Fractured Carbonate Rocks Research Articles

Wettability Alteration Mechanism for Oil Recovery from Fractured Carbonate Rocks

Oil can be recovered from fractured, initially oil-wet carbonate reservoirs by wettability alteration with dilute surfactant and electrolyte solutions. The aim of this work is to study the effect of salinity, surfactant concentration, electrolyte concentration, and temperature on the wettability alteration and identify underlying mechanisms. Contact angles, phase behavior, and interfacial tensions were measured with two oils (a model oil and a field oil) at temperatures up to 90°C. There exists an optimal surfactant concentration for varying salinity and an optimal salinity for varying surfactant concentration at which the wettability alteration on an oil-aged calcite plate is the maximum for anionic surfactants studied. As the salinity increases, the extent of maximum wettability alteration decreases; also the surfactant concentration needed for the maximum wettability alteration decreases. IFT and contact angle were found to have the same optimal salinity for a given concentration of anionic surfactants studied. As the ethoxylation increases in anionic surfactants, the extent of wettability alteration on calcite plates increases. Wettability of oil-aged calcite plates can be altered by divalent ions at a high temperature (90°C and above). Sulfate ions alter wettability to a greater extent in the presence of magnesium and calcium ions than in the absence. A high concentration of calcium ions can alter wettability alone. Magnesium ions alone do not change calcite plate wettability. Wettability alteration increases the oil recovery rate from initially oil-wet Texas Cordova Cream limestone cores by imbibition.

Wettability Impacts on Oil Displacement in Large Fractured Carbonate Blocks

Two-dimensional imaging of water and oil saturations during waterfloods in fractured carbonate rock models was obtained using nuclear tracer imaging and magnetic resonance imaging. Large outcrop chalk and limestone blocks were aged in crude oil to obtain wetting conditions from strongly water-wet to weakly oil-wet. The change in the oil recovery mechanism as the wettability shifted was investigated with and without the presence of fractures. Visualization of local, in situ fluid saturations during waterfloods improved the interpretation of the displacement process and oil recovery mechanisms. Experimental results demonstrate how fractures determine the displacement pattern differently depending on the matrix wettability conditions during waterfloods. At strongly water-wet conditions, the fractures had a minor impact on the ultimate recovery but significantly changed the progression of the water front compared to the unfractured case. At less water-wet or oil-wet conditions, capillary imbibition of water from the fracture to the matrix was reduced and fractures had a major impact on the ultimate recovery and water breakthrough time.

Low IFT gas–oil gravity drainage in fractured carbonate porous media

This paper addresses a study of gas–oil gravity drainage in fractured carbonate rock subjected to gas injection in low interfacial tension. The purpose of the experiments described in the paper was to investigate gas injection in fractured carbonate reservoirs in both secondary and tertiary cases (after water injection), focusing on gravity drainage using equilibrium gas followed by re-pressurization. Gas injection experiments were performed on 20 cm long and low permeable outcrop chalk core surrounded with a fracture established with a novel experimental set-up in reservoir conditions. The core was saturated with binary mixture live oil consisting of C 1 and C 7 of a known composition, while the fracture was filled with sealing material to obtain a homogeneous saturation. After core initialization, the sealing material was removed by increasing the temperature to higher than its melting point and displaced by live oil. Gas was then injected into the fracture and gravity drainage experiments were performed in low interfacial tension (< 0.5 mN/m) where the IFT between the phases were measured experimentally by selecting the proper pressure and temperature. Experiments were performed at different pressures and reversibility of the effect of the interfacial tension was checked by re-pressurization process. The oil recovered from the bottom side of the block was measured versus time. Based on the results of this study, the recovery of oil showed a significant increase by re-pressurization in gravity drainage process. It was also clear that low IFT gravity drainage is capable to recover a significant amount of oil in fractured reservoirs even after water injection.

Inferred fluid flow through fault damage zones based on the observation of stalactites in carbonate caves

Faults and fractures are important factors that control fluid flow in rock masses in hydrothermal, groundwater, and hydrocarbon systems. In this paper we examine local variations in fluid flow as evidenced by the distribution patterns and sizes of stalactites in fractured limestone. We observe that the size and distribution of stalactites relate to fluid flow and is strongly controlled by the fracture apertures, intersection of fractures, and development of damage zones around a fault. Fault damage zones are the volumes of deformed wall rocks around a fault surface that result from the initiation, propagation, interaction, termination, and build-up of slip along the fault. They are divided into tip-, wall-, and linkage damage zones depending on their location along the fault. The pattern of deformation within a damage zone mainly depends on fault tip modes (mode II or III), the 3-D locations around a fault surface, and the evolutionary stage of the fault. The development of different structures within damage zones gives valuable information about fault initiation and termination, fault propagation and growth, and fluid flow. Stalactites indicate fluid flow variation within a fault in that fluid flow is high in dilational jogs, variable along the main fault traces, and low in contractional jogs. Variation in ore fluid flow within faults is also important in controlling the position of ore shoots in structurally-controlled hydrothermal mineral deposits. Thus, the characteristics of fluid flow in fractured carbonate rocks can be related to patterns of damage around faults. Hence, the mapping of damage zones can be applied to the study of fracture-controlled fluid flow in the fields of petroleum geology, hydrogeology, and ore deposits.

Well Management Increases Hydrocarbon Production In Mature Fields: PEMEX E&amp;P Case History

Abstract This paper presents the applied methodology and results obtained from a new Well Management program to improve oil and gas recovery with minimum investments in certain asset units. In addition to the value of the increased production, the following benefits were obtained from this program: learning and applying the teamwork approach of well productivity improvement, adaptation to a cultural change of working as teams to solve difficult problems, and training and transfer of diverse technologies from the interdisciplinary teams to other technical personnel of PEMEX E&amp;P. Introduction The South Region of PEMEX E&amp;P has hydrocarbon production from five exploitation integrated assets including Bellota-Jujo, Cinco-Presidentes, Macuspana, Muspac and Samaria-Luna. The producer fields and reservoirs of these assets consist of Tertiary sandstones and Cretaceous naturally fractured carbonate rocks, and produce all types of petroleum fluids that include dry gas, wet gas, gas-condensate, volatile oil and black oil, with densities ranging from 10 °API to superior quality oils greater than 45 °API. Production in the South Region started in 1958, reaching a peak in 1979 at 1.213 MMSTB/D (continuous black solid line in Figure 1). Although there were several periods of new field development and workover activity, the oil production rate had declined to 463,995 STB/D by December 2004. The decline was caused by pressure depletion and also water invasion. The peak gas rate of 2,853 MMscf/D was in 1981 (showed as a broken line in Figure 1). The gas production rate decline was similar to oil, reaching 1,434 MMscf/D by December 2004. In the first half of 2005, as a result of this strong production decline and in order to comply with the production agreements of PEMEX E&amp;P, the South Region Management designed and implemented a strategy to increase production and to reverse producction decline. The strategy involves priority management decision lines of action for the short-, medium- and long-terms of fields in development and/or mature fields. Short-term projects with minimum investment and excellent economic returns were given top priority based upon Management's hierarchical decision process guidelines. The investment project guidelines for the medium- and long-term projects include technical justification with economic studies based on the best practices established by Reservoir Management(1, 2), with the intent to optimize the exploitation of fields, i.e., maximize the recovery of hydrocarbons, minimize investments and reduce operating and maintenance costs. Under this scenario, different alternatives are evaluated in order to help optimize the decision-making guidelines necessary for reservoir-well-surface facilities to recover primary, secondary and/or tertiary reserves. On the other hand, in order to increase short-term production, it is necessary to plan and implement different schemes to manage and integrate wells from different fields. This is done with the objective of identifying opportunities that increase production easily, based on detailed static and dynamic studies of the productive zones close to and around producing wells, taking into consideration the production behaviour of the different fields, reservoirs and wells.

Experimental Study and Modeling of Gravity Drainage during WAG Process in Fractured Carbonate Rocks

The experimental study and modeling of gravity drainage during Water Alternative Gas Injection, WAG process, in carbonate rock for one of the Iranian off-shore reservoir at lab-scale were carried out. The mechanism of gravity drainage during the WAG process, and its contribution to the oil recovery in the fractured carbonate reservoirs were also studied. In the WAG process alternatively gas is injected during the process and gravity drainage could be happened. Changes in the block dimensions, rock properties, oil properties, gas properties, and fractures properties and their effect on the amount of oil recovered during the gravity drainage mechanism were studied. It would be worth mentioning that Methane, as major constituent of natural gas, was used as injection fluids within the experiments. Also carbonate rock was used as block sample in the physical model within the experiments. The results obtained from the experiments were compared with those obtained from the simulation and the comparison confirmed fair agreement between the results. It was found out that from 1 to 6 percent of oil can be recovered by gravity drainage during WAG process.

Temporal Trends in Nitrate and Selected Pesticides in Mid‐Atlantic Ground Water

Evaluating long-term temporal trends in regional ground-water quality is complicated by variable hydrogeologic conditions and typically slow flow, and such trends have rarely been directly measured. Ground-water samples were collected over near-decadal and annual intervals from unconfined aquifers in agricultural areas of the Mid-Atlantic region, including fractured carbonate rocks in the Great Valley, Potomac River Basin, and unconsolidated sediments on the Delmarva Peninsula. Concentrations of nitrate and selected pesticides and degradates were compared among sampling events and to apparent recharge dates. Observed temporal trends are related to changes in land use and chemical applications, and to hydrogeology and climate. Insignificant differences in nitrate concentrations in the Great Valley between 1993 and 2002 are consistent with relatively steady fertilizer application during respective recharge periods and are likely related to drought conditions in the later sampling period. Detecting trends in Great Valley ground water is complicated by long open boreholes characteristic of wells sampled in this setting which facilitate significant ground-water mixing. Decreasing atrazine and prometon concentrations, however, reflect reported changes in usage. On the Delmarva Peninsula between 1988 and 2001, median nitrate concentrations increased 2 mg per liter in aerobic ground water, reflecting increasing fertilizer applications. Correlations between selected pesticide compounds and apparent recharge date are similarly related to changing land use and chemical application. Observed trends in the two settings demonstrate the importance of considering hydrogeology and recharge date along with changing land and chemical uses when interpreting trends in regional ground-water quality.

Secondary and tertiary gas injection in fractured carbonate rock: Experimental study

The use of CO 2 has received considerable interest as a method of EOR but a major drawback is its availability and increasing cost. Therefore, as the number of CO 2 injection projects increase, an alternative must be considered to meet the economic considerations. For this reason attention has been directed to nitrogen injection which may be a good substitute for CO 2. The purpose of the experiments described in this paper was to investigate the efficiency of oil recovery by CO 2 and N 2 in fractured carbonate rock. The combined effects of gravity drainage and component exchange between gas in fracture and oil in matrix on oil recovery in fractured reservoirs subjected to CO 2 or nitrogen gas injection are experimentally studied. Laboratory experiments have been carried out on a low permeable outcrop chalk, as an analogue to a North Sea reservoir rock. This was surrounded by a fracture, established with a novel experimental set-up. The experiments aimed to investigate the potential of oil recovery by secondary and tertiary CO 2 and nitrogen gas injection at high pressure high temperature condition. The matrix block was saturated using recombined binary mixture live oil (C 1–C 7), while the fracture was filled with a sealing material to obtain a homogeneous saturation. The sealing material was then removed by increasing the temperature which in turn creates the fracture surrounding the core. Gas was injected into the fracture at pressures above the bubble point of the oil. Oil recovery as a function of time was monitored during the experiments. Results from secondary gas injection experiments indicate that CO 2 injection at elevated pressure and temperature is more efficient than N 2 injection. Results from tertiary gas injection experiments also show that injection of CO 2 could significantly recover the oil, even after waterflooding, compared to N 2 injection.

Toward Field-Scale Wettability Modification—The Limitations of Diffusive Transport

Summary Densely-fractured oil-wet carbonate fields pose a true challenge for oil recovery that traditional primary and secondary processes fail to meet. The difficulty arises from the combination of two unfavorable characteristics: First, the dense fracturing frustrates an efficient waterflood; second, because of the oil-wetness, the water pressure exceeds the oil pressure inside the matrix blocks, thus inhibiting spontaneous imbibition of water. In the past decade, using a new class of surfactants, enhanced oil recovery (EOR) researchers have studied the options to chemically revert the wettability of carbonate rock without drastically decreasing the oil-water interfacial tension. These chemicals, termed "wettability modifiers" (WMs), effectively reverse the sign of capillary pressure at the prevalent saturation. With the oil pressure exceeding the water pressure, the capillary pressure becomes the driving force for oil expulsion from the matrix and into the fracture system. Previous publications on chemical wettability modification focused on the performance of different chemical wettability modifiers for a chosen rock/oil/brine system. In some cases, they demonstrated an almost full oil recovery from core plugs. Little attention, however, has been given to the mechanism underlying the transport of the chemical into the matrix block and to the proper scaling of laboratory results to reservoir size. The present study aims to demonstrate that imbibition after wettability modification is diffusion-limited. To this end, the recovery profiles for spontaneous capillary imbibition, as well as for imbibition after wettability modification, are calculated. The results are then used to compare with the data of Amott cell imbibition experiments. It is confirmed that in both cases, the cumulative recovery is initially proportional to the square root of time. Imbibition after wettability modification, however, takes approximately 1,000 times longer than spontaneous capillary imbibition into a water-wet medium. The slow recovery observed in the case of imbibition after wettability modification is in excellent agreement with the assumption that, in the absence of significant spontaneous imbibition, the WM, to unfold its action, must first diffuse into the porous medium. In any diffusion process, the time scale is linked to the square of the length scale of the medium. Therefore, it would take up to 1,000 times longer (an equivalent of 200 years) before the same recovery is obtained from a meter-scale matrix block as is obtained from a centimeter-scale plug in a laboratory in 100 days. Consequently, unless a significantly faster transport mechanism for the wettability modifier is identified, or unless viscous forces or buoyancy enable forced imbibition, the chemical wettability modification of fractured oil-wet carbonate rock does not provide an economically interesting opportunity.

Throughgoing fractures in layered carbonate rocks

Fracture surveys were conducted across a broad anticline in southern Israel in order to investigate the development and geometries of throughgoing fractures in layered carbonate rocks. At Halukim anticline, throughgoing fractures form by the linkage and coalescence of preexisting, bed-confined joints. Thus the internal morphology of these structures is highly segmented, often consisting of vertically aligned zones of subparallel fractures and bed partings linked together across the stratigraphy. The large population (n = 132) of throughgoing fractures represents a continuum of structures at various stages of development that can be classified into three main geometric categories corresponding to increasing levels of brittle strain: incipient, linked, and linked with aperture. Despite the wide variety of internal morphologies and geometries, the throughgoing fractures display a consistent east-northeast–west-southwest orientation, parallel to a set of bed- confined cross joints. The spatial distribution of throughgoing fractures varies as a function of structural position, the highest frequency and estimated strain intensity being located at the fold crest. Results suggest that throughgoing fractures develop only after a critical level of strain is achieved, as quantified by the density of bed-confined joints. Throughgoing fractures are multilayer structures that may greatly enhance the connectivity of a fracture network; therefore, understanding their formation, geometry, and distribution may contribute to efforts of flow modeling in fractured carbonate rocks.

Landslides triggered by the 8 October 2005 Kashmir earthquake

The 8 October 2005 Kashmir earthquake triggered several thousand landslides. These were mainly rock falls and debris falls, although translational rock and debris slides also occurred. In addition, a sturzstrom (debris avalanche) comprising ∼ 80 million m 3 buried four villages and blocked streams to create two lakes. Although landsliding occurred throughout the region, covering an area of > 7500 km 2, the failures were highly concentrated, associated with six geomorphic–geologic–anthropogenic settings, including natural failures in (1) highly fractured carbonate rocks comprising the lowest beds in the hanging wall of the likely earthquake fault; (2) Tertiary siliciclastic rocks along antecedent drainages that traverse the Hazara–Kashmir Syntaxis; (3) steep (> 50°) slopes comprising Precambrian and Lower Paleozoic rocks; (4) very steep (» 50°) lower slopes of fluvially undercut Quaternary valley fills; and (5) ridges and spur crests. The sixth setting was associated with road construction. Extensive fissuring in many of the valley slopes together with the freshly mobilized landslide debris constitutes a potential hazard in the coming snowmelt and monsoon seasons. This study supports the view that earthquake-triggered landslides are highly concentrated in specific zones associated with the lithology, structure, geomorphology, topography, and human presence.

Effect of injection rate, initial water saturation and gravity on water injection in slightly water-wet fractured porous media

The objective of this work was to evaluate methods for improved water injection in fractured carbonate rocks by performing experiments on outcrop core. The experimental setup consisted of a composite of 3 limestone outcrop cores with a total length of 116 cm and average diameter of 6.5 cm. The composite core (matrix) was placed in the center of a plexiglass cylinder, with the annulus between the core and the cylinder wall serving as the fracture. Water injection tests were performed by injecting water from the bottom and producing from the top. This system experienced an advancing oil/water level in the fracture. The composite core was completely immersed for 5–7 days after finishing the experiment; creating changing boundary conditions from partially to fully water immersed. Immersion type experiments were also performed separately. The effect of water injection rate and initial water saturation on oil recovery by imbibition mechanism was investigated experimentally. Water injection tests were performed at three different rates and three different initial water saturations. Breakthrough oil recovery was found to be higher when the water injection rate was low, whilst final oil recovery was less rate dependent. Alteration of initial water saturation was observed to exert minimal effect on final oil recovery, and any observed effect could be classed as experimental error. However, the rate of oil production increased with increasing initial water saturation. The results confirm that oil recovery by water injection is low in this rock type; due to oil retention by capillary forces and wettability effects. Therefore, to overcome oil retaining forces, the effect of reduced interfacial tension (IFT) on oil recovery was investigated experimentally, by choosing a low tension, equilibrated fluid system. This will increase gravity and decrease capillarity effects on the core, which in turn will result in improved recovery. The experimental results indicate that oil recovery is increased mainly due to the decreased ratio between capillary and gravity forces. Li and Horne analytical model, which incorporates both capillary and gravitational effects, was used to scale IFT and dimension successfully. Scaling results indicated that IFT and core dimension, for all experiments, could be scaled by using height of the core as the shape factor. However, using characteristic length ( L a ) as the shape factor, IFT scaling worked well but dimension could not be scaled.

Rocky coast geomorphology and erosional processes: A case study along the Murgia coastline South of Bari, Apulia — SE Italy

Many sites along the Apulian coast (SE Italy) are composed of weathered and fractured carbonate rocks affected by intense erosion and the development of slope instabilities. Here, coastal morphology was mostly produced by Quaternary tectonics, the severe and selective action of modern erosion by sea waves, and locally, was strongly conditioned by human influences. In addition, due to the carbonate nature of rock masses, the role exerted by karst processes has to be considered. This paper provides a critical review of the common eroding processes and factors affecting coastal morphology in a typical Mediterranean coastal carbonate environment. A stretch of the Murgia coastline south of Bari (between San Vito and Polignano a Mare) made up of cliffs and shore platforms interrupted by small pocket beaches was considered. For qualitative and quantitative assessment of shoreline recession, the coastal stretch was monitored by means of field surveys between 1997 and 2003. Furthermore, a comparison of vertical aerial photographs covering the period 1966–1997 (scales 1:33,000, 1:10,000 and 1:5000), topographic maps (scales 1:5000, year 1987, 1:2000, year 1982), and archival terrestrial photographs taken since the 1930s was also employed. In some zones, characterised by a gently sloping shore platform, a significant shoreline retreat was calculated at about 20 m in the last 100 years (0.2 myr − 1 ), which was caused, above all, by human activity. Here, in fact, the presence of small ancient coastal quarries and artificial salinas is widespread; they are located where soft and porous calcarenites crop out. The cliffs are characterized by different types of landslides, with various complex mechanisms of rock slope failure. Cliff recession is episodic and discontinuous in time and space, and occurs in response to single large sea storms, such as that which occurred in January 1999. Between 1997 and 2003, the cliff retreat rates vary within a range of 0.01–0.1 myr − 1 and, in general, decrease where the coast is composed of fine-grained limestones and increase where medium-grained biocalcarenites crop out. Examples of erosion hazard indicators and mass movement typologies are illustrated.

Hydromechanical modelling of pulse tests that measure fluid pressure and fracture normal displacement at the Coaraze Laboratory site, France

In situ fracture mechanical deformation and fluid flow interactions are investigated through a series of hydraulic pulse injection tests, using specialized borehole equipment that can simultaneously measure fluid pressure and fracture displacements. The tests were conducted in two horizontal boreholes spaced 1 m apart vertically and intersecting a near-vertical highly permeable fault located within a shallow fractured carbonate rock. The entire test cycle, both the initial pressure increase and subsequent pressure fall-off, was carefully monitored and used for the evaluation of the in situ hydromechanical behaviour. The field data were modelled using both distinct-element and finite-element modelling techniques, in two and three dimensions. Field test data were evaluated by plotting fracture normal displacement as a function of fluid pressure, measured at the same borehole. The curves for the normal displacement of the fracture as a function of fluid pressure showed hysteresis loops, in which the paths for loading (pressure increase) and unloading (pressure decrease) are different. By matching this behaviour, the fracture normal stiffness and an equivalent stiffness (Young's modulus) of the surrounding rock mass were back-calculated. Evaluation of the field tests by coupled numerical hydromechanical modelling showed that the pressure-increase path of the normal displacement-versus-pressure curve is highly dependent on the hydromechanical parameters of the tested fracture and the stiffness of the matrix near the injection point, whereas the pressure-decrease path is influenced by mechanical processes within a larger portion of the surrounding fractured rock.

Reply to [“Comment on “Testing the interbasin flow hypothesis at Death Valley, California’”] Winograd et al.

We happily respond to Winograd et al. regarding our recent Eos article concerning interbasin flow [Nelson et al., 2004]. We reiterate that we specifically reject interbasin flow only to Death Valley (DV) from Ash Meadows (AM) through the southern Funeral Mountains (FM), but suggest it should be critically reexamined elsewhere. Clearly, fractured carbonate rocks may be transmissive and deliver much water to a well or spring. We question, however, the spatial scales over which interbasin flow has been invoked, involving as it must continuously connected fracture permeability over tens to hundreds of kilometers.

Comment on “Testing the Interbasin Flow Hypothesis at Death Valley, California”

In the 1960s, a major hydrogeologic investigation was conducted at the Nevada Test Site (NTS, Figure 1) that included drilling, hydraulic testing, and hydrogeochemical studies in conjunction with geologic mapping and geophysical surveys. This work demonstrated that a large part of south central Nevada is underlain by thick (several kilometers) highly fractured Paleozoic carbonate rocks that typically act as an aquifer. The aquifer flanks and underlies most of the intermontane basins from east central Nevada southward, through the NTS, to the southern Funeral Mountains east of Death Valley (Figure 1). Water levels measured in many test holes demonstrate that the potentiometric surface in the carbonate aquifer generally is uninterrupted by the ridges that separate the many topographically closed basins of the region.

Evolution of Golpazari-Huyuk karst system (Bilecik-Turkey): indications of morpho-tectonic controls

The Golpazari-Huyuk karst system is located in the Central Sakarya Basin whose geomorphologic evolution is mainly controlled by the Post-Miocene epirogenic continental rise. Drastic change in the drainage pattern and dissection of the carbonate platform were the major consequences of this tectonic movement. Rapid incision of the Sakarya river changed the position of the erosion base which consequently distorted the direction of surface and subsurface flow. The Golpazari and Huyuk plains are two topographically distinct, flat bottomed geomorphic features separated by a carbonate rock relief. The difference in elevation between these 10 km distant plains is 350 m. Morphological, geological and hydrological behavior of the plains suggests that the both have functioned as closed basins connected to each other through subsurface flow paths. Drainage has changed from subsurface to surface after the emplacement of the Sakarya river into its modern course. In this study, the authors suggest a conceptual model to reconstruct the hydrological-geomorphological processes that have been effective in the evolution of this karst area. The methodology is based on the records preserved in the morphological and sedimentological archives as well as the hydrogeological setting in the study area. According to the suggested model, the present landscape which exhibits a late stage of karstification has evolved in three main phases, after an initial stage attributed to Lower Miocene. The first phase represents karstification of carbonate rocks of Jurassic age at the Huyuk area and the limestone of Paleocene age at the Golpazari area. This region must have been significantly elevated from the karstification (erosion) base. The geomorphologic and drainage setting reveal that the karstification was controlled mainly by major drainage elements in Late Miocene-Early Pliocene.The second phase is characterized by the uplift of the region and the subsequent rapid incision of drainage during the pluvial period thereby the ponors that drained the polje were completely clogged and the polje turned out to be a lake in late Pliocene-Early Pleistocene. The third phase consists of a re-arrangement of drainage pattern and related geomorphologic processes mainly controlled by tectonic movements during Early Pleistocene. Consequently, surface drainage started in the Golpazari lake. Meanwhile Sakarya river incised its bed through the fractured carbonate rocks, capturing also the Huyuk depression complex.

Surface and subsurface environmental degradation in the karst of Apulia (southern Italy)

Karst environments are highly vulnerable to a variety of degradation and pollution problems. Geology (fractured carbonate rocks), morphology (presence of a network of cavities produced by karst processes), and hydrogeology (rapid concentrated flow through fractures and conduits) of karst carbonates strongly favour the movement of contaminants towards the water table. In particular, poor quality of subsurface water can derive from polluting substances flowing at the surface, and/or by direct immission of liquid and solid waste into the water table through the systems of conduits and joints in the rock mass. As a consequence, water quality can deteriorate severely, which implies very high economic and social costs in order to clean the polluted sites and restore the original situation. In some cases, such as when the original karst morphology is changed because of anthropogenic interventions, the variations created in the landscape are not recoverable, and a loss of sites of naturalistic interest has to be registered. High vulnerability of a typical karst region of the Mediterranean area is illustrated in this paper by describing some case studies from Apulia, southern Italy. The Apulia region, where karst processes have had a prominent role in the development of the present landscape, is mostly underlain by intensely karstified limestone. Two cases of pollution due to solid waste into karst cavities (Grave di S. Leonardo in the Gargano Promontory and Grave Pelosello in the Murge plateau), landscape transformation in the Minervino Murge area, and degradation of Gravina Monsignore, a typical karst valley in southeastern Murge, are described in the paper. In two out of four cases, degradation of the sites was discovered thanks to activity from local speleologists, who also acted as promoters for cleaning and safeguarding the polluted sites. These examples underline well the mismanagement of karst territories (in particular, the common practice to dump refuse into sinkholes and caves), the pollution of limestone aquifers, and the effects that such pollution in karst areas might have in terms of the risk to public health.

Microbial and Waterflooding of Fractured Carbonate Rocks: An Experimental Approach

Fractures and fractured zones require special attention while formulating a reservoir development plan. They may improve or hinder the oil production. Conductive fracture rocks may provide the required permeability to drain an oil saturated low permeability rock matrix. Low sweep efficiency of many oil reservoirs is the result of channelling of injected water through high permeability zones that are normally associated with naturally fractured systems in heterogeneous reservoirs. In this case, a substantial amount of effort needs to be focused on improving the distribution of injected water in the wellbore through different treatments, such as using gelling agents, cements, cross-linked polymer and emulsions. Other alternatives such as microbial and surfactant based methods have been proposed. This paper presents the results of research conducted on thermophilic bacteria that were obtained from UAE local environment. Coreflooding experiments were conducted on fractured single cores to show the effectiveness of microbial treatment. Different fracture angle orientations of 45°, 90°, and 180° relevant to the axis of the flow were investigated. The effect of matrix permeability on the treatment was also studied. A comparison between water flooding and microbial flooding of fractured systems was conducted. A non-invasive imaging technique—Scanning Electron Microscopy (SEM)—was employed to visualize changes on the surface of the fracture as a result of bacteria flow through the system.

The influence of Zihe Stream on the groundwater resources of the Dawu well field and on the discharge at the Heiwang iron mine, Zibo City area, Shandong Province, China

The Dawu well field, one of the largest in China, supplies most of the water for the Zibo City urban area in Shandong Province. The field yields 522,400–535,400 m3/d from an aquifer in fractured karstic Middle Ordovician carbonate rocks. Much of the recharge to the aquifer is leakage of surface water from Zihe Stream, the major drainage in the area. Installation of the Taihe Reservoir in 1972 severely reduced the downstream flow in Zihe Stream, resulting in a marked reduction in the water table in the Dawu field. Since 1994, following the installation of a recharge station on Zihe Stream upstream from the well field that injects water from the Taihe Reservoir into the stream, the groundwater resources of the field have recovered. An average of 61.2×103 m3/d of groundwater, mostly from the Ordovician aquifer, is pumped from the Heiwang iron mine, an open pit in the bed of Zihe Stream below the Taihe Reservoir. A stepwise regression equation, used to evaluate the role of discharge from the reservoir into the stream, confirms that reservoir water is one of the major sources of groundwater in the mine.