Layer | Fill | Outline |
---|
Map layers
Theme | Visible | Selectable | Appearance | Zoom Range (now: 0) |
---|
Fill | Stroke |
---|---|
Collaborating Authors
Croatia
Abstract Presented in this paper is a novel technique of hydraulic fracture azimuth determination. Full size oriented cores, retrieved after microfracturing, were scanned using X-ray computed tomography (CT) to evaluate the fractures. The SEM/EDAX analysis was applied to confirm the presence of barite particles from drilling mud inside hydraulically induced fractures. The study, performed on core samples from the same sandstone formation of two adjacent fields, showed the good agreement of fracture azimuth data, obtained from CT analysis. Postfrac well production history indicates a significant hydrocarbon productivity increase, without interference to surrounding wells. Introduction Orientation of hydraulically induced fractures has a significant impact on final results of hydraulic fracturing operations. Knowledge of hydraulic fracture orientation can be useful in many reservoir applications. Hydraulic fracture azimuth prediction becomes important in terms of improving recovery efficiency in case of producing wells, or optimizing the areal sweep efficiency in case of water flooding or EOR applications using injection wells. When designing the injection pattern and selecting optimum well locations, fracture azimuth should not be ignored. For waterflooding producing wells located perpendicular to the fracture direction will experience better areal sweep efficiency, than wells, situated parallel to the fracture direction. On the other hand, if fracture orientation can not be predicted, and spacing of wells is less than the designed propped fracture length - the wing of fracture can aim to the neighboring well, causing the failure of both wells. Also, if geological condition cause favorable fracture direction, the wing of fracture can reach the hydraulically isolated part of the reservoir, making it recoverable. A number of techniques and methods for mapping or predicting fracture orientation can be found in literature. These can be summarized as:active fracturing techniques (tiltmeter arrays, triaxial borehole seismic), openhole logging techniques (borehole elongation orientation, television camera, sonic televiewers, impression packers), and predictive oriented core techniques (strain relaxation, compressional-wave velocity, thermal expansion, differential strain curve, fracture point load test or residual stress measurement). Although each of them under proper conditions can give more or less accurate and reliable results, each has limitations. In this paper, a new approach to indirect fracture azimuth measurement, based on oriented core analysis is described. The method involves microfracturing technique (Fig. 1) and X-ray CT scanning of oriented cores. During drilling, just after entering a zone of interest for future stimulation by hydraulic fracturing, the drilling process is temporarily interrupted and microfrac job, using relatively small volume of water base - barite weighted mud is performed. This is followed by coring operation and 3 to 10 m of full diameter oriented core is taken from the bottom of the well. The drilling procedure is then continued. Conventional core analysis is performed by visual inspection or by the use of goniometer to characterize fractures, if found on the core surface. X-ray computed tomography is used for visualization and investigation of fractures inside the rock body. Consecutive CT scanning of oriented core (Fig. 2), is made by taking axial cross sections subsequently reconstructed as tomogram images. Since the core orientation during scanning is known and fixed, fracture azimuth is easily determined (see Fig. 3). Analysis of tomogram series furnishes data on fracture growth and position in the core. Hydraulically made fractures can be filled with mud used for microfrac operation. The presence of solid particles, particularly high density barite, can be easily detected in CT tomograms, to distinguish hydraulically initiated fractures from naturally generated ones. Also, the traces of microfrac fluid can be analyzed after location and detection in the fracture by CT scanning, using the other analytical methods, such as SEM/EDAX or chemical analysis of selected rock specimens. Using the data from tomograms, 3-D reconstruction of hydraulically initiated fracture was made. P. 69
- North America > United States (0.30)
- Europe > Croatia (0.29)
- Geology > Mineral > Sulfate > Barite (0.68)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.55)
- Geophysics > Borehole Geophysics (1.00)
- Geophysics > Seismic Surveying (0.88)
- North America > United States > Colorado > DJ (Denver-Julesburg) Basin > Wattenberg Field (0.99)
- Europe > Austria > Pannonian Basin (0.99)
ABSTRACT: Based on many years of research focusing on a number of significant structures (bridges, tunnels, dams, high rock slopes, etc.) designed and realized in the Adriatic coastal area, we have collected a large quantity of engineering-geological and geotechnical information. To devise engineering geological (IGM) and geotechnical models (GM), it is indispensable to conduct engineering rock-mass classification using one of the widely recognized methods. Starting from the existing RMR and Q classifications, we have developed a new "n" classification which enables a more complete limestone classification and categorization, using a relatively simple procedure. RÉSUMÉ: En se basant sur plusierus annees de recherches portant sur un grand nombre de grands ouvrages (ponts, tunnels, barrages, talus rocheux eleves, etc.) etudies et realises dans la zone côtiere de I'Adriatique, nous avons ramasse une grande quantite des donnees geologiques et geotechniques. La classification de la masse rocheuse selon une des meethodes reconnues dans Ie monde est indispensable pour I'etablissement des modeles de geologie de l'ingenieur (IGM) et des modeles geotechniques (GM). En partant des classifications existantes "RMR" et "Q", nous avons developpe une nouvelle classification "n" qui perment une categorisation des calcaires plus complete, a l'aide d'une procedure relativement simple. ZUSAMMENFASSUNG: Auf Grund unserer langjahrigen Forschungen an einer Reihe großer Objekte (Bruecken, Tunnels, Staudamme, Felswande usw.) die in der adriatischen Kuestenregion errichtet wurden, haben wir eine große Menge von ingenieurgeologischen und geotechnischen Angaben gesammelt. Um ingenieurgeologische (IGM) und geotechnische (GM) zu entwerfen, ist es notwendig, eine Ingenieur-Klassifikation von Gesteinsmassen nach einer der anerkannten Methoden durchzufuehren. Ausgehend von bestehenden Einordnungsverfahren "RMR" und "Q" haben wir eine neue "n" Klassifikation entwickelt, die ein vollstandigeres Einordnen und Kategorisieren von Kalksteinen ermöglicht und verhalnismassig einfach ist. 1. INTRODUCTION Croatia's development in the period after 1990 is marked by an increasing global trend of investing in transportation infrastructure. According to estimates presented in various design solutions, approximately 30 to 50 km of road tunnels are to be built on the following highway routes: Zagreb-Maribor, Zagreb-Split (Zadar), Zagreb-Varaždin, Rijeka-Karlovac, Rijeka- Trieste, Rijeka-Dubrovnik. In addition, about 50 km of tunnels are to be built along the approx. 150 km long valley railway line Zagreb-Karlovac-Rijeka. Furthermore, a tunnel approx. 12–15 km in length is to be built through Ćićarije on the railway line stretching from Rijeka to Pula [Jašarević, 1993]. It should also be noted that an intensive urban development of medium-sized and large cities-aimed at revitalizing the existing city centers-has brought about significant traffic and environmental problems that may be resolved in a rational manner by building appropriate underground structures. This particularly applies to large cities situated along the Adriatic coast (Rijeka, Split, Dubrovnik, Šibenik). From the engineering-geological and geotechnical standpoint, the rational and cost-effective design and construction of underground structures must be based on the knowledge of essential rock-mass properties: occurrence of fissures (discontinuous environment), heterogeneity, anisotropy, and natural (primary) stress. In fact, the fissuring exerts the greatest influence on geotechnical properties, i.e. on the design and construction of underground structures in rock massif, which is why this element has been given an appropriate significance in the rock-mass classification (5 out of 11 classification parameters-Table 2). As to traffic corridors, it is important to note that most significant underground structures have been designed and are to be built in the coastal area of Croatia. Limestone formations from the Jurassic and Cretaceous period are present on over 50% of the total coastal area of the Republic of Croatia. Several classifications and categorizations of limestone formations, based on international experience and many years of research conducted in our country, are presented. In addition, the procedure for determining (selecting) geotechnical parameters required in the corresponding calculations is given.
- Europe > Croatia > Primorje-Gorski Kotar County > Rijeka (1.00)
- Europe > Croatia > Zagreb County > Zagreb (0.85)
- Europe > Italy > Friuli Venezia Giulia > Trieste Province > Trieste (0.24)
- Transportation > Ground > Rail (0.74)
- Materials > Chemicals (0.50)
Abstract This paper describes the results of formation damage study on first horizontal well drilled and completed in Croatia. The specific problem of formation damage caused by polymer mud was evaluated in the laboratory, investigating the rock-fluid compatibility and methods for restoring the reservoir permeability around the wellbore. The source of damage was identified as a vey tough mud filtrate cake as well as the reduction of permeability inside the pore space due to mud filtrate invasion. The two stages well stimulating procedure for damage removal, consisting of soaking and injecting oxidizer, then acid, in two steps, tested in the laboratory, showed promising results. Introduction In the last decade the technology of horizontal wells, because of their enhanced productivity, has become widespread. More than 2000 horizontal wells are completed each year worldwide. Maintaining maximum deliverability from these wells requires that formation damage be minimized. In turn, minimizing or preventing formation damage, which is either created during drilling or removed during well completion and production, requires serious in-depth research. Horizontal wells are usually completed by either setting the predrilled or slotted uncemented liner, or leaving the horizontal section as an open hole. In both cases the production interval is not perforated. This means that the horizontal well lacks the perforation tunnels that are normal used in conventional vertical wells to bypass part of the damage caused by drilling mud invasion. Mud damage, which adversely affects productivity, occurs as a result of several factors. First, in open hole, the filter cake, can be formed both as external and uniform at the formation face and as internal, inside the porous medium around the wellbore. Another problem is the permeability reduction that occurs because of the interaction between the rock and incompatible mud filtrate that penetrates into the vicinity of the wellbore. These two factors, often combined with the heterogeneity of the payzone compound the risk of impaired productivity in horizontal wells. Very often for horizontal wells, the water base polymer-type systems are used as drilling fluids. By their nature, polymers contained in the filter cake are tough and not easy degradable. Moreover, the complexities involved in the study of mud filtrate and rock interactions necessitate more detailed research to identify and control the formation damage in horizontal wells. The most optimistic approaches to this problem are to select of mud system that is as unintrusive as possible, or, because a damage is practically inevitable, to implement a proper damage removal, well stimulation method. Well treatment may include filter cake clean up (using drawdown pressure to initialize production, and/or application of a chemical breaker system to destabilize and remove the filter cake) and/or chemical stimulation targeted toward mud filtrate damage elimination. The findings that relate to problems of productivity impairment due to formation damage of the first horizontal well drilled and completed in Croatia are described in this paper. Case History Well A has been designed as a high rate gas-condensate producer and was drilled into the reservoir inside the already developed field, located in the southern part of Pannonian Basin - the Sava Depression. The well parameters are shown in Table 1. The targeted reservoir was at an average depth of 2400 m (TVD), and has an effective thickness of 29 m. The gas-bearing rock is low to medium compact sandstone (mineral composition is shown in Table 2). According to lithological data from surrounding wells, the reservoir lithology is characterized as laminated sandstone intersected with shale layers, which indicated petrophysical anisotropy as a result of complex sedimentary genesis. After completion, before bringing the well onto production, the slotted liner was briefly cleaned up with 2% HCl through 2 3/8 in. tubing lowered to 2890 m in an attempt to disintegrate and remove the mud filter cake.
- Geology > Mineral > Silicate (0.95)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.56)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.45)
ABSTRACT INTRODUCTION Organic materials generally are recognized as effective inhibitors of the corrosion of many metals and alloys. The efficiency of organic compounds as corrosion inhibitors is associated with chemical adsorption, which includes a variation in the charge of the adsorbed substance and a charge transfer from one phase to the other. The reaction mechanism includes the transfer of one pair of electrons from organic compounds and the formation of coordinate bonds with the metal or alloy. The inhibition efficiency (z) strongly depends on the structure and chemical properties of the layers that are formed under the particular experimental conditions. The extent of adsorption is dependent upon the electronic structure of the metal and the inhibitor, since chemisorption requires a chemical bond between the inhibitor and the metal. Imidazole is a heterocyclic organic compound with three carbon and two nitrogen atoms in the ring (Figure 1). One of the nitrogen atoms is of a pyrrole type, and the other is a pyridine-like nitrogen atom. Therefore, imidazole posesses the properties of pyrrole as well as pyridine. The imidazole molecule shows three different anchoring sites suitable for surface bonding: the nitrogen atom (3, Figure 1) with its lonely sp2 electron pair, the C(4)H-C(5)H- edge and the aromatic ring.1 Imidazoles, therefore, are potentially effective inhibitors. The remarkable efficiency of imidazole derivatives for copper and its alloys2-5 as well as for iron6-10 has been established. In contrast, there is very little information about the inhibition of zinc by imidazole.11 The objective of the present work was to investigate the efficiency of some imidazole derivatives as zinc corrosion inhibitors in hydrochloric acid (HCl). EXPERIMENTAL PROCEDURE Investigation of the inhibiting properties of imidazole derivatives was performed by an electrochemical method using potentiostatic polarization and by a gravimetric method. The experiments were
- Water & Waste Management > Water Management > Water & Sanitation Products (0.82)
- Materials > Chemicals > Specialty Chemicals (0.82)
Abstract. The article covers the production technology as well as the Molve, Kalinovac and Stari Gradac gas fields completion. Specified are the upgrading phases and methods of well completion, from the standpoint of production process optimization and safety, with special accent on the selection of adequate high-alloy steel grades for prevention of the corrosion processes. Experience achieved in the past twelve years has shown that the choice was correct, considering the applied materials as weil as the sealing components and the gas-tight thread joints. No evident damage due to corrosion or any other cause was detected in the past period and we hope that in the majority of cases this will be maintained during the gas wells production life. 1. INTRODUCTION The Molve Gas Field was discovered twenty years ago. Further reservoir engineering was effected seven years later due to extremely severe natural conditions (see Fig. 1). Such conditions were a great challenge at the time, not only for our company, but also for international experts and technologists, and particularly for subsurface and surface well equipment material manufacturers. The first two production wells on the Molve field were equipped and put to production in 1980, after which both reservoir engineering and well construction were intensified, resulting in the completion of the total of 21 wells presently in production, yielding of 200000 to 500000 cubic meters of gas per well daily. The development of the Kalinovac Gas Field began in 1984, and today, there are 14 wells in production, yielding 100000 to 200000 cubic meters of gas per well daily, together with about 120-180 cubic meters of condensate. As can be seen from Table 1, it is a gas-condensate field with extremely severe natural conditions. The Stari Gradac field is the last one in the engineering sequence, covering only 6 completed wells, 3 of them currently in production yielding 50000 to 100000 cubic meters of gas per well daily and 45-85 cubic meters of condensate. Considering the high reservoir pressures, and, especially, high reservoir temperatures, it was necessary to choose the most rational and the safest production completion as well as to conceive the most rational gathering system. We should also .stress the fact that, just recently, the total production of the said three fields amounted to ten billion cubic meters of gas and over two million tons of condensates. 2. GEOLOGY The Molve, Kalinovac and Stari Gradac gas fields are located in the north-western part of Croatia, some 120 km from the capital-Zagreb. Morphologically speaking, it is a low-lying region of the Drava Valley, with an average height of 120 m above sealevel. The ‘Molve’ structure is an asymmetrical anticline cut through its northern part by three reverse fractures. The fluid bearing rocks ar
- Europe > Croatia > Virovitica-Podravina County (1.00)
- Europe > Croatia > Osijek-Baranja County (1.00)
- Europe > Croatia > Međimurje County (1.00)
- (2 more...)
- Europe > Croatia > Virovitica-Podravina County > Pannonian Basin > Drava Depression > Molve Field (0.95)
- Europe > Croatia > Virovitica-Podravina County > Pannonian Basin > Drava Depression > Kalinovac Field (0.95)
- Europe > Croatia > Osijek-Baranja County > Pannonian Basin > Drava Depression > Molve Field (0.95)
- (6 more...)
ABSTRACT Numerous organic compounds serve effectively as corrosion inhibitors in acid media. These include the triple-bonded hydrocarbons; acetylenic alcohols; sulfoxides; sulfides and mercaptans; aliphatic, aromatic, or heterocyclic compounds containing nitrogen (N); and many other families of simple organic compounds or of condensation products formed by the reaction between two different species such as aldehydes and amines. Inhibitors that change the cathodic or anodic processes kinetically also are important additives in the technological processes of metal deposition.1-3 Generally, it has been assumed that the first stage in the action mechanism of the inhibitors in aggressive acid media is the adsorption of the inhibitors onto the metal surface. The processes of adsorption of inhibitors are influenced by the nature and surface charge of the metal, by the chemical structure of the organic inhibitor, by the distribution of charge in the molecule, by the type of aggressive electrolyte, and by the type of interaction between organic molecules and the metallic surface.2-16 Physical (electrostatic) adsorption and chemisorption are the principal types of interaction between an organic inhibitor and a metal surface. Except for anodic polarization, during which the oxide layer thickness increases, the corrosion of aluminum (Al) can be prevented or slowed effectively by the addition of various organic additives to the corrosive media. Interaction of the molecules of the organic additives with the metallic surface changes the corroding metal surface and influences the mechanism of the electrochemical process that occurs at the metal-solution interface. The inhibition efficiency of substituted N-arylpyrroles on the corrosion of Al in perchloric acid
- Europe > Croatia (0.29)
- North America > United States > New York (0.16)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.68)
- Water & Waste Management > Water Management > Water & Sanitation Products (0.61)
- Materials > Chemicals > Specialty Chemicals (0.61)
- Energy > Oil & Gas > Downstream (0.54)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (0.90)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (0.90)
High Slope Stability In the Case of Improvement of the Mechanical Properties of the Rock Mass
Jasarevic, Ibrahim (Faculty of Civil Engineering, University of Zagreb) | Kovacevic, Meho-Sasa (Faculty of Civil Engineering, University of Zagreb) | Kulic, Z. (Faculty of Civil Engineering, University of Zagreb)
ABSTRACT: The rock massif strengthening using micro-reinforced shotcrete (MRS) with polypropylene fibers and prestressed bolts of high rigidity is presented in the paper. The results of carbonate rock complex classification and those obtained by geotechnical laboratory testing of rock samples and micro-reinforced shotcrete, including results of the in situ testing of the strengthened massif's mechanical properties are equally provided. A numerical analysis of a strengthened rock slope over 40 m in height and inclined to approx. 85° was also made and is presented in the paper. RESUME: L'amelioration d'un massif rocheux par beton projete micro-arme à fibres polypropylènes et par ancres precontraintes est presentee dans le present ouvrage. Les auteurs presentent les resultats de classification du complex carbonatique rocheux, les resultats des essais geotechniques en laboratoire effectues sur les echantillons du massif et sur le beton projete rnicro-arme, ainsi que les resultats de l'analyse des caracteristiques mecaniques du massif après amelioration. La simulation numerique du massif rocheux incline à environ 85° et de plus de 40 m d'hauteur a egalement ete effectuee. ZUSAMMENFASSUNG: Im Artikel wird eine Verbesserung des Gesteinmassivs mittels Spritzbeton, mikrobewehrt mit Polzpropzlenfasern, und vorgespannten steifen Ankern dargestellt. Prasentiert sind die Ergebnisse der Klassifikation des Karbonatgesteinkomplexes, der geotechnischen Laboruntersuchungen der Gestein- und Spritzbetonproben, sowie "in situ" Untersuchungen der mechanischen Eigenschaften des verbesserten Gesteinmassivs. Eine numerische Simulation des verstarkten Gesteinhangs mit Neigung von cca 85° und ueber 40 m Höhe wurde durchgefuehrt. 1. INTRODUCTION: The water required by the town of Rijeka has been taken from the water-pumping site Zvir since 1894. This site is presently the axis of the town's water supply system as it provides approx. 70% of all required water in the dry season. However, the capacities of the existing pumping station are limited and can no longer meet the growing water-supply needs of the town. In order to resolve this problem, a team of experts prepared in 1987 a study for the construction of a new pumping-station structure. At that, it was necessary to examine the stability of the water- pumping site, since a roof structure was initially built above the basin and the high and steep rock slope above the Zvir site in the Rječina canyon has on several occasions been "strengthened" by concrete. Several attempts have been made over the last hundred years to ensure the local and, to some extent, the global stability of the slope. However, the local and global stability of the slope still remained inadequate and, for that reason, the main design involving the reinforced-concrete grid composed of horizontal and vertical girders was prepared in 1988. Due to the great quantity of the work and material required to build the grid structure (table 1), it was finally decided to adopt the system of rigid prestressed bolts with reinforced concrete bolt heads which fit harmoniously into the natural environment. In addition, the new design elements are much more rational than those proposed in the previous solution (table 1). 2. ENGINEERING GEOLOGICAL DATA: The slope above the Zvir pumping station is mainly composed of the well bedded Upper Cretaceous limestones and dolomites. The dolomite occurrences have been registered in the retaining wall zone (macroblock I). The Zvir water-bearing site was formed in the tectonically very mobile area where the carbonate mass moves with a relative ease along the plastic surface (mainly composed of flysch). Small changes in pressure directions are sufficient to cause cracking and rotation of macroblocks, so that reverse faults, sometimes of considerable size, are formed in boundary zones. The rotated tectonic blocks become deformed and finally crack thus forming variously fissured and oriented microblocks.
- Geology > Structural Geology (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Dolomite (0.45)
ABSTRACT: The paper presents the present state of the abandoned quanies in the area of Medvednica natural park, which have a devastating effect upon a valuable forest area in close vicinity of the city of Zagreb. An approach to solving the problem of their restoration is proposed. The described approach incorporates the selection of constituents and forms of restoration which may be self-financed with the inclusion of all existing quanies. An interdisciplinary approach, of which parts are shown of example which primarily consider geotechnical aspects, is proposed. RESUME: Cette etude decrit l'etat actuel des carrières desaffectees dans la region du parc naturel de Medvednica, qui ont provoque une forte devastation de ce beau massif forestier situe à proximite immediate de Zagreb. Une approche de la solution du problème de remise en etat est propose. Cette approche suppose un choix de contenus et de formes de remise en etat susceptibles de s'autofinancer, Toutes les carrières sont mises en jeu. II s'agit d'une approche interdisciplinaire, dont une partie est decrite sur les exemples qui esquissent en premier lieu les aspects geotechniques. ZUSAMMENFASSUNG: lm Artikel ist der heutige Stand der verlassenen unsanierten Steinbrueche im Bereich des Naturparks Medvednica dargestellt, womit ein wertvolles Waldmassiv in nachster Umgebung von Zagreb devastiert ist. Ein Zutritt zur Lösung des Sanationsproblems ist vorgeschlagen. Beschreiben ist der Zutritt der die Auswahl von Inhalt und Form der Sanation so voraussetzt dass eine Selbstfinanzierung, unter einschluss aller bestehenden Steinbrueche, möglich ist. Man empfiehlt interdlsziplinaren Zutritt; Teile davon sind an Beispielen dargestellt die vorrangig geotechnische Aspekte behandeln. 1. INTRODUCTION Le developpement de la ville de Zagreb necessitait des volumes importants de materiaux de construction. Pour reduire les frais de transport des materiaux, plusieurs carrières furent ouvertes par le passe dans la region de Medvednica. Naturellement, ces carrières ont eu une influence nefaste sur ce beau massif forestier situe à proximite immediate de Zagreb. L'adoption de la loi proclamant Medvednica pare naturel a claire- ment mis en evidence la collision de l'usage de Medvednica: elle sera bien un centre de loisirs et D'excursions pour les habitants de Zagreb et non pas un gisement de matières premières minerales. La plupart des carrières aujourd'hui desaffectees ne sont pas remises en etat, elles presentent un relief chaotique où predominent des fronts de taille hauts et abrupts et des depôts de steriles desordonnes (Figure 1). Dans ces conditions, aucune remise en etat biologique n'est possible. Un destin pareil est sans doute reserve aussi aux carières en service. Leur situation dans le cadre du pare naturel et les problèmes geotechniques (instabilite du terrain) appellent necessairement une remise en etat. En règle generale, les fonds necessaires à cette operation manquent; il s'ensuit que la remise en etat devrait être autofinancee. Pour cette raison, il est indispensable de definir la nature de l'amenagement des carrières desaffectees, qui soit acceptable sur le plan ecologique et rentable sur le plan economique. L'amenagement des carrières pourrait entraîner directement la remise en etat des carrières, ou bien cette dernière incomberait aux usagers potentiels. Cette etude presente une approche de la solution des problèmes des carrières desaffectees, avec l'aperçu des amenagements possibles et des formes de remise en etat.
Summary Well Dinjevac-1 (Di-1), located 120 km northeast of Zagreb, Croatia, was drilled in 1982 to a total depth (TD) of 5502 m. Mud logs, electrical logs, and drillstem tests (DST's) in the Miocene section of the Pannonian basin indicated hydrocarbon saturation, extremely high temperatures, and relatively high pressures. These Miocene sediments are characterized as compact, low-permeability sandstones. In 1988, the abandoned cement plugs were drilled out and a bottomhole static temperature (BHST) of 242C was measured. Temperature was the critical factor in the design of the completion and testing method. In spite of some minor quality-control and operational problems, five zones were tested successfully, providing all the relevant information about the reservoirs and the formation fluids. The operation incorporated a one-trip, hydraulically set, high-temperature, high-differential packer with a polished-bore receptacle and tubing-conveyed perforating guns with large, deep-penetrating charges. This paper describes the completion and testing objectives, considerations, operations, and results under probably the hottest completion conditions ever encountered. Introduction The hydrocarbon reservoirs of the Pannonian basin, well-known for its large temperature gradient, I have been explored intensively in shallow and medium-depth formations in Hungary and Croatia. Drilling and especially testing of deeper formations, such as Deep Tertiary, were unsuccessful in the past because the technology for working in extrahot (greater than 200C) environments was limited. Limitations included the functional reliability of the drilling and completion fluids, elastomers, lubricants, instruments, and perforating explosives. In the 1980's, oil companies intensified perforating explosives. In the 1980's, oil companies intensified their search for energy sources by drilling zones below 4000 m. Well Or-2 was drilled to a TD of 6102 m. In 1987, a test of the zone at 5540 m was attempted with conventional ball-type testing tools and a retrievable mechanical packer. A temperature of 232C was recorded at 5540 m. For the test, the well was circulated to cool down the wellbore before the through-tubing perforating operation. The test failed because all the elastomers in the downhole tools burned and all the lubricants and greases degraded. When drilled, Well Di-1 was too hot for the commercially available technology of the early 1980's. Hence, testing was postponed. The recent Duboka Drava project (a deep drilling exploration project where a number of wells have bottomhole conditions similar to those of Well Di-1) rekindled the interest in defining possible concepts for completion and testing in such environments. Given the well conditions (multiple zones characterized as extrahigh-temperature, high-pressure, and tight), completion and testing would require a single-run test/completion/perforating string that would allow for tubing movement during stimulation. Additionally, a retrievable, instead of a permanent, system would be required if milling should become necessary. Geology and Drilling History Well Di-1 is located in the Bilogora section of the Drava depression of the Pannonian basin. It is 7 km south of the largest Croatian gas-condensate field, Kalinovac. Its location is related to the Molve-Kalinovac-Stari Gradac line south of the main fault on the Pitomaca brachianticline structure in Miocene sediments (Fig. 1). Well Di-1 was drilled to define potential hydrocarbon reservoirs in the Miocene. A 339.7-mm intermediate casing string was set just above the pressure transition (Fig. 2). Overpressure was recorded from 2400 m to TD with a maximum overpressure of 147 kPa/10 m at 2670 m. A 244.5-mm intermediate casing string and a 139.7-mm liner were required to reach TD. The well encountered three drilling problems related to the subsequent completion and testing operations: damage to the 244.5-mm casing from potential helical buckling, washouts in the 215.9-mm openhole section, and extreme temperatures. Stress analysis of the 244.5-mm casing during the running, cementing, and subsequent drilling operations indicated that the lower section of this intermediate string was exposed to potential helical buckling (Fig. 3).
- Europe > Croatia > Zagreb County > Zagreb (0.26)
- Europe > Croatia > Virovitica-Podravina County (0.24)
- Europe > Croatia > Osijek-Baranja County (0.24)
- (2 more...)
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.56)
- Europe > Slovakia > Pannonian Basin (0.99)
- Europe > Serbia > Pannonian Basin (0.99)
- Europe > Romania > Pannonian Basin (0.99)
- (3 more...)
Summary Eleven hydraulic fracture treatments were performed in deep (3300 to 3800 m[10,830 to 12,470 ft]), extremely high temperature (180 to 195 C [356 to 383OF]), naturally fissured, gas-condensate reservoirs. Formation permeabilitiesat the fractured well locations range from 0.003 to 0.2 md, permeabilities atthe fractured well locations range from 0.003 to 0.2 md, while the initialformation pressure gradient is about 0.13 bar/m [0.57 psi/ft]. The producingfluid is high-gravity gas (0.83 to 1.15 to air) and psi/ft]. The producingfluid is high-gravity gas (0.83 to 1.15 to air) and contains up to 22% CO2 andup to 4% H2S. Job sizes have ranged from 300 to 2000 m3 [80,000 to 528,400 gal]of fluid and 50 to 600 Mg [110,130 to 1,321,590 Ibm] of high-strength proppant. This paper emphasizes the general approach to well completion and stimulationtreatment design, treatment execution, and evaluation. Interesting itemsinclude the engineering of the fracturing fluids to sustain their viscosity atthe extreme temperatures and to reduce leakoff in these highly fissuredformations. An outline of the reservoir description is also given. Posttreatment well production has been excellent in most cases. Well Pi'sincreased from 0.01 to 0.6 m3/d bar2 [0.0017 to 0.1 scf/D-psi] to 0.235 to 7.83m3/d bar2 [0.04 to 1.3 scf/D-psi2]. Treatment results suggest that leakoff canbe controlled with particulate agents, that delayed crosslinking is the onlyway to execute particulate agents, that delayed crosslinking is the only way toexecute these treatments, and that hydraulic fracturing can greatly improve theproduction from naturally fissured formations. Fracture design and theproduction from naturally fissured formations. Fracture design and thepredicted well production are compared with post-treatment performances inpredicted well production are compared with post-treatment performances inselected wells. Introduction After the successful execution and subsequent improved performance of amodest hydraulic fracture treatment in a high-temperature performance of amodest hydraulic fracture treatment in a high-temperature gas-condensate well, it became obvious that a much longer hydraulic fracture was indicated. Thisconclusion was based on the apparent reduction of reservoir permeability causedby the emergence of gas condensate and on the fact that a finite conductivityhydraulic fracture, producing in a fissured formation, exhibits an apparent(effective) length significantly smaller than the real length. Both reasonspoint to the necessity of performing large hydraulic fractures in suchformations. Massive hydraulic fracturing has proved to be the most successfultechnique to improve the productivity of tight gas sands. Deeply penetratingfractures can substantially improve well productivity and ultimate recovery tothe point where uneconomical wells productivity and ultimate recovery to thepoint where uneconomical wells can become profitable. Many works haveillustrated the merits of obtaining long, highly conductive fractures inlow-permeability reservoirs. However, most of these publications deal withmoderate temperature, homogeneous, and (probably) isotropic sandstoneformations. Except for geothermal wells, few high-temperature >180deg.C[>356deg.F]) case histories of hydraulic fractures have been discussed. Thewell-known constant-height, ideal-fracture-geometry models, which assumehomogeneous, isotropic media, may not be applicable in anisotropic, naturallyfissured reservoirs. Other models could be more appropriate in such asituation, as indicated by the analysis of abnormal treating pressures observedduring hydraulic fracture treatments. Some published case studies of fracturingin highly anisotropic formations show not only difficulties with the executionof hydraulic fracturing, but also poor improvement of well productivity. Withthat in mind, we designed and performed Il hydraulic fracture treatments indeep [3300 to 3800 m [10,830 to 12,470 ft]), extremely high-temperature (180 to195deg.C 1356 to 383deg.F]), naturally fissured, gas-condensate reservoirs. Anoverview of these treatments suggests certain answers to questions posed in theliterature. Treatment Considerations The treatments were done in specific formations of three differentreservoirs: Molve, Kalinovac, and Stari Gradac. These reservoirs are located innorth Croatia, close to the Hungarian border, and constitute the main part ofthe Drava depression of the Pannonian basin (Fig. i). Geological and physicalproperties of the Kalinovac field are described in Refs. 1 and 18, while Ref.19 gives a more complete geologic description of the Drava depression. In thisstudy, the reservoir rocks were represented by the following.Devoniancarbonate schists of pronounced fracture porosity and permeability. lower Triassic quarizites/metarenites with distinct microfractures and vuggyporosities. Middle Triassic, early diagenetic, extraordinarily anisotropicdolomites (with almost vertical fractures) from the Molve and Kalinovac fields, and coarse clastic rocks from reservoir formations at the Stari Gradac field. Lower Jurassic, late diagenetic, molitic dolomite from the Molve field only. Miocene carbonate facies (grainstone, wackstone, packstone-typelithotharnian limestone) only from the Molve field. The packstone-typelithotharnian limestone) only from the Molve field. The Kalinovac field, whichis of the same age, is represented by clastic rocks of low flow capacities. Thesame clastic rocks contain no hydrocarbons at the Stari Gradac field. Triassicand Jurassic dolomites have strongly pronounced anisotropic properties. Theyare characterized by an exceptional number of fractures of thesouth-southwestern slope and strike parallel to the main tectonic lines.parallel to the main tectonic lines. In such reservoirs, hydraulic fracturingmay not be successful. Regardless of the origin and geological history of thefissures and natural fractures, the current state of stresses influences theirdisribution and orientation. Because stresses are compressive in nature, themaximum stress would preferentially close fissures normal to its direction. This would result in a permeability anisotropy with a maximum value in thedirection of maximum stress. This configuration is the least favorable forexpected production increase from the hydraulic fracture. Furthermore, the hopeof connecting natural fractures, which generally follow the general trend ofthe manmade fracture, may not be realized to any appreciable degree. Anyintersection of natural fractures by the hydraulic fracture, however, createsunique problems during execution because of the presence of discontinuitiesthat may affect the propagation path of presence of discontinuities that mayaffect the propagation path of the induced fracture and high leakoff caused bythief fissures. Warpinski and Teufel considered the effect of geologicaldiscontinuities on the propagation of a hydraulic fracture, giving criteria forthe fracture to alter its direction. if treating pressures are large enough, shear slippage may be induced along joint or fissure sets. Jeffrey et al. analyzed the condition for effective proppant transport in those situations. When proppant bridging is present, the resulting increase in treating pressuresmay iced to dendritic fracturing. Kiel discussed the advantages of the createdconnected pattern, which results in volume drainage vs. the classic arealdrainage created by a planar fracture.
- North America > United States > Texas (1.00)
- Europe > Croatia > Virovitica-Podravina County (1.00)
- Europe > Croatia > Osijek-Baranja County (1.00)
- (2 more...)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.66)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Dolomite (0.45)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.44)
- Europe > Croatia > Virovitica-Podravina County > Pannonian Basin > Drava Depression > Molve Field (0.99)
- Europe > Croatia > Virovitica-Podravina County > Pannonian Basin > Drava Depression > Kalinovac Field (0.99)
- Europe > Croatia > Pannonian Basin > Stari Gradac Field (0.99)
- (6 more...)