Fiber-optic distributed acoustic sensing (DAS) offers advantages in time-lapse VSP seismic monitoring of an unconventional reservoir. Petrophysical changes to the reservoir due to hydraulic fracturing of the rocks change the character of seismic waves. Repeatable DAS VSP measurements within the stimulated zone can reveal the areas affected by the fracturing. The goal of this study is to assess how these changes affect DAS seismic data acquired before and after stimulation. One of the main advantages of DAS VSP seismic is that receivers cover the entire well including the deviated and horizontal sections. This provides not only velocity/image control in the overburden and target, but also high-resolution images within the frac zone from the horizontal receivers. Another advantage of DAS VSP, if the fiber is permanently installed behind casing, is that the receiver locations are fixed, allowing for high repeatability between surveys.
A fiber-optic cable was installed in a treatment well in the Meramec Shale covering the entire length of the well from surface to target depth, resulting in approximately 1000 recorded channels. The large number of channels, combined with the wide aperture, allowed us to record and locate seismic events from both vertical and horizontal portions of the well. Seismic processing consisted of time-lapse cross-equalization (XEQ) of data using receivers within the vertical portion of the well, where no changes are expected, as proxies to assess the validity of responses observed in the horizontal portion of the well. The XEQ data was then imaged with respect to the monitoring well in order to assess the changes to the reservoir. Complex arrivals within the deviated well were modeled in order to calibrate the wavefield separation prior to prestack Kirchhoff depth migration (PSKDM). The resulting amplitude anomalies in the vicinity of the fibered well have been analyzed in tandem with traditional DAS diagnostic measurements such as crosswell strain and microseismic.
The analysis of this DAS data set demonstrates that current fiber-optic technology can provide enough sensitivity to map seismic anomalies which we can integrate with temperature and strain data for an improved reservoir description. It further demonstrates the value of having DAS receivers within the stimulated zone as they provide in-situ information about the subsurface changes. The importance of the DAS measurements is that they reduce acquisition costs while providing additional monitoring tools from the same hardware.
A challenging problem of automated history-matching work flows is ensuring that, after applying updates to previous models, the resulting history-matched models remain consistent geologically. This paper discusses a project with the objective of leveraging prestack and poststack seismic data in order to reconstruct 3D images of thin, discontinuous, oil-filled packstone pay facies of the Upper and Lower Wolfcamp formation. The Oklahoma City independent has a new-look portfolio and new operational and financial priorities. And now it has enlisted an energy research firm to leverage advanced analytics and machine learning to help get the most out of its assets. The objective of this case study is to describe a specific approach to establishing an exploration strategy at the initial stage on the basis of not only uncertainty reduction, but also early business-case development and maximization of future economic value.
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Bennett, Nicholas (Schlumberger-Doll Research) | Donald, Adam (Schlumberger) | Ghadiry, Sherif (Schlumberger) | Nassar, Mohamed (Schlumberger) | Kumar, Rajeev (Schlumberger Middle East S.A.) | Biswas, Reetam (The University of Texas)
A new sonic-imaging technique uses azimuthal receivers to determine individual reflector locations and attributes, such as the dip and azimuth of formation layer boundaries, fractures, and faults. From the filtered waveform measurements, an automated time pick and event-localization procedure is used to collect possible reflected arrival events. An automated ray-tracing and 3D slowness time coherence (STC) procedure is used to determine the raypath type of the arrival event and the reflector azimuth. The angle of incidence of the reflected arrival is related to the relative dip, and the moveout in 3D across the individual sensors is related to the azimuthal orientation of the reflector. This information is then used to produce a 3D structural map of the reflector, which can be readily used for further geomodeling.
This new technique addresses several shortcomings in the current state-of-the-art sonic-imaging services within the industry. Similar to seismic processing, the current sonic-imaging workflow consists of iteratively testing migration parameters to obtain a 2D image representing a plane in line with the desired receiver array. The image is then interpreted for features, which is often subjective in nature and does not directly provide quantitative results for the discrete reflections. The technique presented here, besides providing appropriate parameter values for the migration workflow, further complements the migration image by providing dip and azimuth for each event that can be used in further downstream boundary or discontinuity characterization.
A field example from the Middle East is presented in which a carbonate reservoir was examined using this technique and subsequently integrated with wellbore images to provide insight to the structural geological setting, which was lacking seismic data due to surface constraints. Structural dips were picked in the lower zone of the main hole and used to update the orientation of stratigraphic formation tops along the well trajectory. 3D surfaces were then created and projected from the main hole to the sidetrack to check for structural conformity. One of the projected surfaces from the main hole matched the expected depth of the formation top in the sidetrack but two were offset due to the possible presence of a fault. This was confirmed by parallel evaluation of the azimuthal sonic-imaging data acquired in the main hole that showed an abrupt change in the relative dip of reflectors above and below the possible fault plane using the 3D STC and ray tracing. Dip patterns from both wells showed a drag effect around the offset formation tops, further confirming the presence of a fault. A comparison of the acquired borehole images pinpointed the depth and orientation of the fault cutting both wells to explain the depth offset of the projected 3D formation top surfaces.
Hao, Qian (Exploration and Development Research Institute & Science and Technology Department of Changqing Oilfield Company, CNPC) | Wang, Jiping (Exploration and Development Research Institute of Changqing Oilfield Company, CNPC) | Han, Dong (Science and Technology Department of Changqing Oilfield Company, CNPC) | Li, Wuke (Exploration & Development Research Institute of Changqing Oilfield Company, CNPC) | Liang, Changbao (South Sulige Operating Company of Changqing Oilfield Company, CNPC) | Dai, Libin (South Sulige Operating Company of Changqing Oilfield Company, CNPC) | Jia, Yonghui (South Sulige Operating Company of Changqing Oilfield Company, CNPC) | Qi, Congwei (TOTAL) | Zhai, Gaoqiang (TOTAL)
South Sulige operation project is an international cooperation development of tight sand gas field located in the Ordos Basin, Northwest China. The economy of the project relies on technical breakthrough to select good drilling location for getting higher Estimated Ultimate Recovery (EUR) rather than partners continually reducing annual investment and cost saving to survive in the global oil price fluctuations in the long run.
Although a total of 306 wells have been drilled and 1648 Km2 of 3D seismic data have been acquired and processed during the past 3 years, well drilling results were not as good as expected in terms of seismic sand thickness prediction and channel sand / shale discrimination. Seismic data quality indeed improved due to large efforts of the processing, even getting clear seismic images at reservoir level, however, at Upper Permian He8 Formation, the main gas producing target layer, seismic interpretation results are still difficulty to distinguish complicated fluvial depositions of this tight sand gas filed.
On the other hand, existing production data indicate that Absolute Open Flow (AOF) of the super good well which accounts for only 3% of the total drilled wells usually exceed 120×104m3/d, annual production of the super good well could exceed 2500 ×104m3, EUR of the super good well may exceed 2.4×108m3. Compared with the ordinary well, EUR of the super good well is 9.6 times that of the ordinary well. As a result, accurate predicting good drilling location and try to capture more super good wells remains the biggest challenge and the most attractive research direction for this international cooperation project.
Therefore, a different approach joint 3G (Geophysics, Geology, Gas Reservoir) integrated study is carried out by an international joint research team from Paris, France and Xi’an, China. This paper shows a new method of combining sedimentological model from wells results (static data include core description, typical channel E-logs parameters, semi-regional synthesis. dynamic data include AOF, annual production, EUR) with low value of Poisson's Ratio (PR) / amplitude maps which were defined in the study, aiming to identify areas where a given dominant fluvial facies could be predicted.
The paper's objective is to share the integrated study approach to get better understanding of such tight sand reservoir, and the proposed methodology opens new opportunities for predicting good drilling location, increase the probability of capturing more super good wells, lower the project development risk with best practices approach.
Khan, Muhammad Hanif (Independent) | Maqsood, Tahir (Tullow Pakistan) | Jaswal, Tariq Majeed (Pakistan Oilfield Ltd) | Mujahid, Muhammad (Spec energy DMCC) | Malik, M. Suleman (Qatar Petroleum) | Jadoon, Ehtisham Faisal (UEP Pakistan) | Hakeem, Uray Lukman (Qatar Petroleum)
This article investigates the seismic reflection geometries (possible reservoir) of Paleogene of Offshore Indus Basin Pakistan (shelf area) from 2D seismic and make an analogue with the proven carbonate reservoir geometries found in countries such as Canada and Middle East. The 2D seismic data are used to interpret the possible carbonate features and methods to identify them and define its depositional setting on the carbonate platform. The offshore Indus Basin is tectonically a rift and a passive continental margin basin, located in Offshore Pakistan and Northwest India where carbonates were deposited on the shelf and the deep offshore area during early post-rift phase. In the deep offshore area, carbonates were set on volcanic seamounts during the Paleogene age. In Paleogene, the Indian Plate was passing through the equator in the conditions of warmer water with appropriate water salinity, where those conditions were suitable for the growth of organisms responsible to develop reefs in the Offshore Indus area. The available seismic data analysis has indicated the possible presence of different carbonate reefs on the shelf. The seismic data enabled to define the possible carbonate Rimmed shelf depositional model in the area. The aim of this article is to highlight and analogue carbonate seismic geometries, their internal architecture in the Paleogene interval of the Offshore Indus Basin (shelf area) and how to identify them, which may help for further exploration in Offshore Indus Basin.
Microseismic monitoring of multi-stage hydraulic fracturing has emerged as a key technology for unconventional stimulation wells to show the 3D propagation of the induced fractures. Monitoring the dynamic growth of these fractures gives insight into the quality of the completion design as well as better understanding of reservoir characteristics and rock properties.
The lack of industry standard format for microseismic data resulted in major challenges on different aspects of transmission, interpretation and archiving. This has raised the need to establish a standard format for both raw and basic processed microseismic data.
Basic processed data for each microseismic event is processed remotely in the field and transmitted in near real-time to central offices to be mapped and integrated with other data types using specialized technologies to enable timely decision making. Data should contain the minimum and sufficient information to characterize and indicate the location and magnitude of the induced fractures.
Raw microseismic files are large in size and typically delivered to data proponent in external storage devices at the end of the hydraulic fracturing operation. These files should contain additional attributes collected at the field for all microseismic events and stages such as trace header description, geophone orientation and specification. Both basic processed and raw microseismic data must be captured in a standard format to be stored in a corporate database to safeguard company assets, ensure data integrity and availability for future operations.
Data standardization for both basic processed and raw microseismic was developed by compiling the minimum data requirements from subject matter experts. The new standard for basic processed data consists of a vendor-neutral format that is suitable for all service companies and compatible with major interpretation and visualization technologies. This standard mainly focuses on setting guidelines for microseismic events location and magnitude. Raw microseismic files are in "SEGY" format that include additional meta data attributes such as frac stage number, treatment and monitoring well.
Solutions used to address current microseismic data exchange challenges went beyond data standardization to include modification of existing real-time data transmission system, interpretation technologies and database schema to accommodate and visualize microseismic data at different stages.
Future challenges of microseismic will include the need for technology and data transformation to adopt new generation processing technologies and algorithms to enable on-site data analytics and huge data transmission. This new approach will automate filtering signal from noise to streamline real-time signal transmission and ensure integrity. This session will focus on highlighting microseismic current and future data challenges including discussions on some of the proposed solutions.
The bioclastic limestone reservoirs of Cretaceous period occupy an important position in the petroleum industry of Middle East. It is the carbonate heterogeneity that is challenging the accuracy of the reservoir prediction, which brings forward higher requirements for the seismic data quality. Besides, some seismic data are processed more than 10 years ago, the signal to noise ratio (SNR) is relative low due to the random noise and coherent noise like acquisition footprint anomalies. The acquisition footprint artifacts caused by acquisition and processing seriously suppress the true stratigraphic features, which can result in pitfalls in seismic interpretation, seismic attribute analysis as well as seismic inversion. While the pre-stack seismic data is usually unavailable, which means that the noise can hardly be subtracted by conventional pre-stack seismic processing workflows, such as statics, high-resolution velocity analysis and ground roll attenuation. Consequently, a comprehensive post-stack seismic data conditioning workflow is necessary to solve the above problems.
In order to improve the post-stack seismic data quality, a comprehensive data conditioning workflow are applied for noise suppression. Firstly, structural-oriented filtering is utilized to attenuate random noise and partial acquisition footprint artifacts. Then 2D waveform transform of seismic amplitude and filtered seismic attribute in x-y domain are calculated, to separate acquisition footprint anomalies (large wave number in kx-ky domain) from true structural signal (small wave number in kx-ky domain) by interactive analysis. The application of Laplace-Gaussian (LoG) filter deserves an obvious improvement in acquisition footprint suppression workflow. The comprehensive noise attenuation workflow in this paper can effectively remove both periodic and non-periodic noise to obtain higher signal to noise ratio (SNR) for post-stack seismic volume. In this way, the stratigraphic features (tidal-channel, reef-beach complex) can be more clearly depicted and some artifacts caused by noise will disappear in seismic attribute calculation, seismic inversion and reservoir prediction.
Liu, Jinpeng (Data Processing Company, Geophysical-COSL) | Zhong, Mingrui (Data Processing Company, Geophysical-COSL) | Fang, Zhongyu (Data Processing Company, Geophysical-COSL) | Dan, Zhiwei (Data Processing Company, Geophysical-COSL) | Sun, Leiming (Data Processing Company, Geophysical-COSL)
With the deepening of exploration and development, exploration in the south China sea is faced with increasingly complex geological targets, including complex fault blocks, lithological targets, middle and deep strata, small scales and more subtle and complex exploration targets. At present, the internationally recognized best seismic solution is "two wide and one high" acquisition and processing, namely wide azimuth, broadband, high-density field observation system and targeted processing. In the aspect of wide azimuth acquisition and processing, domestic land acquisition has also developed greatly, and in the past few years, there has also been a heated debate on the advantages and disadvantages of wide and narrow azimuth acquisition in complex areas. However, in the aspect of offshore acquisition, wide-azimuth acquisition is rarely carried out. The main reason is that the construction cost and difficulty are higher. With the primary 3d coverage of some mature areas on the sea, it is still unable to meet the exploration needs. In the past, the seismic observation system design was mostly based on the seismic acquisition and survey lines in accordance with the direction of vertical structure strike, so as to facilitate the accurate imaging of the main structure or the construction along the long axis of the work area according to the cost of offshore acquisition. However, in fact, the fault strike in the tectonic development area is complex and changeable, and there is no uniform rule. Some small faults that control the trap are completely perpendicular to the large structural strike, so the old 3d will lead to some poor fault imaging. According to the practical test data analysis, found that the different line direction observed data imaging effect is different, therefore some recently in the south China sea area for the secondary multi-dimensional three-dimensional attempt at sea to achieve multiple acquisition costs are relatively low, and the construction is convenient, but if you want to achieve benefit maximization, must consider the joint use of composite materials. Compared with the factors that need to be considered in collection and processing, it is much more complex, and the development of processing is relatively lagging behind. The main anisotropy is not fully considered, and relatively simple superposition is often difficult to reflect the effect of multi-direction.
A pre-exploration well was drilled in the Xihu Sag of East China Sea basin, and commercial oil and gas flow had been achieved. But the oil and gas bearing trap had a big depth with low closure height and small area. The resolution of seismic data acquired by towed streamer is low, so it's difficult to obtain seismic velocity precisely. There were great risk and uncertainty in description of the trap and distribution of gas-bearing sandstone, reservoir prediction of sweet spot, direct hydrocarbon indication, and reserves assessment.
In consideration of the drilling platform on the trap, seismic acquisition technique of walkaway VSP and walk around VSP were introduced, meanwhile some innovative methods in source, receivers and geometry were applied. Twenty three-component hydrophones were composed as signal receivers which had a sample interval of ten meters in the well, two straight shot lines and two loop shot lines were designed around the drilling platform. Besides, volume and depth of air gun array were optimized, and the sailing route of seismic source vessel was planned properly in order to improve the efficiency of collecting work.
The collecting work of walkaway VSP and walk around VSP was accomplished efficiently, and more than seventy kilometers VSP seismic data was achieved. Afterwards, the new data was processed finely in company with zero offset VSP data, so high resolution VSP profiles and accurate seismic velocity were obtained. Reprocess to original seismic data acquired by towed streamer was implemented on the basis of walkaway VSP and walk around VSP data. The quality of normal seismic data was improved through reprocess constrained by walkaway VSP data, and S/N and resolution were much higher than old data. So it would be credible to research the distribution of gas-bearing sandstone and direct hydrocarbon indication using the reprocessed seismic data.
It was the first time to use joint acquisition technique of walkaway VSP and walk around VSP in offshore China which was an important breakthrough. High resolution VSP seismic profiles and precise seismic velocity could be acquired, and the data was important basis for refined evaluation of pre-exploration targets. It's very necessary to popularize and utilize these new techniques further.