Utilization of thermal waters from oil deposits of the caucasus

Geot/ierraics ( I 9 7 o )

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Issvt 2

U. N. Symposiumon the Developmentand Utilization of GeothermalResources, Pisa z97o. Vol. 2, part 2

Utilization of Thermal Waters from Oil Deposits of the Caucasus G. M. SUKHAREV *, S. P. VLASOVA * ~

Y. K. TARANUKHA *

ABSTRACT During the exploitation of many gas-oil fields of the Caucasus a great quantity of thermal water is obtained, This water, with great economical effect, is sometimes used for hot water supplying of industrial and agricultural enterprises and for heating different commercial services etc.. Great prospects for a wide utilization of thermal waters are opened in connection with the developing of the oil deposits, namely of the productive horizons of the Middle Miocene deposits. From only one oil field (in the October district of the north Caucasus) 5.6-6.2 million m s of water is annually extracted together with the oil. During the whole period of development up to the 1st of January 1969, 260 million ms of water at the head of many wells is higher than 80 °C. The extraction of heat by water out of the interior of the oil field amounted to 15.8.10 ~z cal for the 55 year period. For •generating the same quantity of heat it would be necessary to burn 1.58 million tons of mazut, or 2.3 million tons of coal, or about 2.0 billion m 3 of natural gas. The development, over many years, of Middle Miocene deposits led to a considerable decrease of hydrodynamic levels and expansion of cones of depressions for scores of kilometers. As a result of this there followed the reduction of yield and even the exhausting of many thermal springs. Approximately 90% of the large total recovery of the aggregate amount of liquid from Middle Miocene deposits was from 3-4 levels. A sharp reduction in the recovery of liquid from levels and in connection with the considerable development of some deposits resulted in the increase of hydrodynamic levels. Water of the earlier productive horizons are now the source of thermal supplying of some industrial enterprises. Long regime observations of thermohydrodynamic parameters showed high reliability of hydrodynamic systems in the Neogene deposits. It was observed that while using thermal waters it is nee. essary to make up their reserves artificially. To determine allowable recovery of thermal water and, in connection with this, to determine the quantity of water injected into the stratum for the recovery of its resources, thermal calculations have been made according to the scheme ineluding convection, transportation of heat in the stratum and heat transfer of the surrounding rocks in the vertical direction. The calculations showed that the most favourable conditions of work of the considered hydrodynamic system, the Black Mountains - Peredovoy ridges, can be created by recovery and injection of 100,000 or 50,000 m 8 water per day. The linear distance between the injected and exploited wells is 5000 meters. At the injection and the extraction of 25,000 m s water/day, the temperature of the level will not appreciably decrease. In the near future in the Caucasus, side by side with the direct utilization of theiT~.~l energy of the underground waters, the extraction from them of iodine, bromine and other elements can be organized. Thermal mineral waters can have a still wider use for balneology purposes. The Caucasus is a vast territory of the Soviet Union well known for its large reserves of various rain* Groznyj Oil Institute, Groznyl, USSR. 1102

eral deposits, among which an important part undoubt-

edly is of oil and gas. The exploitation of some oil deposits has been already going op for 75-100 years. A great number of prospecting jobs for oil, gas and other useful minerals are taking place nowadays. During the process of deep drilling, high temperatures (220 °C) have been recorded and abundant inflows of thermal waters up to 70,000 m3/d have been obtained, which opens great prospects for widescale use of the earth's supplies of heat. In connection with the solution of the problems of using thermal waters, the Caucasus geothermic field was the object of thorough study for many years (SugJ-tAREV ~.r AL. 1962a, 1962b, 1966). The stratigraphic section of the region is known to be represented by the complex of various rocks beginning with Pre-Cambrian-Paleozoic to present day ones. The upper part of the Meso-eenozoic section is sandy-argillaceous sediments of the Pliocene, Upper and Middle Miocene; below them there are argillaceous rocks of the Maikop strata which are underlain by earbonatic-terrigenous formations of Eocene-Paleocene, Cretaceous and Jurassic. Pre-Mesozoic deposits include a stratum of differently metamorphosed sedimentary and partially igneous reeks from Permian up to Pre-Cambrian. Pliocene, Upper and Middle Miocene deposits are characterized by a geothermal degree exceeding 30 m/°C, In certain cases (in the considerable clayeyness of Pliocene-Mioccne deposits) the geothermal degree decreases to 10-20 m/°C (the deposits of Pontic stage of the Western Kuban depression, Sarmat stage of TerskoDagestan oil-and gas-bearing regions and others. The thermal resistivity of sandy-argillaceous rocks of Pliocene, Upper and Middle Miocene ranges from 0.32 to 1.20 mh °C/kcal. The geothermal degree for Maikop predominantly argillaceous deposits as a rule is less than 20 m/°C, while thermal resistivity ranges from 0.75 to 1.00 mh °C/kcal. In the regions where the Maikop deposits become sandy, one can see the increase of the geothermal degree up to 30-40 m / ° C and the decrease of thermal resistivity to 0.48-0.80 mh °/kcal. The average geothermal degree of Eocene-Paleocane deposits of Pre-Caucasus exceeds 40 m / ° C when thermal resistivity is 0.51-0.66 mh °C/kcal. High thermal degree (above 40 m/°C) and small values of thermal resistivity (0.38-0.44 mh °C/kcal)

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FIG. 1. - Map of geoisotherms of the Caucasus along the fop of the Upper Cretaceous deposits. 1 - wells in which measurements of temperatures were taken; 14 number of the well; 103 temperature, OC; 1610 depth of top occurrence of the Upper Cretaceous deposits; 2 geoisotherms along the top of the Upper Cretaceous deposits in OC; 3 outcrops of Upper Cretaceous deposits to the surface; 4 regions without Upper Cretaceous deposits.

are determined in Upper Cretaceous deposits in the region charaoterized by considerable jointing of limestones. The geothermal degree for Lower Cretaceous deposits varies from 30 to 90 m/‘C, thermal resistivity of rocks equals 0.38-0.62 mh “C/kcal. For the Jurassic complex, geothermal degrees are 18.0-80.0 m/Y, thermal resistivity of rocks is 0.30-0.60 mh “C/kcal. Thus high geothermal degrees have been determined for Pliocene-Miocene, Eocene-Paleocene and Mesozoic deposits. The smallest geothermal degrees are characteristic of the Maikop deposits. Within the boundaries of the Great and Minor Caucasus, a greater part of the Pre-Mesozoic and Meso-

Cenozoic deposits outcrops. The considerable hypsometric uplift, a highly-developed hydrogeographic net, and an abundant quantity of precipitation cause water infiltration into rocks whose intensive circulation produces cooling in the interior of the earth. Low temperatures and high values of the geothermal degree are evidence of this. At the same time thermal anomalies sometimes come into existence near fractures and volcanic focuses. The thermal condition of the sedimentary mantle of the Pre-Caucasian foredeep and Kura-Arax intermontane depression depends upon tectonics, presence of the strata of different geothermal characteristics in the Meso-Cenozoic section, changing of their thickness, manifestation of the latest tectonic movements, under1103

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. Fio. 2. - - Map o~ geoisotherms o~ the Caucasus Jor the depth o] 2000 metres. 1 Wells in which measurements of temperatures were taken; 6 number of the well; 40.4 temperature at the depth of 2000 m in °C; 2 geoisotherms in °C; 3 outcrops to the surface of Eocene-Paleocene and older deposits.

ground water dynamics and so on. All the above mentioned factors provide a very interesting picture of the distribution of the thermal area. The character of the temperature distribution underground in the territory under exploration is well shown on the isotherm maps on the top of the different stratigraphic horizons (Figure I) and on the maps for the depths of 500-1000-2000-2500 and 3000 m, (Figure 2) and on the maps of the geoisothermal surface of 50 and 100 °C. The geothermal pecularities of the region including the area of the Alpine folding and young Post-Ercynian platform are determined first of all by its abyssal structure. Indeed, the highest values of the thermal flow have been determined for meganticlinoriums of the Great and Minor Caucasus-regions, where abyssal 1104

processes were and still are very intensive. High seism i c i t y of the lower rock strata and Quaternary volcanism illustrate this. The Post-Ercynian platform is a small part of the vast territory where geosynclinal processes ceased before the Paleozoic era and is characterised by comparatively low values of thermal flow. In the light of modern ideas about the depth of the structure of the interior of the earth, higher thermal streams in the Alpine folded regions are explained from the point of view of abyssal tectonic processes: the process of active zonal melting, which corresponds to the geosynclinal stage of the formation of the crust for which large capacities of the upward-moving easily melted components and high thermal streams are

characteristic, and also the process of inflow and outflow of the abyssal material. Simultaneously with the growth of the uplift, their denudation and redeposition of the substance in the depressions, compensating reflowing of the abyssal substance from under loaded areas (of the seas and abyssal basins) begin to act, which is also accompanied by intensive abyssal heat transportation. The regular thinning of the ~ granitic stratum >> from the axial part of the meganticlinorium of the Caucasus towards intermontane and submontane downwarp and the Black and the Caspian seas, testifies the connection of the development of the uplift and downwarp zones with the process of crust formation. Thus, within the limits of the meganticlinorium of the Great Caucasus a tremendous efflux of heat from the interior of the earth has been noted. For well No. 36 of the Leftbank (Levoberezhni) polymetaUic deposit (Sadono-Unalskay anticline of the central uplift) q = 4.63 Ix cal/cm' see. The flow for well No. 10 of the Karmadon mineral water deposit (central uplift) is close to it (the flow in the well No. 36) and is 3.38 tx cal/cm2sec. In the first case the anomaly value of the flow is due to the peculiarities of the abyssal formation of the interior, and heat generation because of the latest tectonic movements; in the second case, it is due to the high position of the Kazbec volcanic chamber. Considerable positive thermal anomalies are found in the districts of the Chegem and Elbrus volcanoes. Numerous thermomineral springs saturated with chlorine and carbon dioxide are the results of former volcanic activity and are confined to the lines of the large disjunctives stretching far to the top of magmatic chambers. Very interesting regularities have been noted by us along the south-eastern end of the Great Caucasus. For the Apsheron periclinal bowing with the adjoining water area of the Caspian Sea, a great range of values of thermal flow (0.79-2.16) Ix'cal/cmZsec is charactedstic. The greatest thermal stress of the lower rock strata is registered for western and central Aspheron anticlinoriums, a little less for eastern Aspheron anticlinorium, and a minimum one for western and eastern Aspheron synclines. It has been determined that the most active thermal processes take place along with complication of structures caused by mud volcanoes: Lockbatan, Bibihaibat, Balahany - Sabunchy - Ramany, Zikh, Peschany and some others. Immersion of folds and attenuation of folding is accompanied by decrease of thermal streams. Thus the asymmetric brachy-anticline Bibihaibat is complicated by the buried (fossil) volcano ~ Bukhta ~ and by a series of disturbances. Here, the greatest value of thermal streams is registered in the dome of the structure, near t h e mud volcano (q = 3.23 Ix cal/cm'-'sec), the roots of which are located deep in the interior of the earth. The mud volcano, situated on the south-eastern pericline of the same fold, is

clearly marked by higher values of thermal flow (2.16 [t cal/cm2sec). Moving off the mud volcano, the magnitude of the flow lowers to 1.4 [~ cal/cm2sec. The same phenomenon has been noticed along Lockbatan. The north-eastern part of the Samhetsk-Karabakh anticlinorium of the Caucasus Minor at its conjugation zone with the south-western side of the Kura depression is characterized by higher values of thermal flow (1.42-2.29) IX cal/cm2sec. Here the developed folds of the third order are orientated in transversal direction with respect to the main strike of folds of the Caucasus Minor. It is noteworthy that the structure of SamhetskKarabakh anticlinorium is complicated by emplacement of intrusive bodies of various sizes; presence of abyssal fractures has also been noticed there. The higher values of the thermal flow of the north-eastern part of Samhetsk-Karabakh anticlinorium co-ordinate very well with the high magnitude of thermal flow determined by us for the regions of the Caucasus Minor included in the territory of the Armenian SSR (more than 2 IX cal/cmZsec). Higher seismic activity is related with these regions. To the north-northeast of the Causasus Minor towards the Kura depression, a decrease in the magnitude of thermal flow is noted: from (2.29-1.91) Ix eal/ cm2 see along Kazanbulag to 1.42 IX cal/cm2sec along Naftalan. The eastern part of the Kura depression is in the process of intensive downwarping and as a result of this the boundary of the depression is expanding. The amplitude of the overall swing of the Quaternary movement sometimes reaches 2000 m. Minimum values of thermal flow (0.5-0.75)IX cal/cm2sec have been determined for the Lower Kura depression. The distribution of thermal flow values within the limits of the foredeep and the Epigertsen platform has the following features. The Stavropol dome is a large transversal uplift of Paleozoic folded base which divides extremely large depression zones. The thermal flow has the maximum values for the pre-Caucasus regions 2-3.4 IX cal/cm-'sec. For the east-Kuban depression, situated between the Stavropol arch and the northern slopes of the Great Caucasus, the thermal flow values range from 1.3 to 1.8 IX cal/cm2sec. High values of the flow have been registered for the Adighey structural projection up to 2.2 IXcal/cm'sec. In numerous wells drilled on the west-Kuban sag the flow ranges from 0.98 to 1.44 It cal/cm~sec. Minimum values are characteristic for the central most immersed part of the sag. For swell-like uplifts and structural projection (Yeisko-Berezansk group of uplifts, Kalnibolotsky bar and others) of the north of the Azov-Kuban depression, the thermal flow ranges from 1.28 to 1.81 Ix cal/ cm2sec. Higher thermal flow has been determined for one more transversal uplift the Mineral Vody projection (2.02-2.43 IX cal/cm2sec). Considerable values of thermal flow have been registered at the western part of the Tersk-Kuma depression and along the Tersk-Ca1105

spian sag (1.6-2.02 I~ cal/cm~sec) which is the result of rather intensive tectonic processes taking place there. An essential part in creation of thermal anomalies belongs to abyssal breakings through which, due to the presence of very compact and metamorphic rocks of high heat conductivity intensive transfer of abyssal heat to higher rocks probably takes place; generation of heat is also probable. As examples of the above stated we may take an interesting thermal anomaly in the region of Sadon polymetallic deposit, thermal anomalies along the development of Yeisk-Prikumsk, Kabardin-Sarpinsk and other sutural zones and a whole series of abyssal breakings. Let us consider the Sadon thermal anomaly somewhat more thoroughly. The Sadon-Unalsky antieline, to which an ore deposit is attached, is complicated by a great number of lateral and transversal dislocations with a break of continuity. The largest ones are the Glavny Roodny and Sadon-Unalsky breakings. The first is traced for a distance of 3-3.5 km, the second for several dozens of kilometers in the granites of Pre-Cambrian or Lower-Paleozoic and igneous volcanic formations of peat, In a number of mines from the Krasnaya ~, adit to horizon II in the breaking zone, a sharp rise in rock temperature up to 35-36°C is observed. Moving off the main breaking zone the rock temperature drops sharply. The breaking zone is marked by strongly broken down rocks. Here we have an intensive manifestation of vertical and lateral stress; narrowing of openings is also observed. Nevertheless, it should be noted that heat anomalies are not recorded over all abyssal fractures. In some cases this may be due to lack of a sufficient number of geothermic observations, in others to difference in time of laying and renewal of fractures. In sedimentary strata, particularly in hydrodynamic active zones, variations in values of geothermal gradients and in intensity of heat flow from horizon to horizon is observed; comparatively low temperatures of rocks are also observed there. Inconstancy in values of thermal flow along the cross section is presumed to be due to the influence of the movement of underground water on the pattern of heat distribution. Calculation of the convective component of thermal flow intensity along the wells, located in a hydrodynamic active zone, has shown that in some eases it is several times the conductive component. The thermal waters of the Caucasus are valuabt~ and useful materials. They are widely utilized ever," where. In the Krasnodar territory near the settlement of Tulsky a water spout up to 4000 mS/d has been obtained from well No. 27, the temperature at the mouth being 86 °C. The thermal waters are used by hot houses of the Maikop state vegetable and dairy farm. At present, a hydropathic is functioning on the thermal waters obtained from well No. 1 in the town of" Labinsk. -1106

There are also hydropathics in the town of Maikop and in the Kossak village of Velikaya. In Maikop over a period of more than 10 years well No. 8 has been producing water with a mouth temperature of 75 °C. The initial output of the well has been 5000 mS/d. Thermal waters are used for balneological purposes in the town of Khadizhensk and the settlement of Akhtirsky. Underground heat was first used at dairy farms and for everyday necessities of life on a collective farm of the Predgorny district in Stavropol territory. Here 1000 mS/d of water having the temperature 47.5 °C and surplus piestic head pressure 32 atm have been obtained from Albian-Aptsky sandstones. High surplus pressure has provided a spontaneous water supply to the points of consumption, and poor mineralization made this exploitation possible without the need to construct any heat-exchangers. In Kabardin-Balkaria, thermal waters are applied for district heating and the hot water supply of such buildings as the hydropathics, mud baths, the • E1brus ~ sanatorium, the spa clinic, for heating medicinal mud, in baths, showers and in the swimming pool. Used hot water passes to hot houses functioning all the year round, where vegetables and flowers are grown. The total annual saving from applying thermal waters in Kabardin-Balkaria is 2000-2500 tons of conventional fuel. In Chechen-Ingushia, hot waters are used for heating hot houses. Hot water of the Braguny springs are used for heating the hospital. Hot subsurface water-application in Dagestan has been in use since 1949. In the town of Makhachkala, thermal waters are used in boiler units of the refinery, for heating the workmen settlement, and the buildings of the section of the USSR Academy of Sciences, in bath houses and for bottling. We have mentioned only a few examples of thermal water application. It should be noted that in the near future thermal waters will be in use in many branches of the Caucasian Republic's national economy. In fact, consideration will be given to great streams of thermal waters obtained in practically all regions of the Caucasus (Figure 3). Many hot and superheated waters contain higher amounts of iodine, bromine, boron, strontium, lithium, fluorine and other elements. These elements can be looked upon as raw materials for chemical enterprises. Successful application of thermal waters is preceded by thorough geological, hydrogeologieal and geothermal study. A considerable amount of thermal water is obtained in a producing oil field. In addition, oil fields and whole oil regions have been the subject of thorough study for many decades. Observation over many years makes it possible to begin the utilization of hot waters without additional prospecting. In the Caucasus, for instance, the Terek-Sunzha oil area is one of the most thoroughly studied oil regions. Oil

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FIo. 3. - - Map o/ outputs o/ thermal waters /or some wells and springs oJ the Caucasus 1 - thermal springs referring to deposits of Mesozoic age; 2 thermal springs referring to the deposits of Cenozoic age:

3 - wells which gave inflows of waters out of the deposits of Mesozoic age; 4 . wells with waters out of deposits of Cenozoic age; 5 - output of water more than 10,000 ma/d (numerator), the temperature of water at the mouth of the well or at the vent of the spring, °C (denominator); 6 - output of water from 1000 to 10,000 ma/d (numerator), temperature of water at the mouth of the well or at the vent of the spring, 0C (denominator); 7 . output of water from 100 to 1000 ma/d (numerator), temperature of water at the mouth of the well or at the vent of the springs, °C (denominator). deposits confined to Karagan-Chokrak sand strata have already been exploited here over a period of 50-75 years. Many productive strata have been almost exhausted; this, in combination with high pressure and poorly mineralized waters of sodium bicarbonate type in the Middle Miocene deposits, makes favourable conditions for the application of the thermal waters of these strata in national economy. Meso-Cenozoic and Post-Pliocene deposits are also included in the Terek-Sunzha region. As to the tectonic structure, one can clearly see the northern monocline of the eastern part of the Caucasian rocky formation, the Sunzha syncline lying north of the monocline, the anticlinal fold zone of Sunzha and Terek an-

ticlinoriums and the syncline zone dividing them (Figure 4). For many decades the main productive strata of the above-mentioned territory have been the Karagan-Chokrak deposits. The Karagan horizon is lithologically expressed by thick sand strata interbedded with clays and a few marl bands. In terms of lithology, the Chokrak horizon deposits are divided into two parts: the lower (argillaceous one) composed of clays with marl bands and argillaceous siderites, and the upper (sandy-argillaceous one) represented by alternation of thick sand strata and clays. In the Karagan horizon section there are 13 sandy strata, and 7 in the sandy-argillaceous upper part of the Chokrak. The main feeding area of the Middle Miocene deposits is within the boun-

1107

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Schematic hydrogeological cross-section o[ the Terek-Sunzha oil and gas-bearing region.

1 . injection well; 2 - producing wells; Oj . Quaternary deposits; N~a ap+ak- Apsheron-Akchagilsk stages; Ntt mt. M~tichesky stage; N18 sm- Sarmat stage; NI2 kg - Karagansk horizon; NI~ ~ . Chokraks horizon; N,]+p~ - Maikop suit=; Pg~÷~ - Foraminifer series; Cr2 - Upper Cretaceous deposits; Cr, - Lower Cretaceous deposits; ] . Iurassic deposits; L - Distance between injection and producing wells equal to 500 m.

dary of the northern monocline (Chorny Gory), where they outcrop at absolute elevation marks of + 6 0 0 + +950 m. From the feeding area, waters migrate to the north and north-cast in the direction of submergence of the water-hearing complex. Within the limits of the Sunzha and Petropavlovsk synclines, rocks submerge to great depths and waters which are in them reach temperatures of 120-160 °C. The fine accumulating properties of sandy strata (porosity 20-30%, permeability over 2.0 darcy) caused rapid water migration and the diffusion of poorly mineralized water of sodium bicarbonate type in the Middle Miocene deposits of the Terek-Sunzha region (according to V. A. SOLIN'S classification). Waters heated at great depths, when migrating. have no time to lower their temperature considerably and on approaching the Octyabrsky anticline, intensively convey their heat to surrounding rocks. In connection with the above statement, high temperatures were recorded in the Karagan-Chokrak deposits within the limit of the Octyabrsky oifield. Here the water temperature at the well heads reaches 80-90°C. The main drainage area of water-bearing Middle Miocene horizons is situated within the limits of Peredovih (Terek and Sunzha) ridges, where powerful springs of thermal waters Mamakai-Yourtovsky (with a temperature of 70°C), Goryachevodsk (80-90°C), Braguny (89-91°C), Gudermess (63.5-75°C), Sernovodsk (40-70°C) and many others were known long ago. In the early stages of exploitation of the KaraganChokrak deposits, the liquid extraction from productive strata of oilfields was not large and output of springs remained almost constant. A sharp increase of production led to the drop of hydrostatic levels, to the spreading of cones of depression for dozens of kilometres which caused spring output decrease up to complete depletion. 1108

Let us consider the influence of the exploitation of productive strata of Karagan Chokrak deposits in the Octyabrsky oilfield upon some of the above-named spring debits. The Octyabrsky oiflield is situated in the southern outskirts of Grozny. In Karagan horizons I, II, III, IV, VII, VIII, X, XI, XII, XIII, XIV and in Chokrak XV, XVI d, XVIII, XIX, XX and XXII strata are oil-bearing. Exploitation of this oilfie~d was begun in 1913. By the 1't of Ianuary, 1969, more than 56 millions tons of oil and about 260 millions m ~ of water with temperatures up to 81 °C had been produced at many well heads. About 90% of the total liquid extraction was produced from strata XIII, XVI, XX and XXII. 5.6-6.2 millions m ~ of water is extracted annually together with oil. Water heat flux (when lowering temperature to 20°C) from the depths of the Octyabrsky oilfield was 15.8×10 ]2 kcal for 55 years. In order to obtain such an amount of heat it would have been necessary to burn 1.6 millions tons of mazut or 2.3 million tons of coal, or about 2 billion m a of natural gas. The main oil deposits are under water pressure. Stratum XIII of the Octyabrsky oilfield came into operation in 1916. For the first time a gusher with an output of 52 t/d was produced from well No 1/25. The high productivity of this stratum was confirmed in the following years. The outflows of pure oil from these walls amounted to 616 t/d (well No. 4/23). During the first years the exploitation of the stratum was extremely slow. Till 1926 only 15 wells were drilled in this stratum. In the period of 1926-1930, 44 more wells came into operation in stratum XIII. Annual oil production increased steadily and in 1930 it reached its maximum (Figure 5a). At the beginning of exploitation the output of the eastern Goryachevodsk spring attached to the same stratum XIII amounted to 1230 mS/d. In 1926 with daily liquid extraction from stratum XIII amount-

ure 5b). Since 1957 the total liquid recovery from stratum XIII has decreased and does not exceed 2000 m3/d, while hydrodynamic levels increase. In 1969 the levels reached +222.7 m as compared with + 6 0 m in 1952. In the area of Goryachevodsk the minimum level (112 m) was marked in lune, 1957. In the following years levels were seen to increase at a rate of 0.01 m/d. The west Goryachevodsk spring was completely exhausted in 1928 as a result of exploitation of stratum XVI in the Octyabrsky oilfield and stratum XII (its analogue) in the Solyonaya Balka of the Starogroznensky oil field and the output of the Braguny spring decreased. The first oil from stratum XVI of the Octyabrsky oil field was produced in 1916. However, due to insufficient geological study of the field and tech-

ing to 2850 m 3, the output of the spring decreased to 1037 mS/d, and in the following years 1927-29 to 907520 m3/d. In 1930 liquid extraction from stratum XIII reached its maximum i.e. 6400 mS/d. The water output of the eastern Goryachevodsk spring decreased to 250-320 m3/d in 1930, at the beginning of 1931 was equal to 166 m3/d and at the end of November 1931, 51 m3/d. In 1932 the spring was exhausted. From 1930 to 1932 in the Octyabrsky oilfield the rate of decreasing hydrodynamic level in stratum XIII was 0.145 m/d. In 1942-43 in connection with the halt in production of many wells, one could observe an increase in the level at the rate of 0.3 m/d. In 1944-1952 a considerable drop in the hydrodynamic level was observed again because of intensive liquid recovery (Fig60000-

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5 . - - a ) Curves of extraction o/ the total liquid/rom stratum XIII o[ the Octyabrsky oil field (1916-1969). 1 - total yearly extraction of liquid; 2 - the extraction of the total-liquid; (summarized accumulation). b ) Hydrodynamic levels o/stratum XIII during its development and operation (1916-1969). 3 - initial level; 4 - state of the hydrodynamic level for the outlined well No. 1/28 (stratum X I I I ) ; 5 - state dynamic level of stratum X I I I ; 6 - point of the outflow of the eastern Goryachevodsk spring.

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1109

nical inadequacy, prospecting and exploitation of stratum XVI were not carried out. Intensive exploitation of stratum XVI began in 1926 after a gusher (1752 t/d) arose from well No. 2/17. By the end of 1927, nine wells had been producing from this stratum, 1048.6 thousand tons of oil having been produced in one year. In 1928-32 the number of producing wells and the oil production from stratum XVI increased quickly (Figure 6a). Maximum oil production (4,873,000 tons) from this stratum was achieved in 1931, all the oil ha~/ing been produced in dehydrated state as a gusher. Then the water production increased sharply and made up 52.8% of all the produced fluid. Pro-

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gressive well flooding caused a sharp decrease in oil production. The oil production in 1941 proved to be 166.6 thousand tons i.e.29 times less as compared with 1931. For this period the annual water production increased almost 64 times. Since 1943, intensive fluid production has bccn obtained from a great number of wells (G. T. MOVMIGA 1961). As fluid production from the stratum decreased sharply in 1957, hydrodynamic levels which were at the points of +30.4 m in 195256 increased steadily (Figure 6b). The commercial oil content of stratum XXII was determined in 1927 by well No. 12/I,~,the output of the gusher of dehydrated oil being 488 tons a day. Only

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1926

1931

193G

1941

1946

t951

19SS

196i

1066

A +200

I

Illl

',100

m ,

.

Ig2S

1931

.

.

.

.

1936

, .

.

.

.

.

.

1941

, m

/

.

t9.46

1951

1956

1961

1966

B giG. 6. - - a) Curves of extraction oJ the total liquid trom stratum X V I o/the Octyabrsky oil field (1926.1989). 1 - annual liquid extraction; 2 - total liquid extraction ( s u m m a r i z e d accumulation). b) Hydrodynamic levels o/ stratum XVI during its development and operation (1926-1969). 3 - initial level; 4 - state of hydrodynamic level from stratum XV]; 5 - point of the outflov o f the western Goryachevodsk spring; 6 - point of outflow of Braguni spring.

1110

one well was producing from this stratum till 1930. In 1930-32 ten wells with an initial output from 71 to 522 t/d were drilled into stratum XXII. The oil production achieved its maximum (854,000 tons) in 1932. After 1933, oil production from the wells decreased and water recovery increased as the water table approached the bottoms of the holes. Well hydration was especially intensive in 1934-36 when the water content in produced liquid increased from 2.6% (1933) to 89.5% (1936). The method of intensive liquid recovery has been applied since 1935. 25.2 thousand tons of oil and 925.5

thousand tons of water were produced from stratum XXII in 1940, flooding being 97.4% (Figure 7a). Only 2 wells were producing from this stratum in the sixties• 2000 tons of oil and 249.3 thousand tons of water were produced from this stratum in 1958. Water content was 99.2% (G. T. MOVMIC,A 1961). Annual oil production amounted to 2.6 thousand tons and that of water to 452.8 thousand tons in 1968. Figure 7b illustrates hydrodynamic level changes for stratum XXII in the period of its exploitation. In neither of the abovementioned strata have levels in the hydrodynamic sys. o . "+

~

2500

,+

I-,,

.f.j.f'~'~

sr ell

OD

./I ,~.//

2000 r-

g X

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///"

1900

+0 tlC

//

X

tE

"~o I000 0

0

W

t~ 7

'IO

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ID 0

0

•

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°

,"

,

1932

1937

1942

1947

1959

1957

Iglt,'/'

1982

,4

+400

13 J

*200

1927

~

m

f

1932

1937

1942

1947

1952

Ig57

1962

Igs7

B FIG. 7. ~ a) Curves of extraction of the total liquid #om stratum X X l l ot the Octyabrsky oil field (1927-1969). 1 - annual liquid extraction; 2 - total liquid extraction (summarized accumulation). b) Hydrodynamic levels o/stratum XXII during its development and operation (1927-1969). 3 - initial level, 4 - approximate state of hydrodynamic level of stratum XXII; 5 - point of outflow of Sernovodsk spring• IIII

tern of the Chorny Gory-Sunzha and Brauguny ridges reached the initial data. Presumably it may be predicted that this will take place in the near future and then the Goryachevodsk springs will begin producing again. At the present time strata XIII, XVI and XXII of the Octyabrsky oilfield are almost exhausted, this creating favourable conditions for utilizing the thermal waters of these and other strata for the district heating of Grozny. High oil efficiency up to 0.96 was really achieved from strata XIII, XVI and XXII in the Octyabrsky oilfield. In connection with utilizing thermal water for the construction of geothermal stations, and for town district heating, the authors examined the temperatures of wells which have been out of operation for a long time, explored the thermal-physical properties of rocks, and calculated the magnitude of heat flow coming out of the deep strata within the boundaries of the Octyabrsky oilfield. The factors of thermal-physical parameters of lithological-stratigraphic sections were determined by steady state methods. Dozens of samples of various sodimentary rocks were examined in air-dry and damp states in the temperature range from 15-20 to 90-100°C. Thermophysical parameters were determined for sandstones, siltstones and days. Thermai conductivity of days in the Sarmat stage, the Karagan and Chokrak horizons, changes from 1.10 to 1.43 kcal/mla °C. Siltstone values of thermal conductivity usually being higher (1.81-2.19 kcal/mh°C). A great number of thermalphysical constant definitions were made for various sandstones selected from different strata of Karagan and Chokrak horizons. Their thermal conductivity ranges from 1.78 to 3.85 kcal/mh °C. The calculation of heat flow intensity was made for two lithologically different zones of the section. The harmonic average of thermal conductivity for the thicb ness of Sarmat clays is equal to 1.16 kcal/mh °C, the value of the geothermal degree 9.48 m/°C (geothermal gradient 0.1051 °C/m). The heat flow intensity is 3.38 1~ cal/cm~sec. For sandy argillaceous deposits of Chokrak and Karagan horizons, the geothermal degree is 15.7 m/°C (geothermal gradient 0.0635 °C/m). The harmonic average value of thermal conductivity is 1.99 kcal/ mh °C, the heat flow intensity 3.51 I~ eal/cm2sec. The geothermal exploration which was carried out proved the hydrodynamic system to be highly reliable. The higher heat flow intensity for the Sarmat, Karagan and Chokrak horizons witnesses the intensive and lasting influence of hot waters on the temperature conditions of the area. The thermal waters of the Karagan-Chokrak complex in the Terek-Dagestan region are a source of a cheap heat energy. Having drilled producing well s 4000 m deep in the Petropavlovsk syncline at t h e distance of 5.5 km to the north-east from the Octyabrsky oil1112

field, hot waters of a temperature of up to 160°C can be obtained from Karagan-Chokrak deposits. To recover resources of thermal waters, in some wells of the Octyabrsky oil field injection can be used (Figure 4). As it was necessary to establish an allowable rate of thermal water and determine the amount of injected water for recovering resources of thermal waters, the authors had to make heat calculations. These calculations were made to explain the nature of temperature changes in the stratum when water is injected. They are made according to LAUVERI~R'S (1955) calculation scheme which takes into account convection transportation of heat in the stratum and heat conductivity of surrounding formations in a vertical direction.

T--To

T 1 - To--'

, eric l

where OoI ~ - ~1

~

] ! × ao{~-~,

2~,/Blr-~J ,

is a unit function

when {r-~} < 0

o0(~--~} = 0;

when{~-~}> 0

Ool:-~} = 1;

4.),.x 4.),.t = h 2"c1"v' "~-- h"C2 , B =

C2 C

T -- temperature of the stratum, °C, while injecting water O m~/d at the time t T. -- initial temperature of the stratum, oc T , - temperature of injected water at the head of the stratum, °C 1 -thermal conductivity factor of the surrounding bed rocks in kcal/m h oC Cl -- total heat capacity of water injected into the stratum, kcal/ms °C C 2 - - volumetric heat capacity of the water-saturated stratum, kcal/ms °C C ~ volumetric heat capacity of surrounding rocks, k c a l / m 3 oC. h -- stratum thickness, m v -r a t e o f filtration, m/h x ~ linear distance, m The experimental investigations of the flow of heat in a stratum while injecting hot water into it, carried out at the Institute of Geology and Development of Combustible Minerals by G. E. MALOFEVEV (1962), agreed closely with the test results and calculations according to H. A. LAUWm~a's formula. Strata XIII and XVI of the Oetyabrsky oil field were chosen as the object of research. Their total effective thickness is 100 m; permeability 1.8 dare)'; porosity 23 %. The thermal conductivity of the surrounding rocks is assumed to be 1.26 kcal/mh°C; volumetric heat capacity of the qnjected liquid into the stratum is 1000 kcal/m 8 °C; volumetric heat capacity of the water-saturated stratum 520 kcal/mS°C; volumetric heat capacity of the surrounding reeks 660 kcal/m~°C. The calculations were made for an assumed production of thermal water from the system equal to 25,000, 50,000

and 100,000 m3/d for the points 2000, 3000, 4000 and 5500 m away from the injection wells. The hydrodynamic system is assumed to work in severe conditions, when the amount of injected water is equal to the amount of water produced. The replenishment of possible losses of water in the stratum while injecting is assumed to be due to the natural feed of the strata within the boundaries of the Chorny Gory (Black Mountains). It was assumed that the initial temperature of the producing wells was: 1) 2) 3) 4)

for for for for

the the the the

wells wells wells wells

5500 4000 3000 2000

m m m m

away away away away

-

160 149 141 134

oc. °C. °C. °C.

The temperature at the bottom of the producing well was assumed to be 120 °C. The result of the calculations are given in Figures 8, 9, 10. As can be seen from the Figures, the tempera-

ture of the stratum is decreased most effectively, by injecting 100,000 m 3 of water daily. When the injection and recovery is 100,000 m3/d the velocity of water flow is 0.01 m/h. The front part of the injected water will reach the producing wells 5500 m away from the injection wells in 14 years; 4000 m in 10 years; 3000 m in 7.5 years; 2000 m in 5 years. The reduction of the stratum temperature under given conditions of the work of this system (O = -- 100,000 m3/d) will take place: 1) When the distance between the producing and injection wells is 2000 m in ten years 2) 3000 - in 16 years 3) 4000 - in 22 years 4) 5500 - in 32 years The temperature of the stratum will decrease more intensively during the first years of its cooling. In the subsequent years the rate of the temperature fall will decrease sharply.

T'C 180

140

120

"-

~~.

80

U

"~

~---~..~..~.__..~.~_

40

lo

15

20

25

30

35

40

45

50

Fie, 8. - - Diagram of changing temperature o~ the stratum versus time 'during the pumping out and injection of water . 100,000

ma/d. 1 - (------) d u r i n g the injection of w a t e r at the h e a d of the s t r a t u m w i t h the t e m p e r a t u r e 50 °C; 2 - ( ) d u r i n g the injection of w a t e r at the h e a d of the s t r a t u m w i t h the t e m p e r a t u r e of 20 °C; 5500 m - the distance b e t w e e n injection a n d prod u c i n g wells; 4 0 0 0 , 3000, 2000 linear distance f r o m the injection well.

1113

T'C leo

\'\

140,

120'

I00

80'

40

=dlu 5

1o

18

20

~15

SO

35

40

45

FIG. 9. - - Diagram o/changing temperature of the stratum versus time during pumping out and injection of water . 50,000 mS/d. 1 - during the water injection at the head of the stratum with t o = 50 °C; 2 . during the water injection at the head of

the stratum with t° = 20 °C; 5500 m - the distance between injection and producing wells; 4000, 3000, 2000 m . linear distance from injection wells.

When recovering and injecting 100,0(30 m3/d water into the stratum (as calculations have shown), the most rational distance between producing and injection wells is 5500 m. The cooling of the strata in this case will take place in 32 years. In 50 years of work of the given system the temperature of the recovered liquid will decrease to 100°C or 83°C, when water is injected with the temperature of 50 and 20 °C respectively. Let us consider the rate of cooling of the stratum when injecting 50,000 m3/d of water into it. The rate of filtration in this case is 0.006 m / h . The time of advancing of the front part of the injected water for the producing series of wells will be: 1) for the wells located at the distance of 2000 m - 8 years 2) 3000 m - 13 years 3) 4000 m - 17 years 4) 5500 m - 23 years 1114

The sharp decrease of temperature, as one can see from the diagram, will begin in 20, 30 and 4 0 years at the points 2000, 3000 and 4000 m away from the injection wells. For the wells of producing series located at the distance of 5500 m the decrease of the stratum temperature will begin only in 54 years. In 55 years if 50,000 mJ/d of thermal water is recovered by the wells located 5500 away from the injection wells, the temperature of the recovered water will fall by 10°C, this fall taking place during the last 2 years of production. The best results (when the stratum temperature will not fall at the points 5500, 4000 and 3000 m) may be obtained when 25,000 m 3 of thermal water is injected and recovered daily. The velocity of the water flow in this case i6 0.003~ m / h . The front part of the injected water will approach the wells of producing' series 5500, 4000, 3000, 2000

leo

l

l

I

J,~IW+

140

120

80

m~

.40+

20..

i

I0

I~ ------

20

~

I

~0

,,,

i

W

40

15

~0

--- '['. lob 55

2

FIe. 10. - - Diagram of changing temperature of the stratum versus time during pumping out and injection of water - 25,000 ma/d. 1 - during water injection at the head of the stratum with t o = 50 °C; 2 - during water injection at the head of the stratum with t o = 20 °C; 5500 m - distance between the injection and producing wells; 4000, 3000 and 2000 m - linear distance from injection wells.

m a w a y from the injection series a n d this will h a p p e n in 41, 30, 22 a n d 15 years respectively. W h e n 100,000 m3/d, 50,000 m3/d, 25,000 m3/d is injected into the stratum, the process of cooling of this s t r a t u m proceeds less intensively w h e n the temperature of the used injected w a t e r is 50°C. T h e h y d r o d y n a m i c system above described is as yet one of the most reliable a n d deeply studied in the Caucasus for a p r o l o n g e d p e r i o d of utilization of therm a l waters. The thermal waters of this h y d r o d y n a m i c system can be used for heating of large setflemants, industrial enterprises, agriculture a n d for generating electrical energy. Continuous and c o m p a r a t i v e l y simple replenishment of resources of thermal waters guarantees the reliability of this h y d r o d y n a m i c system for quite a long p e r i o d of time.

REFERENCES LAo'v~a~.~ H. A. 1955 - - The transport of heat in an oil layer caused by the injection of hot fluid. Appl. sei. Res. See. A, 5. MALAFEYEV G. E. 1962 ~ The comparative value of the formulas for the estimation of the heating of the stratum during the injection of the hot liquid. Ne~tyanoe Chozyaistvo, 4. S u ~ G. M., T x ~ r o r d ~ Y. K., Vt.~aOVA S. P. 1962 a Geothermal peculiarities of the oil and gas deposits of the Caucasus. Soviet Geol., 12. S ~ G. M., T~nLn~a~tA Y. K., Vt~SOvA S. P. 1962 b - New data about the geothermal features of the oil and gas deposits of the Caucasus. (On the problem of geothermal zoning). Rep. Acad. Sci. USSR, 146, 5, SUtHAl~V G. M., VLASOVAS. P., T ~ Y. K. 1966 - The solution of some questions, connected with the resurrection of the resources of the submn'face thermal watch during their utilization in the national economy (on the base of the hydrodynamic system of the Terek-Sunzha oil and gas-bearing region). Rep. Acad. Sci. USSR, 168, 4. 1115