The Eastern Mediterranean hosts some of the largest and most prolific gas reservoirs in the region. These reservoirs have been deposited as slope submarine channels and basin floor turbidite sand sheets. The quantity and quality of production is often controlled by the architectural elements encountered. Slumped and deformed facies could hinder production in submarine channels of the slope setting, which are limited in lateral extent. Although laterally continuous and parallel thinly bedded turbidite sheets of the basin floor offer great lateral extent, they often exhibit poor vertical connectivity and low apparent resistivity due to thinly bedded sand/shale sequences.
An exploratory well was drilled in the Offshore Nile Delta targeting slope and basin floor deposits. Although seismic attribute interpretation provided a general outline of the area, there remained the uncertainty of whether the depositional setting encountered by the penetrated succession belonged to slope channels or basin floor setting. The value added through borehole image integration provided information regarding some unanswered questions: 1) Are sidewall cores representative of surrounding lithology? 2) Do sedimentary features support a slope or basin floor model? 3) Are there natural fractures to enhance porosity? 4) What is the reason for low porosity in the sands? 5) Are there additional thin beds between channel elements?
To answer all these questions, detailed structural, sedimentological and sand count analyses were performed on the micro-resistivity image, logged over a 500 m succession. Interpreted electro-facies differentiated the internal architectural elements from structural events within the penetrated succession. Slumping and water escape structures supported a slope channel setting while dip patterns directly above channel fills were interpreted as levee complexes of nearby channels. Sand counting of the image resistivity arrays included all possible thin beds that could contribute to pay while excluding all deformed facies that would hinder production performance.
Geometric attributes such as coherence and curvature are useful for delineating a subset of seismic stratigraphic features such as shale dewatering polygons, injectites, collapse features, mass transport complexes and overbank deposits, but have limited value in imaging classic seismic stratigraphy features such as onlap, progradation and erosional truncation. In this study we review the success of current geometric attribute usage and discuss the applications of newer volumetric attributes such as reflector convergence and reflector rotation about the normal to the reflector dip. While the former attribute is useful in the interpretation of angular unconformities, the latter attribute determines the rotation of fault blocks across discontinuities such as wrench faults. Such attributes can facilitate and quantify the use of seismic stratigraphic workflows to large 3D seismic volumes.
In this paper we provide a review of the data processing required for successful discrimination of unexploded ordnance (UXO) with electromagnetic induction sensors. We present the time-domain dipole model commonly used for UXO discrimination and highlight some of the challenges encountered in real data sets from demonstration projects conducted by the Environmental Security Technology Certification Program (ESTCP). In particular, we show how magnetic soil response can be effectively modelled as an additional dipole source. We then compare sensor platform performance at a recent demonstration where small (e.g. 37 mm) ordnance were buried.
Channel texture is an acoustic expression of a fluvial facies derived from 3D seismic data. The Gray Level Cooccurrence Matrix (GLCM) technique has been proven to be a promising method for seismic texture analysis. However, while we try to extract seismic texture attributes, there is uncertainty on how to select the optimal GLCM parameters which significantly affect the final results and the speed of process. In this paper, we study the relationship between GLCM parameters and final seismic texture results to simplify the computation of GLCM. The real seismic data is not a good test data because of noise interferences. So, we build an ideal synthetic channel reservoir model that is derived from a modern meandering river. Then we simulate a noise-free post-stack seismic data set using a 3D Gaussian beam method. With the synthetic channel model data, we will show how to select the two key GLCM parameters. Selecting various combination of the two most key parameters (Gray levels and Window size), we extracted the four GLCM secondary statistical measurements (Energy, Entropy, Contrast, and Homogeneity). Based on theoretical equations and the horizontal slices of texture, we ultimately reach a proper co-occurrence matrix parameter for fluvial reservoir from our synthetic channel model. Finally, applications of the GLCM parameters are successful applied to a 3D data in Bohai Bay.
The initial Bonga field development was based on a "green field?? integrated saturation model using Gulf of Mexico (GoM) data as analogue. In an earlier revision of the Field Development Plan, the relative permeability and capillary pressure models were based on steady-state and centrifuge special core analysis (SCAL) experiments from a few Bonga Main wells and also integrating GoM data. The saturation modeling was dependent on permeability classes (intended to be, but not explicitly representative of the facies). As production continued over the years, several attempts have been made at history-matching the observed performance history of the reservoirs that constitute the Bonga field. The results indicate that a review of some of the input parameters including the relative permeability and capillary pressure model are required to obtain a reasonable history match of the reservoir performance.
The predominant facies types in Bonga field include Channel Storey Axis (CSA), Channel Storey Margin (CSM) and Inter-channel Thin Beds (ICTB). A relationship was observed between the raw SCAL data and the different facies classes from detailed core description. Current production and recent drilling/logging information coupled with 4D seismic monitor indicate preferential sweep from some of the facies. This may have a significant impact on the ability to maximize recovery from the various facies in the reservoirs.
This study focuses on developing a facies-dependent saturation model that honors the current understanding of the waterflood performance of Bonga reservoirs. Good history-matched, robust and fit-for purpose models were obtained using this methodology. This has led to better evaluation of the recovery efficiency and flood pattern of the field which has been used to support further field development options and optimize production from existing wells.
Soleimani, Arash (Schlumberger Oilfield Services) | Penney, Richard K. (Schlumberger) | Hegazy, Osama (Schlumberger) | Bin Ngah, Ab Wahab (WNPOC) | Elhaj Sulliman, Abdalla (Sudapet Co Ltd) | Tewari, Raj Deo
Many fields in the Middle East suffer from low recovery and declines in primary production due to low oil gravity (<20 API) and viscosities above 100 cP. The studied field contains well in excess of 1 billion barrels in place with overall recovery expected to be less than 10% without EOR. 75% of the STOIIP comprises 20 API oil with 120-160 CP viscosity while the remainder comprises 17 API with 800 cP viscosity. Complicating matters, the three main sandstone reservoirs vary from braided fluvial streams in Upper formation (A), to thick sheet sands in the middle formation (B) and thinner sands separated vertically by thin shales in the Lower formation C.
In this study EOR techniques have been assessed for these three formations in order to recommend suitable development options for the field. Simulation schemes were developed for the following seven recovery mechanisms, including, water flood, chemical EOR - polymer and ASP, thermal EOR - CSS, steam flood, SAGD and in-situ combustion. Due to geological and fluid variation in these three formations, EOR mechanism behaves differently in terms of recovery for each reservoir.
The three most promising techniques, ASP, steam flood/CSS and insitu combustion were then developed to optimise pattern spacing and injection rates for each technique and for all three formations in this field.
Heterogeneity and geological factors have different impacts on the various EOR mechanisms, including convective methods like ASP and polymer flooding and convective-conductive methods like Thermal EOR. Overall, thermal EOR has been found to be more effective and economically feasible for this field, in particular for the heterogeneous formation with high viscosity oil. Different EOR techniques could be considered for each formation due to the variation in heterogeneity,
with recovery also changing from one formation to another due to fluid viscosity.
Different thermal schemes, for example varying the number of steam injection cycles before continuous steam injection, have been suggested for each formation in respect to its heterogeneity and oil properties. It is also noted that a SAGD EOR process can be more effective in certain formations in this field.
Zhen, Yang (Shool of Mines, China University Of Mining And Technology) | Chencheng, Huang (Shool of Mines, China University Of Mining And Technology) | Wang, Shugang (Department of Energy and Mineral Engineering, Penn State University)
Since several mine inundation on disasters happen in china andU.S. in the past, researchers have paid more and more attention to the In Seam Seismic (ISS) method which can be applied in detecting the uncertain boundaries in a coal seam. The uncertain boundaries are mapped by the reflected channel waves. Wave propagation has been studied for several decades, but is still remains very difficult to identify the reflected channel waves effectively in a coal seam due to the rock-coal-rock structure. SH wave plays an important role in the rock-coal-rock structure, so this paper focuses on modeling SH wave propagationin a rock-coal-rock structure with a Gaussian pulse as an explosion source. Our results show that the SH wave will be excited in different modes in a coal seam due to different positions of a seismic source and different angles of truncation, which is the key to map the uncertain boundaries to avoid disasters such as Quecreek and Wangjialing coal mine accidents. Finally, the rock-coal-rock is a natural filter for SH waves in a coal seam in practice, so it is still important to select the right filter before mapping uncertain boundaries based on the ISS technique.
Uncertain abandoned voids, old workings gobs, and faults are potential threats to live of coal miners and can also increase the cost of underground mining. Nine miners were trapped over 3 days in a mining accident after the continuous mining section cut into an abandoned mine accidently at the Quecreek Mine, Pennsylvania, in the United States, on July 24, 2002 . In china, 152 miners were trapped in the underground due to the water flooded into working area accidently, and 38 miners lost their lives in this mining accident on March 28, 2010 . If gas and water accumulations can be detected ahead of mining, the risk of mining can be reduced. Many different techniques have been developed to address such problems, but most havelimited usefulness or high cost. Drilling is the main exploratory method used ahead of working faces. It directly detects prospective coal area, but the information provided by sampling drilling may be incomplete or inaccurate. The technique of indentifying the differences of velocity and attenuation of seismic wave between the coal and the surrounding rocks has been used for coal exploration .Another method is to use transmitted waves between boreholes to determine void and discontinuities . Surface reflection is not a cost-effective and accurate method for detecting voids . Thus, the most effective method to locate the void in a coal seam may be the Seam Seismic Method.Wave propagation in a coal seam has been an interesting problem since last decade, because it is very difficult to identify the reflected channel waves . Since several mine inundated disasters happen in U.S. and China, researchers have paid more and more attention to ISS to explore how to detect the uncertain boundary in coal seam. The key of ISS is that the uncertain boundary is mapped by the reflected channels waves.
This paper presents hydraulic fracturing and flooding experiments with cohesionless sand designed to investigate the injectivity mechanisms. Tests are performed in 2-foot cubic sand packs in a stiff steel chamber and subjected to controlled 3-D confining stresses. Multiple injection stages of a heated low viscosity dyed gel-water solution that solidifies to preserve the invaded zone morphology are done. Post-test examination of the solidified invaded zones displays a multilayered structure of sand developed during the flooding and/or fracturing stages of injection. Under flooding conditions a uniform sand structure is observed with a smooth boundary between the layers corresponding to fluid injected on the earlier stage and outwardly displaced by the following injection. In contrast with that, a heterogeneous, turbulent invaded zone structure with clearly visible irregular higher porosity/permeability “channels” is formed under fracturing conditions. The fluid injected after a “fracturing stage” moves primarily through these channels (bypassing the previously injected fluid) with a significant injectivity increase (up to 35-40%). No discrete fractures are observed. A cyclic low frequency injection rate is also shown to be an alternative method to fracturing for improving injectivity. Improved injectivity in this case is achieved without creation of any noticeable disturbance to the sand structures, like channels, and maintains a more uniform fluid distribution.
Some of the unconsolidated sand formations such as those offshore in the Gulf of Maxico and offshore Western Canada contain high viscosity oil and might be considered for water or polymer flooding to improve recovery and enhance oil production [1, 2]. Flooding in unconsolidated sand could lead to fracture initiation and propagation . Fracturing may be related to the presence of small quantities of impurities and solids in the injection fluid (discrete fracture formation) as well as to a high injection rate (diffusive fracture formation). Although fracturing enhances permeability and injectivity of sand reservoirs, fracture initiation and growth must be under control to avoid intercepting production wells and other undesirable consequences of fracture creation.
For unconsolidated sand, there are currently no sound theoretical predictions for fracture initiation and propagation. There are still a only limited number of published laboratory studies of the flooding/fracturing processes in unconsolidated sand [4-7,11] for relevant ranges of in-situ stress, injection rate and injection fluid rheology, including limited experiments dedicated to studying the effect of flow enhancement by injection rate and pressure pulsing [8, 9]. All these publications describe tests performed in isotropic or biaxial stress conditions. They do not replicate the typical fully 3-D field stress conditions, with different minimum, intermediate and maximum principal stresses. In order to better quantitatively characterize flooding/fracturing in cohesionless sand, the study presented in this paper was carried out on cubical sand packs with different confining pressures in the three principal directions. It is a modified and upgraded pressure chamber previously used in our studies of hydraulic fracture initiation and propagation . In this paper we report the observation and characterization of the effect of constant and cyclic injection rate on the waterflooding mechanism and injectivity in oil-wetted air-saturated and water-saturated cohesionless sand.
Zheng, Jinhai (State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, College of Harbor Coastal and Offshore Engineering, Hohai University) | Zhao, Yinghui (State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, College of Harbor Coastal and Offshore Engineering, Hohai University) | Liu, Pei (State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, College of Harbor Coastal and Offshore Engineering, Hohai University) | Chen, Kefeng (State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, College of Harbor Coastal and Offshore Engineering, Hohai University, Nanjing Hydraulic Research Institute) | Tang, Cui (CCCC Second Harbor Consultants Co., Ltd)
Ramirez, Jorge (Department of Civil Engineering, Aalborg University) | Frigaard, Peter (Department of Civil Engineering, Aalborg University) | Andersen, Thomas Lykke (Department of Civil Engineering, Aalborg University) | Christensen, Erik Damgaard (Department of Mechanical Engineering, Technical University of Denmark)