3 . ,, '.
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in the flooding efficiency Ev over a large area due to the permeability reduction and ~he resultant improvement in the mobility ratio M can be deduced, the part p~ayed by the degree of displacement Ed in the increased oil recovery can be demonstrated directly in the flood;ng installation.
Example 7 shows that in steam flooding of oil-containing drill cores with a substance effective in the vapor phase, utilizing the process according to the in-vention, the pressure difference between core entry andcore exit compared with the comparison test was substanti-ally increased. This increased pressure difference corre-sponds to a reduced permeability and thus to an increased flooding efficiency Ev over a large area in the deposit, which cannot be manifested in a small drill core, but can onLy be demonstrated in a field trial. The oil recovery data in Table 11 show that there were no adverse effects on the other components of the overall ultimate oil re-covery, namely on the degree of displacement Ed, by intro-ducing vaporous substance B.

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Examp~e 1:

Reduction in permeability in aqueous phase For the flooding tests, cylindrically cut drillcores of Valendis sandstone having a porosity ~f about 23%, a permeability in the range of 0.9 to Z~5.10 12mZ, a diameter of 3.9 cm and a length of 50 cm were used as a model formation. Each core was inserted into a steel tube and cast on both sides with a temperature-resistant cement mix. Flanges were then welded on the ends of the steel tubes. The cores prepared in this way were evacu-ated, flooded ~ith carbon dioxide, re-evacuated and then saturated with deionized water~ The pressure difference between core entry and core exit was measured whilst pump-ing through deionized water at 20C. The initial perme-ability of the core concerned was calculated from this using the Darcy equation~
A core was installed in a compression-resistant, thermostat-controllable flooding facility, which was equipped with a temperature measuring instrument, pressure gauges at the entry and exit and a pressure-maintaining Z0 valve, and heated under pressure to a temperature of 150C. Deionized water was pre-heated in a fluidized-bed heater to 150C and pumped through a substance tank at a thermostatically controlled temperature of 15ûC.
The substance tank contained substance A embedded in glass wool and whose relevant physical data are recorded in Table 1.
T a b l e Substance A:
Chemical composition: 1,5-dihydroxynaphthalene Melting point: 265C
Density: 1.50.103 kg/m3 Solubility in distilled water:
Temperature (C) 20 60 100 150 160 170 180 200 250 Solubility (kg/m3) 0.46 1.12 2.8 10 13 17 21 33 1ûO
The solution of substance A, saturated at 150C, was injected into the core. After the passage OT a volume `:

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of liquid corresponding at least ~o one pore volume of the core (1 PV), the injec~ion ~as interrupted and the core cooled to 2ûC Consequen~ly, the precipitation o~ the substance in solid -form in the pore space was initiated and the desired saturation of the pore space with substance A
produced. Finally, the perrneability was again determined at 20C. The reduction in permeabil;ty according to the invention is expressed by the reduction factor R, the ratio of the permeability after substance saturation to the initial permeability. The same procedure was re-peated with other, but similar cores at 160C, 17ûC and 180C with solutions of substance A saturated at these temperatures. For comparison, a flood test was also carried ou~ without substance A, using pure water at 150C.
The results are compiled in Table 2. The amount of solid substance left in 1 PY (saturation Ss in per-centages by volume) is obtained from the difference in solubility of the substance before and after cooling.
T a b l e Z
Reduct;on in permeability as a function of the saturation of rock pores with substance A

Substance none A A A A
Flooding temperature (C) 150 150 160 170 180 Flooding volume tPV) 1.2 1.2 1.1 1.1 1.0 Cooling time (h~ 24 50 24 20 48 Initial permeability measurement:
Injection rate ~m3s~1.10~ 9 ) 4 9 ~ 4 4 7. 2 48.6 28.1 50.0 Differential pressure tbar) 0~140~08 0~14 0~10 0~09 Permeabi lity (m2 10-12) 1~48 2r47 1~45 1.17 2.32 Permeabi lity measurement after saturation:
Injection rate (M3s~1.10 9) 48~650~0 33.3 28.3 33.3 Differential pressure (bar) O~i4 0~19 0~44 0~65 1~35 Permeabi lity (m2,1o-12) 1~45 1~10 0~32 0.18 0.10 __ .

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Reduction factor R 0.98 0.45 0.22 0.16 0~04 Saturation S5 (XPV) 0 0.64 0.84 1.10 1.37 PV: Pore volume Reduction factor R: Ratio of permeability after substance saturation to initial permeabil;ty Sa~uration Ss Saturation with substance in X of PV
Example 2:
Reduction in permeability in the steam phase Drill cores of 6 cm diameter and 60 cm length com-posed of the Valendis sandstone described in Example 1were used as core material. The cores installed in steel tubes were evacuated, flooded ~ith carbon d;ox;de, re-evacuated and then saturated with deionized water. Deion-ized ~ater was pumped at a constant rate into the flui dized-bed heater of the flood;ng facility. Saturated steam of 275C was produced by evaporation. The substance tank contained sublimable substance B, embedded ;n glass wool. The relevant physical data of substance 8 are re-corded in TabLe 3.
T a b l e 3 Substance B:
Chemical composition: 9,10-anthraquinone Melting point: 286C
Density: 1.44_103 kg/m3 Temperature (C) 100 180 20D 220 245 Z75 Vapor pressure ~mbar) 0.002 0.73 2.4 6.7 23 85 The saturated steam, saturated ~ith substance B
at 275C, emerg;ng from the substance tank was injected into the drill core~ The changes in the pressure diffe-rence between core entry and core ex;t, wh;ch representsa measure of the permeability, were recorded.
For compar;son, an analogous test was carried out without substance B, but otherwise under the same conditions.
The results are shown in Table 4.
T a b l e 4 Reduction in permeability of the rock for steam . ~ , ~_ ~ rj r~

Substance none B
Temperature tC) 275 275 Injection rate (m3.s~1,1o-9) 18.1 18~2 Speed of the steam front (m.S~1.1o-6) 13.6 13.9 Transport capacity of the steam (kg/kg3 - 0.01Z7 Saturation with substance Ss t%PV~ - 1.9 Pressure difference (bar) as a function of injection volume:
0.5 PV 0.06 0.07 0.8 PV 0.05 0~08 1.0 PV 0.03 0.08 1.2 PV 0.02 0.08 1.5 PV 0.01 0.12 1.8 PV below 0.01 0.22 Example 3:
Reversibility of the permeability reduction The drill core, which in Example 1 was treated at 160C with solution of substance A saturated at this temperature and then cooled, was flooded with hot water of 1ûooc- After each flooding volume of 1 PV, the sys-tem was cooled to 20C, the pressure difference during the flowing-through with water of 20C was measured and the permeability calculated from it. The reduction factor after the partial elution is obtained as a ratio of the last-found permeability to the ;nitial permeability.
The results are compiled in Table 5.
~ T a b l e 5 Flooding volume (PV water) 0 1 2 Flooding temperature (C) 100 100 35 Initial permeability (m2.1~12) 1.45 1.45 1.45 . .

Inj ecti on rate (m3~s~1.10~9) 33.3 33.3 33~3 Pressure difference (bar) 0.44 0.25 0.16 Permeability (m2.10~12) 0.317 0.558 0.872 Reduction fac~or R 0.22 0.38 0.60 Saturation Ss (% PV) O.R4 0.65 0.46 Example 4:
Complete reversibility of the permeability reduction The drill core which in Example 1 was treated a~
170C uith solution of substance A saturated at this temperature and then cooled~ was flooded with 1.4 PV water at 174C- Then the permeability was determined at 20C.
The results are compiled in Table 6.
T a b l e 6 15 Flooding volume (PV water) 0 1.4 Flooding temperature ~C) - 174 Initial permeability (m2.10~12) 1.17 1.17 Injection rate (m3.s~1.10 9) 28.3 28.3 Pressure difference (bar) 0.65 0.11 20 Permeability (m2.10~12) 0.18 1.08 Reduction factor R 0~16 0.92 Saturation Ss (X PY) 1.10 0 Subsequently, the core was examined for residual substance. No residue of substance A could be demonstrated~
Example 5:
Oil recovery of drill cores by hot-water tlooding Cylindrically cut drill cores of Valend;s sand-stone having a porosity of Z3%, a permeability of 0.9 to

2.5 m2.1012, a diameter of 6 cm and a len~th of 60 cm were, as described in Example 1, installed ;n steel tubes, purged with carbon dioxide and saturated with deionized water. Subs~quently, they were flooded with crude oil in deposit-similar conditions at 50C and an average pressure of 30 to 35 bar~ The crude oil had a viscosity of 1,200 mPa.s at 20C, of Z10 mPa.s at 44C, of 71 mPa.s , at 80C and a density of 0.938 at 20C and of 0.889 at 44C. An initial oil saturation of 87 to 92% pore volume ~as rea~hed.
An oil-sa~urated drill core was installed in each case in a compression-resistant, thermostat-con~rollable flooding facility. Deionized water was pre-heated at 180C in a flu;dized bed heater and pumped through a sub-stanse tank thermostatically controlled at 180C con~ain-ing substance A or substance C embedded ;n glass wool.
1D During flowing through the substance tank, a solution saturated with substance A or substance C was produced, which was injected into the drill core.
The solubility data of substance A have already been recorded in Example 1, Table 1. Table 7 reproduces the relevant physical data of substance C.
T a b l e 7 Substance C:
Chemical composition: Tyrosine Melting point: 317C
2D DensityO 1.46.103 kg/m3 Solubility in distilled water:
Temperature (C) 20 40 60 80 100 180 Solubili~y (kg/m3) D.3 0.68 1.4 Z.7 5.0 30 The progression of the temperature front in the deposit was simulated in the flooding facility in the ~ay now described. At the start of the flooding test, the drill core installed in a steeL tube was outside the heat-ing chamber thermostaticalLy controlled at 180C and had a temperature of 21c. Dur;ng the flooding process, the 3D steel tube with the core was slo~ly pushed at a constant rate into the heat;ng chamber. The temperature front was in each case at the entry of the heating chamber4 The temperature profile was recorded o~er the entire core length by temperature sensors.
The fluida issuing from the core were collected in a separator and, after the passage of 1.8 to 2.2 PV, the volume of oil produced determined. Table 8 contains the test results of three comparison tests without using a substance, three flooding tests ~ith substance A and t~o .

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v ~ O o ~ ~ c v a~ C
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~ ~ rG ~1 ~ ~ ., .n u ~
O ~ ~ , ., ~ .n E '~ ~ ~ .~ ~ ~ V
_ n ~ y ~ O C ~ V C ~ a) ~ ~, r_ E n _ _ ,, o ~ . ._ o _ ,_ o .n Cn rl rY ~

..

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~ 3~

~ 19 -Example 60 Oil recovery of drill cores by hot-water floodlng Oil recovery tests with substance D ~ere carried out in the way described in Example S with the sarne drill cores and the same crude oil. The test conditions were identical as far as possible with the cond;tions in ExampLe 5; only the flooding of the drill cores was at a slightly lo~er average pressure of 20 to Z5 bar. Table 8 reproduces the relevant physical data of substance D, Table 10 contains the test results of a comparison test without using a substance and of two flooding tests with substance D.
T a b l e 9 Substance D
Chemical composition: 4,4'-dihydroxybiphenyl Melting point: 275C
Density: 1.25 Solubility in distilled water and in simulated deposit water T (C3 20 40 60 80100 200 20 Solubility in distilled ~ater tkg/m3) 0.034 0.106 0.2450.512 1.470~ 60 _ .
Solubility in simulated deposit 25 water 0.024 0.054 0.119 0.295 0.940 _ .
+ Empirical value: 1.3 , .

T a b l e 10:
Improvement in the degree o~ oil displacemen~ with ho~.-water flooding Substance none D D
5Initial oil volume ( 3 1o-6) 3 35 3.35 2.75 Initial oil saturation Soj 0.8~ 04875 0.88 Initial core temperature (C) 21 21 21 Flooding temperature (C) 180 180 180 Transport capacity of the hot water ~kg/m3) - 32.0 32.0 Injection rate ~m3.S~1,1o-9) 7.67 8.83 5.72 Front speed (m.s~1.10~9) 6.54 6.67 6.94 Calculated substance saturation Ss (X PV) - 3.7 2.7 Iniection volume (PV) 1.8 2.1 1.6 Produced oil volume (m3.10~6) 1.13 1.5 1.30 Residual oil saturation Sor 0.58 0.48 0.45 Degree of oil displacement Ed 0~34 0.45 0.47 Example 7:
Steam flooding of oil-saturated drill cores The preparation of the drill cores and their satu-ration ~ith crude oil was carried out as described in Example 5.
Saturated steam of 245C was produced by evapo-ration of deionized water in the fluidized-bed heater of the flooding facility, saturated with the sublimable sub-stance B during the ~lowing through of the substance tank 3~ thermostatically controlled at 245C, and injected into an oil-saturated drill core. The progression of the tem-perature front in the deposit was simulated in the way now described. At the start of the flooding test, the drill core installed in a steel tube was outside the heat-ing chamber thermostatically controlled at 245C of theflooding facility and had a temperature of 21C. During the flooding process, the core was slowly pushed at a :
- . .:..., ~.
:

constant rate into the heating chamber. The ~emperature front in each case was at the en~ry of the heating charn~er.
The steam flooding test with substance a ~las re-peated in slightly altered condi~ions. Furthermore, a co~parison test without substance ~ was carr;ed out. The results are compiled in Table 11.
T a b l e 1 1 Steam flooding of oil-saturated dr;ll cores Substance none 9 a 10 Initial oil saturation SO; 0.87 0.91 0.87 Initial core temperautre (C ) 21 21 21 FLooding temperature (C) 245 245 Z45 Transport capacity of the steam (kg/m3) - 0.0061 0.0061 15 Injection rate (m3s,~1.1o-9) 20.5 21.8 23.3 Speed of the steam front (m.S-1.1 o-6) 5. 56 5. 83 6.67 Calculated substance saturation Ss (X PV) - 2.6 2.4 20 Pressure difference after 2.0 PV
(bar) 1.5 4.8 3.0 Pressure difference after 3DO PV
tbar) 0.4 1.1 1.4 Pressure difference after 3~8 PV
tbar) 0~2 0.9 0.9 Injection volume at steam break-through (PV) 5.8 5.9 5.5 Degree of displacement Ed 0-75 0.76 0.73 Residual oiL saturation Sor 0.22 0.22 0.24

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the enhanced oil recovery of under-ground mineral oil deposits by selective, reversible re-duction of the permeability using hot-water and/or steam flooding, wherein hot water and/or water vapor is injected, at least at times, into the deposit via one or more injection boreholes, as a flooding medium which con-tains an active amount of one or more substances scarcely water- and oil-soluble at the temperature of the deposit but well soluble or volatile in hot water and/or water vapor, the melting point of which lies above the tem-perature of the deposit and which move with the hot water or the steam through the deposit and which, by precipi-tation as a solid, temporarily and reversibly constrict the pores of the deposit preferably at that part of the temperature front which is advancing fastest, until flooding medium flowing on after dissolves of evaporates the solid again, which has the overall effect of an areal and vertical equalization of the temperature front.

2. A process as claimed in Claim 1, wherein the flooding medium is hot water.

3. A process as claimed in Claim 1, wherein the flooding medium is water vapor.

4. A process as claimed in Claim 1, wherein the flooding medium is a mixture of hot water and water vapor.

5. A process as claimed in Claims 1, 2 and 4, wherein the substance soluble in hot water is 1,5-diydroxynaph-thalene.

6. A process as claimed in Claims 1, 2 and 4, wherein the substance soluble in hot water is 4,4'-dihydroxybi-phenyl.

7. A process as claimed in Claims 1, 3 and 4, wherein the substance volatile in water vapor is 9,10-anthraquinone.

8. A process as claimed in Claims 1 or 2, wherein the effective substance volume is added to the flooding medium continuously or discontinuously at a concentration of 0.0002 to 0.3 kg substance/kg flooding medium.

9. A process as claimed in Claim 1 or 2, wherein the effective substance volume is added to the flooding medium continuously at a concentration of 0.0002 to 0.05 kg substance/kg flooding medium.

10. A process as claimed in Claims 1 or 2, wherein the effective substance volume is added to the flooding medium discontinously at a concentration of 0.002 to 0.3 kg substance/kg flooding medium.

11. A process for the enhanced oil recovery of underground mineral oil deposits by selective, re-versible reduction of the permeability using hot water flooding at an injection temperature of 150° to 250°C.
and/or steam flooding at an injection temperature of 200,° to 350°C, wherein hot water and/or steam is in-jected, at least at times, into the deposit via one or more injection boreholes, as a flooding medium which contains an active amount of one or more substances scarcely oil soluble at the temperature of the deposit and a water solubility of below 3 kg/m3water at 20°C.
but well soluble or volatile in hot water and/or steam, the melting point of which lies above the temperature of the deposit and which moves with the hot water or the steam through the deposit and which, by precipita-

Claim 11 continued....

tion as a solid in an amount of up to 4.3% of the pore volume, temporarily and reversibly constricts the pores of the deposit until flooding medium flowing on after dissolves or evaporates the solid again, which has the overall effect of an areal and vertical equalization of the temperature front.

12. A process as claimed in Claim 11, wherein the substance soluble in hot water is 1,5-dihydroxynaphtha-lene.

13. A process as claimed in Claim 11, wherein the substance soluble in hot water is 4,4'-dihydroxybi-phenyl.

14. A process as claimed in Claim 11, wherein the substance volatile in water vapor is 9,10-anthraquin-none.

15. A process as claimed in Claim 1, 11 or 12, wherein the substance is thermally and chemically stable under deposit conditions.