Fernando Rodriguez-De La Garza

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

Gravity Drainage and Oil Reinfiltration Modeling in Naturally Fractured Reservoir Simulation

The gravity-drainage and oil-reinfiltration processes that occur in the gas-cap zone of naturally fractured reservoirs (NFRs) are studied through single porosity refined grid simulations. A stack of initially oil-saturated matrix blocks in the presence of connate water surrounded by gas-saturated fractures is considered; gas is provided at the top of the stack at a constant pressure under gravity-capillary dominated flow conditions. An in-house reservoir simulator, SIMPUMA-FRAC, and two other commercial simulators were used to run the numerical experiments; the three simulators gave basically the same results. Gravity-drainage and oil-reinfiltration rates, along with average fluid saturations, were computed in the stack of matrix blocks through time. Pseudofunctions for oil reinfiltration and gravity drainage were developed and considered in a revised formulation of the dual-porosity flow equations used in the fractured reservoir simulation. The modified dual-porosity equations were implemented in SIMPUMA-FRAC (Galindo-Nava 1998; Galindo-Nava et al. 1998), and solutions were verified with good results against those obtained from the equivalent single porosity refined grid simulations. The same simulations—considering gravity drainage and oil reinfiltration processes—were attempted to run in the two other commercial simulators, in their dual-porosity mode and using available options. Results obtained were different among them and significantly different from those obtained from SIMPUMAFRAC.