Nintoku Yazawa

Integrated Geostatistical Reservoir Characterization of Turbidite Sandstone Deposits in Chicontepec Basin, Gulf of Mexico

This paper presents a pixel-based hierarchical geostatistical modeling of submarine fan turbidite sandstone deposits in Tajin and Agua Fria fields of Chicontepec basin in the Gulf of Mexico. Methods are discussed for identifying and dividing the stack of heterogeneous siliciclastic sediments in these fields, using sequence stratigraphy, petrophysical well log characteristics, geological facies model and 3D seismic data. An integrated multidisciplinary geostatistical reservoir characterization is conducted in two main steps. First, a largescale reservoir framework of multiple sequence and subsequence surfaces is constructed based on the integration of data sources of geologic well markers, petrophysics, and seismic horizons. Second, high-resolution 3D distributions of reservoir properties are generated, accounting for inherent inter-relationship among reservoir property data and the three main data scales of log, sub-sequence layer and sequence interval. At onset, shale volume content in Tajin field and total porosity in Agua Fria field are modeled. Block kriging, trend model, and conditional thickness-weighted Bayesian scheme are presented for the integration of data types and data scales. Facies distributions in Tajin are modeled by indicator kriging conditioned to Vsh content, and hence to seismic. Porosity distributions are by sGsim collocated with Vsh for each facies group, and water saturation distributions are collocated with porosity. Permeability distributions are function of porosity, water saturation, facies and sub-sequences. In Agua Fria, effective porosity and facies are by p-field related methods. Patterns of sand continuity and pay sand connectivity are derived and uncertainty in their prediction is evaluated. Introduction There has been a great interest in the industry in the past decade to use multi-disciplinary geostatistical techniques for integrated reservoir characterization in various types of reservoir depositional environments. Research in industry and academia is making advances in better utilization of seismic data for generating interwell data and information in reservoir areas where well data is non-existent. Although seismic does not have the vertical resolution of well logs, its areal sampling coverage is dense, providing some details of reservoir unreachable by wells. In the past several years, we have embarked on developing technology to integrate geological, geophysical and reservoir engineering information for reservoir management and field development of Chicontepec fields. It is recognized that development of an integrated geostatistical methodology, verified by field data, will be an appropriate approach for this purpose. As a case study, Tajin field and nearby Agua Fria and Coapechaca fields are selected for the development and benchmarking of this technology to be expanded later to other fields in this basin. Results of our initial work are documented in previous publications. Chicontepec basin, with a giant field area of 123 km in length and 25 km in width, has been formed by a complex system of submarine fan and turbidite sediments deposited in an eroded deep-water canyon originally formed in the Gulf of Mexico. The first field in the basin was discovered in 1931 and commercial production commenced in 1952. The Chicontepec reservoirs consist of Upper Paleocene-Lower Eocene alternating sandstone and shale bodies. These bodies do not present a continuous laminar extension throughout the field, and a wide variation in clay-shale content is recognized. It is crucial to improve reservoir characterization; especially distribution of sand-shale bodies and their pay connectivity, in order to optimize filed development planning and management of the Chicontepec reservoirs. Geostatistical techniques can be categorized in two types: pixel-based and object-based methods. Pixel-based methods are largely used to characterize reservoir parameters and structures, but they are not designed to explicitly reproduce geometric shapes as their final goal. Object-based methods are suitable to represent geological features with certain geometric attributes, provided that adequate data on the geometry of geological features such as channels and turbidite SPE 84052 Integrated Geostatistical Reservoir Characterization of Turbidite Sandstone Deposits in Chicontepec Basin, Gulf of Mexico Maghsood Abbaszadeh, SPE, Innovative Petrotech Solutions, Inc., Osamu Takano, Hiroshi Yamamto, Japan Petroleum Exploration Co., Tatsuo Shimamoto, SPE, Teikoku Oil Corp., Nintoku Yazawa, SPE, Japan National Oil Corp., Francisco Murguia Sandria, David H. Zamora Guerrero, Fernando Rodriguez de la Garza, SPE, PEMEX Exploration y Production

Effective permeability estimation for naturally fractured reservoirs.

Appropriate modeling of naturally fractured reservoirs is one of the most important and challenging issues in reservoir characterization. In simulation, a dual porosity or dual permeability model is applied when fractures are well developed to form a fracture network. On the other hand, the single-continuum approach, where the fracture system is represented by effective permeability, is commonly used if fractures are discrete or disconnected. Focusing on the latter case, this paper proposes a semi-analytical technique to evaluate effective permeability for periodically or randomly fractured media including infinitely thin, infinite-conductivity fractures.The complex variable boundary element method is used to compute potential fields and streamlines in the two-dimensional space for discretely distributed fracture systems under the periodic boundary conditions. Effective permeability is evaluated first for discrete fracture systems of regular patterns to demonstrate the validity of the method and to examine the sensitivity of the effective permeability to the variations in the basic fracture parameters. With a constant total length of fractures, systems of varied fracture lengths show higher effective permeability than systems of uniform fracture length. 500 distributions of stochastic fractures are next generated to establish correlation between effective permeability and the fracture parameters, total length L, mean length m, and standard deviation of fracture length ?D. Sensitivity to the parameters shows that non-zero a increases effective permeability, that the incremental gain of effective permeability is proportional to L, and that the larger m, the larger effective permeability. The effective permeability tensors are also determined for oriented fractures. Analyses by non-parametric regression show that the diagonal elements, kxx and kyy, are highly affected by the angle between the oriented fractures and the pressure gradient, while the off-diagonal elements, kxy and kyx, are strongly affected by both the total length and the angle.