Abdel M. Zellou

Seismically Driven Reservoir Characterization Using an Innovative Integrated Approach: Syd Arne Field

This paper presents an innovative integrated workflow applied to the characterization of a fractured chalk reservoir in the Danish North Sea. The methodology uses simultaneous integration of geophysical, geological and engineering data to produce an improved reservoir description. Integrating dynamic flow data with the geophysical and geologic information in 3D, reservoir properties - porosity and effective permeability - are generated using artificial intelligence tools. The strength of this technique lies in the fact that property modeling is not constrained to match upscaled well data and consequently these data serve to validate the outcome. This workflow builds upon a methodology that has been used successfully for the characterization of fracture distribution. The technique has been extended to include the generation of seismically derived models of porosity and matrix permeability.The objective of the approach is to improve the ability to capture the heterogeneity of key reservoir properties, and thus use the resulting reservoir model to both provide improved predictive ability and identify previously undiscovered development opportunities. The application and outcome of this integrated workflow to the Syd Arne field is presented in this paper.

Improved Reservoir Simulation With Seismically Derived Fracture Models

History matching and simulation of naturally fractured reservoir is a recurring challenge to many oil and gas companies seeking to manage and develop fractured reservoirs. Several techniques have been applied in the past to match past production and pressure history that have been proven unreliable. This paper describes a methodology to improve the simulation of fractured reservoir using seismically driven reservoir characterization. The methodology presented in this paper uses the integration of geophysical, geologic, and engineering data simultaneously to improve the reservoir description. At the root of the reservoir characterization lays the more and more accurate seismic data collected on most of the reservoirs around the world. The initial use of this seismic information is made possible through high-resolutioninversion and spectral imaging. These two processes allow a better imaging of key reservoir properties that have an important impact on fracturing. Based on this seismically driven reservoir characterization, the reservoir properties necessary as inputs to the reservoir simulator, i.e. fracture porosity and permeability, are generated using artificial intelligence tools and core measuremenst as fracture indicators. The usefulness of the derived seismic attributes is illustrated on a specific reservoir where a new well was recently drilled. The drilling results indicate that the derived seismic attributes can be used successfully to locate highly fractured areas. Using the generated seismic attributes in an integrated fracture modeling approach allows for a better modeling of the “plumbing” of the reservoir through a correct estimation of the fracture permeability and porosity. These improved fracture properties lead to a history match of the well performances. Examples of such history matches are given for illustration purposes.

Seismically Driven Characterization, Simulation and Underbalanced Drilling of Multiple Horizontal Boreholes in a Tight Fractured Quartzite Reservoir: Application to Sabria Field, Tunisia

This paper describes the application of the Continuous Fracture Modeling (CFM) workflow to the Sabria field in Tunisia. This workflow consists of four steps. The first step in the workflow is to interpret key seismic horizons and use them in high resolution inversion and spectral imaging to create impedance and frequency-dependent seismic attributes. The second step consists of building seismically constrained geologic models of lithology and other petrophysical properties. The third step consists of using the derived geologic models along with all the post-stack seismic attributes and additional geomechanical models to derive high resolution 3D fracture models. The fourth step is to use the derived fracture models in a reservoir simulator to verify the validity of the models by their ability to match past individual well performances and to design optimal well trajectories that intercept a large number of fractures and produce economical oil rates. This workflow was applied to the Sabria field in Tunisia and was followed by actual drilling. The seismic attributes and the appropriate geologic and geomechanical models were used as input in REFRACT, a fracture modeling software, to create accurate 3D fracture models. The resulting fracture porosity and permeability were input in a reservoir simulator. All the past individual well performances were matched, confirming the reliability and accuracy of the derived fracture models. The resulting simulation and fracture models were used to plan multiple horizontal boreholes, drilled underbalanced from a single platform. The resulting oil production from the boreholes and the recorded logs confirm the validity of both the fracture and simulation models.

Continuous Fracture Modeling of a Carbonate Reservoir in West Siberia

The field is located in the southeastern part of the West Siberian basin in Novosibirsk oblast (Fig. 1). It was the first field in the basin where commercial oil was produced from the Paleozoic basement. The reservoir consists mostly of limestones and dolomites that are intensively fractured and contain numerous vugs in some zones. The reservoir properties of the matrix are generally negligible, and the production potential of wells is mostly associated with natural fractures and vugs. The presented study was our first project in Russia where a complete integrated approach was implemented to properly characterize a fractured reservoir. The approach included the following tasks: 1) Identification of fractured intervals in wells using a special technique of BKZ logs processing, 2) Spectral imaging and high-resolution inversion of the seismic data, 3) structural analysis of the field, 4) construction of the reservoir properties model, 5) construction of the fracture distribution model using the Continuous Fracture Modeling approach (CFM). A comprehensive description is available on a previous publication 1 . The final geologic model served as a basis to select the locations for the new wells. The new locations were proposed in the zones with the most intensive development of a network of natural fractures (according to the model). The drilling was associated with significant losses of drilling mud that was an indirect indication of presence of significantly fractured zones. The wellbore image FMS that was recorded in the well, showed a good level of correspondence between the model forecast and the actual result. The well contains interval of numerous fractures and large vugs. Eventually, the well showed a good production results and currently is one of the best producers in the field. As such, we recommend application of the described integrated approach for modeling complex fractured reservoirs in the other fields of Russian Federation.

Fractured Reservoir Characterization Using Post-Stack Seismic Attributes: Application to a Hungarian Reservoir

Efficient development of fractured reservoirs has been notoriously difficult. This inefficiency arises from the difficulty in locating the fractures in the reservoir. By synergistically combining seismic data, containing the interwell information, with geologic and engineering data at the wells, we develop a fracture model that honors the various datasets and successfully predicts the location of fractures within the reservoir. The reservoir consists of fractured metamorphic basement, with a hereogeneous distribution of both porosity and fractures. Thirteen wells exist in the field, 5 of which were used in building the reservoir model. Seismic inversion and spectral decomposition were applied to a 3D seismic survey covering the field in order to generate attributes used in the fracture characterization. In addition to the 4 post-stack seismic attributes, gamma ray, porosity, and resistivity models and 9 geomechanical attributes were generated for the fracture modeling. Using these 16 attributes and the fracture intensity at the control wells, a fracture model was built for the reservoir using the continuous fracture modeling (CFM) approach. Validation using the blind wells indicates that the fracture model was able to successfully predict both the highly fractured zones and the relatively unfractured zones within the reservoir.

Seismically Driven Improved Fractured Reservoir Characterization

Characterization of naturally fractured reservoir is a recurring challenge for many oil and gas companies that manage and develop fractured reservoirs. Several techniques have been applied in the past to characterize these complex reservoirs; most of them have been proven unreliable. This paper will describe a methodology to improve the characterization of fractured reservoir using seismic attributes derived from prestack and post-stack high resolution inversion and spectral imaging. The methodology presented in this paper uses the simultaneous integration of geophysical, geologic, and engineering data to improve the reservoir description. At the root of this reservoir characterization technique is the increasingly accurate seismic data collected on most of the reservoirs world-wide. Extensive use of this seismic information is made possible through the use of pre-stack high-resolution elastic inversion, post-stack high resolution inversion, and spectral imaging. These processes allow the derivation of seismic attributes that are extremely relevant to fracturing and could also be used as input in the continuous fracture modeling approach. Based on this seismically driven reservoir characterization, the fractured reservoir properties could be accurately estimated in 3D. An application of this technology and workflow is presented on a very complex fractured reservoir.