Cut-Off Determination for Multilayer Sandstone Reservoir Based on Rock Type by Using Combination of Open Hole Log Data and Production Logging Data

Abstract The Harash Formation was previously known as the Ruaga A and is considered to be one of the most productive reservoirs in the Zelten field in terms of reservoir quality, areal extent, and hydrocarbon quantity. To date, nearly 70 wells were drilled targeting the Harash reservoir. A few wells initially naturally produced but most had to be stimulated which reflected the field drilling and development plan. The Harash reservoir rock typing identification was essential in understanding the reservoir geology implementation of reservoir development drilling program, the construction of representative reservoir models, hydrocarbons volumetric calculations, and historical pressure-production matching in the flow modelling processes. The objectives of this study are to predict the permeability at un-cored wells and unsampled locations, to classify the reservoir rocks into main rock typing, and to build robust reservoir properties models in which static petrophysical properties and fluid properties are assigned for identified rock type and assessed the existed vertical and lateral heterogeneity within the Palaeocene Harash carbonate reservoir. Initially, an objective-based workflow was developed by generating a training dataset from open hole logs and core samples which were conventionally and specially analyzed of six wells. The developed dataset was used to predict permeability at cored wells through a K-mod model that applies Neural Network Analysis (NNA) and Declustring (DC) algorithms to generate representative permeability and electro-facies. Equal statistical weights were given to log responses without analytical supervision taking into account the significant log response variations. The core data was grouped on petrophysical basis to compute pore throat size aiming at deriving and enlarging the interpretation process from the core to log domain using Indexation and Probabilities of Self-Organized Maps (IPSOM) classification model to develop a reliable representation of rock type classification at the well scale. Permeability and rock typing derived from the open-hole logs and core samples analysis are the main K-mod and IPSOM classification model outputs. The results were propagated to more than 70 un-cored wells. Rock typing techniques were also conducted to classify the Harash reservoir rocks in a consistent manner. Depositional rock typing using a stratigraphic modified Lorenz plot and electro-facies suggest three different rock types that are probably linked to three flow zones. The defined rock types are dominated by specifc reservoir parameters. Electro-facies enables subdivision of the formation into petrophysical groups in which properties were assigned to and were characterized by dynamic behavior and the rock-fluid interaction. Capillary pressure and relative permeability data proved the complexity in rock capillarity. Subsequently, Swc is really rock typing dependent. The use of a consistent representative petrophysical rock type classification led to a significant improvement of geological and flow models.

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STATUS AND TRENDS IN LOGGING

Geophysics ◽

10.1190/1.1440084 ◽

1970 ◽

Vol 35 (1) ◽

pp. 93-112 ◽

Cited By ~ 2

Author(s):

Hilton B. Evans

Keyword(s):

Digital Processing ◽

Acoustic Parameter ◽

Physical Parameters ◽

Log Data ◽

Oil Companies ◽

Service Companies ◽

Open Hole ◽

Multiple Measurements ◽

Processing Techniques ◽

Parameters Of Interest

Logging service companies are attempting to provide a fairly good selection of devices which have proven to be popular with the oil industry. However, the introduction of new devices or new services is being limited because oil companies are standardizing the logging‐suites run in their various geographic operating areas. Some of these new techniques appear to have significant applications. Recently, standard logging‐suites and evaluation‐techniques have evolved; these can be evaluated in terms of open‐hole and cased‐hole applications and the physical parameters of interest. Generally, these standard procedures depend on the differences in responses of multiple electrical and porosity devices. The multiple measurements are input to response equations which yield the parameters of interest. Although mining companies have been slow to adopt logging techniques, the use of logging devices and interpretation methods in nonpetroleum mineral (groundwater, nonmetals, metallic sulfides, etc.) exploration and evaluation, and in providing geophysical survey parameters is increasing. Nuclear, electrical, acoustic, and other methods are utilized, and newer applications of these to exploration, particularly in lithology determination, suggest themselves. Log digitizing and computer processing of log data have become routine in most major oil companies, but techniques, programs, and equipment vary significantly. Currently, commercial digitizing services are too expensive to be used extensively; the per‐log costs, however, are declining as more digitizing companies offer competitive services. Two basic commercial systems for transmission and computation of log data are functioning. To date, these systems yield “quicklook” reconnaissance parameter computations. Current research and development emphasis is on pulsed neutron‐spectroscopy and acoustic‐parameter measurements and on digital processing techniques.

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