Carbonate Outcrops Research Articles

Responses of plant water uptake to groundwater depth in limestone outcrops

The study of plant water uptake from groundwater is important to garner an improved understanding of ecohydrological processes and groundwater management. However, little is known about how fluctuations in groundwater depth influence plant water absorption in carbonate outcrop regions. This study quantified the plant water uptake patterns and plant responses to different groundwater depths at four distinct sites. The aquifers of the boreholes CF10 (4 to 10 m groundwater level) and CF12 (2 to 9 m groundwater level) basically consisted of porous and fissure media. The aquifer of borehole CF13 (historically sustained 0 to 1 m groundwater level) was dominated by fissure and conduit media, while that of borehole CF18 (2 to 3 m groundwater level) was comprised on rocks with considerable small-sized dissolution pores and seams. Borehole water, referred to as rock water in this study, is defined as a potential water source that plants can absorb. The IsoSource model, based on the dual stable isotopes of δ D and δ18O was employed to estimate soil and rock water contributions to the plant xylem water. The results revealed that the groundwater depth of the CF10, CF12, and CF13 boreholes had significant negative correlations with the total precipitation of the previous ten days. At the CF10 site, Toona sinensis and Caesalpinia decapetala absorbed soil water during the rainy season, and rock water during the dry season. At the CF12 site, Toona sinensis primarily absorbed rock water during rainy season and soil resident moisture during the dry season, while the water utilization proportion of Caesalpinia decapetala fluctuated significantly in different seasons. At the CF13 site, rock water was the dominant water source for both plant species during the rainy and dry seasons, while soil water was the main water source for both plants in the CF18 site. The proportion of rock water absorption by plants did not directly statistically correlate with groundwater depth; however, it did with the total precipitation of the previous two and fifteen days, respectively. Nevertheless, groundwater depth is a comprehensive embodiment of precipitation and the structure of karst water-bearing media. Therefore, the plant absorption of rock water is not only contingent on groundwater depth but also on the karst water-bearing media. For the first time, the isotopic values of borehole water were employed to estimate the contributions of plant water sources to improve calculations. The above results indicated that field surveys of hydrogeological structures and high precision monitoring were equally indispensable toward facilitating the restoration of vegetation and groundwater management in fragile rocky desertified ecosystems.

Ecological characterization of cold-seep epifauna in the South China Sea

Site F, an active cold seep situated on the northeastern continental slope of the South China Sea (SCS), has not been systematically surveyed since its first discovery in 2007. Here we report the results of a ROV transect survey of this cold seep conducted in 2018, which mapped the distribution of the substrates and quantified epifauna along parallel dive tracks. The site, measuring 180 m × 180 m, is characterized by a central part of authigenic carbonate outcrops with crevices releasing gas bubbles, which support high densities of bathymodiolin mussels Gigantidas platifrons (up to 273 individuals m−2) and galatheid squat lobsters Shinkaia crosnieri (up to 300 individuals m−2). On more condensed carbonate crusts, G. platifrons and the munidopsid squat lobsters Munidopsis spp. are present at low densities. The outskirts of the site are dominated by soft sediment, with bacterial mats and sparsely distributed G. platifrons and their shells, as well as the vestimentiferan tubeworm Paraescarpia echinospica. Sampling in various locations of the cold seep yields 10 new records of epibenthic animals as determined by watching the captured videos, morphological analysis as well as sequencing the COI and 16S rRNA gene sequences. Stable isotope analysis showed that biogenic methane is the main carbon source for most of the macrobenthos in this community. Many of these SCS cold seep macrobenthos have been reported from hydrothermal vents of the Okinawa Trough, indicating high connectivity between the two chemosynthesis-based communities in the Western Pacific.

Improving Spatial Resolution of Multispectral Rock Outcrop Images Using RGB Data and Artificial Neural Networks.

Spectral information provided by multispectral and hyperspectral sensors has a great impact on remote sensing studies, easing the identification of carbonate outcrops that contribute to a better understanding of petroleum reservoirs. Sensors aboard satellites like Landsat series, which have data freely available usually lack the spatial resolution that suborbital sensors have. Many techniques have been developed to improve spatial resolution through data fusion. However, most of them have serious limitations regarding application and scale. Recently Super-Resolution (SR) convolution neural networks have been tested with encouraging results. However, they require large datasets, more time and computational power for training. To overcome these limitations, this work aims to increase the spatial resolution of multispectral bands from the Landsat satellite database using a modified artificial neural network that uses pixel kernels of a single spatial high-resolution RGB image from Google Earth as input. The methodology was validated with a common dataset of indoor images as well as a specific area of Landsat 8. Different downsized scale inputs were used for training where the validation used the ground truth of the original size images, obtaining comparable results to the recent works. With the method validated, we generated high spatial resolution spectral bands based on RGB images from Google Earth on a carbonated outcrop area, which were then properly classified according to the soil spectral responses making use of the advantage of a higher spatial resolution dataset.

Application of Miscible Ethane Foam for Gas EOR Conformance in Low-Permeability Heterogeneous Harsh Environments

SummaryUnconventional plays pose a challenging set of operational conditions, including high temperature, high salinity, low permeability, and fracture networks. Aggressive development of these plays and the low primary recovery factors present an opportunity for using enhanced oil recovery (EOR) methods. This work presents a laboratory investigation of miscible ethane (C2H6) foam for gas EOR conformance in low-permeability, heterogeneous, harsh environments [<15 md, 136,000 ppm total dissolved solids (TDS) with divalent ions, 165°F]. The use of C2H6 as an alternative to carbon dioxide (CO2) offers several operational and availability strengths, which might expand gas EOR applications to depleted or shallower wells. Coupling gas conformance also helps improve displacement efficiencies and maximize overall recovery. Minimum miscibility pressure (MMP) displacement tests were performed for dead crude oil from the Wolfcamp Spraberry Trend area using C2H6 and CO2. Aqueous stability, salinity scan, and static foam tests were performed to identify a formulation. Subsequent foam quality and coreflood displacement tests in heterogeneous carbonate outcrop cores were conducted to compare the recovery efficiencies of three processes: gravity-unstable, miscible C2H6 foam; gravity-stable, miscible C2H6; and gravity-unstable, miscible C2H6 processes. Slimtube tests comparing C2H6 to CO2 resulted in a lower MMP value for C2H6. We identified a stable surfactant blend capable of Type I microemulsion and persistent foams in the presence of oil. Corefloods conducted with gravity-unstable miscible C2H6 foam, gravity-stable miscible C2H6, and gravity-unstable miscible C2H6 recovered 98.4, 61.9, and 42.6% oil originally in place, respectively. Our work shows that miscible C2H6 injection processes achieved significant recoveries even under gravity-unstable conditions. The addition of foam provides better conformance control, enhancing overall recovery at the laboratory scale, showing promise for field applications.

Morphological and petro physical estimation of Eocene tight carbonate formation cracking by cryogenic liquid nitrogen; a case study of Lower Indus basin, Pakistan

Significant amounts of hydrocarbons are contained in tight carbonate rocks like those within the Indus basin of Pakistan, but due to their unconventional nature, their extraction is difficult. This can be completed/conducted by properly characterizing its mineralogical, geochemical and microstructural properties. In this context, Hydraulic fracturing and acidizing are the most common fracture stimulation techniques. However, they suffer significant technical and environmental flaws. Liquid Nitrogen (LN2) fracking is considered as one of the best alternatives compare to hydraulic fracturing or acidizing due to its eco-friendly nature. In fact, after exposer to LN2, super cryogenic feature of the rock causes porosity, permeability and fracture conductivity enhancement due to thermal shock without any environmental consequences. The effect of Liquid Nitrogen fracking on tight carbonate outcrops collected from the Indus basin is investigated in the present study. Scanning Electron Microscopy (SEM) reveals the clear appearance of wide pore fractures with sizes from 4 μm to 50 μm, when subjected to liquid Nitrogen (LN2) treatment ranging from 30 to 90 min’ duration. Furthermore, SEM and Atomic Force Microscopy (AFM) images also indicate clear pore fractures in tight carbonate rocks along with increased pore connectivity. Moreover, following liquid nitrogen treatment of up to 90 min the permeability of tight carbonate increases by 53% and increases in porosity by 73%. Results from SEM studies suggest that visible fractures occur in the tight carbonate samples with liquid nitrogen treatment because of the freezing temperature (−196 ⸰C) of Liquid Nitrogen. In addition to this, Nano indentation moduli depict significant decreases in tight carbonate rocks, both before and after exposure to LN2, as a result of increases in liquid rock compressibility. In this regard, a 50 mN force decreased from 50.57 GPa to 24.37 GPa and for a 200 mN force this decreased from 45.77 GPa to 26.67 GPa. This research depicts the significant effect of Liquid Nitrogen freezing on the fracturing of carbonate rocks.

Alkaline-surfactant-polymer formulation development for a HTHS carbonate reservoir

There are many HTHS (high temperature, high salinity) carbonate reservoirs where temperature (>80 °C) and salinity (>30,000 ppm) are high. The goal of this study was to develop an alkaline-surfactant-polymer (ASP) formulation for a high temperature (~100 °C), high salinity (~60,000 ppm) giant carbonate reservoir with low surfactant retention, an essential requirement for low chemical cost. Phase behavior tests were conducted with anionic surfactants, alkali, co-solvents, brine, and crude oil to identify chemical formulations with ultra-low IFT under reservoir conditions. Corefloods were first conducted in outcrop carbonate cores and then in reservoir cores. The effluent was analyzed for oil, surfactant, pH, salinity and viscosity. Surfactant adsorption on carbonate surfaces decreases at high pH. Ammonia and a new organic alkali ethoxylated diisopropylamine (DIPA-10EO) were studied for this application since there is both anhydrite and dolomite in the formation. Sodium carbonate cannot be used as the alkali in rocks containing anhydrite, and sodium hydroxide cannot be used as the alkali in rocks containing dolomite. Ultralow IFT (~0.001 mN/m) was achieved with several ASP formulations using the reservoir oil. The first three core floods in Indiana limestone yielded excellent tertiary oil recoveries of 85.2, 89.5 and 91.8%, and very low surfactant retentions of 0.06, 0.02, and 0.11 mg/g-rock, respectively. The reservoir coreflood resulted in 93.6% tertiary oil recovery and a final oil saturation of 1.2%. The surfactant retention was 0.083 mg/g-rock. The chemical formulation developed here is applicable to this high permeability, non-fractured, HTHS carbonate reservoir. Future research should address other carbonate reservoir issues such as fractures and low permeability.

Study of alternating acid fracturing treatment in carbonate formation based on true tri-axial experiment

Acid fracturing is a useful technique to stimulate carbonate reservoirs. Nowadays, acid leak-off becomes a vital problem during the operation of acid fracturing. In order to encounter this issue, alternating acid fracturing has been developed. However, the fracture propagation and the interaction between hydraulic fractures and natural fractures/caves during alternating acid fracturing are ambiguous. Hence, a series of alternating acid fracturing experiments covering coupling mechanics and chemical interaction were conducted for the first time. In this study, slick water, self-generating acid, cross-linked gel, and gelled acid were used as a fracturing fluid whereas the specimens for this experiment are carbonate outcrop which excavated from Dengsi Formation. The results show that: (1) acid fracturing can reduce fracturing pressure effectively as the acid will etch and weaken the natural fractures to let them easily connecting each other; (2) different pad fluid properties will have different impacts on the acid fracturing performance; (3) the interaction of hydraulic fractures and natural filled caves can be divided into five categories, and two of them had been observed in the experiments. Moreover, a new curvature-calculation algorithm has been developed based on the 3-D scanning technology. The results have a great significance for acid fracturing design and physical simulation experiments.

<p><strong>A new paleopteran genus and species from the late Carboniferous of Avion France, (Insecta: Palaeodictyopterida: ?Diaphanopterodea)</strong></p>

The Carboniferous outcrop near Avion, in the Department of Pas-de-Calais, northern France, is very rich in fossil insect wings, which are preserved alongside thousands of plant fragments. Its entomofauna is very diverse, including representatives of the Palaeodictyoptera, Odonatoptera, Archaeorthoptera, Caloneurodea, Paoliida, Dictyoptera, Plecoptera, and the oldest representatives of the clades Acercaria and Holometabola (Nel et al., 2013, Prokop et al., 2013, 2014; Coty et al., 2014; Schubnel et al., 2019a, b). The fossil insects were found in ‘Terril N 7’, a slag heap located in the Avion area comprising Moscovian-aged sediments derived from Liévin coal mines 3 and 4, specifically the Bolsovian or Westphalian C (311–308 Ma) ‘faisceaux de Ernestine’, and the Asturian or Westphalian D (308–306 Ma) ‘veines Arago, Dusouich, Marthe’ informal beds (Bruno Vallois, 2013, pers. comm.).

Olivine-Carbonate Mineralogy of the Jezero Crater Region.

A well-preserved, ancient delta deposit, in combination with ample exposures of carbonate outcrops, makes Jezero Crater in Nili Fossae a compelling astrobiological site. We use Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) observations to characterize the surface mineralogy of the crater and surrounding watershed. Previous studies have documented the occurrence of olivine and carbonates in the Nili Fossae region. We focus on correlations between these two well-studied lithologies in the Jezero crater watershed. We map the position and shape of the olivine 1 μm absorption band and find that carbonates are found in association with olivine which displays a 1 μm band shifted to long wavelengths. We then use Thermal Emission Imaging Spectrometer (THEMIS) coverage of Nili Fossae and perform tests to investigate whether the long wavelength shifted (redshifted) olivine signature is correlated with high thermal inertia outcrops. We find that there is no consistent correlation between thermal inertia and the unique olivine signature. We discuss a range of formation scenarios for the olivine and carbonate associations, including the possibility that these lithologies are products of serpentinization reactions on early Mars. These lithologies provide an opportunity for deepening our understanding of early Mars and, given their antiquity, may provide a framework to study the timing of valley networks and the thermal history of the Martian crust and interior from the early Noachian to today.

Lenticular-bedding-like bioturbation and the onshore recognition of carbonate drifts (Oligocene, Cyprus)

ABSTRACTThe fine-grained carbonate deposits of the Oligocene to early Miocene of Cyprus are the most characteristic example of onshore outcropping carbonate drifts. These deposits were analyzed from a sedimentological and ichnological perspective, in order to determine the origin of the lenticular bedding characteristic of such deposits. The facies at the two study sections, Tsada and Petra Tou Romiou, consist of an alternation of thin, poorly cemented, intensely bioturbated marly limestone intervals and thick cemented wackestone intervals with abundant bioturbation and “lenticular bedding.” The ichnoassemblage, comprising Zoophycos, Thalassinoides, and Planolites is attributable to the Zoophycos Ichnofacies. The alternation of intervals with medium to well-preserved traces with completely biogenically homogenized facies reflects changes in substrate consistency related to changes in bottom-current velocity or to sedimentation. The presence of lenticular-bedding-like structures in the study deposits, traditionally considered diagnostic of bottom-current action in carbonate-drift outcrops, is shown to be exclusively the result of bioturbation. In the study sections, the “lenticular bedding” is the result of the coalescence of successive Zoophycos structures, which are readily preserved because they are constructed in the historical layer. It is proposed that the overlap of abundant isolated cone-shaped burrows of Zoophycos is the origin of the putative lenticular bedding recorded in the Oligocene fine-grained carbonate deposits of Cyprus, traditionally identified as drifts. Since this bedding is not related to currents in the study sections, the consideration of these carbonate deposits of Cyprus as drifts should be reevaluated. This has crucial implications for the recognition of carbonate drift outcrops elsewhere. Onshore carbonate drift outcrops wherein lenticular bedding is the main diagnostic criterion should be revisited and evaluated ichnologically.

The contributions of hydrogeoarchaeology to the study of the urban water supplies to the old Roman Arunda from the Llanos de la Arena springs (Serranía de Ronda, province of Málaga)

The settlement of Arunda, now known as Ronda (Malaga) was located in the neighbourhood of La Ciudad, upon an Iberian oppidum. In the 1990s, some Roman levels were discovered with part of the potable water distribution system using pressure. This finding corroborated the Roman origins of the Fuente de la Arena aqueduct that brought water from the Llanos de la Arena springs, 6 km away, at the foot of the Sierra de Jarastepar. Jarastepar carbonate outcrops make up an aquifer with an area of 25 km2 whose recharge is produced exclusively by infiltration of precipitation (8.9 hm3/year). The Llanos de la Arena springs drain a sector of this aquifer with average resources of 1.6 hm3/year. The aqueduct was built not before the end of the 1st century AD and, was more probably constructed in the following century, coinciding with an extremely arid period in the south of the Iberian Peninsula (ca. 150 BC-150 AD). The elements identified are: the caput aquae, the brick specus with a ceramic pipe, an aerial section of more than 200 m and the well-known Predicatorio Tower (the beginning of a siphon to the other elevated end of the city). The aqueduct of the Fuente de la Arena is a relevant infrastructure that captured enough water resources to guarantee thesupply to Arunda, even when unfavourable weather conditions occurred. This suggests that the activities that were taking place in the city were much more than a mere settlement.

Chemosynthesis influences food web and community structure in high-Arctic benthos

Cold seeps are locations where seafloor communities are influenced by the seepage of methane and other reduced compounds from the seabed. We examined macro-infaunal benthos through community analysis and trophic structure using stable isotope analysis at 3 seep locations in the Barents Sea. These seeps were characterized by high densities of the chemosymbiotic polychaetes Siboglinidae, clade Frenulata (up to 32120 ind. m-2), and thyasirid bivalves, <i<Mendicula cf. pygmaea (up to 4770 ind. m-2). We detected low δ13C signatures in chemosymbiotic polychaetes and in 3 species of omnivorous/predatory polychaetes. These δ13C signatures indicate the input of chemosynthesis-based carbon (CBC) into the food web. Applying a 2-source mixing model, we demonstrated that 28-41% of the nutrition of non-chemosymbiotic polychaetes originates from CBC. We also documented large community variations and small-scale variability within and among the investigated seeps, showing that the impact of seepage on faunal community structure transcends geographic boundaries within the Barents Sea. Moreover, aggregations of heterotrophic macro- and megafauna associated with characteristic seep features (microbial mats, carbonate outcrops, and chemosymbiotic worm-tufts) add 3-dimensional structure and habitat complexity to the seafloor. Cold seeps contribute to the hydrocarbon-derived chemoautotrophy component of these ecosystems and to habitat complexity. These characteristics make the cold seeps of potential high ecological relevance in the functioning of the larger Arctic-Barents Sea ecosystem.

Influence of Halide Anions Cl–, Br–, and I– on the Zeta Potential of Oil-Wet Carbonate Surfaces

The benefits of injecting dynamic water (fluids with designed ionic composition) in carbonate reservoirs have been confirmed in various studies. The underlying mechanisms, however, resulting in enhanced oil recovery, are still not fully understood, which complicates the design of new efficient dynamic water formulations. In the current work, we study the effect of Arabian Gulf seawater and the addition of halide anions (Cl–, Br–, and I–) on carbonate surface alteration. Calcite and carbonate outcrop surfaces were aged with model oils (containing asphaltene, stearic acid, or a mixture of both) to render the rock more oil-wet and afterward conditioned in different dynamic water formulations. The surface charges at different treatment stages were investigated by zeta potential measurements to identify which dynamic water is most effective in altering the aged surfaces back to a more water-wet condition, which is believed to be more beneficial for enhanced oil recovery. Aging in model oils led to an increase ...

Large-scale true tri-axial fracturing experimental investigation on diversion behavior of fiber using 3D printing model of rock formation

The complex carbonate reservoir is characterized by strong heterogeneity, developed natural fractures, and high temperature. In order to enhance its stimulation effect and hydrocarbon production, temporary plugging and diverting acid fracturing technology was proposed. However, using traditional downhole tools is high-risk and costly, sometimes even ineffective to achieve diversion of fractures. Compared with mechanical diversion assisted with tools, fibers diversion has become an effective and low-cost alternative for safe, tool-free and convenient operation. It has been pilot applied in some fields and the stimulation results are favorable. However, the temporary plugging and diversion behavior of fibers has not been systemically studied. Hence, based on the reproduced fracture model by 3D printing technology, a series of experiments were performed to investigate the effect of carrier fluid type, the length and concentration of fibers, and injection rate on temporary plugging. Furthermore, based on the modified true tri-axial fracturing system, four groups of experiments were also conducted to verify the feasibility of fiber-assisted diverting acid fracturing, in which natural carbonate outcrop cubic blocks with the dimension of 300 mm × 300 mm × 300 mm were used. The results of temporary plugging experiments show that the temporary plugging effect of HPG fracturing fluid is better than that of slick water. In addition, the effect of temporary plugging increases with increase of fiber length, concentration, and injection rate. Under experiment condition, the fibers with the length of 6 mm and the concentration of 1 wt%, and the injection rate of 60 mL/min are recommended. When the horizontal principle stress difference was below 5 MPa, the results of true tri-axial diverting fracturing experiments show that two mutually perpendicular fractures was created on the end face of the cubic core, which verifies the validity of fiber-assisted diverting fracturing. However, it's difficult for the fracture created during fiber-assisted acid fracturing to divert when the horizontal principle stress exceeds 7.5 MPa. Moreover, it can produce a fracture that is nearly parallel to the previously created fracture. This study deepens the understanding on the mechanisms of fiber-assist diverting acid fracturing and provides fundamental for field treatment design.

Petrogenesis and tectonic significance of mafic-ultramafic rocks from southwestern Yunnan, China

This study focuses on the mafic-ultramafic lavas of the Early Carboniferous outcrop in Mangxin, southwestern Yunnan, China. Picrites with 26–32 wt% MgO and a quenched texture are the most significant components of this rock association. This article divides the Mangxin picrites into two types. The mantle potential temperature (Tp) of these picrites is higher than the Tp range of mid-ocean ridges and reaches that of mantle plumes. According to their geochemical characteristics, type-1 picrites probably formed from the melting of the mantle plume head and were contaminated by the ambient depleted mantle, whereas type-2 picrites formed from the melting of mantle plume tails. These plume-related mafic-ultramafic rocks in Mangxin and the ocean island basalt (OIB)-carbonate rock associations in many areas of the Changning–Menglian belt provide significant evidence for the improvement of previous models of the Palaeotethyan oceanic plateau.

Facies, depositional environments, and anatomy of the Subis build-up in Sarawak, Malaysia: implications on other Miocene isolated carbonate build-ups

Isolated carbonate build-ups of Miocene age are important hydrocarbon reservoirs in SE Asia and globally. The architecture of the build-up rim and fore-reef talus is poorly understood. The Subis build-up is one of the cycle I–II carbonate outcrops exposed along the coastal Sarawak in an area of 5 × 6 km2, with an exposed thickness of 390 m. This provides an opportunity to document the composition and architecture of rim and talus deposits in an isolated build-up as an analogue for similar gas-bearing structures located offshore Central Luconia, in Malaysia, which were neither drilled nor cored so far. This paper documents sedimentological characteristics, lateral and vertical facies relationships, of the marginal sections of a build-up in a large quarry exposing the Subis Limestone. The Subis Limestone is composed of massive and branching corals, coralline red algae, benthic foraminifera, bivalves, gastropods, echinoids, and occasionally bryozoans and sponges. Eight microfacies types and four environments were defined to describe the Subis Limestone: outer talus, inner talus, reef rim, and lagoon. Nine genera of benthic foraminifera were interpreted, confirming an early Miocene age (cycle II) of the succession. Three major backstepping events were observed at the build-up, where they developed inward towards the center of the build-up.

Age and Paleobathymetry of Salodik Group in PohPagimana section, East Arm of Sulawesi Based on Foraminiferal Assemblages

Planktonic and benthic foraminiferal assemblages were used for age and paleobathymetry analysis of outcropping carbonate succession of the Salodik Group in Poh–Pagimana section, East Arm of Sulawesi. Twenty spot samples of carbonate rocks were collected from cut slope along the road between Poh and Pagimana. Age analysis conducted for each sample by its planktonic foraminifera assemblages and group into their age interval. The age range from Early Eocene to Pliocene. Benthic foraminiferal assemblages indicate paleobathymetry ranging from middle shelf to upper bathyal settings. Age analysis of the studied section show an older sediments (Early–Middle Eocene) overlie younger sediment (Early Miocene). This is interpreted as the evidence of thrust fault in the Poh–Pagimana section as part of thrust sheets of Batui thrust complex which imbricated on deformation zone. The youngest sediment which have suffered deformations shown by disordered age sequence is Pliocene in age (N20-21). The Eocene to Pliocene carbonate succession in the studied section was deposited relatively in the more basinward position compared to the carbonate-dominated sediments in the Tomori area which was deposited in the more landward position.

3D-RVSP experimental study above a carbonate outcrop for coal resource exploration

In the areas where carbonate rocks expose to the near surface, there are several intractable issues in conventional surface seismic, including (1) weak reflection energy, (2) complex wave field and (3) serious static correction. Therefore, the seismic imaging result suffers significantly. However, RVSP is able to achieve reflected data with high quality since it generates seismic waves in borehole and receives seismic waves at the surface. In order to verify the applicability of RVSP technique in complex areas, this study carried out a 3D-RVSP seismic experiment in Wulunshan coal field, southwest China. Compared with the surface seismic data, RVSP data show higher signal-to-noise ratio, wider frequency band and weaker surface wave interference. In addition, two imaging methods (conventional CDP transform stack and novel equivalent-surface conversion) were implemented for RVSP data imaging. The imaging results show that the smaller and deeper structures can be revealed better by equivalent-surface conversion method than by CDP transform stack method. Hence, this study demonstrates that RVSP is an efficient method applied in the area with complex surface condition.

Implication of heterogeneities on core porosity measurements

Heterogeneities within core samples affect the accuracy of the laboratory measured core plug interconnected porosity. The laboratory measures the volume averaged porosity of the interconnected pores, <ϕm>. For homogeneous cores this is the correct porosity ± any experimental error. However for heterogeneous cores when any embedded material (unknown or ignored) has a differing porosity, ϕi, to that of the containing outer shell, ϕo, there will be increased uncertainty. We show that the difference between the measured volume averaged porosity, <ϕm>, and the porosity of the outer shell of the core, ϕo can be quantified by our Heterogeneity Factor, H. H is defined as (<ϕm>- ϕo)/ϕo and given by H = F(R-1), where F is the ratio of the bulk volume of the embedded material to the total core bulk volume (measured), VBi/VBm, and R is the ratio of the embedded and the host outer porosity, ϕi/ϕo. The core plug homogeneous model can create increased error bounds in porosity for heterogeneous plugs.When H is zero there is no error in the porosity measurement due to heterogeneity, but when H≠ 0 then the differences can be significant and increases the experimental error bound. We present graphs for relevant industry scenarios to demonstrate the effect of any inclusions in the measured porosity. We find that when F is ∼0.1 i.e., inner included porosity is 10% of bulk volume, the relative error between <ϕm> and ϕo can reach ∼30% and even larger differences when F > 0.1. We then give a real example from a faulted vuggy outcrop carbonate which demonstrates extra porosity uncertainties, even for a very small vug. Finally we discuss the possible effect of embedded clay intrusions emitting adsorbed gas on grain/pore volume determinations of porosity using gas expansion, a common laboratory method of porosity determination.Appreciation of core heterogeneity on the precision of the laboratory porosity measurements is essential to improve the confidence in the error bounds for the quality control of laboratory core porosity measurements, and of the porosity distribution frequency for inputs to statistical methods such as Monte Carlo analysis for oil-in-place estimations, STOIIP.

Characterization of Natural Vuggy Fractured Porous Medium: Its Physicochemical Properties, Porosity and Permeability

The aim of this work was to obtain the physicochemical properties by SEM, XRD, FTIR analyses and the surface characteristics from carbonate outcrops cores such as pore diameter, surface area, porosity and permeability. The methods used to characterize them were Scanning Electron Microscopy, SEM; X Ray Diffraction, DRX; Fourier Transform Infrared Spectroscopy, FTIR. The porosity and permeability of natural vuggy fractured porous medium from core samples was determined obtained in the laboratory with conventional procedures. The cores have smooth and rough surfaces with porous with several sizes. Some crystals appear in preferential zones mainly composed by calcium, carbon and oxygen. Apparently into free spaces were found the organic materials, organic residues of crude oil. The cores have smooth and rough surfaces with porous with several sizes. Some crystals appear in preferential zones composed by calcium, carbon and oxygen. Apparently into free spaces were found the organic materials, organic residues of crude oil. The main inorganic compound in cores is calcite, (CaCO3). The porosity was for porous core 26% and for solid core 8.5%. The values obtained show that the cores have permeability where the fluid migrates through the particles at 2.23 × 10-4 cm/s.