Augustine, M. (Oil and Natural Gas Ltd) | Murthy, A. V. R. (Oil and Natural Gas Ltd) | Boindala, Amitha (Oil and Natural Gas Ltd) | Bahuguna, Somesh (Schlumberger) | Talreja, Rahul (Schlumberger) | Pattanaik, Sambit (Schlumberger) | Kalita, Deepika (Schlumberger) | Das, Sourav (Schlumberger)
Madanam field in Cauvery basin in the east coast of India, has fractured gneissic basement. As exploration focus moved to unconventional reservoirs, the gneissic basement of Madanam was seen as a potential reservoir. However, ambiguity existed about the fluid flow through the basement. For example, in Madanam field, one well (well A) flowed whereas another well (well B) located 8.5 km away had minor flow from the basement reservoir that lasted 2 days. The main purpose of this study was to find possible reasons for this anomalous behavior. This study was conducted by integrating sonic and image measurements with a geomechanics workflow to identify critically stressed open fractures. Further, this work aims to provide a fit-for-purpose solution to optimize and prioritize testing zone selection in near real time.
Mallick, Tanmay (Shell India Markets Private Limited) | Garg, Ashutosh (Shell India Markets Private Limited) | Choudhary, Manish (Shell India Markets Private Limited) | Nair, Saritha (Shell India Markets Private Limited) | Pal, Sabyasachi (Shell India Markets Private Limited) | Jana, Debadrita (Shell India Markets Private Limited) | Singh, Abhinav (Shell India Markets Private Limited) | Goudswaard, Jeroen (Shell India Markets Private Limited) | Faulkner, Andrew (Shell India Markets Private Limited) | Salakhetdinov, Ravil (Shell India Markets Private Limited)
A new seismic and quantitative reinterpretation was carried out for a brownfield in Western Desert, Egypt to improve depth predictability, de-risk appraisal well locations and to better understand producer-injector connectivity.
The study field is located in the Western Desert, Onshore Egypt and comprises of Upper Cretaceous tidal channel systems across four key reservoir levels where sand thicknesses range from 2 to 15 m. The field was discovered in 1993 but development drilling only commenced in 2008. The last integrated field study was performed in 2012. The analysis of wells drilled post-2012 indicated that there is a considerable depth difference along the flanks of the structure between seismic predicted depths and actual well tops (>50 m). The fault interpretation also required a re-look so as to reduce the lateral uncertainty of the main boundary fault and explain the lack of injection response in some areas of the field. This necessitated an update of seismic interpretation, static and dynamic models. A new interpretation could help identify attic volume upsides and help mature new appraisal and producer-injector locations. Further work was also proposed to test the feasibility of using seismic inversion for facies discrimination.
The available Pre-Stack Depth Migration (PreSDM) data was re-interpreted as part of the project. The fault interpretations were quality checked using Semblance/Dip maps, sand box models and wherever possible, were tied to the fault cuts seen in previously drilled wells. The time horizon correlation and seismic polarity were verified and were also cross-checked with the P-Impedance volume before being used in the static modelling workflow. The PreSDM Interval velocity model was used for depth conversion, where an anisotropy correction was applied to tie the wells. Vok and Polynomial methods were also applied, which in turn were used to derive depth uncertainty estimates. The update in the main bounding fault interpretation generated new appraisal locations in the deeper levels. The new interpretation was tested against the results from the latest drilling campaign in the field, and nine out of ten wells were within the one standard deviation uncertainty range.
Simultaneous inversion of the seismic data was also carried out as part of the project using the acoustic, shear and density data from 6 wells over the field. The inverted P-Impedance and S-Impedance were converted to Net to Gross (NtG), and were checked against the remaining 24 wells, which helped in validating the property cubes.
Forward wedge modelling suggested that individual sands of less than 15 m thickness would not be resolved from seismic due to seismic bandwidth limitations. Still, a review of inversion data together with geological insights and dynamic data helped to identify the high NtG areas across the reservoirs.
The integrated interpretation of inverted volumes with well and production data resulted in new insights into the field and helped to mature new appraisal and development well locations.
The analysis of the geothermal structures requires the use of various types of information, such as geologic, geophysical (temperature measurements, time/depth seismic sections, velocity models) and hydro-geological data. Two- and three-dimensional distributions of temperatures and a two-dimensional distribution of geothermal gradient were obtained based on the temperature values recorded in boreholes until the depth of 4000 m. By comparing the geothermal gradient and temperature maps with the geological sections, we notice the presence of near vertical deep faults in the areas characterized by high values of geothermal gradient and temperature; in addition, some of these faults cross intrusive bodies. The paths for the fluid movement are represented by the deep faults.
Remote sensing of fractures with elastic waves is important in fields ranging from seismology to non-destructive testing. While previous analytic descriptions of scattering mostly concern very large or very small fractures (compared to the dominant wavelength), we present an analytic solution for the scattering of elastic waves from a fracture of arbitrary size. Based on the linear-slip model for a fracture, we derive the scattered amplitude in the frequency domain under the Born approximation for all combinations of incident and scattered wave modes. Our analytic results match laser-based ultrasonic laboratory measurements of a single fracture in clear plastic, allowing us to quantify the compliance of a fracture.
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.
Hornbach, Matthew J. (The University of The West Indies) | Brown, Lyndon (The University of Texas) | Mann, Paul (The University of The West Indies) | Frohlich1and, Cliff (The University of The West Indies) | Ellins1, Kathy (The University of The West Indies)
Kingston, Jamaica, the capital of the Caribbean island nation of Jamaica is prone to infrequent but devastating earthquakes and tsunamis, yet the locations of the faults responsible for generating these geohazards are poorly known. During the past few hundred years, at least two earthquakes have triggered severe liquefaction across Kingston and generated tsunami within the Harbor, resulting in significant destruction. The goal of our study is to (1) determine the location of faults in Kingston Harbour, (2) assess whether these faults are active, (3) determine whether harbor faults triggered local tsunami reported during the 1692 and 1907 Earthquakes, and (4) from this, constrain the risk of future geohazards across the region. Here, we focus our analysis on recent results from our January 2011 chirp seismic imaging survey of Kingston Harbour. These data reveal a complex fault system extending across the harbor and evidence for multiple slide and liquefaction events. Using sea-level curves as a means of constraining age, we suggest these faults are active. Our study suggest east Kingston where the Cement Factory, twp power plants, a fuel-depot, Highway A4—the only east-west thoroughfare extending east of Kingston, The Norman Manley Airport, and the town of Port Royal are all prone to significant damage during the next earthquake in this region.
The objective of this project is to analyze the rock strength of the shale caprock of the Forties field in the North Sea that could relate to shale instability and more importantly to reactivation of the pre-existing faults in the region, which in turn could cause well drilling problems. Using fault slip theory and constructing Mohr diagrams, we anticipate a decrease in the coefficient of friction of the pre-existing planes of weakness due to known layering and fractures within the shale caprock, resulting low unconfined compressive strength (UCS) of the rock. Mapping low UCS values in the field was achieved by relating UCS to rigidity, μ, values obtained from the wells, and extending this relationship laterally using 3D seismic.
The southern basin of Trinidad has been a producing hydrocarbon province over the last 110 years. Tens of thousands of oil wells dot the landscape in the southwestern portion of the island. Although exploration and development teams have a wealth of well data, it has unfortunately been accompanied by a large dearth of useful seismic data. In 2010 Petrotrin embarked upon the first 3D project to be acquired over its core production fields. Acquisition was completed in March 2011 with final processing expected to be completed in December 2011. The local geological, human and historical factors have made acquisition of seismic data on land in Trinidad a difficult process. This presentation outlines some of the design and operational elements used to mitigate the negative effects of these influences; shows their successes and pitfalls and indicates what is necessary to improve on further seismic projects.
The Hoop Fault complex in the Southwestern Barents Sea presents an imaging challenge to accurately model the sharp velocity contrast across a major fault boundary. Improperly accounting for this velocity discontinuity would lead a poorly focused image and false structures. We present an approach that leverages interpreted fault planes as well as marker horizons to drive and constrain tomographic velocity updates.
We present a new data adaptive method for smoothing 3D post-stacked seismic attributes. This method reduces random noise while preserving structure without prior information of the structure orientation. Our method works by smoothing the data along a set of orientations defined within a neighborhood sub-window; the best result is then selected for output. The best orientation often approximates the true structure orientation embedded in the data; therefore, the embedded structure is preserved. The selection criterion for the “best” orientation depends on the data type and purpose of maneuver: it can be 1) minimum deviation, and 2) maximum or minimum or absolute-maximum summation. Our method can be further combined with median, alpha-trim, symmetric near neighbor, or edge-preserving filters. Based on preliminary results, our method effectively reduces random noise, eliminates footprints, and enhances coherence and curvature attributes. We also foresee its usage in processing of seismic data, such as to enhance auto-picking of horizons, first arrivals and refraction events.