Reservoir Research Articles

Application of volume fracturing technology in tight oil reservoirs of Shengli oilfield

Application of volume fracturing technology in tight oil reservoirs of Shengli oilfield

Formation and distribution of marine-continental transitional lithologic reservoirs in Pingbei slope belt, Xihu sag, East China Sea Shelf Basin

Formation and distribution of marine-continental transitional lithologic reservoirs in Pingbei slope belt, Xihu sag, East China Sea Shelf Basin

Geology-engineering integration for low-permeability and thin marginal reservoirs: a case study on Zanazour oilfield, Pre-Caspian Basin

Geology-engineering integration for low-permeability and thin marginal reservoirs: a case study on Zanazour oilfield, Pre-Caspian Basin

The application of airborne LiDAR technology to landslide survey: A case study of Zhangjiawan Village landslides in Three Gorges Reservoir area

The application of airborne LiDAR technology to landslide survey: A case study of Zhangjiawan Village landslides in Three Gorges Reservoir area

Correlating three Upper Permian Zechstein-2-Carbonate outcrops across the Eichsfeld-Altmark Swell – Facies, reservoir properties, and outcrop analogue potential

Die Reservoireigenschaften in Karbonatgesteinen sind verschiedenen Ablagerungstypen zugeordnet. Ein Verstandnis der lateralen Faziesverteilung der Karbonate kann somit der Schlussel zu einem besseren Verstandnis der Lager- stattenkontinuitat, -geometrie und -qualitat darstellen. Im Fokus dieser Arbeit stehen drei Zechstein-Karbonat-Aufschlusse (Zweiter Zyklus, Stassfurt, Ca2) am SW-Rand des Harzes. Diese Karbonate wurden am Sudrand des Sudpermischen Beck- ens auf der Eichsfeld-Altmark-Schwelle, einem NNE–SSW streichendem Palaohochgebiet, abgelagert. Es werden Ablagerungsgebiete des Plattformhanges, des Plattformrandes und der inneren Plattform in jedem Aufschluss unterschieden. Basierend auf dieser Interpretation konnen die untersuchten Aufschlusse uber den Verlauf der Schwelle uber eine Entfernung von 25 km korreliert werden. Die erhobenen Daten werden mit Reservoirdaten eines 130 km in NW-Rich- tung liegenden Feldes, welches eines der untersuchten Ablagerungsgebiete widerspiegelt, verglichen. Porositaten der Platt- formhang-Karbonate im Aufschluss (ca. 6 %) und Reservoir (ca. 4 %) sind vergleichbar, jedoch sind die Permeabilitaten in den Aufschlussgesteinen reduziert. Die erhohten Permeabilitaten der Reservoirgesteine konnen moglicherweise durch Mi- krorissbildung erklart werden. Beste Reservoirqualitaten zeigen die Karbonate des Plattformrandes, die im Bereich des Zentrums der untersuchten Schwelle die grosten Machtigkeiten aufweisen. Zusammen mit der Korrelation der untersuchten Ablagerungsgebiete uber eine Lange von 25 km konnen diese Informationen in Untergrundmodelle der Zechstein-2-Kar- bonate in NW Deutschland eingefugt werden. Um ein mogliches Aufschlussanalog, welches wichtige zusatzliche Informationen uber laterale Reservoirheterogenitaten liefern kann, zu definieren, werden Untergrunddaten uber die Verteilung der Ablagerungsraume des jeweiligen Feldes benotigt.

Seismic oil-water contact detection, supported with pressure data, for hydrocarbon in-place estimation

With good quality seismic data, fluid contacts can be detected in an area of favourable rock physics. The oil-water contact (OWC) inferred from seismic data is validated using other independent data. Where there is an agreement between a seismically-derived OWC and other supporting data, this approach can be used as a reliable technique in reservoir delineation. A field example is presented from deepwater offshore Nigeria, typified by stacked-turbidite sands of Upper to Middle Miocene age. The volumetric estimate of in place volumes for the field was initially based on the lowest known oil (LKO) penetrated by wells as the deepest oil limit. Consequently, the actual field performance and history matching of the dynamic model suggested the oil-in-place was underestimated. The seismically-derived OWC, when supported by pressure and production data, justified an increased hydrocarbon in place estimate. In a block calibrated by wells, seismically-derived OWCs agree with results from the well pressure-depth plot and within the range of depth uncertainty. This provided confidence in using seismic OWC estimates to define oil downdip limits in blocks where the contact has not been penetrated. Thus, in place additions were achieved by extending the lowest oil limit(LKO) downdip to the seismic OWC.

Analysis of Water Circulation Characteristics for Hydraulic and Water Temperature Investigation in Paldang Reservoir

Analysis of Water Circulation Characteristics for Hydraulic and Water Temperature Investigation in Paldang Reservoir

Improvement of sensing margin and reset switching fail of RRAM

To develop a high voltage read margin ΔVrd, deep reset engineering and defect engineering are proposed. To realize the defect engineering, the amount of oxygen vacancy of the resistor was controlled by optimizing the material of the reservoir (RSV) and switching oxide. We investigated the barrier height modulation, which was formed by the Ru bottom electrode (BE) having a high work function, to demonstrate the concept of deep reset engineering by reducing the set current (Iset) of the HfO2 resistor (1R) to the turn-on current (Ith) of the selector device (1S). Further, we identified the causes of the negative set fail through the chemical analysis of the HfO2/BE TiN interface to improve the reset switching fail. Unstable TiON and TiOx chemical species, which present in the interface of HfO2/BE TiN, take oxygen from the resistor HfO2 and create the parasitic defect (or filament), which was injected from BE TiN. To improve the negative set fail of RRAM, we proposed the O3 surface treatment of BE TiN at a high temperature (∼320 °C) and the BE Ru with a superior oxidation resistance. By using deep reset engineering, we successfully increased the ΔVrd of 1S1R by more than 0.5 V. We also demonstrated that Ru BE and the O3 surface treatment of BE TiN improved both the reset window and the negative set.

Closure to “Influence of Daily Regulation of a Reservoir on Downstream Navigation” by Yizi Shang, Xiaofei Li, Xuerui Gao, Yanxiang Guo, Yuntao Ye, and Ling Shang

Closure to “Influence of Daily Regulation of a Reservoir on Downstream Navigation” by Yizi Shang, Xiaofei Li, Xuerui Gao, Yanxiang Guo, Yuntao Ye, and Ling Shang

An assessment of knowledge of prevention and management of Rabies in interns and final year students of Shri M. P. Shah Government Medical College, Jamnagar, Gujarat

Background: Rabies is one of the most important zoonotic diseases in India. Dogs are the main reservoir of rabies in India. In Southeast Asia, untreated, improperly treated or neglected cases lead to thousands of death yearly. Rabies can be completely prevented through proper management, but once contracted its almost always fatal. Objectives: To assess the knowledge regarding preventive measures, post-exposure prophylaxis, wound management and use of RIG among the interns and final year medical students of Shri M.P. Shah Government Medical College, Jamnagar, Gujarat. Materials and Methods: It is a cross-sectional study conducted in July, 2013. Data was collected using pre-tested questionnaire from 100 interns and final year students of Shri M.P. Shah Government Medical College, Jamnagar, Gujarat. Results: It was seen that only 59% knew that vaccination of dogs was an essential preventive measure, 80% and 68% agreed that pre-exposure vaccination and educating the people regarding pre- and post-exposure prophylaxis were useful, respectively. Also 89% and 59% were aware that wound should be washed immediately and antiseptics should be applied, respectively. 50% and 29% were not aware of the schedule and dose of the PEP, respectively. Only 35% knew about both IM and ID route of administration of PEP. Only 66% were aware that the site of administration of PEP is deltoid. Conclusion: The study showed that there was no proper knowledge about the prevention and management of rabies in the study population which needs to be overcome immediately with proper training.

Seismic facies analysis and reservoir characterization based on isochronous stratigraphy frame

The concepts and methodologies of sequence stratigraphy or seismic stratigraphy have been applied in the seismic facies analysis and reservoir characterization based on seismic data. But one of the most important factors for getting good results in this kind of application is the coupling of seismic sequence and sedimentary sequence. Our study has showed that more accuracy and meaningful results can be achieved from seismic facies analysis and reservoir characterization based on isochronous stratigraphy frame compared with the results from diachronous stratigraphy frame. By comparative researches, we develop our own seismic facies analysis and reservoir characterization approaches under isochronal stratigraphy frame which mainly include (1) identifying the seismic terminations as the top and bottom of one large sequence stratigraphy, (2) reconstructing the seismic volume to build iso-geological time frame, (3) doing seismic facies volumetric analysis on this new geological time equivalent frame, and (4) identifying the inter detailed sequences and the interior of reservoirs by well log calibration to get final results about the distributions of sedimentary sequences, variation of reservoirs in 3D, etc.. The proposed approaches have been applied to several studies of the carbonates reef and shoal reservoir characterization aiming for gas exploration in eastern Sichuan Basin. The results from our studies have proved that the proposed methodologies and workflows are valid and better results have been achieved.

Computation of Porosity Using Sand and Carbonate Rock Physics Models in an Iranian Oilfield

In this case study, we have employed post stack inversion, guided by rock physics, to estimate reservoir porosity in an Iranian oil field. The reservoir, based on the lithology and porosity information can be divided into 8 zones and 19 subzones with lithologies comprised of shale, sand and carbonates. Among them, three zones above WOC are carbonate and sandstone. We use different rock physics model to estimate porosity from wire line and seismic data. The procedure uses stack and estimated wavelet to determine the elastic parameter: Pwave impedance. Different rock physics model were applied to relate acoustic impedance (AI) to porosity. This allowed performing rock physics analysis, not only on well log data, but also on seismic data (post stack inversion results). The poststack inversion of AI within the target zone was projected onto the template to generate porosity volume. One of the most important issues in carbonate rock physics is fracture distribution. Petrophysical analysis in carbonate sections of the reservoir shows that fracture distribution is limited and production is mostly from matrix porosity. Fractures in the carbonate zone are mostly joints with 0.5 mm opening and 15 cm in length, so the isotropic medium assumption can be made. The results show that Nur-Dvorkin (1996) model and Raymer-Greenberg-Castagna (1997) are appropriate for predicting porosity in sandstone and carbonate zone of the reservoir respectively and predict porosity up to 30% which shows good agreement with the porosity values measured from well log data.

Reducing Uncertainty in Seismic Interpretation using Crosswell Seismic

Crosswell seismic is an emerging technology which provides highly detailed images of the subsurface at reservoir scale. The technology has the potential to delineate complex structure, help verify existing interpretation and also can be used to monitor changes in the reservoir caused by enhanced recovery strategies. The technology employs tomographic surveying, whereby the transmitter and receiver are deployed in separate wells. Interwell structure and velocity can be obtained from reflection processing and direct wave processing respectively. In this paper an example of crosswell seismic is discussed where the technology produced high-resolution images of the geology between wells at 8 to 10 times the resolution of surface 3-D seismic data and revealed numerous faulted compartments in the reservoir previously unseen in the surface seismic. These results have lead to a new understanding of the field and improved the well design process.

Value-add and safe drilling from 4D AVO evaluation in the Enfield oil field, North-West Shelf, Australia

The Enfield oil field, on the Australia?s Greater North- West Shelf, started production in July 2006, and has already seen significant benefit from 4D seismic monitoring. The technique is particularly applicable in Enfield due to faulting and baffles within the reservoir, the need for multiple water injection wells, and the presence of a gas cap. Full-field monitor surveys in February 2007 and December 2008 have made major contributions to reservoir management and identification of infill drilling opportunities. This paper highlights the 2009 development drilling in the field?s Sliver Block, where 4D not only supported the business case for a new production and water injection well, but also provided important information to enhance safe and efficient drilling. 4D AVO analysis involved extraction of changes over various source-receiver offset ranges, driven by a rock property model in which nears and mids tend to show pressure changes, while fars and ultra-fars show saturation changes. A clear 4D AVO signal on the early monitor showed the drilling target area to be pressured up by a distant injector, contrary to pre-4D expectations. The later monitor confirmed this, and also showed the oil target intact ? with no significant water sweep. Using 4D, significant overpressure in the target was predicted. Accordingly, casing schemes for the wells were redesigned to enable safe reservoir entry; the distant water injector was shut in prior to drilling; and appropriate heavy brine was ordered for completion operations. Actual pressures fell within the predicted range, and a safe and successful drilling campaign was achieved.

Prospect Identification using AVO Inversion and Lithology Prediction

Identifying prospects within a large study area is traditionally a time consuming process. Schlumberger Reservoir Seismic Services have produced an efficient prospect screening tool in the form of a well log calibrated gas sand probability cube derived from AVO inversion attributes. Pre-stack simultaneous AVO inversion was performed on a 5048 sq/km multi-client seismic survey to compute seismic elastic attributes (acoustic impedance, Poisson?s ratio and density) which can be used to generate lithology and fluid properties. The survey was acquired in 2008 and is located offshore between the giant Io/Jansz and Scarborough gas fields on Australia?s NW shelf, with potential gas reservoir?s situated at multiple levels within a complex geological setting. Well log data from within the survey area were calibrated to the seismic, from which wavelets were estimated for each angle stack using the angle-dependant reflectivity logs. Low frequency models were derived using log data from wells both inside and outside the survey extents, in conjunction with seismic velocities and guided by interpreted horizons. Elastic attribute logs were generated from the wells and used to produce non-Gaussian lithology probability density functions (PDF), which in turn are utilised to generate a 3D gas sand probability cube from acoustic impedance and Poisson's ratio volumes. The gas sand probability cube can be loaded into a 3D visualisation software package where techniques such as volume rendering and opacity are applied to quickly and efficiently screen for potential prospects from which gas sand geobodies can be extracted for volumetric analysis and further reservoir characterisation.

Seismic monitoring of CO2 Geosequestration: CO2CRC Otway project case study

The CO2CRC Otway Project is Australia?s first demonstration of the deep geological storage of carbon dioxide. Its test site is located in Victoria, onshore. Within the bound of the first phase of the Otway project ~61000 tonnes of CO2/CH4 mixture were injected into depleted gas reservoir located at a depth of 2 km. Second phase of the project is dedicated to injection of small amount (up to 10 000 tonnes) of CO2-rich gas to saline aquifer at depth of ~1.3 km. Time-lapse seismic is a powerful tool for imaging of changes in the subsurface such as migration of CO2 within reservoir and assurance monitoring of possible leakage to other formations. However imaging of gas-into-gas injection (phase I) or injection of very small amounts (phase II) using land seismic are complicated problems. To meet these challenges a comprehensive seismic program is developed and being implemented. It includes surface and borehole time-lapse seismic surveys. First 3D survey was acquired in year 2000 to find gas fields in the area, two more surveys were shot in 2008 (pre-injection baseline) and 2009 (first monitor, ~31 000 tonnes of gas were injected to the date of survey), next survey is scheduled at January, 2010. A number or repeated 2D surveys were acquired over last several years to optimize 3D seismic acquisition technique and investigate repeatability of land seismic data.

3D inversion of transient electromagnetic data from the Alvheim field, North Sea

SUMMARY We present a case study leading to the 3D inversion of transient electromagnetic (EM) data for delineating reservoir extent at the Alvheim field in the Norwegian sector of the North Sea. The survey was conducted in July and August 2008 using a two ship operation and ocean bottom cables. One ship laid a receiver cable with 30 receiver nodes on the sea floor. The second ship placed a source cable used to generate a coded transient signal on the sea floor. The configuration of the source and receiver spread was analogous to 2D seismic acquisition, as the system was rolled along to obtain multi-fold coverage of the subsurface. The survey spanned 20 km, resulting in measurements of 1270 source-receiver locations. The electric fields for each source-receiver pair were measured and deconvolved with the source current to determine the impulse response function. Preliminary inversions were made for each source-receiver pair using a 1D model, and the results were stitched to a 2D image. Having defined a background model, all data were then simultaneously inverted in 3D with focusing regularization. This revealed high resistivity volumes corresponding to the known hydrocarbon-bearing reservoirs of the Alvheim field.

3-D tomographic Q inversion for compensating attenuation anomalies

The propagation of seismic wave through viscoacoustic media is affected by the attenuation that is caused by the quality factor Q, resulting in significant loss of signal strength and bandwidth. Gas trapped in sediment is an example of such media. Seismic images of geological structures underneath shallow gas often suffer from resolution degradation and the effect of amplitude dimming, making the identification and interpretation of the structures difficult. This in turn affects the ability to accurately predict the reservoir properties. Thus, there is a need to compensate the attenuation anomalies due to Q. In this paper, we present a workflow of Q estimation and compensation that is based on our previous work on amplitude tomography. Our new approach involves utilizing tomographic inversion for estimating Q from prestack depth migrated common image gathers that fully honours the wavepaths. By filtering the seismic data into different frequency bands and measuring the effect of attenuation on amplitudes in each band, the frequency dependent effect, which was ignored in our previous amplitude tomography work, of attenuation is fully taken into account, thereby allowing Q to be estimated from our tomographic method. By using the estimated Q volume in one of the migration methods that incorporates Q in the traveltime computation, we demonstrate, through realdata examples, that our workflow provides an optimal compensation solution that resolves amplitude, phase and bandwidth distortions due to seismic attenuation.

Bayesian Stochastic Inversion (A case study from an Iranian oil field)

We have implemented an estimation procedure whereby wireline data can be extrapolated away from existing well using geostatistical inversion of post-stack 3D seismic data. This procedure works directly in a fine-scale stratigraphic grid, and is conditioned by well and seismic data. It uses a Bayesian framework and a linearized, weak contrast approximation of the Zoeppritz equation to construct a joint log-Gaussian posterior distribution for Pwave impedances. Variograms are also estimated from well-log, seismic data and acoustic inversion results that define the expected degree of lateral smoothness away from the well. A sequential Gaussian Simulation algorithm is applied to sample the posterior PDF and generates multiple, high-resolution realizations of the acoustic impedance which can be utilized to generate stochastic realizations of petrophysical variables that not only honor the well-log data, but most importantly, that fully honor the 3D seismic. Sensitivity analysis was also performed to find the optimum values for S/N ratio, Variogram ranges and prior standard deviation. We had just one well in the area and preferred to keep it to perform quality control of the inversion results. Without constraining with well, geostatistical inversion still can be used to estimate acceptable static reservoir model for the subsequent simulation and planning of in-fill drilling and/or enhanced-oil-recovery operations.

Land VSP seismic sources evaluation: CO2CRC Otway project case study

It is widely accepted that, depending on acquisition technique, vertical seismic profiling (VSP) can provide us with extremely valuable information on seismic velocities (both P and S), attenuation and anisotropy of s eismic properties of the earth. Subsurface images, obtained with offset or 3D VSP could demonstrate superior resolution, signal-to-noise ratio and repeatability of surveys in comparison to standard surface seismic. These potential benefits are of great importance for both reservoir characterisation and time-lapse seismic monitoring. However in order to achieve them VSP surveys should be acquired with proper survey design and optimal source and receiver characteristics.